Some studies on a single cylinder Di-Diesel Engine with coconut biodiesel (come) and triacetin additive blends as alternate fuel


Doctoral Thesis / Dissertation, 2010
109 Pages

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CONTENTS

Abstract

List of Figures

List of Tables

Nomenclature

Chapter I LITERATURE SURVEY AND INTRODUCTION OF THE PROBLEM
1.1 Survey of Additive Research by earlier authors
1.2 Types of Additives
1.2.1. Metal-Based Additives
1.2.2. Oxygenated Additives
1.2.3. Depressants and Wax Dispersants
1.2.4. Ignition Promoters
1.2.5 Diesel-Vegetable Oil Blends
1.3 Additives for Diesel-Biodiesel Blends
1.3.1 Characteristics of Biodiesel & Blends versus Diesel
1.3.2. Lubricity Additives
1.3.3. Cetane Number Additives
1.3.4 Stability Additives
1.4 Perspectives
1.5 Conclusions
1.6 Introduction to the problem
1.6.1 Selection of biodiesel
1.6.2 Advantage of Coconut Oil Methyl Ester (COME) over the conventional fuel used in diesel engine
1.6.3 Free fatty acid advantages with coconut biodiesel
1.6.4 Blend of Coconut Oil biodiesel [COME]
1.7 Selection of Additive
1.8 Engine cylinder Vibration studies
1.9 Introduction to present work (COME-Triacetin additive blends)

Chapter II TRANSESTERIFICATION OF EDIBLE VEGETABLE OIL (COCONUT OIL)
2.1 Transesterification of Vegetable Oils
2.2 Process employed for making methyl esters
2.2.1 Introduction
2.2.2 The Process
2.2.3 First stage (Acid catalyzed)
2.2.4 Second stage (Base catalyzed)
2.2.5 Washing
2.3 Properties of the Bio-Diesel
2.4 Summary

Chapter III COMBUSTION HEAT RELEASE RATE CALCULATIONS
3.1 Heat release based on Ist Law of thermodynamics
3.2 In-cylinder heat transfer

Chapter IV EXPERIMENTAL SET UP AND EXPERIMENTATION
4.1 Experimental setup
4.1.1 Direct injection (DI) Diesel Engine
4.1.2 Engine Loading System
4.1.3 Eddy Current Dynamometer
4.1.4 Piezo Electric Transducer (S111A22, SN9982)
4.2 Exhaust Gas Analyzer (DELTA 1600- L)
4.2.1 Technical Specifications of analyzer
4.2.2 Features of Delta 1600-L Analyzer
4.3 Smoke Density Tester (Diesel Tune 114)
4.4 Vibration Analyzer Equipment
4.5 Experimentation Procedure
4.6 Error Analysis
4.7 Summary

Chapter V RESULTS AND DISCUSSION
5.1 Study of cylinder pressures during combustion
5.2 Net and cumulative heat release rate comparison
5.3 Performance Analysis
5.4 Discussion on Engine Emissions
5.5 Summary of results on engine performance
5.6 Engine vibration study
5.6.1 Engine Knock estimation

Chapter VI CONCLUSIONS
6.1 Conclusions
6.2 Scope for future work

REFERENCES
Appendix – A
Appendix – B
Appendix – C
Appendix – D

ABSTRACT

Fast depletion of fossil fuel, increasing of pollution to peak levels and to follow stringent rules in controlling emissions made to shift over to alternate, renewable, pollution free fuels. Particulate matter (PM) or smoke emission and oxides of nitrogen (NOx emissions) are the two important harmful emissions in diesel engine. Fuel companies and the researchers around the world are devoted to reduce such emissions with different ways. Fuel modification, modification of combustion chamber design and exhaust after treatments are the important means to alleviate such emissions. In this context, engine researchers are hunting for suitable oxygenated alternative fuels for diesel engine. Biodiesel is an oxygenated fuel evaluated from vegetable oil. But there are some setbacks in the context of emissions, especially NOx, second one is polymerization at higher temperatures. Some of the esters like Coconut methyl ester worthy as an alternative fuel which contains lesser proportion of C18 molecule fatty acids which are instrumental in increasing particulate matter and NOx as well. The presence of oxygen in the fuel molecular structure and lower volatility play important role in better combustion of the fuel mixture even at reduced calorific value of the fuel because of molecular oxygen which replaces the carbon and hydrogen molecules contributing to rise in the lower calorific value of the fuel. Hence for a neat biodiesel operation, keeping in view of these setbacks additive is mixed to make suitable for replacement.

In the present work, neat COME-Triacetin additive blends are experimented in lieu of the neat diesel fuel. Pure coconut oil methyl ester itself as an additive has advantages in the operation of the engine. Attention is bestowed upon the reduction of HC, NO, CO2, CO and smoke emissions, and the same is successfully achieved with the 10% Triacetin and 90% COME blend fuel. Vibration on the engine cylinder in three directions of the engine cylinder and on the foundation were measured and analyzed to elicit information about the nature of combustion since the combustion itself is the exciter. The pressure signatures are tallied with time waves eliminating the time lag in between exciter (combustion in the cylinder itself) and the cylinder head vibration. Triacetin being an antiknock fuel, with 10% blend emanated as a best blend with its contribution to reduce cylinder vibration in vertical direction of the cylinder. The time wave resembles attenuated sine wave replete with pure harmonics indicating smoother combustion with lesser engine detonation.

By analyzing the measured in-cylinder pressure data and the derived heat release rate, it is observed that the addition of Triacetin increases the ignition delay and the amount of heat release in the premixed combustion duration, but shortens both the diffusive burning duration and the total combustion duration. On the emission side, the smoke and other emissions including NO are reduced without any cognizable trade off with other components of the emissions.

LIST OF FIGURES

Chapter-1Literature Survey and Introduction

1.1 Improvement in PM with oxygenates with (BMEP=0.75 MPa)

1.2 Improvement in NOx emissions at three BMEP DGM conditions

1.3 Oxygen content fuels

1.4 Smoke emissions with highly oxygenated fuels

1.5 Influence of EGR on NOx emissions with DMM 100

1.6 Coconut biodiesel FAMES

1.7 PM effects of different methyl ester fuels

Chapter - II Transesterification of Edible Vegetable Oil (Coconut oil)

2.1 Mechanism of the base-catalyzed transesterification process

2.2 Process chart for Coconut Oil Methyl ester (COME)

2.3 Step-wise process of Biodiesel formation

2.4 Raw Coconut Oil Heating

2.5 Separated Glycerin after Acid Treatment

2.6 Preparation of Sodium Methoxide

2.7 Base Treatment to remove Free Fatty Acids

2.8 Settlement of Glycerin after Base Treatment

2.9 Collected Free Fatty Acids (Glycerin)

2.10 COME with Soap in water Washing

2.11 COME with clear Water

2.12 Final stage of (Heating) COME

Chapter - III Combustion Heat Release Rate Calculations

3.1 Input pressure data signatures drawn at different loads in limited range of 3300 to 4300 crank angle with of 75% COME + 25%Triacetin blend fuel run

3.2 Net heat release rate at different loads in limited range of 3300 to 4300 crank angle with 75%COME+25%Triacetin blend fuel

3.3 Cumulative heat release rate at different loads in limited range from 3300 to 4300 crank angle with 75%BD (COME) + 25%Triacetin blend fuel

C hapter - IV Experimental Setup and Experimentation

4.1 Schematic diagram of Data integration circuit taking data from the encoder and the pressure transducer

4.2 Line diagram of Experimental Setup

4.3 Eddy Current dynamometer

4.4 Dynamometer control panel

4.5 Piezo-electric transducer

4.6 Connector cable

4.7 Crank Angle Encoder

4.8 Engine Data Logger

4.9 Computer to log the data from the Engine data Logger

4.10 Delta 1600-L Exhaust Gas Analyzer

4.11 Diesel Tune Smoke Analyzer

4.12 Exhaust suction gun to collect the gas sample

4.13 DC-11 Vibration Analyzer with acceleration pickup

Chapter - V Results and Discussion

5.1 Input pressure data signatures drawn at limited range of 3400 to 4000 crank angle for diesel, biodiesel and for all biodiesel additive blends at full load

5.2 Delay period plot for diesel, biodiesel and biodiesel - additive blends at full load

5.3 Input pressure data signatures drawn for limited range of 3400 to 4000 crank angle for diesel, biodiesel and for biodiesel- additive blends at 75% full load

5.4 Delay period plot for diesel, BD and BD - additive blends at 75%full load

5.5 Net heat release rate for diesel, BD and BD - additive blends at full load

5.6 Net heat release rate for diesel, BD and BD - additive blends at 75% full load

5.7 Cumulative heat release rates for diesel, BD and BD - additive blends at full load

5.8 Cumulative heat release rates for diesel, BD and BD - additive blends at 75% full load

5.9 Variation of brake thermal efficiency verses equivalence ratio of the engine

5.10 Variation of brake specific fuel consumption verses equivalence ratio of the engine

5.11 Variation of fuel consumption with brake power of the engine

5.12 Variation of equivalence ratio with Load on the engine

5.13 Variation of peak pressure verses load on the engine

5.14 Variation of IMEP verses load on the engine

5.15 Variation of brake thermal efficiency verses load on the engine

5.16 Variation of exhaust temperature verses equivalence ratio of the engine

5.17 Variation of Max. DP wrt TDC verses load on the engine

5.18 Variation of indicated power verses load on the engine

5.19 Variation of hydrocarbon emission verses load on the engine

5.20 Variation of carbon monoxide emission verses load on the engine

5.21 Variation of carbon dioxide emission verses load on the engine

5.22 Variation of NO emission verses load on the engine

5.23 Variation of smoke level verses load on the engine

5.24 Variation of average spectrum values of the engine at no load

5.25 Variation of average spectrum values of the engine at 25%full load

5.26 Variation of average spectrum values of the engine at 50%full load

5.27 Variation of average spectrum values of the engine at 75%full load

5.28 Variation of average spectrum values of the engine at full load

5.29 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 5% triacetin and 95% bio-diesel

5.30 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 10% triacetin and 90% bio-diesel

5.31 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 15% triacetin and 85% bio-diesel

5.32 Time wave recorded vertical on the cylinder head during explosion stroke at Full load operation and it’s corresponding combustion pressure trace of blen fuel with 20% triacetin and 80% bio-diesel

5.33 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 25% triacetin and 75% bio-diesel

5.34 Time wave recorded vertical on the cylinder head during explosion stroke at Full load operation and it’s corresponding combustion pressure trace with neat bio-diesel operation

5.35 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace with neat diesel operation

5.36 Full-load curve and knocking operating regions under the assumption for different burnt mass fractions ‘X B’

5.37 FFT spectrum indicating Knocking frequency and acceleration amplitude for neat diesel application. Vibration Measurement is made in the radial direction of cylinder in line crank shaft axis

5.38 FFT spectrum indicating Knocking frequency and the acceleration amplitude for neatBio-diesel application. Vibration Measurement is made in the radial direction of cylinder in line crank shaft axis

5.39 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 5% Triacetin+ 95% Biodiesel blend application. Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

5.40 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 10% Triacetin+ 90% Biodiesel blend application. Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

5.41 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 15% Triacetin+ 85% Biodiesel blend application Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

5.42 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 20% Triacetin+ 80% Biodiesel blend application Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

5.43 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 25% Triacetin+ 75% Biodiesel blend application. Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

LIST OF TABLES

1.1 Oxygen content and molecular formula of different oxygenated fuels

1.2 Fatty acid distribution of common biodiesel feed stocks

1.3 Cut times for C8 to C18 Coconut oil FAMES

1.4 Properties of Triacetin (C9H14O6)

2.1 Properties of Diesel and Coconut Oil Methyl Ester

4.1 Specifications of the DI Diesel Engine

4.2 Measuring ranges and calibration values of Delta 1600 - L

4.3 Precision levels of Delta 1600 - L

4.4 Resolution of Delta 1600 – L

4.5 Specifications of the vibration (FFT) Analyzer

4.6 Properties of COME – Additive (Triacetin) blends

5.7 Full load combustion Parameters

NOMENCLATURE

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CHAPTER I LITERATURE SURVEY AND INTRODUCTION TO THE PROBLEM

Particulate matter (PM) or smoke emission and oxides of nitrogen (NOx emissions) are the two important harmful emissions in diesel engine. Fuel companies and the researchers around the world are devoted to reduce such emissions with different ways. Fuel modification, modification of combustion chamber design and exhaust after treatments are the important means to alleviate such emissions. In this context, engine researchers are hunting suitable alternative fuels for diesel engine. Among different alternative fuels, oxygenated fuel is a kind of alternative fuel. Diethylene glycol dimethyl ether (DGM), dimethoxy methane (DMM), dimethyl ether (DME), diethyl ether (DEE), methyl tertiary butyl ether (MTBE), dibutyl ether (DBE), dimethyl carbonate (DMC), methanol , ethanol and Triacetin (antiknocking agent for gasoline) have played their role to reduce diesel emissions. These fuels can either be used as a blend with conventional diesel/biodiesel fuel or as an additive or as a neat fuel. The presence of oxygen in the fuel molecular structure plays an important role to reduce PM and other harmful emissions from diesel engine.

The present work reports on the effect of Triacetin on bio-diesel combustion and exhaust emissions. It has been found that the exhaust emissions including PM, total unburnt hydrocarbon (THC), carbon monoxide (CO), smoke and engine noise were reduced with oxygenated fuels without any trade off between exhaust components. NOx emissions were reduced and in some cases were increased depending on the engine operating conditions. The reductions of the emissions were entirely depended on the oxygen content of the fuel. It has been reported that the combustion with oxygenated fuels were much faster than that of conventional diesel fuel. This was mainly due to the oxygen content in the fuel molecular structure and the low volatility of the oxygenated fuels. The lower volatile oxygenated fuel evaporated earlier and very good air-fuelmixing was achieved during combustion eventually resulted in lower exhaust emissions.

1.1 Survey of Additive Research by earlier authors

Due to price hike in 80’s and the rapid depletion of fossil fuels researchers concentrate research on alternative fuel. Methanol and ethanol were proved to be effective alternative fuels long ago for internal combustion (IC) engines. The oxygen in the methanol and ethanol molecule helps to make complete combustion when combusted with atmospheric oxygen. Most recently DME, oxygen content of 34.7% by weight has been noticed as one of the promising alternative fuels for IC engine. DME can be derived from natural gas, coal or even from biomass sources. Zhang et al. [2008] reported lower diesel emissions including smoke, THC, carbon dioxide, NOx, while slight increase in CO was noticed with DME compared to those of conventional diesel fuel. Authors reported the reason of reducing exhaust emissions were due to the presence of oxygen in the DME, absence of C-C bond, shorter ignition delay and instantaneous vaporization of DME. Like DME, DEE is another oxygenated fuel that has a very high Cetane number.

Iranmanesh et al. [2008] reported lower smoke and THC emissions due to higher cetane number and oxygen content of DEE. Authors also found lower CO emissions at high load condition, but higher at low load condition, also lower NOx emissions were realized with DEE-diesel blends. Kapilan et al. [2008] conducted experiments with 5 % DEE and found lower CO, THC and smoke emissions while a slight improvement in thermal efficiency was observed. Yeh et al. [2001] investigated the effect of fourteen different oxygenated fuels on diesel emissions, especially PM and NOx emissions. Authors found that for PM reduction, the most effective oxygenates on equal oxygen content basis were the C9 – C12 alcohols in both the engine and vehicle testing. No significant NOx emissions were increased with oxygenates.

The current work focuses on diesel emissions, biodiesel emissions (especially the NO emissions) special emphasis on PM, smoke and NOx emissions with oxygenated fuels. The effects of liquid oxygenated fuels on diesel and biodiesel combustions are discussed in this work as many researchers worked on liquid oxygenated fuels. The advantages of using liquid fuel are: easy transportation, easy injection to the combustion chamber and require less space to store. The role of fuel oxygen on PM and NO emissions was investigated with the previous research works. The target of the work is to make a correlation between fuel oxygen and the exhaust emissions.

Fujia et al. [2008]investigated the effect of fuel oxygen on total PM and other exhaust emissions of various biodiesels with oxygenated fuels like ethanol, DMC and DMM. They reported that the total PM emissions were reduced with all biodiesels compared to that of diesel fuel. THC emissions with all biodiesel reduced from 45-67%. Like THC, CO emissions were also reduced by 4-16% with the biodiesels. On the other hand, NOx emissions were increased with the addition of fuel oxygen content. Authors extended their research with three oxygenated fuels like ethanol, DMC and DMM. 10-30% ethanol was blended with PME, 10-20% DMC was added to WME and 10-20% DMM was added to CMEand concluded thatreductions in PM, THC and CO emissions and the increase in NOx emissions were due to the oxygen content in the fuel.

Zannis et al. [2004] conducted engine experiments with two oxygenated fuels, such as Diethylene Glycol Dimethyl Ether (Diglime – C6H14O3) and Diethylene Glycol Dibutyl Ether (Butyl-Diglime – C12H26O3), and one biodiesel (RME). These two oxygenated fuels and RME were blended with conventional diesel fuel (D1) maintaining oxygen content of 3 to 9%. The blended fuels were termed as DOX1, DOX2 and DOX3. The effect of fuel oxygen content on exhaust emissions at various engine loads was investigated. Authors reported relative changes of emissions between base fuel (diesel fuel) and oxygenated fuels DOX1 and DOX3. Soot, CO and THC emissions were reduced with increasing oxygen content for all loads. The reductions were higher for higher percentage of oxygen (9%) in the fuel blends and at high load condition. Authors reported that the reduction of soot, THC and CO emissions with increased fuel oxygen, which prevent to form soot emissions as less available carbon in fuel molecule. Authors also reported that the increase of local oxygen concentration enhances soot oxidation. On the other hand, NOx emissions were increased for higher oxygen content in the fuel. The additional oxygen in fuel rich region in conjunction with the increase in gas temperature due to the increase of cylinder pressure during combustion phase favors the formation of thermally generated NOx emissions.

Nurun Nabi [2000] also performed engine experiments with different oxygenated fuels and investigated the effects of fuel oxygen on diesel emissions and combustion. In Figure 1.1, PM emissions were shown with soluble organic fraction (SOF) and insoluble fraction (ISF), which is actually termed as dry soot. The results in figure 1.1 show the PM with neat diesel fuel, DGM100 and ENB100. Remarkable reduction in PM (Fig. 1.1)

and other emissions (not shown) were reported by the author. NOx emissions were also reduced with the oxygenated fuels (Figure 1.2). In Figure 1.1, only DGM was added to the conventional diesel fuel at volumetric percentages of 0, 25, 50, 75 and 100. Author concluded that it was oxygen, not the kinds or the chemical structures of the oxygenated fuels (Figure 1.3), was responsible for lower exhaust emissions. Author also found the lower adiabatic flame temperature which caused the lower NOx emissions with oxygenated fuels. Author extended their research applying EGR with oxygenated fuel Diethylene glycol dimethyl ether (DGM), remarkable reductions in both smoke and NOx emissions were realized compared to those of diesel fuel.

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Fig. 1.1 Improvement in PM with oxygenates

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Fig 1.2 Improvement in NOx emissions (BMEP=0.75 MPa) with DGM at three BMEP conditions

Nurun Nabi [2000] also attempted smokeless stoichiometric diesel combustion with a combination of high EGR, highly oxygenated fuels and a three way catalyst. Figure 1.4 shows the smoke emissions with neat Dimethoxy methane (DMM) and different kinds of highly oxygenated liquid fuels at stoichiometric and high (30 vol%) EGR conditions. The smoke emissions formed easily at these conditions. Neat DGM and DGM based fuels blended with ordinary diesel fuel or different kinds of oxygenated fuels shown in Table 1.1. From figure 1.4 it is observed that smoke emissions decreased sharply and linearly, and became zero at an oxygen content of 38%. The smoke free diesel combustion was also confirmed with two other oxygenated fuels of oxygen content of 40 and 42%. From this study it was suggested that DGM80+MeOH20 (DGM80+DMC20 (oxygen content of 40%) and DMM100 (oxygen content of 42%) were suitable for partial load high EGR and high load stoichiometric diesel combustion.

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Fig. 1.3 Oxygen content fuels (source: Nurun Nabi)

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Fig. 1.4 Smoke emissions with highly oxygenated fuels(¢ =1, EGR=30%)

(source: Nurun Nabi)

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Fig .1.5 Influence of EGR on NOx emissions with DMM 100(source: Nurun Nabi)

Table 1.1 Oxygen content and molecular formula of different oxygenated fuels (source:NurunNabi)

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[5-Fujia et al, 7-Nurun Nabi, 8-Anand et al, 10-Sathiyagnanam et al, 13-Yanfeng et al]

Figure 1.5 shows the influence of EGR on NOx emissions using DMM100. DMM100 realizes smoke free diesel operation at any engine conditions as discussed in Figure 1.4.The extreme right end points of figure 1.5 represent to the stoichiometric condition where a three-way catalyst is believed to be effectively reducing NOx emissions. Significantly low NOx emissions were achieved by applying high EGR (30%) at different excess air conditions where high NOx emissions reductions with a three-way catalyst are difficult. It can be seen from the figure 1.5, that 30 % EGR produces NOx emissions below 100 ppm at any excess air condition. With oxygenated fuel and stoichiometric diesel operation significantly increase the maximum BMEP, which was found to be as high as 0.9 MPa without applying EGR. To achieve ultra low diesel emissions, author incorporated a three way catalyst in a diesel exhaust system.

Anand and Mahalkshmi [2007] investigated the influence of EGR and oxygenated fuel on diesel combustion and exhaust emissions. Authors used DEE as oxygenated fuel and blended with diesel fuel up to 30 vol%. Authors incorporated 5% EGR using 20 vol% DEE to diesel fuel. Without applying EGR, lower NOx emissions were resulted from DEE blended fuels compared to diesel fuel, while higher smoke emissions were realized with the same blends. Authors also reported simultaneous NOx and smoke emissions with DEE20 when applied EGR. 80% NOx emissions were reduced with 15% EGR using 20 vol% DEE to diesel fuel. At full load under 15 vol% EGR conditions with 20 vol% DEE, the smoke emissions were reduced to 2.1 Bosch smoke units (BSU) from the baseline smoke level of 4.2 BSU. The reductions were due to the oxygen availability in DEE, which supplies oxygen during combustion.

Miyamoto et al. [1996] conducted experiments with eight kinds of oxygenated fuels to investigate the effect of low content oxygenate additive (maximum 10 vol%) on diesel emissions. The oxygen contents of the neat oxygenated fuels were ranging from 12.3 to 53.3 wt%. When blended these oxygenates with conventional diesel fuel, particulate and smoke emissions were suppressed significantly without increasing NOx. THC and CO emissions were also decreased slightly. Oxygen content in the blended fuels and the low volatility of the fuel were the reasons for decreasing the emissions.

Sathiyagnanam et al. [2008] conducted diesel engine experiments with DMM and dimethoxy propane (DMP). Authors blended DMM and DMP as additives (1 ml to 3 ml) to diesel fuel and conducted the experiments by introducing a diesel particulate filter (DPF). The experimental results were compared with and without DPF using the two oxygenated additives (DMM and DMP) and diesel as a base fuel. It was found that smoke and PM emissions were reduced with the addition of DMM and DMP to diesel fuel. Smoke and PM emissions reduction was higher with DPF. NOx emissions on the other hand were higher and reported that higher by 13 g/kWh with DMM and 16 g/kWh with DMP blended fuels.

Lu et al. [2005] investigated the spray characteristics and diesel exhaust emissions with three oxygenated fuels, namely ethanol, DMC and DMM. Authors investigated the spray characteristics (Sauter mean diameter (SMD) and axial mean velocity distribution) while the engine experiments were performed with DMC-diesel hybrid fuels. For spray analysis DMM was blended to diesel fuel at blending ratios of 25 and 50 vol%, while for DMC the ratios were 10, 20 and 30 vol%. It was found that the droplet diameter of the DMM-diesel hybrid fuels decreased with increased axial distance from the injector tip. Compared to diesel fuel, the mean axial velocities of DMM-diesel hybrid fuels were higher. The lower SMD and higher axial mean velocity with DMM-diesel hybrid fuels were due to the inherent properties of lower kinematic viscosity and surface tension of neat DMM. Concerning exhaust emissions it was reported that the smoke and NOx emissions were reduced markedly with DMC-diesel hybrid fuels. The reductions were higher with the higher percentages of DMC to diesel fuel. The reduction of NOx emissions was due to the shorter combustion duration, while presence of oxygen in hybrid fuels was additional reason for reduction in smoke emissions.

Wang et al. [2009] carried out engine experiments with several oxygenated fuels like biodiesel, ethanol, DMM and DMC. The authors used different oxygenated blends with diesel fuel. The biodiesels used in the experiments were derived from palm oil, waste cooking oil and acidified oil. It was found that the dry soot in PM emissions decreased significantly as the fuel oxygen content increased. SOF, which is a constituent of PM were found to be higher. Authors also investigated the effect of Cetane number on SOF emissions. It was found that with the increase in fuel Cetane number SOF emissions decrease. Authors found that an oxygenated fuel blend of 50% biodiesel, 15% DMC and 35% diesel fuel (oxygen content of the blend is 15.46%) met the Chinese 4th stage standard, which is equivalent to Euro IV for heavy duty engines without modifying or using any after treatment device.

Yanfeng et al. [2007] did experiments with a new kind of oxygenated fuel, 2-methoxyethyl acetate (MEA) of oxygen content of 40.7 wt%. Authors reported significant reduction in smoke emissions with MEA blends. THC and CO emissions were also reduced with higher blending percentages of MEA to diesel fuel. However, the MEA blends had almost no effects on NOx emissions. Authors suggested that 15% MEA blend is suitable for diesel emissions, engine power and fuel economy.

Guo et al. [2005] attempted engine experiments with a new oxygenated fuel, methyl 2-ethoxyethyl carbonate (MEEC) by introducing an ether group to DMC molecule. MEEC was blended with diesel fuel from 15 to 25 vol%. For a 25% MEEC blend with full load condition, CO was decreased by 29.2 to 40.5%, smoke by 0.3 to 0.5 BSU. NOx emissions were also decreased by 15.9% when the 15% MEEC was blended with diesel fuel. Output power of the engine was not noticeably changed with MEEC blends; however 2.5 to 5.5% fuel consumption was increased with 20% MEEC. BSFC was improved by 10% when the engine was fuelled with 20%MEEC.

Cheng et al. [1999] carried out experiments with two oxygenates, DMM and DEE blended with conventional diesel fuel and a Fischer-Tropsch (F-T) diesel fuel to investigate their exhaust emissions reduction potential. Both DMM and DEE reduced PM emissions. Like PM, NOx emissions were also reduced with these blends. 35% less PM was observed with DMM30, while 30% less PM emissions were resulted in with DEE30 compared to diesel fuel. F-T fuel also reduced PM emissions by 29%. NOx emissions, on the other hand were reduced by 1-10% with F-T, DMM and DEE blends. Fuel conversion efficiency (thermal efficiency) was reduced with the tested fuels compared to diesel fuel.

Chen and Wang et al. [2008] investigated the effect of fuel oxygen on diesel emissions and performance. Authors blended ethanol and biodiesel to diesel fuel. The blending percentages of ethanol to diesel fuel were 10, 20 and 30%, while the biodiesel percentages were 5 and 10%. Engine torque was reduced and BSFC was increased with blended fuels. Using the diesel ethanol and biodiesel blends the PM was reduced significantly and the reduction was found to be significant at higher percentages of oxygen in the fuels. NOx emissions were slightly increased or the same as baseline diesel fuel. THC emissions with oxygenated blends were reduced under most operating conditions. CO emissions were increased at low to medium load conditions, but reduced at high load condition.

Tat and Wang et al. [2007] tested for diesel engine exhaust emissions with biodiesel. Authors used soy methyl ester (soy biodiesel) and high oleic methyl ester to investigate the brake specific NOx, THC, CO and smoke emissions. Both biodiesels are some sort of oxygenated fuels as approximately 11 wt% oxygen contain in their molecular structures. The brake specific THC and the smoke emissions were lower with the two biodiesels compared to diesel fuel. The brake specific NOx emissions with two biodiesels were higher than those of diesel fuel. The reasons of higher NOx emissions with biodiesels are as follows: the higher proportion of unsaturated fatty acid compositions in the biodiesels, advance injection timing leads to earlier ignition, which leads to higher peak cylinder temperatures. Biodiesels produce less soot than diesel fuel, which may increase NOx emissions.

Around the world, there is a growing increase in biofuels consumption, mainly ethanol and biodiesel as well as their blends with diesel that reduce the cost impact of biofuels while retaining some of the advantages of the biofuels. This increase is due to several factors like decreasing the dependence on imported petroleum; providing a market for the excess production of vegetable oils and animal fats; using renewable and biodegradable fuels; reducing global warming due to its closed carbon cycle by CO2 recycling; increasing lubricity; and reducing substantially the exhaust emissions of carbon monoxide, unburned hydrocarbons, and particulate emissions from diesel engines. However, there are major drawbacks in the use of biofuel blends as NOx tends to be higher, the intervals of motor parts replacement such as fuel filters are reduced and degradation by chronic exposure of varnish deposits in fuel tanks and fuel lines, paint, concrete, and paving occurs as some materials are incompatible. Here, fuel additives become indispensable tools not only to decrease these drawbacks but also to produce specified products that meet international and regional standards like EN 14214, ASTM D 6751, and DIN EN 14214, allowing the fuels trade to take place. Additives improve ignition and combustion efficiency, stabilize fuel mixtures, protect the motor from abrasion and wax deposition, and reduce pollutant emissions, among other features.

Nu´bia M. Ribeiro et al. [2007] explained two basic trends are becoming more relevant: the progressive reduction of sulfur content and the increased use of biofuels. Several additives’ compositions may be used as long as they keep the basic chemical functions that are active.

Emissions from diesel engines seriously threaten the environment and are considered one of the major sources of air pollution. It was proved that these pollutants cause impacts in the ecological systems, lead to environmental problems, and carry carcinogenic components that significantly endanger the health of human beings. These can cause serious health problems, especially respiratory and cardiovascular problems. Increasing worldwide concern about combustion-related pollutants, such as particulate matter (PM), oxides of nitrogen (NOx), carbon monoxide (CO), total hydrocarbons (THC), acid rain, and photochemical smog and depletion of the ozone layer has led several countries to regulate emissions and give directives for implementation and compliance. Ulrich et al [2003], He et al. [2003] suggested that clean combustion of diesel engines can be fulfilled only if engine development is coupled with diesel fuel reformulation or additive introduction.Yanfeng et al. [2007], Gu¨ru et al. [2002], Pereira et al. [2002] suggestedthe methods to reduce PM and NOx emissions include high-pressure injection, turbo charging, and exhaust after treatments or the use of fuel additives, which is thought to be one of the most attractive solutions.

Pereira et al. [2002] studied on engine exhaust contains volatile organic compounds (VOCs), which embody unburned fuel emissions and other VOCs generated as by products of incomplete combustion (PIC). Some VOCs described as being of health concern are acetaldehyde, acrolein, benzene, 1, 3-butadiene, formaldehyde, and naphthalene. Gasoline and diesel powered vehicles are the largest source of VOCs in most urban areas.

Diesel oil is a fuel derived from petroleum and consists mainly of aliphatic hydrocarbons containing 8-28 carbon atoms with boiling points in the range of 130-370 °C. It is a blend of fractions of hydrocarbons heavier than those of the hydrocarbons in gasoline and with a lower H/C mass ratio, which determines the high emission of carbon compounds per unit of energy delivered to the engine. A reduction in consumption and improvements in the quality of diesel oil have been the object of study by various specialists, motivated by growing demands in the transport and electric sectors.

Commercially available diesel oil is a combination of fossil diesel and several additives, which are added in several amounts to perform specific functions. Among others, there are additives to (1) reduce pernicious emissions; (2) improve fluid stability over a wider range of conditions; (3) improve the viscosity index, reducing the rate of viscosity change with temperature; (4) improve ignition by reducing its delay time, flash point, and so forth; and (5) reduce wear with agents that adsorb onto metal surfaces and sacrificially provide chemical-to-chemical contact rather than metal-to-metal contact under high-load conditions.

There is also an increasing trend to use blends with biomass products such as vegetable oil, ethanol and biodiesel by increasing the use of alternative fuels. Blends of diesel and biodiesel usually require additives to improve the lubricity, stability, and combustion efficiency by increasing the Cetane number. Blends of diesel and ethanol (E-diesel) usually require additives to improve miscibility and reduce knock.

Diesel additives can also be classified according to the purpose for which they are designed. Preflame additives are designed to correct problems that occur prior to burning and include dispersants, pour point depressants, and emulsifiers, which act as cleaning agents. Chao et al. [2000] described that flame additives are used to improve combustion efficiency in the combustion chamber, to increase cetane number, to reduce the formation of carbon deposits, to avoid oxidation reactions and contamination of fuel and filters clogging by rust, and to inhibit potential explosions caused by changes in static electricity. Yang et al. [1998] suggested that Postflame additives are designed to reduce carbon deposits in the engine, smoke, and emissions.

1.2 Types of Additives

1.2.1 Metal-Based Additives:

Yang et al. [1998], Kasper et al. [1999], Myamoto et al. [1987] experimented on some metal-based additives and reported effective in lowering diesel emissions. They may reduce diesel emissions by two ways. First, the metals either react with water to produce hydroxyl radicals, which enhance soot oxidation, or react directly with carbon atoms in the soot, thereby lowering the oxidation temperature. When these additives are used after combustion in the engine, the metal acts as a nucleus for soot deposition. As per Burtscher et al. [1999], Jelles et al. [1999] usually, the additive is added as a metal-organic compound, and it is emitted in the particulate phase as oxide, on soot particles or forming new nanometer-sized particles by homogeneous nucleation of the additive.

Danilov [2001] studied, the ferrocene additives, it was found in particular that they form condensation sites (hypothetically iron oxides) before the formation of carbon particles in the combustion zone. Carbon particles are condensed on them and are totally burned in the following stages of the process. Additionally, ferrocene reduces carbonaceous matter in combustion by more efficient burnout rather than by the inhibition of soot formation. Kasper et al. [1999] explained that ferrocene vapor leads to particle formation early in the flame, that is, below the soot inception point of an unseeded flame.

Additives called “smoke suppressants” reduce emissions of black smoke (actually soot) with the exhaust gases from diesel engines. Black smoke is formed in engine overloading and in fuel system malfunctions. Danilov [2001] suggested that some metal compounds can cause soot to burn, primarily barium, manganese, and calcium compounds, and are proposed as smoke-suppressant additives. Truex et al. [1980]investigated the effect of barium fuel additives on carbonaceous particulate (soot) emissions. Barium has been shown to be the most effective of 40 metals tested in reducing carbonaceous particulate emissions. Various investigators have reported 20-75% reductions invisible smoke emissions from diesel exhaust by using barium fuel additives.

1.2.2 Oxygenated Additives:

Song et al. [2003] worked on fuel additives of oxygenated compounds. The idea of using oxygen to produce a cleaner burning of diesel fuels is half a century old. Since that early work, numerous researchers have reported the addition of a variety of oxygenated compounds to diesel fuel. Some oxygenate compounds used are ethanol (He et al. [2003], Satge´ de Caro et al. [2001], Shi et al. [2005], Xing-Cai et al. [2004]), acetoacetic esters and dicarboxylic acid esters (Anastopoulos et al. [2001]), ethylene glycol monoacetate (Lin and Huang [2003]), 2-hydroxy-ethyl esters (Rezende et al. [2005]),diethylene glycol dimethyl ether, sorbitan monooleate and polyoxyethylene sorbitan monooleate (Lin and Wang [2004]),dibutyl maleate and tripropylene glycol monomethyl ether (Marchetti et al. [2003]), ethanol and dimethyl ether (Song et al. 2003]), dimethyl ether (DME), dimethyl carbonate (DMC) and dimethoxy methane (Yanfeng et al. [2007]), 1-octylamino-3-octyloxy-2-propanol and N-octyl nitramine (Satge´ de Caro et al. [2001]), dimethoxy propane and dimethoxy ethane (Jiang et al. [2001]), biodiesel (Shi etal. [2005], Geller and Goodrum [2004], Knothe, Matheaus et al.[2003]), and a mixture of methanol and ethanol (Chao et al. [2000]).

Marchetti et al. [2003] considered Oxygenated additives for reducing the ignition temperature of particulates. However, the reduction of particulate emissions through the introduction of oxygenated compounds depends on the molecular structure and oxygen content of the fuel, and also depends on the local oxygen concentration in the fuel plume as per Kitamra et al. [2001]. To reduce particulate emissions, fuel-compatible oxygen-bearing compounds should be blended with diesel to produce a composite fuel containing 10-25% v/v of oxygenate. Therefore, the composition of diesel and the use of additives directly affect properties such as density, viscosity, volatility, behavior at low temperatures, and the Cetane number (He et al. [2003], Gu¨ru, et al. [2002], Song et al. [2003], Shi et al. [2005], Anastopoulos et al. [2001], Lin and Huang [2003], Knothe and Matheaus et al. [2003], De Menezes et al. [2006], Ladommatos et al. [1996]).Zabetta et al. [2006] showed that the ignition temperature of particulates from seed-derived oils (SO) and from blends of SO with diesel fuel (DF) can be lower than that of particulate from neat DF.

According to De Menezes et al.[2006] by increasing the concentration of additives (e.g., ethanol and ethyl tert-butyl ether or tert-amyl ethyl ether), there is a reduction in the cetane number, and an increase in hydrocarbons leads to a decrease of CO up to 20% in relation to diesel fuel alone. The fuel cetane number decreases with an increase of ethanol content in the fuel because of the low cetane number of this alcohol. Another factor that influences the decrease in cetane number level is the incomplete combustion of the ethanol-air mixture. Factors causing combustion deterioration, such as high latent heats of evaporation, could be responsible for the increased CO emission. Another reason for the high CO emission is the increase in ignition delay. This leads to a lower combustion temperature at lower and medium loads (Chao et al. [2000], Shi et al. [20005], Xing-Cai et al. [2004]).NOx emissions decrease with ethanol addition (Xing-Cai et al. [2004]).In addition, Shi et al. [2005], Hansen et al. [2005] concludeda measurable increase of the concentration of oxygen in combustion products from the blends was observed. This may be another cause of the NOx increase.

He et al. [2003], Satge´ de Caro et al. [2001], Shi et al. [2005], Hansen et al. [2005] studied the presence of some oxygenated additives (ethanol, 1-octylamino-3-octyloxy-2-propanol, and N-octyl nitramine) results in the formation of a lubricant film with beneficial anti-wear properties. The increase volatility of the mixture is also apparent as a lower flash point at ambient temperature. Although this does not have a direct effect on engine performance, such mixtures would be subjected to the legislation concerning fuel handling.

As per Bhide et al. [2003] DME is a potential ultra clean diesel fuel. Dimethyl ether burns without producing the smoke associated with diesel combustion and can be manufactured from synthesis of gas or methanol. However, DME has a low viscosity compared to diesel fuel and has insufficient lubricity to prevent excessive wear in fuel injection systems. A strategy in order to obtain cleaner-burning fuels with satisfactory properties is the use of diesel-DME blends. The viscosity of blends of DME with various fuels and additives, including low-sulfur diesel fuel, soybean oil, biodiesel, and various lubricity additives, was characterized over a range of blend ratios. It was observed that none of the additives or fuels provides adequate viscosity when blended with more than 50% DME. Viscosity, rather than lubricity, may be the limiting factor in using DME. Song et al. [2003] affirmed that there are conflicting results regarding the effect of the structure of an oxygenated compound blended with diesel on the reduction level of the particulate emissions. Authors concluded that DME was still more effective than ethanol in reducing aromatic species.

Diesel fuels with low sulfur content are characterized by poor anti-wear properties. It is believed that, when the sulfur content in the fuel is less than 0.05%, special anti-wear additives should be used. For example as per Danilov [2001], the most common additives of this type contain carboxylic acid derivatives: esters, amides, products of the transesterification of vegetable oils and animal fats with alcohols or phenols, hydrocarbons with several polar functional groups, amino groups, or hydroxyls.

Ethylene glycol monoacetate was found to be a promising candidate as an oxygenated diesel additive due to its low-poison and oxygen-rich composition properties (Lin andHuang [2003]).Experimental results showed that increasing the ethylene glycol mono-acetate ratio in diesel fuel caused an increase in the brake-specific fuel consumption while the excess air and oxygen emission concentrations decreased.

The 2-methoxyethyl acetate (MEA) can be easily blended with diesel, with little change in the fuel delivery system, engine power, and fuel consumption. Experiments showed that MEA was a good oxygenated additive of diesel for compression- ignition engines and can be used to decrease emissions of smoke, HC, and CO concluded by Yanfeng et al. [2007]. Other environmentally safe additives for diesel fuels were tested: high-molecular-weight monohydric, dihydric, trihydric, and tetrahydric alcohols; carboxylic and polycarboxylic acids; C24-C65 mono- or poly- carboxylic acid esters with two to three carboxyl groups and C2-C9 multihydric alcohols with 2-10 hydroxyl groups; mixtures of synthetic or plant esters of mono-, di-, tri-, and tetrahydric C2-C18 alcohols and carboxylic acids with C3-C45 acyls; the product of the reaction of aromatic triazole (tolyl- triazole) and a C10-C40 fatty acid; and so forth. The studies showed the weak effect of the additive compounds containing carbonyl, ether, and ester groups on the anti-wear properties of the fuel. Spirkin et al. [2001] presented that following compounds are in ascending order with respect to anti-wear effectiveness: ethers, aldehydes and ketones, esters, alcohols, and acids.

DMC is usually used as an oxygenated additive to improve combustion and reduce emissions of diesel engines. Wang and Huang et al. [2000] concluded that Dimethyl carbonate presents good blend fuel properties and reduces smoke almost linearly with its concentration. However, it is difficult to fuel diesel engines, directly with DMC due to its low cetane number and high latent heat of vaporization. The addition of 10% dimethyl carbonate in the fuel promotes a smoke reduction of 35-50%, and also apparent reductions of hydrocarbons and carbon monoxide densities were attained with a slight increase in NOx emissions. The engine fueled with dimethyl carbonate emitted almost smokeless exhaust gas because this oxygenated fuel has no C-C bonds in the molecules. To study DMC combustion in diesel engines, Xiaolu et al. [2006] proposed an approach that combines internal exhaust gas recirculation with a small injection of diesel fuel to ignite the DMC. Preliminary studies demonstrated that this engine can be fueled with DMC with an almost zero level of smoke and a low exhaust gas temperature. This DMC-fueled engine has lower NOx emissions and 2-3% higher effective thermal efficiency than the engine operated with diesel in moderate and high load zones.

The chemical agent diglyme, which is used as an oxygenated additive to diesel fuel, improves combustion characteristics of diesel engines, boilers, and furnaces. The emulsification properties of a multiphase emulsion of the oil-in-water-in-oil (O/W/O) type added with this oxygenated agent were investigated by Lin et al. [2004]. Experimental results show that the viscosities of O/W and W/O two-phase emulsions increase with an increase of their inner phase content and the addition of diglyme. The addition of a diglyme agent to the emulsions deteriorates the emulsification activity and emulsification stability of W/O and O/W/O.

1.2.3 Depressants and Wax Dispersants:

Yu-Hui and Ben-Xian [2006] performed experiments onpetroleum distillate fuels contain n-paraffin waxes that tend to be separated from the oil at low temperatures. The waxes generally crystallize as an interlocking network of fine sheets, thereby trapping the remaining fuel in cage like structures and causing cold-flow problems such as clogging of fuel lines and filters in engine fuel systems. Several techniques have been used to minimize the problems caused by the wax deposition, and the continuous addition of polymeric inhibitors is considered to be an attractive technological alternative. The addition of copolymers such as polyacrylates, polymethacrylates, or poly (ethylene-co-vinyl acetate) (EVA) inhibits the deposition phenomenon; those copolymers are composed of a hydrocarbon chain, which provides the interaction between additives and paraffin, and a polar segment that is responsible for the wax crystal morphology modification necessary to inhibit the aggregation stage. Those copolymers are known as cold-filter plugging point (CFPP) additives or pour point depressants (PPDs). EVA copolymers present a good efficiency as diesel fuel CFPP additives.

The addition of PPDs has been proved to be an efficient way to inhibit the wax deposition of diesel fuels. However, the complexity of the oil is far beyond current commercial PPD products. So far, it mainly depends on syntheses of numerous candidate compounds followed by repeating experimental measurements in order to improve the efficiency of PPDs. Wu et al. [2005] used molecular dynamic simulation to investigate the interaction between crystal planes of wax and EVA, as well as its derivatives with different branches, on the basis of the model of wax. The side-chain effects on adsorption energy and equilibrium adsorption conformations were studied under different kinds and numbers of branches. They concluded that side chains introduced by propylene were a benefit to the affinity between the EVA-type molecules and alkanes in the wax plane, comparing with those branches introduced by butylenes. Molecular dynamic simulation calculations indicated that EVAP with one branch adjacent to the VA (vinyl acetate) group would be a better PPD additive than EVA in diesel fuels.

Marie et al. [2004] studied on performance of wax dispersant additives is especially important in countries with long winters. It was shown that traditional depressants (polyacrylates and copolymers of olefins and vinyl acetate) do not prevent separation during cold storage by reducing the solid point of the fuels. As a result, the fuel separates into two layers: an upper, clear layer and a lower, cloudy layer rich in waxes. Both layers are mobile, but when fuel is taken off of the lower layer, the engine misses. Special additives, wax dispersants or precipitators solve the problem. Their effect consists in the formation of very small wax crystals with high sedimentation stability. They are acid amides, polymers modified with amino groups, and so forth.

Gu¨ru et al. [2002] studied the high freezing point of diesel fuel causes clogging of filters, and hence there are some difficulties when it is used in cold conditions. In order to reduce the freezing point of the fuel, about 100 ppm of paradine is added, commonly after refining. The mechanism of action of additives that control the sedimentation of paraffin crystals after their crystallization in model diesel oil has been studied by Marie et al. [2004]. The chemical analysis of the crystals and detailed measurements of the sedimentation phenomenon give new insights into this complex process. Thus, the wax anti settling additives used for preventing wax crystal sedimentation adsorbs onto surfaces of wax particles and provides them with enhanced colloidal stability. The settling rate is not related to the size of the crystals or to the viscosity of the liquid medium, but to the ability of the additives to prevent the aggregation of wax crystals.

1.2.4 Ignition Promoters:

In internal combustion engines operating on diesel fuel, Suppes et al. [2001] concluded that cetane number of the fuel is one of the most important characteristics of the combustion process. Improved ignition is detected as a decrease in the ignition delay time, the ignition delay time being measured as the time between the start of fuel injection and detectable ignition. Shorter ignition delay times have been directly correlated with a faster startup in cold weather, reduced NOx emissions, and smoother engine operation. Zinenko et al. [2002] stated cetane number is a function of the composition and structure of the hydrocarbons present in the diesel. It decreases with an increase in the aromatic hydrocarbon content and increases with an increase in the n-paraffin and olefin content. The utilization of Cetane-improving additives is necessary to avoid difficulties in cold starting and other performance problems associated with low Cetane numbers. Ignition promoters have traditionally been given to alkyl nitrates (e.g., amyl nitrate, hexyl nitrate, and octyl nitrate), but compounds like alkyl peroxides have also been proposed (Danilov [2001], Schabron and Fuller [1982]).

The commercial market considers several factors when selecting and using cetane improvers; these include (a) efficacy toward improving ignition properties, (b) hazards associated with storage and transport, (c) additional costs associated with diluting cetane improvers to allow safe transport, and (d) nitrogen content (Suppes et al. [2001]). Alkyl nitrates are characterized by relatively high efficiency and simultaneously, many serious drawbacks. They are toxic, corrosive and worsen the color of the fuels during storage.

For this reason, the attempts to create ignition promoters based on other compounds are ongoing, and organic peroxides have received the most attention. Among the organic peroxides, symmetric dialkyl and diaryl peroxides are of practical interest. They are more stable in storage and heating and do not decompose on contact with water, olefins, and others compounds which can be present in commercial fuels (Danilov and Mitusova et al. [2003]). In another work, Suppes et al. [2001] experimented withnitrate derivatives of soybean oil were synthesized and evaluated as an alternative to 2-ethylhexyl nitrate (EHN), which currently dominates the Cetane improver market. The synthesized additive exhibited NOx-reducing capabilities similar to that of EHN when used in a diesel fuel. They also provided significant lubricity enhancement to the fuels at the same concentrations used to provide the Cetane enhancement. Depending on the product, these additives exhibit increased stability and lower volatility than EHN. Commercially competitive enhancements of both ignition-related properties and lubricity were achieved in a single product.

1.2.5 Diesel-Vegetable Oil Blends:

The heating value of vegetable oils is similar to that of diesel fuel. However, their use in direct injection diesel engines is restricted by some unfavorable physical properties, particularly their viscosity. The viscosity of vegetable oil is approximately 10 times higher than that of diesel fuel. Therefore, the use of vegetable oil in direct injection diesel engines creates poor fuel atomization, incomplete combustion, carbon deposition on the injector, and fuel buildup in the lubricant oils, resulting in serious engine fouling. The possible treatments explained by Dmytryshyn et al. [2004] andemployed to improve the oil viscosity include dilution with a suitable solvent, emulsification, pyrolysis, and transesterification to obtain biodiesel.

Al-Hasan [2002] conducted several experiments by using biomass and vegetable oils as alternative fuels or blended with diesel fuel. A study in Indonesia is an example, where palm oil was used as an additive to fuels. A study in which oil was extracted from Pistachia Palestine (PP) fruits is another example. Mixtures of such oil with diesel fuel were tested to determine the potential of the oil as a diesel additive, and successful results were obtained without any engine modifications. It was shown that the addition of PP oil to diesel fuel decreases both the brake power and thermal efficiency of the test engine and increases the brake-specific fuel consumption. This is due to the lower heating value of the PP oil compared to diesel fuel. Jatropha oil was blended with diesel by Forson et al. [2004] in a proportion of 2.6% by volume, and it was found that the oil can be used as an ignition-accelerator additive for poor diesel fuels.

Stumborg et al. [1996] studied that hydro-processed vegetable oils can be used for diesel fuel improvement as well. In 1996, Canadian researchers investigated the use of conventional refinery technology to convert vegetable oils into a product resembling diesel fuel. It was found that the use of a medium severity refinery hydro-process yielded a product (super cetane) in the diesel boiling range with a high cetane value (55-90) and the impact of the “super cetane”/ diesel mixture on engine emissions is similar to the impact cetane enhancement via a nitrate additive when added to conventional diesel fuel. An attractive advantage of hydro-processing over esterification includes lower processing cost.

1.3 Additives for Diesel-Biodiesel Blends

At present, concern about environmental regulations has been the major reason to look for alternative fuels. The use of biodiesel has presented a promising alternative in the world. It is not only a renewable energy source, but it can also reduce the dependence on imported oil and support agricultural subsidies in certain regions. Pinto et al. [2005] studied several aspects with the aim of making possible use of biodiesel as fuel. They include appropriate sources of raw material, comparative studies between emissions of diesel and biodiesel, development of new catalysts and new technological routes for the biofuel production, development of qualitative and quantitative methods for its characterization, and so forth. Authors presented a critical analysis on the most used oil sources, the catalysts, methods to verify the transesterification yields, the comparative studies on emissions from fossil diesel and blends with biodiesel in variable proportions.

1.3.1. Characteristics of Biodiesel & Blends versus Diesel:

Christopher and Weaver [2002] in the final report on biodiesel explained the usage of neat biodiesel in terms of emissions of PM and NOx in relation to natural gas. “Biodiesel” is a mixture of alkyl esters of fatty acids of biological origin, which can be used as fuel for diesel engines. Common feed stocks for biodiesel production include soy oil, rapeseed (canola) oil, and recycled “yellow” grease from restaurants. Waste grease from restaurant grease traps and mustard seed oil as a co-product with “organic” insecticides are potential future sources. In general, use of 100% biodiesel in place of petroleum diesel increases NOx emissions slightly, while sharply reducing NMHC, CO, polynuclear aromatic hydrocarbons, and other toxic species. The solid carbon fraction of the PM emissions is greatly reduced, while the soluble organic fraction of the PM emissions increases. The effect on total PM mass depends on the operating conditions. Under typical heavy-duty truck duty cycles, the solid carbon effect dominates, and PM emissions are reduced by 20 to 60%. Under lightly-loaded duty cycles (such as a diesel pickup truck or SUV) the effect on SOF dominates, so that total PM emissions increase. The NOx increase with biodiesel may also be reversed at light loads. Biodiesel emissions also depend on the feedstock used: saturated fats give lower NOx and better PM reductions, but the product tends to congeal in cold weather. For practical biodiesel feed stocks, the estimated NOx increase in a heavy-duty truck cycle would be about 5%. Overall, the emission effects of 100% biodiesel compare unfavorably to natural gas as a substitute for diesel fuel.

Biodiesel is defined as alkyl esters of fatty acids, obtained by the transesterification of oils or fats, from plants or animals, with short-chain alcohols such as methanol and ethanol. It has an engine performance comparable to that with conventional diesel and could be used pure or blended with diesel (Pinto et al. [2005], Pimentel et al. [2006]). Biodiesel is nonflammable, nonexplosive, biodegradable, and nontoxic. Besides its usage provide reduction of many harmful exhaust emissions. A nearly complete absence of sulfur oxide (SOx) emissions, particulate and soot, and reduction in polycyclic aromatic hydrocarbons emissions can be achieved.

However, there are some technical problems associated with the use of biodiesel fuels. The use of some of them includes an increase in nitrogen oxide (NOx) exhaust emissions, which have stringent environmental regulations, and relatively poor low-temperature flow properties compared to diesel. Another problem is the oxidation stability of biodiesel. The esters of unsaturated fatty acids are unstable with respect to light, catalytic systems and atmospheric oxygen. Since diesel fuels from fossil oil have good oxidation stability, automobile companies have not considered fuel degradation when developing diesel engines and vehicles. It is one of the key issues in using vegetable oil - based fuels, and attention is given to the stability of biodiesel during storage and use. These problems could be circumvented by using additives.

Scherer et al. [2001] studied about additives that can improve the low-temperature performance of diesel-biodiesel blends. The low-temperature properties include the solidification point, pour point, and cold filter plugging point (CFPP). In 2001, a patent reported the use of block copolymers of long-chain alkyl methacrylates and acrylates as pour point depressants and flow improvers, suggesting their use as biodiesel fuel additives. Barbour et al. [2003] focused on the improvement of cold filter plugging performance in pure biodiesel and diesel-biodiesel blends. Many additives such as ethylene-vinyl acetate copolymers, polymethacrylates, and styrene-maleic anhydride copolymers, allegedly reduce CFPP. Ming et al. studied some additives (synthesized or commercially available) suitable for reducing the pour point and cloud point values of palm oil methyl esters (POME). Ming et al. [2005] among the additives studied in this research were Tween-80, dihydroxy fatty acid (DHFA), acrylated polyester prepolymer, palm-based polyol, a blend of DHFA and palm-based polyol at a 1:1 ratio, an additive synthesized using DHFA and ethyl hexanol, and castor oil ricinoleate. All additives improved the low-temperature properties of biodiesel and presented significant reductions in both the pour point and cloud point of POME.

Chiu et al. [2004] studied about cloud points and pour points have been routinely used to characterize the cold flow operability of diesel fuels in the petroleum industry. Cloud points are useful as fuel quality control specifications for refiners when blending fuels in cold climates and also as low-temperature operability indicators for diesel-powered operators when used at cold ambient temperatures. At the cloud point, long-chain hydrocarbons (or saturated fatty acid ester in biodiesel) begin to form small wax crystals, and when enough wax crystals with diameters exceeding 0.5 mm have precipitated, the fuel appears cloudy. As temperatures decrease below the cloud point, crystals continuously grow and agglomerate until they are large enough to plug fuel filter systems. Eventually, the fuel can gel up and cease to pour even though much of the fuel has not frozen. Pour points are useful for characterizing the suitability of a fuel for wide storage and pipeline distribution. Dunn and Bagby [1995] studied and reported that blending petroleum diesel with soybean biodiesel could improve its low temperature characteristics. Results showed that blending 20-30% soybean biodiesel with diesel improved the pour point, reducing it by 10 °C.

Barbour and Duncan et al. [2002] studied about surfactants additives that are used to reduce injector tip deposits. The patent reported the use of a product from a succinic acylating agent and a polyamine, having at least one condensable primary amine group, as a surfactant.

1.3.2. Lubricity Additives:

Dmytryshyn et al. [2004], Lang et al. [2001], Hughes et al. [2002], Karonis et al. [1999] observed that fuel lubricity can be enhanced by the addition of lubricity additives. They comprise a range of surface-active chemicals. They have an affinity for metal surfaces, and they form boundary films that prevent metal-to-metal contact that leads to wear under light to moderate loads. Much research shows that the addition of lubricity additives is not necessary in low-sulfur diesel-biodiesel blends once vegetable oil methyl esters enhance the fuel lubricity.Bhatnagar et al. [2006] concluded that the mixture of fuel and additive provides a stable film on the metal surface and substantially reduces the wear scar diameter.

Hillion et al. [1999] showed that the presence of mono-and diacylglycerols in the range of 100-200 ppm provides sufficient anti-wear capacity to safely ensure normal operation of the motor injection system, even when using a low-sulfur diesel. Some years later, Knothe and Steidley [2005] compared the lubricity of numerous fatty compounds to that of hydrocarbon compounds found in diesel. According to their study, fatty compounds possess better lubricity than hydrocarbons, because of their polarity-imparting oxygen atoms. Additionally, pure free fatty acids, monoacylglycerols, and glycerol possess better lubricity than pure esters, because of their free OH groups. An order of oxygenated moieties enhancing lubricity (COOH >CHO > OH > COOCH3 > C-O > C-O-C) was obtained from studying various oxygenated C10 compounds. Another experiment, with pure C3 compounds containing OH, NH2, and SH groups, shows that oxygen enhances lubricity more than nitrogen and sulfur. The addition of biodiesel improves the lubricity of low-sulfur diesel more than pure fatty esters, indicating that other biodiesel components cause lubricity enhancement at low biodiesel blend levels. The addition of polar compounds such as free fatty acids or monoacylglycerols improves the lubricity of low-level blends of esters in low-lubricity diesel. This result suggests that these species, considered as contaminants resulting from biodiesel production, are responsible for the lubricity of low-level blends of biodiesel in low-sulfur diesel. A similar study published by Hu et al. [2005] showed that methyl esters and monoacylglycerols determine the lubricity of biodiesel. Authors concluded that free fatty acids and diacylglycerols can also affect the lubricity of biodiesel, but not so much as monoacylglycerols. Triacylglycerols almost have no effect on the lubricity of biodiesel.

In recent years, Anastopoulos et al. [2001], Geller and Goodrum[2004] studied fatty acid methyl esters (FAMEs), commonly known as biodiesel, have successfully been used as diesel fuel lubricity improvers. The lubricity improvement observed from vegetable-oil-based methyl ester additives is greater than that observed when the methyl ester of only one fatty acid is added at the same concentrations. Previous studies have shown that fatty acid esters derived from vegetable oils have increased diesel fuel lubricity at concentrations of less than 1%. It has been also observed that the fatty acid composition of FAME mixtures may have an impact on their effectiveness as lubricity enhancers. Factors such as saturation, chain length, and hydroxylation could influence the performance of these additives as lubricity enhancers. Oils which contain a high concentration of hydroxylated fatty acids, such as castor oil, produce a FAME mixture with much more effective lubricity than oils that do not contain any hydroxylated fatty acids. The structure of these FAMEs facilitates formation of hydrogen-bonded complexes that enhance the lubricity of mixtures containing these components. The hydroxyl group is significant because it facilitates plasticization and adhesion of the oil esters. When the unsaturation of these FAMEs increased, lubricity enhancement also increased. In the C18 series methyl stearate, methyl oleate, methyl linoleate, and methyl linolenate, methyl linoleate demonstrated the best performance as a lubricity-enhancing additive, and methyl stearate was the least effective. The increase of unsaturation reduces the cetane number, and the increase in chain length increases the cetane number. Besides, increasing the number of double bonds (and their position in the chain) results in a lower cetane number. Branching in the chain is a factor that decreases the cetane number as is shown by use of hexadecane and 2,2,4,4,6,8,8-heptamethylnonane as high- and low-quality standards in the cetane scale. Biodiesel from palm oil when blended with diesel oil in a proportion of 15%, for example, increased brake power and reduced exhaust emissions compared to base diesel.

Henly. [2000] proposed additionally, several types of lubricity additives have been proposed. Non-acidic lubricity additives consisting of a mixture of C8-30-hydrocarbyl-substituted succinic anhydrides and an alkanolamine were reported. Anastopoulos et al. [2005] discussed some results, concerning the influence of adding low amounts of specific types of biodiesel, aliphatic amines, tertiary amides, acetoacetates esters, and esters of dicarboxylic acids on the behavior of the steel-on-steel systems, lubricated with low-sulfur diesel fuel. The obtained wear results by Dmytryshyn et al. [2004] showed that various classes of additives improved fuel lubricity. In another work, biodiesel was produced from four vegetable oils (canola oil, green seed canola oil from heat-damaged seeds, processed waste fryer grease, and unprocessed waste fryer grease) using methanol and KOH as a catalyst. The methyl esters of the corresponding oils were evaluated to find their diesel additive properties. Results show that, from the four biodiesels produced, the best choice to use as an additive was canola methyl ester, mainly due to the enhancement of the fuel’s lubricity number. A beneficial effect on the lubricity of diesel fuel also was observed by Kalam and Masjuki [2002],when biodiesel was produced from rapeseed oil, sunflower oil, corn oil, used fried oil, and olive oil at low concentrations (0.15-0.5% by volume). Recently, esters of C8-C18 saturated and unsaturated fatty acids produced by the transesterification of vegetable oils with polyhydroxy alcohols have found considerable use as addictives.

1.3.3. Cetane Number Additives:

Hamilton et al. [1999] studied that cetane number measures the readiness of the fuel to autoignite when injected into the engine and is one of the most significant properties to specify the ignition quality of any fuel for internal combustion engines. An increase in cetane number decreases the delay between injection and ignition. One of the more obvious effects of running on a low cetane number fuel is an increase in engine noise. In general, aromatics and alcohols have a low Cetane number.

Cetane number value also affects the NOx and particulate matter emissions from diesel, biodiesel, and diesel-biodiesel blend engines, as noted by several authors (McCormick et al. [2001]). A NOx increase results from the advancing injection time of biodiesel and diesel-biodiesel engines as compared to diesel ones by Monyen et al. [2001], Tat, Van Gerpen, Soylu et al. [2000], Szybist et al. [2005]. A high cetane number leads to a reduction of both emissions, and a lot of studies were carried out by Hamilton et al. [1997], Labeckas and Slavinskas [2006] to decrease the NOx emission by increasing the cetane number. Some strategies have been Tat and Van Gerpen [2003] byproposed to overcome this effect, such as detection of the presence of biodiesel in the fuel and retarding of the static injection time, or by blending biodiesel with other fuels or additives. McCormick et al. [2001] proposed for instance, a diesel blend consisting of 46% Fischer-Tropsch diesel fuel, a diesel basestock containing 10% aromatics, and a 1 vol % di-tert-butyl peroxide or 0.5 vol % 2-ethyl-hexyl nitrate (EHN). In all cases, the reduction of the NOx emissions came from the increase of the Cetane number of the fuel. In addition, Hess et al. [2004] studied the effect of antioxidant addition on NOx emissions from an 80% diesel and 20% biodiesel blend and concluded that the 2-EHN additive increased the cetane number of the fuel, leading to a shorter ignition time and thus to a decrease in NOx emissions.

The cetane number of biodiesel ranges from 48 to 67 depending on several parameters such as oil processing technology and climate conditions where the feedstock (vegetable oil) is collected and mainly the fatty acid composition of the base oil as per Ramadhas et al. [2006]. It is well-known that the overall properties of biodiesel are determined by the properties of the several fatty acids which, in turn, depend on the structural features of the fatty acids stated by Knothe [2005], McCormick et al. [2001]. They comprise chain length, degree of un-saturation, and branching of the chain. Among these properties, cetane number is especially affected by the structural features of the various fatty esters. The presence of double bonds in fatty acids will lower the cetane number value, and then strategies are addressed to shift the fatty pool of a vegetable oil toward saturated moieties which improve the ignition quality of the derived biodiesel, but the oxidative stability may compromise cold flow properties as informed by Knothe, Bagby and Rayan III [1998]. Due to the inverse relation between cold flow and oxidative stability (and cetane number), the design of an optimal fuel for all environments can be a quite difficult task. However, information obtained from simulated mixtures of oil can provide insight for the ideal fatty acid composition for fuel. Additives can play an important role, in this case, providing adjustment of the cetane number value that could not be fitted only by the composition of the diesel-biodiesel blends. A way to get oil with an increased oxidative stability and cetane number combining oleic acid and stearic acid was proposed. Such fuel couldused in warmer rather than cooler climates because of the decreased cold flow associated with increased saturated fatty acid content. In addition, to combine oxidation stability (and cetane number) with enhanced lubricity, Kinney and Clemente [2005] suggested the mixture of oleic acid and ricinoleic acid, in soybean oil.

Oleochemical carbonates have recently found increasing interest in commercial applications, including as biodiesel additives, due to their relatively direct synthesis in addition to their properties. Kenar et al. [2005] studied the physical and fuel properties (cetane number, low-temperature properties, kinematic viscosity, lubricity, and surface tension) of five straight-chain C17-39 and three branched C17-33 oleochemical carbonates in order to evaluate their potential as biodiesel additives. These compounds showed cetane numbers ranging from 47 to 107 depending on carbon chain length and branching. For the same number of carbons, the cetane numbers of carbonate were lower than those of fatty alkyl esters with an interruption of the CH2 chain by the carbonate moiety. The carbonates did not significantly affect cold flow or lubricity properties at concentrations up to 10,000 ppm. It was concluded that the properties of carbonates resembled those of fatty alkyl esters with similar trends resulting from compound structure and therefore were promising as cetane number additives.

On the basis of previous knowledge that compounds that enhance the octane number have a negative effect on the Cetane number and vice versa, Serdari et al. [2000] studied amines of various structures as potential diesel additives, with the aim of stating the impact of the structure of these compounds on diesel and biodiesel fuel quality, mainly on cetane number and on cold-flow properties.It was found that, as the chain length increased, the amine enhanced the cetane quality; in addition, methylation seemed to increase the cetane number to a larger extent than ethylation. It was concluded that the mono-dianol polyamides investigated enhanced the cetane number and also have good cold-flow performance; therefore, they may act as additives for both diesel and biodiesel fuels. The tertiary methylated fatty amines have the additional advantage of being produced from renewable starting materials (fatty acids). Tetrakis (dimethylamino) ethylene showed the best performance, but its oxidation stability must be evaluated in more detail, because of its olefinic nature.

Bhide et al. [2003] considered DME also as an additive to biodiesel and diesel-biodiesel blends, due to its high cetane number. However, even small additions of DME (25%) into diesel fuel significantly reduce the viscosity of the final mixture, showing that viscosity is the limiting factor in blending DME with diesel fuel.

1.3.4 Stability Additives:

Ivanov et al. [2004]focused special attention on the stability of biodiesel during its storage and use. Esters of unsaturated fatty acids are particularly unstable to the action of light. When exposed to air during storage, autoxidation of biodiesel can cause degradation of fuel quality by affecting properties such as kinematic viscosity, acid value, and peroxide value. One approach for increasing the resistance of fatty derivatives against autoxidation is to treat them with oxidation inhibitors (antioxidants).

Mittelbach and Schober[2003] investigated the influence of different synthetic and natural antioxidants on the oxidation stability of biodiesel from rapeseed oil, sunflower oil, used frying oil, and beef tallow. The four synthetic antioxidants pyrogallol (PY), propylgallate (PG), tert-butylhydroquinone (TBHQ), and buty-lated hydroxyanisole (BHA) produced the greatest enhancement of the induction period. The induction periods of methyl esters from rapeseed oil, used frying oil, and tallow could be improved significantly with PY, PG, and TBHQ. A good correlation was found between the improvement of oxidation stability and fatty acid composition. Schober and Mittellbach [2004] investigated the potential of different synthetic phenolic antioxidants to improve the oxidation stability of biodiesel prepared from different feed stocks. At antioxidant concentrations of 1000 mg/ kg, an improvement in oxidation stability could be achieved with all antioxidants tested. Variation of antioxidant concentrations between 100 and 1000 mg/kg showed that the efficiency of the antioxidants varied depending on the different types of biodiesel. Evaluation of the influence of antioxidants on critical biodiesel fuel parameters showed no negative impacts on viscosities, densities, carbon residues, CFPP, and sulfated ash contents of the different biodiesel samples. However, in terms of acid values, a noticeable increase could be observed at antioxidant levels of 1000 mg/kg. At lower antioxidant concentrations, this increase was much lower, and the values remained within the required limits.

Miyata et al. [2004] also presented the results of oxidation stability testing on biofuels. Oxidation stability was determined using three test methods, ASTM D525, EN14112, and ASTM D2274. The effects of storage condition, biofuel composition, and antioxidants on the degradation of biofuels were all studied. To further enhance stability, the addition of the antioxidants was effective, but in some cases, it also adversely affected the stability of biofuels. Dunn et al. [2005] examined the effectiveness of TBHQ, BHA, butylated hydroxy- toluene (BHT), and PG in mixtures with soybean oil fatty acid methyl esters (SME). PG, BHT, and BHA were most effective. Phase equilibrium studies were also conducted to test the physical compatibility of antioxidants in SME-diesel blends. The study recommended BHA or TBHQ (loadings up to 3000 ppm) for safeguarding biodiesel from effects of autoxidation during storage. BHT is also suitable at relatively low loadings (210 ppm after blending). PG showed some compatibility problems, and it may not be readily solubilized in blends with larger SME ratios.

1.4 Perspectives

Two basic trends are driving the up-to-date research and marketing of diesel additives: the progressive reduction of sulfur content and the increasing use of biofuels. The first should be applied not only to diesel but also to their blends (E-diesel, biodiesel-diesel, biodiesel-ethanol-diesel, and vegetable oil mixes). The additives for biofuels must observe emission regulations, motor; combustion requirements, their composition and concentration are highly dependent on the biodiesel source.

The recent introduction of ultralow-sulfur diesel (ULSD or S15) with less than 15 ppm, for example, 97% of the 500 ppm current on-road diesel, is specified by ASTM D975 in North America and EN540 in Europe and aims to reduce NOx and particle emissions as well as enable latest-technology high pressure common rail and other fuel-injection equipment (FIE) systems to operate properly. Although, it is more expensive, have a lower lubricity and lower energy content (MGP), and might be prone to seal leaks and wear-related problems.

These regulations also apply to any diesel fuel products, which must be clearly labeled if they meet or do not meet the ULSD specifications. Additives will also need to comply with these requirements. The growing popularity of biodiesel blends is closely related with emissions legislation and the increasing desire for renewable energies, although their economic viability will depend on international crude oil prices and on the market price of biodiesel co-products.

Although biodiesel is renewable and has good lubricity, it has several drawbacks that will need to be addressed: it is more expensive than diesel, has lower energy content, has water contamination, does not have good operation under cold weather, is corrosive, often contains methanol, has short shelf life, and affects fuel filters.

Most of the biodiesel specifications are unregulated as yet, resting on a big concern regarding recycled oils. Nevertheless, most engine original equipment manufacturers approve B2 or B5, and all major FIE manufacturers approve B5; some (Cummins, Case, and New Holland) approve B20 in certain engines. The identification of efficient additives should boost their regulation. Although there is no formal specification for blended biodiesel, it is expected to meet ASTM D975 standards (which mean bio and ULSD blends).

Biodiesel has also a huge cross-section of consumers with very different levels of knowledge and needs: environmentalists, the “budget conscious”, farmers, and state or city authorities. It will probably bring more problems, and there are not as many solutions; thus, new additive formulations will be needed to work for different problems. The most pressing are those preventing cold weather problems needing a heater, quicker Degradation/oxidation, corrosion of metal parts, rubber seals leakage, and filters choking quicker. Cold additives are needed for improving the cold-flow properties of biodiesel for applications as a neat fuel and in blends with petro-diesel, improving the cloud point, pour point, cold filter plugging point, and low temperature flow.

Depending on the biodiesel source, its specifications and, consequently, the additive requirements will vary. The most known sources of oils/fats are usually SME, rapeseed (canola) methyl ester, palm methyl ester, and yellow greases (e.g., waste cooking oil). They yielded the range of possible specifications that allowed the institution of ASTM 6751 (North America) or EN14214 (Europe), to which biodiesel should comply. In recent years, several new biodiesel sources have been reported: rapeseed oil, palm kernel oil, rice bran oil, corn oil, castor bean oil, Jatropha curcas, sun flower oil, and plant sledges. Each of these biodiesels will need to be studied with known and new additives. Specially recycled fast food oil and homemade fuel will especially need additives to avoid lots of repair work.

To make biodiesel economically viable, it is also necessary to propose new uses for its co-products, one of them as an additive. In the process of biodiesel production through basic catalysis, glycerol is obtained as a co-product in an amount equal to 10% of the esters by weight. Thus, in the interest of maintaining international glycerol value, a combination of biodiesel and glycerol ethers has been suggested by Spooner- Wyman et al. [2003] as an additive to diesel fuel. The study used a screening methodology to evaluate some glycerol derivatives. The total PM, total volatile fraction, NOx, CO, THC, CO2, and O2 were measured for several blends and a base fuel. On the basis of total PM emissions and other considerations, from the study de Andrade and Miguel et al. [1985], Pereira and de Andrade et al. [2002] concludes that di-butoxy glycerol is a promising candidate for blending in diesel fuel. There are studies that mention diesel fuel additives containing glycerol acetals and glycerol acetal carbonates.

Last but not least relevant is the definition of worldwide regulations. It is likely that compliance to North American and European regulations by other regions of the planet will not be straight forward due to the specificities of the local sources of biodiesel and of the weather conditions. This item is quite relevant for worldwide energy trade barriers that might become forbidden. If this issue is not clear in reasonable time, the diplomatic and world trade organizations might find themselves facing issues that are quite hard to overcome. Here, worldwide approval of additives might become an indispensable tool.

It is necessary to highlight the worrisome lack of available toxicity studies and information regarding how the new additives and fuels modify the toxicity of the engine exhaust emissions, both in terms of PICs and the unburned additives themselves, as well as secondary toxic species formed during atmospheric transport. This kind of information is indispensable to evaluate potential positive and/or negative environmental impacts associated with additives and fuel choices, avoiding a situation that decisions be made on the basis of mainly economic considerations.

1.5 Conclusions

Due to the worldwide effort to make renewable energy economically viable as well as to use cleaner fuels, additives will become an indispensable tool in global trade. Their technical specifications not only cover a wide range of subjects but also most subjects are interdependent. This makes the expertise of additives technology indispensable in the global trade of fuels. It is likely that, as energy sources become cleaner and renewable, it may be found that facing issues that are quite hard to overcome and diesel additives may become a worldwide indispensable tool. The additives share in the world market should increase in the next few years as long as energy sources become cleaner and renewable.

In this work, biodiesel with higher degree of saturation of iodine value ‘7’ is chosen to ensure fuel stability. The additive Triacetin (C9 H14 O6) is used as anti-knocking agent and higher molecular oxygen paves way for consistent and better combustion in both premixed and diffused zones and reduces the tail pipe emissions. More overall oxygen content may reduce torque generation, but with the perspective that the combustion is regulated by additive usage may create a hope that the above set back may be alleviated.

1.6 Introduction to the problem

The exhaust emissions of diesel engines are considerably very high. In view of mandatory instructions from international pollution control board, the tail pipe emissions of automobile engines should come down to lower levels. To comply with the pollution norms, the engines should use alternative fuels like biodiesel fuel and alcohols which have the capability to reduce emissions from the engine. Biofuels like ethanol, biodiesel have become an attractive alternative to petro diesel as it conquers the dependency on foreign petroleum and offers lower pollutant emissions in the present context of emission legislation Agarwal [2007],Haupt et al. [2004],Huang et al. [2009],Chen and Shuai et al. [2007]. Most attractive attribute of biofuel is of its low or no sulphur content and it can be used in diesel engines as direct fuels or as blends. The choice of biodiesel is also a criterion to replace petro diesel with the suggested one at the same time it should have longer shelf life and non corrosive. It is a proven factor that biodiesel emits lesser pollutants except in the case of NOx. These pollutants should be also reduced by using a very small percentage of fuel additives blending with biodiesels.

1.6.1 Selection of biodiesel:

Diaz and Galindodescribed that in the petroleum language the ideal diesel fuel is 100% normal paraffin (n-paraffin) is fully saturated hydrocarbon, which means it is 100% oxidation stable. As such, it is resistant to oxidation, not prone to bacterial growth, corrosionrust formation, polymerization and gumming even without any anti-oxidant additive. Being 100% saturated, the ideal diesel is easy to burn, has high cetane number, and produces low NOx emission. These are the features of diesel fuel with high level of saturated component. However, the ideal diesel is not attainable because commercial diesel fuel contains a mixture of other components which are of lower oxidation characteristic such as olefins, iso-parrafins, and aromatics. These components are unsaturated hydrocarbon which means the fuel is a bit more difficult to burn and is prone to oxidation, bacterial growth, corrosion, polymerization, clogging etc, which result in deterioration of fuel quality. For this reason, multi-additive packages are made integral part of diesel fuel formulation to reduce the problem of oxidation stability as well as to improve other performance parameters of commercial diesel fuel. Logically, the diesel fuel in natural state (unadditized) closest to the ideal diesel in content of saturated hydrocarbon, will have better oxidation stability, higher cetane number, lower NOx emissions, less prone to bacterial growth, corrosion, and polymerization.

In comparison, Coco biodiesel is 91% saturated carbon consisting of more than 60% medium carbon chain making it a lot easier to burn. In petroleum language, it is like 91% n -paraffin (only 9% short of the ideal diesel condition). That is why it conforms to Tier 3 diesel standard even without an additive. Furthermore, its carbon chain contains an oxygen molecule provided by nature which ensures more efficient combustion.

Following is the comparative content of saturated and unsaturated carbon chain in their natural state. The level of saturated hydrocarbon (unadditized) will determine the comparative oxidation stability of the fuels

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C oco biodiesel is the only diesel fuel in the world that is closest to the ideal diesel condition in oxidation stability . Additives are not needed in coco biodiesel to attain oxidation stability because it is highly oxidation stable, neither will it require additive for lubricity because it is a lubricity enhancer by itself

In terms of lubricity, oxygen content, mild solvency, and compliance to diesel fuel specifications, all methyl esters or biodiesels are alike. However, in terms of oxidation stability (i.e. level of saturated carbon) as well as distillation range (i.e. carbon length and temperature range in which diesel turns to vapor), biodiesels differ from each other. Coco biodiesel consist of mostly saturated medium carbon chain and has wide distillation range. Rapeseed and soybean consist of unsaturated long carbon chain and has narrow distillation range. With this coco biodiesel has better rate of volatility for combustion, better cold start ability, better solvency and detergency, superbly better oxidation stability, and even in small quantity adding to diesel fuel, it is the only biodiesel that substantially reduces NOx emission. This makes a world of difference for which coconut oil biodiesel is a premium class of biodiesel and has the following properties.

1. Highly processed coco biodiesel has cetane number of 70. (Additized local ADO is 51 to 55. PNS minimum is 48. European Standard EN590 minimum is 51). Cetane number is a measure of the “ignition delay” or the time gap from fuel spray to combustion. Simply it is a measure of combustion efficiency of the fuel much like octane is for gasoline. Higher the cetane number better is the combustion efficiency.
2. It has oxygen content of 11% provided by nature that enhances combustion. It serves as combustion booster.
3. It has inherent solvency feature that cleanses, declogs and protects the functional parts of the fuel system. It restores fuels system efficiency.
4. It has excellent lubricity feature. A 1% of blend can enhance the lubricity of diesel fuel by as much as 30%. It is a lubricity enhancer by itself.
5. It has a wide distillation (or volatility) range that gives good cold start ability.
6. It is 91% saturated carbon and therefore burns easily. Further more than 60% of its component is medium carbon chain which means they have lower ignition temperatures. It is only 9% short of the ideal diesel (100% n-paraffin) and is not prone to bacterial growth, corrosion, polymerization, gumming and others.
7. It has a flash point of 1070C and therefore about twice safer in handling and storage than fossil diesel.
8. It has high oxidation stability in its natural state (i.e. without additive) and is equal to or better than commercial diesel that has been additized with oxidation stabilizer.
9. Being highly saturated, it is hydrophobic (repels water).
10. Being a hydrocarbon (referred as carbohydrate due to its oxygen content), it is like a diesel component in its true sense just as olefin is a diesel component. It is not an additive having a different chemical ingredient like organo metallic additives.
11. Being a highly saturated carbon chain, it is the only biodiesel that reduces NOx emission in exhaust gases.
12. It is biodegradable, non-toxic and contains practically zero sulfur

1.6.2 Advantage of Coconut Oil Methyl Ester (COME) over the conventional fuel used in diesel engine:

a) Bacterial growth on storage:

The issue of bacterial growth on storage was found to occur in unadditized rapeseed and soybean biodiesel under a worst-scenario testing. However, this does not occur in coco biodiesel because it is highly oxidation stable than the additized diesel supplied by oil companies. Once the diesel fuel is additized, COME will enhance, rather than reduce, the oxidation stability and quality of the total blend. There may be minute quantity of insoluble just as there will be in neat diesel fuel but these are far below standard limit. Insoluble are not cultivable bacteria or fungi.

b) Lack of engine test since COME only has test on physical properties:

Caltex is obviously unaware of the development of COME since they have been consistently against the development of coco biodiesel. They have declared this in their position paper submitted to congress on the biofuel bill and they are not expected to be nationalistic. Their concern is purely commercial. As to the long term severe endurance tests for 1% COME blend (a product which possesses physical properties superior to petro diesel which is even compliant to Tier 3 standard). USNREL had stated that such kind of test is unnecessary on just 1% blend. Although it is understandable that such severe endurance test is a normal protocol for organo metallic additives since they have different chemical structure, one should realize that coco diesel is not an additive and does not have a different chemical structure. It is a diesel component just like olefins in diesel and has similar carbon structure as in the case of diesel.

c) Need for comprehensive evaluation on technical viability of COME:

The establishment of biodiesel standards in EN 14214 (EU) and ASTM D6751 (US) had been based on comprehensive evaluation on the technical viability of their test sample which were rapeseed (for EN) and soybean (for ASTM). Based on the test evaluation, a blend of up to 5% had been accepted and allowed in the WWFC standard for diesel. Up to 5% blend is also recognized by the Fuel Injection Equipment (FIE) manufacturers, provided the appropriate test standards are met. It is of course with the assumption that rapeseed and soybean biodiesels are treated with oxidation stabilizing additive. Coco biodiesel conforms to all EN and ASTM standards. If rapeseed and soybean are prone to oxidation yet 5% is allowed after the comprehensive technical evaluation, it goes without saying that a blend of only 1% COME being superior in oxidation stability, more than satisfies the technical viability and should not be a concern or an issue at all.

d) Reaction of COME with water:

This issue might have been prompted by some publication that biodiesel is hygroscopic (absorbs water). This condition might be true with unsaturated biodiesels such as rapeseed and soybean, but coco biodiesel being 91% saturated and repels water.

e) Storage handling and blending problem of COME:

COME is easiest to store safely and handle because of its high flash point compared to the conventional fuel. Its high oxidation stability minimizes the problem of bacterial growth. The additive package contained in the total blend of diesel will be enhanced rather than reduced. COME has specific gravity nearly the same as diesel of 0.87 and 0.86 respectively so it is quickly miscible with each other. Therefore, it can be directly blended easily with diesel in tank truck loading facility similar to their dosing procedure for additives.

f) Phase separation of COME with diesel:

COME and diesel have nearly the same specific gravity and they are very miscible with each other. Furthermore with presence of water can also cause phase separation, as COME is hydrophobic which means it repels water. The presence of water in the blend will more likely come from normal condensation that will be absorbed by the unsaturated components of thediesel fuel or from water contamination in storage tank. It is unlikely that it will be absorbed by the 1% COME blend!

g) Corrosion from poor oxidation stability of COME:

The key feature of COME is its high saturated medium carbon chain which means highly oxidation-stable. This concern is valid only on rapeseed and soybean biodiesel, where most of the negative concerns originated.

h) Supply uncertainty of COME vis-à-vis the fuel requirement:

The 1% blend requires only 70 million liters out of 7 billion liters demand for diesel fuel. Coconut oil export is 1 billion per year and 70 million only accounts for 7%. Furthermore, current COME production is already in excess of 100 million per year which can easily address the 1% requirement.

i) Demand for coco biodiesel will increase the cost of domestic cooking oil:

The 1% coco biodiesel will eat up only 7% of the annual export volume of coconut oil and not the current total domestic volume. It is not substantial as to influence an increase in the price of cooking oil. Besides, the price of vegetable oil is governed by a worldwide price index for vegetable oil (Rotterdam index), just as the price of petroleum fuel has price index (Dubai for crude oil) and (MOPS for finished petroleum products) and oil companies should know this.

j) Additional investment in infrastructure in order to handle pre-blending:

Again coco biodiesel is very miscible with diesel. It can simply be mixed directly in the storage tank or can be dosed by line injection similar to their current dosing of additives. While there could be some preparatory cost involved, it does not fall in the purview of large capital investment for infrastructure. Nevertheless, there are many options on how a pre-blend can be implemented. Oil companies can make this issue difficult or simple depending on where their position lies.

k) Coco biodiesel has lower heat energy and therefore produces less power:

If coco biodiesel is used as 100% diesel substitute, it may have some reduction in power because it is true that the thermal energy of coco biodiesel is approximately 6% lower than normal diesel (similar to the thermal energy of kerosene). However, the Bio-fuels Bill requires only 1%, and its effect on thermal energy is only 0.0006 of the total thermal energy of blended diesel. It is too insignificant to affect engine power, much less become an issue.

l) Use of coco-biodiesel has risk of soap formation in storage or engine:

Soap formation occurs with the reaction of fatty acid and alkali’s (i.e. sodium hydroxide or potassium hydroxide). Unwashed and un-reacted fatty acids and alkalis in esterification process of biodiesel may be present if production procedure process is not proper or lacks quality control.

1.6.3 Free fatty acid advantages with coconut biodiesel:

Table 1.2 Fatty acid distribution of common biodiesel feed stocks (source: James)

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Fig. 1.6 Coconut biodiesel FAMES (source: James)

Table 1.3 Cut times for C8 to C18 Coconut oil FAMES (source: James)

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Fig. 1.7 PM Effects of different methyl ester fuels (source:Christopher)

It can be observed that C18 fatty acids are low in concentration in Coconut biodiesel which renders an advantage of lower particulate and NOx emission.

1.6.4 Blend of Coconut Oil biodiesel [COME]:

A blend of coco-biodiesel even with just 1% will have two main actions:

1) It restores engine efficiency: Old engines with heavy carbon soot deposits and with clogged or partially clogged fuel nozzles will be cleansed and declogged in a short period of time to restore fuel spray atomization efficiency. It will likewise provide film lubricant layered on metal surfaces of the fuel pump and injector unit (known as “boundary lubrication”).
2) It will enhance combustion efficiency, cold start ability, acceleration response by its oxygen content, wide distillation range, high content of saturated carbon ( i.e. easy to burn), and high cetane number. Result is efficient combustion, cleaner air, and additional mileage; reduce maintenance & repair expense, prolonged engine life, and driving satisfaction.

Summary

Although it appears that there has been so much “witch hunting” for every conceivable negative issue that could be attached to coco biodiesel, they are nevertheless worthwhile discussion exercises (or test) in determining the true excellence of coco biodiesel. Since all the negative issues sourced from other biodiesels turn out to be positive issues in coco biodiesel, one can say in spiritual sense that coco biodiesel is truly God’s gift to our country because it is a perfect diesel in its natural state.

Thus so far, there are no valid and properly founded technical issues that challenge the excellence of COME as biodiesel. There are indeed many issues of fear and apprehension from oil companies but much of it can be eliminated by simply knowing and appreciating the features and technical excellence of this premium biodiesel.

1.7 Selection of Additive

Fuel additives are chemical substances that are added to gasoline, diesel, kerosene and other fuels to improve certain properties. In most of the cases, additives are used for higher compression ratios to gasoline-air mixture in the engine, which in turn can improve the efficiency and power of the gasoline engine. Some fuel additives however, may impart environmental and health risks. Normally additives are used to boost the combustion hence improves fuel economy at very lower emission rates.

In the present work Triacetin [ C9H14O6, 99% pure and manufactured by Sisco Research Laboratories Ltd, Mumbai] has been selected as fuel additive and its properties are shown in table 1.4. Triacetin (also named Glycerin Triacetate) is the tri-ester of glycerol and acetic acid and has the following properties.

Table 1.4 Properties of Triacetin (C9H14O6)

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1) It is usually applied to the cigarette filter as a plasticizer in tobacco industry.
2) It is also used in food industry as solvents, flavorings and humectants.
3) It is widely used as component in pharmaceutical products as humectants, a plasticizer in chewing gum and a very good solvent.
4) It can also be used to fuel additive as an anti-knocking agent which can reduce engine knocking in gasoline.
5) Used as a fuel additive to improve cold flow and viscosity properties of biodiesel.
6) It can be used as a flavor and essence fixative and lubricate in cosmetics.
7) It has high solvency power and low volatility make Triacetin a good solvent and fixative for many flavors and fragrances.
8) It is also generally recognized as a safe animal feeds, as a pesticide adjuvant, and in food packing.
9) Improves the shelf life of biodiesel as it can take in to the extent of 7% of water.

The main advantage of this additive is easily soluble in biodiesel, suppress the knocking of engine, improve efficiency and reduce the tail pipe emissions. In this work triacetin additive at various percentages with COME (by volume) blends are used to study the performance, exhaust gas analysis, smoke density and vibrations of engine.

1.8 Engine cylinder Vibration studies

Testing of the new additive may change the vibration signatures of the cylinder. Hence it is proposed to take up engine vibration study also to verify any abnormal knocking or detonation of the engine in comparison. Study of frequency spectrums and time waves divulged some information about the combustion propensity with alternative fuel (Ref : Timothy A Dunton, Doctoral theses of Grover Zurita Viillarroel [2001], Roger Johnsson [2004]).

1. 9 Introduction to present work (COME-Triacetin additive blends)

In the present work, neat COME-Triacetin additive blends are experimented in lieu of the neat diesel fuel. Pure coconut oil methyl ester itself as an additive has advantages in the operation of engine. Attention is bestowed upon the reduction of HC, NO, CO2, CO and smoke emissions, and the same is successfully achieved with the 10% Triacetin and 90% COME blend fuel. Vibration on the engine cylinder in three directions and on the foundation were measured and analyzed to elicit information about the nature of combustion since the combustion itself is the exciter.

The following chapter-II deals with the Preparation of Coconut Oil Methyl Ester (COME) for the experimental work.

CHAPTER – II TRANSESTERIFICATION OF EDIBLE VEGETABLE OIL (Coconut oil)

The use of vegetable oils requires certain modifications in their properties to replace diesel fuel in conventional diesel engines. Considerable efforts have been made to develop the vegetable oil derivatives that would approximate the properties and performance equal to the hydrocarbon-based diesel fuels. The problem of substituting pure vegetable oils (edible) with diesel fuel is mostly associated with high viscosity (Tat and Van Gerpen [1999]). Reduction of viscosity can be effected by any of the processes like Transesterification, Mineralization, Preheating and Pyrolysis. The process of Mineralization consumes more time and Pyrolysis brings about irregular molecular break down. Hence transesterification of coconut oil is taken up in this work to experiment on a laboratory based DI diesel engine with an additive to enhance the combustion of biodiesel. Experimentation was performed on esterified coconut oil called Coconut Oil Methyl Ester (COME) at different percentages of selected additive.

The vegetable oil under consideration is coconut oil. The procedure adopted for the esterification is in two steps, to attain final coconut oil methyl ester by complete separation of glycerin. First stage is acid esterification,using sulfuric acid and methanol to remove free fatty acids followed by the second stage is the base esterification (transesterification) with methanol and sodium hydroxide combine which is called as sodium methoxide. The formed methyl ester was water washed, to remove soaps and finally heated to get pure COME, which can be used for experimental work.

2.1 Transesterification of Vegetable Oils

Transesterification is the general term used to describe the important class of organic reactions, where the esters are be transformed into another through interchange of alkyl groups. This is also called as alcoholysis. The transesterification is an equilibrium reaction and the transformation occurs by mixing the reactants. However, with the presence of a catalyst accelerates considerably by the adjustment of equilibrium condition in reaction and equation for transesterification is given below.

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The basic constituent of vegetable oils is triglyceride. Vegetable oils comprise of 90-98 percent of triglycerides and small amounts of mono, diglycerides and free fatty acids. In transesterification of vegetable oils, the triglyceride reacts with alcohol in the presence of a strong acid or base, producing the mixture of fatty acid alkyl esters and glycerol. The overall process was the sequence of the three consecutive and reversible reactions in which the di and monoglycerides were formed as intermediates. In the stoichiometric reaction, one mole of triglyceride requires three moles of alcohol. However, excess of the alcohol is used to increase the yield of alkyl esters and to allow the phase separation from the formed glycerol. Several aspects that including the type of catalyst (base or acid), vegetable oil molar ratio, temperature, purity of the reactants (mainly water content in alcohol) and free fatty acid contents have influence in the process of transesterification. So in this work the reactants of high purity have been used (methyl alcohol with 99% purity) in the process. In the base-catalyzed process, the transesterification of vegetable oils proceeds faster than the acid-catalyzed reaction together with alkaline catalysts, which are less corrosive than acidic compounds.

The mechanism of the base-catalyzed transesterification reaction in vegetable oil is shown in the Fig. 2.1. In the first step (eqation.1) of reaction the base with alcohol, produces alkoxide and the protonated catalyst. The nucleophilic attack of an alkoxide with the carbonyl group of the triglyceride generates a tetrahedral intermediate, from which an alkyl ester and diglyceride are formed. The latter deprotonates the catalyst and regenerates the active species, which enables it to react with a second molecule of alcohol, and then starting another catalytic cycle. Diglycerides and monoglycerides are converted by the same mechanism to a mixture of alkyl esters and glycerol.

Alkaline metal alkoxides (as CH3ONa for the methanolysis) are the most active catalysts, since they give very high yield in short reaction times even if they applied at lower molar concentrations. However, they require the absence of water, which makes it inappropriate for typical industrial process. Alkali metal hydroxides (KOH or NaOH) are cheaper than metal alkoxides and less active. Nevertheless, they are good alternatives, since they can give the same high conversion of vegetable oils into methyl esters just by increasing the catalyst concentration by 1 or 2 folds.

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Fig. 2.1 Mechanism of the base-catalyzed transesterification process

2.2 Process employed for making methyl esters

2.2.1 Introduction:

In making of biodiesel fuel efficiently from used vegetable oils and animal fats, the major problem to be avoided is soap formation. Soap is formed during base-catalyzed transesterification (using lye) when sodium ions combine with free fatty acids present in used (and some virgin) vegetable oils and animal fats. Soap decreases the yield of methyl esters because they bond with water. The bonded esters can be washed out in the washing stage, but this makes water separation more difficult also increases the consumption of water.

The first-stage process is not transesterification, but pure and simple esterification (Canakci and Van Gerpen, Jeromin et al. [1999]). Esterification is followed by transesterification, but under acid conditions, it is much slower than under caustic conditions and it won't covert complete oil into methyl ester as the conversion reaction is much more equilibrium sensitive. For the first stage, it forms a compound out of an acid and alcohol. The alcohol is still methanol, but instead of using lye (sodium hydroxide), the catalyst in this reaction is sulfuric acid (battery acid). It requires at least 95% pure sulfuric acid as one of the common chemicals, just like lye. The percentage of biodiesel yield is depending upon the quantity, quality, type of catalyst used and reaction time, temperature and stirring speed maintained during the transesterification process (Freedman et al. [1984], Jaturong Juputti et al. [2006], Tangsathitkulchai et al. [2004], Gajendra Kumar et al [2010]). The sulfate ion from sulfuric acid combines with the sodium ion in the lye during the second-stage reaction to form sodium sulfate, which is a water-soluble salt and is removed in the water wash. With this, no sulfur remains in the biodiesel fuel product. The step wise biodiesel formation and its process chart are shown in figures 2.3 and 2.2.

PROCESS CHART

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Fig. 2.2 Process Chart for Coconut Oil Methyl Ester (COME)

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Fig. 2.3 Step-wise process of Biodiesel formation

2.2.2 The process:

1. The edible oil (Raw Coconut Oil) is filtered using surgical cotton to eliminate water and solid particulate matter.
2. The oil is heated to 1050C temperature and maintained it for fifteen minutes to remove all the water content from oil. For a successful and complete reaction, the oil must be free of water. After that oil is allowed to cool.

2.2.3 First Stage (Acid catalyzed):

The free fatty acids can be reduced to esters by Methanol with acid catalyst. The following is the sequence of process:

1. One liter of cooled oil is heated to 350 C to melt the solid fats present in the oil.
2. Methanol of 99 % pure, 120 ml per liter of oil [CH3OH, Make: Merck Specialties Pvt. Ltd, Mumbai] is added to the heated oil and stirred for five to ten minutes. Methanol is a polar compound and oil is strongly non-polar, hence suspension of oil will form in the process.
3. Two milliliter and 98 % pure sulfuric acid [H2SO4, Make: Merck Specialties Pvt. Ltd, Mumbai] was added for each liter of oil by using a graduated eye dropper.
4. The mixture is stirred for one hour in a closed conical beaker maintaining at constant temperature of 550C.
5. Heating is stopped and the mixture is continued to stirring for about one more hour.
6. The mixture is allowed to settle for four hours in a decanter to remove the glycerin and chemical water separated from methyl ester.

2.2.4 Second Stage (Base catalyzed):

1. For each liter of oil, 200 ml of methanol (20% by volume) and 97% pure 6.5 grams of lye [Sodium Hydroxide (NaOH), Make: Central Drug House (P) Ltd] is added. The mixture is stirred thoroughly until it forms a clear solution called “Sodium Methoxide ”.
2. Half of the prepared sodium methoxide is poured into the oil and stirred for fifteen minutes continuously. This will neutralize the sulfuric acid.
3. The mixture is heated to 550C and the whole reaction is maintained at the same temperature in a closed container.
4. Remaining sodium methoxide is added to the mixture and stirred at 500 to 600 rpm in the temperature range of 550 to 580C for about one hour. The solution turns into brown silky in colour which shows that the whole reaction is completed.
5. Now the mixture is poured into a decanter and allowed it to settle for 6 hours. As glycerin is heavier than the biodiesel, it will settle at the bottom. The settled glycerin is separated from the biodiesel.

2.2.5 Washing:

1. Bubble wash method is used to remove soaps. Since the process is designed to yield neutral ester, finally there is no need to monitor pH value of the biodiesel. Two milliliter of 98% pure Orthophosphoric acid [H3PO4, Make: Qualigens Fine Chemicals] is added to the biodiesel for first water wash with bubbling.
2. One third of distilled water by volume is added to the biodiesel and bubble washed for about half an hour.
3. The mixture is allowed to settle in a decanter for one hour then water with soap or foam can be separated off from the biodiesel.
4. The process of washing is repeated till the biodiesel separated with clear water.
5. Finally collected biodiesel without soap from decanter is heated to 1050C to dispense with traces of water then preserved for experimental work.

[Figures 2.4 to 2.12 indicate the process step by step in chronological order to convert raw coconut oil into biodiesel that is Coconut Oil Methyl Ester (COME)].

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Fig. 2.4 Raw Coconut Oil Heating

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Fig. 2.5 Separated Glycerin after Acid treatment

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Fig. 2.6 Preparation of sodium Methoxide

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Fig. 2.7 Base treatment to remove Free Fatty Acids

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Fig. 2.8 Settlement of Glycerin After base treatment

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Fig. 2.9 Collected Free Fatty Acids (Glycerin)

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Fig. 2.10 COME with soap in water washing

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Fig. 2.11 COME with clear water

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Fig. 2.12 Final stage of (Heating) COME

The above process was used to prepare the required quantity of COME from coconut oil in Fuels laboratory of Marine Engineering Department, A. U. College of Engineering. Then the author employed IS test methods (IS: 1448) to establish the properties of prepared methyl ester as per the standards at HPCL, Visakhapatnam and Chemical Engineering Department of A. U. College of Engineering. The results of properties are tabulated as shown in table 2.1.

2.3 Properties of the biodiesel

Table 2.1 Properties of Diesel and Coconut Oil Methyl Ester

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2.4 Summary:

The laboratory based DI diesel engine is used in the present study to test with COME and Triacetin additive blends at an injector pressure of 200 bar without changing any engine parameter.. This is an attempt to investigate application of Triacetin additive with COME to run the engine for better combustion, reduced exhaust emissions and compare the performance with biodiesel, Petro-diesel and blends of additive and COME.The following chapter (Chapter III) deals with the mathematical modeling for the computation of Net Heat Release Rate (NHRR) and Cumulative Heat Release Rate (CHRR) during the combustion on the basis of first law of thermodynamics taking heat transfer from the combustion gases into consideration. The baseline data used for computation of Net Heat Release Rate analysis is the combustion pressure – crank angle history in the combustion chamber.

CHAPTER-III HEAT RELEASE RATE CACULATIONS

Pressure crank angle history is obtained from the engine data logger for the defined engine load. After obtaining data from the combustion cycle, net heat release rate is calculated based on the first law of thermodynamics. Heat transfer from the gases to cylinder is computed, and deducted from the gross heat release rate to arrive at net heat release rate and presented in the form of graph. The computed Heat Release Rate (NHRR and CHRR) profiles are shown in figures 3.2 and 3.3,for the recorded pressure data of the engine cylinder in figures 3.1.

When analyzing internal combustion engine, the in-cylinder pressure has always been an important experimental diagnostic due to its direct relation to the combustion and work producing processes. The in-cylinder pressure reflects the combustion process involving piston work produced on the gas (due to changes in cylinder volume), heat transfer to the combustion chamber walls as well as mass flow in and out of crevice regions between the piston, piston rings and cylinder liner. Thus for an accurate knowledge of how the combustion process propagates through combustion chamber is required and each of these processes must be related to cylinder pressure Richard stone[1999],Heywood [1988], so the combustion process can be distinguished. Reduction of an effective change in volume, heat transfer and mass loss at the cylinder pressure is called heat release analysis and is done within the framework of the first law of thermodynamics, when the intake and exhaust valves are closed, i.e. during the closed part of engine cycle. The simplest approach is to consider cylinder contents as a single zone, whose thermodynamic state and properties are modeled, being uniform throughout the cylinder and represented by the average values. As no spatial variations are considered, so the model is said to be zero-dimensional. Models for the heat transfer and crevice effects can be easily included to analyze. Krieger R. B., Borman have contributed a lot to develop the Heat release rate models for the I C engines.

3.1. Heat release based on Ist Law of thermodynamics

On thebasis of first law of thermodynamics the heat release model is:

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The gas temperature can be found from the equation of state (Abbildung in dieser Leseprobe nicht enthalten), since the pressure and volume are known, and it has been assumed mass is constant. The gas properties vary with temperature, but the variation is modest, it is acceptable in most cases to evaluate the properties at the gas temperature computed in the previous increment. Equations below can be used to evaluate the properties Abbildung in dieser Leseprobe nicht enthalten and R, from which ‘Abbildung in dieser Leseprobe nicht enthalten’ can be evaluated. Once the gas temperature has been evaluated, it is possible to estimate the heat transfer, by assuming wall temperature and employing a heat transfer correlation.

An approach was adopted by Krieger and Borman [1966], who provided polynomial coefficients from the curve fit to combustion problem calculations for weak mixtures (Abbildung in dieser Leseprobe nicht enthaltenAbbildung in dieser Leseprobe nicht enthalten1) of Abbildung in dieser Leseprobe nicht enthalten with air.

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Where

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With gas constant given by

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3.2. In cylinder heat transfer

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Assumed surface temperature= 350k

Annand and Ma [1971] have developed the equation:

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And for a compression ignition engine Watson and Janota 1982 suggested:

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The derived graphs for the net heat release and cumulative heat release rates have been envisaged in figures 3.2 to 3.3. The values have been calculated from the real time combustion pressures logged by Pressure- crank angle data logger using excel chart.

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Fig. 3.1 Input pressure data signatures drawn at different loads in limited range of 00 to 7200 crank angle with 75%BD(COME) + 25%Triacetin blend fuel run

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Fig. 3.2 Net heat release rate at different loads in limited range of 3400 to 4100 crank angle with 75%BD (COME) + 25%Triacetin blend fuel

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Fig. 3.3 Cumulative heat release rate at different loads in limited range from 3300 to 4300 crank angle with 75%BD (COME) + 25%Triacetin blend fuel

The following chapter (Chapter-IV) deals with experimental set up and experimentation. A laboratory based direct injection diesel engine is used to test triacetin additive blendeds with COME at various percentages by volume.

CHAPTER IV EXPERIMENTAL SET UP AND EXPERIMENTATION

The experimental setup consisting of DI diesel engine installed in the engines laboratory, Department of Marine Engineering, AndhraUniversity.Coconut oil methyl ester (COME) was prepared in fuel’s laboratory and alternate fuel application was taken up n with Triacetin additive. COME is mixed with additive thoroughly and injected in the suction of engine at 200 kg/cm2. Additive at 5%, 10%, 15%, 20% and 25% by volume are mixed with COME and experimented on the engine for performance, exhaust gas analysis, smoke density and vibrations.The COME and blends resultsare compared with neat diesel for full load range of the engine operation. The crank case oil dilution is regularly tested to verify the extent of contamination if any.Experimentation is carried out at various engine loads (Engine Loading device is eddy current dynamometer) to record the cylinder pressure and to compute heat release rates with respect to the crank-angle. Engine performance data is acquired to study the above mentioned parameters along with engine cylinder vibration and engine pollution parameters. Engine cylinder vibration in FFT form is monitored at each load and for COME and itsblends simultaneously to compare the cylinder excitation frequencies with the base line frequencies using diesel oil. Time wave forms on the cylinder head are also recorded to analyze the combustion for heat release rates. Since the combustion in the cylinder is the basic exciter, the vibration study of the engine cylinder is measured through FFT and time waveforms. These factors are the representatives of combustion propensity. The smoke values in HSU and exhaust gas analysis of different constituents of exhaust are measured and compared.

4.1 Experimental setup

The experimental setup consists of the following equipment:

1. Single cylinder DI engine loaded by eddy current dynamometer
2. Engine Data Logger
3. Exhaust gas Analyzer
4. Smoke Analyzer
5. Vibration Analyzer

The schematic diagram of Fig. 4.1 representsthe instrumentation arrangement for the experimental setup. Piezo electric transducer is fixed (flush type) to the cylinder body (with water cooling adaptor) to record the pressure variations in the combustion chamber. Crank angle is measured by using crank angle encoder. Exact TDC position is identified by the valve timing diagram and fixed with a sleek mark on fly wheel and the same is used as a reference point for the encoder. With respect to this point signals of crank angle will be transmitted to the data logger. The data logger synthesizes the two signals and final data is presented in the form of a graph on the computer using C7112 software.

Vibration accelerometer is mounted on the cylinder head, preferably on the bolt connecting to head and cylinder to record the engine vibrations using DC-11 data logger which directly gives spectral data in the form of FFT, the overall vibration levels. This FFT data recorded is collected by On-Time window based software designed by e-predict Inc., Argentina. The time waveforms are obtained on the cylinder head by DC-11 in OFF-ROUT mode and are presented in graphic form by Vast-an doss based software, designed by VAST, Inc., Russia.

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Fig. 4.1 Schematic diagram of Data Integration circuit taking data from the encoder and pressure transducer

4. 1.1 Direct injection (DI) Diesel Engine:

The DI diesel engine [Make: Kirloskar, Pune] is used for conducting the experimentation. The details of the engine are given below table 4.1

Table 4.1 Specifications of the DI Diesel Engine

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4.1.2 Engine Loading System:

The line diagram of experimental setup is shown in Fig. 4.2. The engine is loaded with eddy current dynamometer and a spring balance as shown in Fig. 4.3. The load on the engine can be changed with the help of dynamometer control panel shown inFig. 4.4. Full load capacityof the engine is measured bythe spring balance and equal to 40 kg. This dynamometer is popular for its stable and consistent readings which shall not be changing with minor variation in the engine speed.

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To accommodate the crank angle encoder, the dynamometer is fixed in parallel to the engine with a belt drive coupled to the engine as shown in Fig. 5.3.

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Fig.4.3 Eddy current dynamometer

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Fig.4.4 Dynamometer control panel attached to the engine

4.1.3 Eddy Current Dynamometer:

- Speed: 1000-2000 rpm
- Accuracy ratings +/- 0.3 % to 0.5 % full scale
- Type of Loading: Eddy Current Dynamometer with 24 kg on its spring balance represents the Maximum Load on the Engine.

4.1.4 Piezo Electric Transducer (S111A22, SN9982):

A Piezo-electric transducer shown in Fig. 4.5 is flush type and fixed into the engine cylinder head for obtaining the combustion chamber pressure data continuously which is being received by the engine data recorder in Fig. 4.8 through the connector cable Fig. 4.6.The transducer is water cooled with a specially designed adapter. The pressure data along with the data from the crank angle encoder in Fig. 4.7 is integrated by the C7112 software which finally depicts data in the form of Pressure - Crank angle graphs. The graphs encompass 7200 of crank revolution (for one cycle) on the abscissa and the combustion pressure in bar on ordinate which is representative of one working cycle in the case of a 4-stroke engine. The pressure - volume, logP- logV, and Net Heat Release Rate per degree of crank are calculated with a suitable computer program making use of combustion pressure as the baseline data,Fig. 4.9 shows the computer to log the data used the experimental work.

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Fig. 4.5 Piezoelectric Transducer

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Fig. 4.6 Connector cable

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Fig.4.7 Crank Angle Encoder

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Fig.4.8 Engine Data Logger

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Fig. 4.9 Computer to log the data from the Engine data Logger

4.2 Exhaust Gas Analyzer (DELTA 1600- L)

The DELTA 1600- L inFig. 4.10 [Make: M/S MRU GmbH GERMANY]measures the exhaust gas emissions of Carbon Monoxide (CO), Carbon Dioxide (CO2), Hydro Carbon (HC) with the means of infrared measurement. Oxygen (O2) and Nitrogen Monoxide (NO) are measured with the means of electro chemical sensors. The analysis of these five gases are processed by an integrated micro processor and shown in the display. Simultaneously, the excess air value is also calculated. At the end of measurement, the measured values, date and time are recorded and documented by an integrated printer. This instrument is calibrated with propane gas at regular interval of time after usage.

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Fig. 4.10 Delta 1600-L Exhaust Gas Analyzer

4.2.1 Technical specifications of analyzer:

Table 4.2 Measuring ranges and calibration values of Delta 1600-L

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Table 4.3 Precision levels of Delta 1600-L

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4.2.2Features of Delta 1600-L Analyzer:

- Continuous emission analysis
- Illuminated and graphical LCD display
- Serial interface RS 232
- Response time 15 seconds
- High accuracy and performance through 16-bit microprocessor

Table 4.4 Resolution of Delta 1600-L

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4.3 Smoke density tester (DIESEL TUNE 114)

This smoke density meter mainly contains the following elements as shown in figures 4.11 and 4.12.They are 1) Exhaust gas pipe with holder 2) Exhaust probe 3) Pump unit 4) Calibration paper5) White filter paper disc and 6) Filter paper holder. The features of this equipment are as follows:

- Voltage: 4.5 V- (dry cell battery)
- Range: 0-10 FSN unit
- On- Load testing

4.4 Vibration Analyzer Equipment

The DC-11 FFT analyzer shown in Fig. 4.13 made by DPL group Canadais a digital spectrum analyzer and data collector specifically designed for machine conditionmonitoring, advanced bearing fault detection and measurement diagnostics. The following are the measurements that can be made by the instrument DC-11.

- Time wave form (oscilloscope) in OFF-ROUTE mode.
- FFT auto spectra
- Envelop spectra selected by multiple band pass filters
- Rotation speed
- Amplitude and phase on rotation speed and its harmonics

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Fig. 4.11 Diesel Tune Smoke Analyzer collect the gas sample

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Fig. 4.12 Exhaust suction gun to

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Fig. 4.13 DC-11 Vibration Analyzer with acceleration pickup

Table 4.5 Specifications of the Vibration (FFT) Analyzer

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4.5 Experimentation Procedure

The experimentswere conducted on the engine operated at normal room temperatures of 280C to 330C in the Department of Marine Engineering, AndhraUniversity. Dual fuel (blends) operation of Coconut oil methyl ester (COME) and with a Triacetin additive is taken up at five (5%, 10%, 15%, 20%, and 25%) different percentages by volume and properties of blend fuel are shown in table 4.6. Neat diesel oil and pure biodiesel are also implemented at five discrete part load conditions to enable for comparison. The data collection is done independently for the above said oils. The engine is run at 1500rpm continuously for one hour in order to achieve thermal equilibrium under operating conditions. After this period, the combustion pressure is monitored at each degree of crank revolution for every load on the engine. Fuel consumption andthe engine vibration on cylinderwerealso measured at all loads. From the P-θ signatures obtained, the net heat release rates have been derived for the above said esters with the software designed based on the Gatowski heat release rate model. Exhaust gas emissions and smoke measurements were also made at different loads. The same procedure is repeated for the dual fuel operation with additive and COME injection to compare the performance of the engine for comparative analysis.

4.6 Error Analysis

Experimental errors:

It should be noted that all of the data collected by the data acquisition system used in this experimental study is subject to small errors. The errors due to the data acquisition systems used in this study are on the order of 0.02% for the 12 bit system and 0.001% for the 16 bit system and are considered negligibly small when compared to the other sources of error.

The error in the values of the engine torque is ±0.1 Nm. Thus, the uncertainty in the values of torque is estimated to be in the range of 0.14–0.07%. The error in the measurements of the engine speed is ±1 rpm. Thus, the uncertainty in the values of the engine speed is estimated to be in the range of 0.1–0.02%.

The error in the measurement of the fuel and water flow rates may be estimated by considering the error in the electronic balances, which have 0.1 g resolutions. The timer used in the test has a resolution of 0.1 s. Hence, the uncertainties in the values of the water and fuel flow rates are estimated to be in the range of 0.4–0.7%.The error in the measurements of temperatures during the tests may be estimated by considering the error in the type of thermocouples used. Such an error for type T is 2.2 C or 0.75%, whichever is greater, and for type K, it is 2.2 C or 0.75%. Thus, the uncertainty in the measurements of temperature is estimated to be in the range 2–5%.

An error analysis for the derived quantities, such as engine power, brake specific fuel consumption, thermal efficiency, heat rejection to the coolant water, heat lost through the exhaust gases, energy supplied to the engine and unaccounted heat losses, is performed. The error analysis by considering the method of Kline and McClintrok indicates that the uncertainty is in the range of 3–7%.It should be clearly noted that the estimated errors in the measurements of the basic and derived quantities do not significantly influence the overall uncertainty in the final results.

4.7Summary

The fuel consumption for the COME with additives at various proportions is measured with reference to 1kg/hr diesel fuel consumption for full range of engine load. The consumption is measured at all defined loads both with U-tube manometer and fuel Rota meter. This is an attempt to evaluate the engine performance for comparison, which is taken up in the chapter V. The threshold mass flow rate after which the crank case dilution starts was identified.Heat release rate values are derived from the pressure- crank angle signatures by a suitable computer program. Engine vibration is monitored by assessing the vibration on the cylinder head in three directions. The time waveforms are measured on the cylinder head while the engine is running at different loads.

Exhaust gas and smoke analysis is taken up to classify the merits and demerits. The results are elaborately discussed in the next chapter-V.

CHAPTER-V RESULTS AND DISCUSSION

Coconut oil methyl ester (COME) along with viscosity improver triacetin blended to improve viscosity properties of biodiesel. Various above blends with different triacetin quantities are tested to explore the benefits in total replacement of diesel in this experimentation. Normally, diesel fuel or biodiesel detonates to certain extent due to combustion heterogeneity. This detonation trend can be contained to some extent by certain triacetin percentage mixed as an additive to COME biodiesel. Triacetin is known for its anti-knocking property with gasoline. Proportions with percentages ranging from 5%, 10%, 15%, 20% and 25% by volume have been tried with biodiesel as main fuel and the engine performance has been evaluated. Improvement in most aspects can be observed with certain amount of blend percentage. The knocking frequency has been calculated based on sonic frequency in the engine diametric direction and the percentage of triacetin was arrived at, with the reduction in knocking amplitude at the calculated frequency of knocking. The engine tested was the laboratory based, four stroke, vertical single cylinder, direct injection diesel engine, which generates 5 hp at a rated rpm of 1500. The auto ignition temperature of triacetin is 4580C, which is higher than that of diesel and biodiesel. The calorific value of triacetin is in the range of 20,000 kJ/kg which is lower than that of COME biodiesel fuelvalue 36,000 kJ/kg. Triacetin contains 44% of molecular oxygen which doesn’t allow the main fuel to starve out of Oxygen under engine loading conditions. Triacetin improves the shelf life of biodiesel as can take in to the extent of 7% of water. Coconut oil methyl ester itself has an advantage of lower iodine value of seven (which is an indication of degree of unsaturated condition) for more shelf life.

5.1 Study of cylinder pressures during combustion

Combustion pressures in the combustion chamber have been recorded with respect to the TDC position. For specific study of the start of combustion and the specific heat of fuel mixture employed, small combustion duration from 3500 to 4000 which encompasses the TDC position in between at 3600 has been chosen. There is relative pressure rise at the start of combustion due to temperature rise because of lower specific heat of mixture and higher convective heat transfer coefficient for various mixtures. Thermal properties of the bio-fuel change with the blending of soluble triacetin. The blend with 10% Triacetin, as can be seen from the figures 5.1 to 5.4 has shown improvement in the combustion pressure generation starting from the start of combustion at full load and three fourth’s full load. This particular blend has proved its consistent performance in the tail pipe emissions and engine cylinder vibrations. The pressure variations at two important loads, which normally every diesel engine is advised to run have been shown in the above said figures. The modus operandi of pressure variation is same for the two loads taken into consideration.

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Fig. 5.1 Input pressure data signatures drawn for limited range of 3400 to 4000 crank angle for diesel, biodiesel and for all biodiesel-additive blends at full load

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Fig. 5.2 Delay period plot for diesel, biodiesel and biodiesel-additive blends at full load

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Fig. 5.3 Input pressure data signatures drawn for limited range of 3400to 4000 crank angle for diesel, biodiesel and for biodiesel-additive blends at 75%full load

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Fig. 5.4 Delay period plot for diesel, BD and BD - additive blends at 75%full load

5.2 Net and cumulative heat release rate comparison

The net and cumulative heat release rate graphs at full load and 75% full load are shown from 5.5 to 5.8. It can be observed that the net heat release rate peak is increasing with the increase of triacetin in the blend. The 10% Triacetin blend falls in between the diesel and biodiesel in the net and cumulative heat release aspects and emerges as the best alternative to the conventional diesel. The cumulative heat graphs decipher consistent performance both in the premixed and diffused combustion zones for 10% triacetin blend with biodiesel. The 5% triacetin joins the band wagon of 20% and 25% triacetin blends with respect to the low profile diffused combustion as shown in the figures 5.5 to 5.8.

Ignition delay decreased in the case of 10% Triacetin blend as this blend is optimal in reducing vibration and to improve combustion quality. Heat release rate curves (5.5 to 5.8) computed indicate better performance in case of 10% triacetin blend in the premixed as well as in diffused zone. With the increase of triacetin quantity in the blend, the diffused combustion deterioration has taken place as seen in the figures. The 5% triacetin blend could not gain sensible heat from the air fuel mixture and converse is true for the 10% blend. This trend can be observed from the pressure crank angle diagrams as shown in figures 5.1 to 5.4. There is dramatic change in the process coefficient with the percentage of triacetin mix especially at 5% and 10% which affects Abbildung in dieser Leseprobe nicht enthalten and Abbildung in dieser Leseprobe nicht enthalten values. The cumulative heat release rate curves also exhibit the same thing in the case of 5% and 10% triacetin mixes with an advantage to 10 % triacetin blend in the diffused combustion zone. There is a rapid fall of heat release in case of 5% triacetin.

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Fig. 5.5 Net heat release rates for diesel, BD and BD – T additive blends at full load

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Fig. 5.6 Net heat release rates for diesel, BD and BD-T additive blend at 75%full load

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Fig. 5.7 Cumulative heat release rates for diesel, BD and BD-T additive blend at full load

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Fig. 5.8 Cumulative heat release rates for diesel, BD and BD-T additive blend at 75%full load

5.3 Performance Analysis:

Figures 5.9 and 5.10 indicate thermal efficiency and brake specific fuel consumption of the fuel alternates shown in the right hand side index box. Biodiesel and diesel exhibited best performance at lower equivalence ratios. Biodiesel, as it is known, generated better thermal efficiency at all loads. Referring to the equivalence ratio for the fuels tested, it has increased with the increase of triacetin in the blend but the extent of increase is comparatively lower than that when compared to neat diesel and biodiesel. This may be because of lower calorific value and higher boiling point of triacetin. Figures from 5.11 to 5.18 depict different engine parameters with respect to equivalence ratio and engine load in KW. All parameters exhibited uniformity, except the differential pressure of combustion for 25% triacetin blend which has increased abruptly with the load on the engine as shown in figure 5.17 indicating the maximum blend percentage one can try up to. For 10% triacetin blend fuel table 5.1 depicts the better performance in the generation of combustion pressure and its parameters.

Table 5.1 Full load combustion Parameters

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Fig. 5.9 Variation of brake thermal efficiency verses equivalence ratioof the engine

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Fig. 5.10 Variation of brake specific fuel consumption verses equivalence ratio of the engine

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Fig. 5.11 Variation of fuel consumption with brake power of the engine

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Fig. 5.12 Variation of equivalence ratio with Load on the engine

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Fig. 5.13 Variation of peak pressure verses load on the engine

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Fig. 5.14 Variation of IMEP verses load on the engine

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Fig. 5.15 Variation of brake thermal efficiency verses load on the engine

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Fig. 5.16 Variation of exhaust temperature verses equivalence ratio of the engine

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Fig. 5.17 Variation of Max. DP wrt TDC verses load on the engine

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Fig. 5.18 Variation of indicated power verses load on the engine

5.4 Discussion on Engine Emissions

Black color pillars indicate the absolute values of the diesel fuel emissions and other negative side colored stalks indicates decrease from the absolute value of diesel. For example, in the figure 5.19, yellow stalk indicate HC emission of biodiesel and at full load the absolute value of HC emission for the biodiesel is 132-72= 60ppm. The extent of decrease in that particular emission value can be easily observed in the graph.

Hydrocarbon emissions decrease with the loading of the engine and 10% triacetin blend produced remarkable value of decrease (99 ppm). Biodiesel is known for its efficiency to reduce emissions except NOx. Triacetin blend with biodiesel further helped in the reduction of HC by 27ppm.

Carbon monoxide emissions (figure 5.20) are reduced better at lower loads and CO2 emissions reduction (figure 5.21) is nominal at .all loads of the engine.

NO emission trade off is not observed with HC emission because the figure 5.22 envisage decrease of NO emission with the load and with the increase of triacetin percentage. For 10% triacetin the decrement is 300 ppm at full load operation of the engine.

Smoke levels in HSU for neat biodiesel at the loads tested are the best, when compared to the other fuel blends tested as shown in figure 5.23. The most competitive blend emerged is 20% triacetin in the context of smoke emission with respect to biodiesel.

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Fig. 5.19 Variation of hydrocarbon emission verses load on the engine

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Fig. 5.20 Variation of carbon monoxide emission verses load on the engine

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Fig.5.21 Variation of carbon dioxide emission verses load on the engine

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Fig. 5.22 Variation of NO emission verses load on the engine

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Fig. 5.23 Variation of smoke level verses load on the engine

5.5 Summery of Results on engine performance

The performance and emission parameters were measured for diesel, COME and COME with Triacetin additive blends without modifications in the engine operating parameters, andthe results are summarized as follows:

- Brake Thermal Efficiency: Figure 5.9 gives the details of brake thermal efficiency versus equivalence ratio of neat fuel and the blends. It can be ascertained from the figure that the equivalence ratio is increasing with the triacetin additive percentage. This is because of lower calorific value of the additive compared to the biodiesel. The maximum equivalence ratio difference observed is nearly 0.15 when triacetin is being added. The 10% triacetin blend yielded better thermal efficiency curve at higher loads as can be observed.
- Brake Specific Fuel Consumption: Figure 5.10 envisages the BSFC performance of the engine with different blend fuel versions and for 10% triacetin blend the part load performance is observed better corroborating with the brake thermal efficiency as described above.
- Exhaust Gas Temperature: Fromfigure 5.16, there is marginal fall in the exhaust gas temperatures with respect to increase in the load on engine by using higher percentages of triacetin and this may be because of lower heat release rate in the diffused combustion at lower calorific value of the blended fuel.
- Hydrocarbon (HC) Emission: There is 75% maximum reduction in HC emission with the triacetin blending which can be observed from the figure 5.19. As the load on the engine increases, the HC emission decreases at all percentages of blend fuels tested.
- Carbon monoxide (CO) Emission: CO emission also reduced by 50% [maximum] from figure 5.20 and trade off with other emissions has not been observed.
- Carbon Dioxide (CO2) Emission: From figure 5.21, there is a reduction of nearly maximum 10% of CO2 emission with the blends and at higher loads.
- Nitrogen Oxide (NO) Emission: NO emission decreases with the load on the engine and especially more decrease can be observed at three fourth of full load. Nearly 28 to 29% maximum decrease in this emission can be observed with the triacetin blend from figure 5.22.
- Engine smoke levels have been decreased substantially with the triacetin additive application as shown in figure 5.23.

5.6 Engine vibration study

Figures 5.24 to 5.28 indicate the average spectrum values of the engine cylinder run at different loads and different combinations of blend fuels which also include neat diesel and biodiesel. The engine run with 10% triacetin blend at full load generated lowest vibration levels at the points defined.

The time waves were recorded on the cylinder head and the wave form in the explosion stroke is isolated and represented against pressure signature to study the inner details of combustion (figures 5.29 to 5.35). This plotting is based on nullifying the delay period between the peak pressures generated in the combustion chamber to the maximum

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Fig. 5.24 Variation of average spectrum values of the engine at no load

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Fig. 5.25 Variation of average spectrum values of the engine at 25%full load

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Fig. 5.26 Variation of average spectrum values of the engine at 50%full load

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Fig. 5.27 Variation of average spectrum values of the engine at 75%full load

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Fig. 5.28 Variation of average spectrum values of the engine at full load

vibration peak in the time wave form picked up from the explosion stroke. This gives a better picture of understanding of the ignition propensity with different fuel combinations.

The increase in delay period can be ascertained from 0.20ms to 1.70ms for 5% to 25% triacetin blends which can be observed from the figures 5.29 to 5.35. There is simultaneous rise in the engine vibration after the start of ignition with respect to increase in triacetin percentage. And triacetin 25% blend (figure 5.33) reflected knocking condition of the engine with the vibration acceleration,and amplitude rise to about 40g which is coinciding with the differential pressure rise explained earlier (figure 5.17),whereas 10% triacetin blend (figure 5.30) exhibited smoother combustion with pure harmonic reduction during explosion stroke, eliminating mixed frequencies. The envelope of the time wave exactly coincides with the pressure variation in synchronous exhibition of the two signatures i.e. pressure exciter and vibration generation wave.

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Fig. 5.29 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 5% triacetin and 95% bio-diesel.

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Fig. 5.30 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 10% triacetin and 90% bio-diesel

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Fig. 5.31 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 15% triacetin and 85% bio-diesel

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Fig. 5.32 Time wave recorded vertical on the cylinder head during explosion stroke at Full load operation and it’s corresponding combustion pressure trace of blen fuel with 20% triacetin and 80% bio-diesel

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Fig. 5.33 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace of blend fuel with 25% triacetin and 75% bio-diesel

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Fig. 5.34 Time wave recorded vertical on the cylinder head during explosion stroke at Full load operation and it’s corresponding combustion pressure trace with neat bio-diesel operation

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Fig. 5.35 Time wave recorded vertical on the cylinder head during explosion stroke at full load operation and it’s corresponding combustion pressure trace with neat diesel operation

5.6.1 Engine Knock estimation

The phenomenon of knock has been a major limitation for CI and SI engines since the beginning of their evolution. Engine knock has its name from the audible noise that results from auto ignitions in the unburned part of the gas in the cylinder. The most probable locations for harmful self-ignitions lie in the proximity of hot surfaces, i.e., piston, cylinder walls and in the largest possible distance from the injector &spark plug. This can be explained by the concept of pre-reaction level. In this notion, the auto ignition is a result of the chemical state of the unburned gas exceeding a critical level in which enough of highly reactive radicals are formed, leading to a spontaneous ignition. This pre-reaction level, being proportional to the concentration of radicals, increases over a period of time, primarily under the influence of high temperatures and secondarily, high pressures. The pressure in the cylinder can be assumed to be spatially constant (it varies with time) since the speed of sound, at which the pressure is equalized. In contrast, the temperature varies significantly within the cylinder volume. In the unburned gas, regions of the highest temperature levels are located in the boundary layers close to hot surfaces. In those regions the flow of gas is slow and therefore the heat from the walls is transferred to a small volume during a long period of time.

If the mass fraction of unburned gas at the time of auto ignition is large and its pre-reaction level is high (i.e., close to critical), several adjacent hot spots are ignited and merge to a fast expanding “reaction region” such that all of the highly reactive unburned gas burns almost at once. Under these conditions the chemical reactions spread faster than the speed of sound, resulting in insufficient pressure equalization. This in turn leads to shock waves and consequently to harmful pressure peaks in the cylinder.

The pressure waves resulting from knocking combustion have a characteristic frequency that depends mostly on the characteristic length of the oscillation and the speed of sound in the combustion chamber. Assuming that the cylinder is filled with air (modeled as an ideal gas) at a temperature of 20000K [Abbildung in dieser Leseprobe nicht enthalten], the speed of sound is

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Where B is the cylinder bore and Abbildung in dieser Leseprobe nicht enthaltenthe vibration mode factor. This parameter Abbildung in dieser Leseprobe nicht enthalten can be approximated using the analytical solution of the general wave equation in a closed cylinder with flat ends. For the first circumferential mode this yields Abbildung in dieser Leseprobe nicht enthalten= 1.841. For an engine with a bore of B = 80mm = 0.080m the frequency related to knock therefore is

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and severe knock only occurs if auto ignition starts before XB = 70%, 75%, or 80%.

Figure 5.36, envisages the mean effective pressures for bio-diesel and petro-diesel at full load engine operation falling in the knocking zone and for blends with triacetin the mean effective pressures fall below 6.5 bar and hence no severe knocking at 1500rpm.Figures 5.37 to 5.43envisage the amplitudes of knocking frequencies with neat oils and with triacetin blends. This indicates that at 10% triacetin blend, the knocking amplitude is minimum for the reading taken on the cylinder head of the engine, in the radial direction and in line crank shaft. This direction is chosen with the view that there won’t be mixed effect like piston slap in other radial direction and thrust transfer to the piston in the vertical direction and thus knocking can be fully realized in the direction inline crank. The knocking frequencies are varying by little margin around 6500Hz because of the combustion temperature variation with respect to the blend combination of triacetin.

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Fig. 5.36 Full-load curve and knocking operating regions under the assumption fordifferent burnt mass fractions ‘X B’

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Fig. 5.37 FFT spectrum indicating Knocking frequency and acceleration amplitude for neat diesel application. Vibration Measurement is made in the radial direction of cylinder in line crank shaft axis

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Fig. 5.38 FFT spectrum indicating Knocking frequency and the acceleration amplitude for neatBio-diesel application. Vibration Measurement is made in the radial direction of cylinder in line crank shaft axis

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Fig. 5.39 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 5% Triacetin + 95% Biodiesel blend application. Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

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Fig. 5.40 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 10% Triacetin + 90% Biodiesel blend application. Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

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Fig. 5.41 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 15% Triacetin + 85% Biodiesel blend application Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

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Fig. 5.42 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 20% Triacetin + 80% Biodiesel blend application Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis

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Fig. 5.43 FFT spectrum indicating Knocking frequency and the acceleration amplitude for 25% Triacetin + 75% Biodiesel blend application. Vibration Measurement is made in radial direction of the cylinder in line crank shaft axis The following chapter (Chapter VI) deals with conclusions of the experiments done on DI diesel engine withbiodiesel-triacetin additive blends at various percentages by volume.

CHAPTER-VI CONCLUSIONS

Experiments were conducted with neat petro diesel, COME and COME-Triacetin [C9H14O6] additive blends at 5%, 10%, 15%, 20% and 25% by volume on DI diesel engine. The general performance, combustion, emissions and engine vibration results are compared with neat diesel. Based on results the conclusions have been drawn as follows.

6.1 Conclusions

1. The equivalence ratio is increasing with the triacetin additive percentage. This is because of lower calorific value of additive compared to the main biodiesel and the maximum equivalence ratio difference observed is nearly 0.15, when triacetin is being added. 10% triacetin blend yielded better thermal efficiency at higher loads.
2. In all blended fuel versions, the BSFC of the engine for 10% triacetin blend at part load performance is better in the same way as in the case of brake thermal efficiency.
3. At 5% triacetin blend fuel, the process coefficient may have effect at the beginning of combustion and continued its effect in the premixed and diffused combustion zones also. The solubility of the triacetin with the biodiesel brings in certain changes in fundamental properties and hence the behavior with 5% blended biodiesel.
4. The blends with triacetin produced IMEP lesser than 6.5 bar eliminating them in the knocking zone. 10% triacetin blend, even though produced 7.2 bar IMEP, can be regarded as safe which is marginally below the IMEP ranges of diesel and biodiesel in the 80% burnt mass fraction zone at 1500 rpm.
5. For this particular engine cylinder dimensions, the knocking frequency can be calculated taking into consideration of the overall combustion temperature as 2000 0K. Knocking level can be assessed from the FFT graphs obtained by the engine vibration recorder. The readings on the cylinder head, in radial direction and in line to the crank axis has been chosen to quantify the amplitudes at knocking frequencies. It is understood that 10% blend of triacetin with biodiesel produced lowest amplitude at the knocking frequency around 6,500Hz.
6. The delay period is increasing with the increase of triacetin percentage, but at 25% of triacetin with biodiesel blend there is abrupt rise in the cylinder vibration indicating knocking condition of the engine. This is also coinciding with the abrupt differential pressure rise in pressure-crank angle plots with 25% triacetin blend.
7. There is fall in exhaust gas temperatures with increase in load on the engine and at higher percentages of triacetin. This may be because of lower heat release rates in the diffused combustion process by virtue of lower calorific value of the blended fuel.
8. There is a maximum of 75% reduction in HC emission with the COME-Triacetin additive blends. As load on the engine increases, the HC emission decreases at all percentages of blends tested.
9. Maximum of 50% CO emission is reduced with the use of 90%BD+ 10%T blend fuel and 10% reduction of CO2 emission with this blend fuel at higher loads.
10. NO emission has decreased with load on the engine and especially more decrease can be observed at three fourth full load. Maximum of 28% to 29% decrease is obtained in this emission. It is obvious that there is no trade off between HC and NO, because both have decreased to cognizable extent.

6.2 Scope for future work

Injection advance and retard can be tried and performance can be evaluated vis-a vis the results obtained above in the future scope of work.

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APPENDIX-A

Performance and Emission curves not shown in results are appended below

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Fig.A1 Variation of exhaust temperature with load

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Fig.A2 Variation of bsfc with brake power

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Fig.A3 Variation of smoke emission with load

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Fig.A4 Variation of fuel consumption with load

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Fig.A5 Variation of HC emission with load

Fig.A6 Variation of CO2 emission with load

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Fig.A7 Variation of CO emission with load

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Fig.A8 Variation of NO emission with load

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Fig.A9 Variation of oxygen with load

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Fig.A10 Variation of peak pressure with load

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Fig.A11 Variation of I M E P with load

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Fig.A12 Variation of fuel consumption with load

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Fig.A13Variation of Equivalence ratio with Load

Fig.A14 Variation of BSFC with load

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Fig.A15 Variation of peak pressure with load

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Fig.A16 Variation of I M E P with load

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Fig.A17 Variation of exhaust temperature with load

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Fig.A18 Variation of thermal efficiency with load

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Fig.A19 Variation of smoke emission with load

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Fig.A 20 Variation of HC emission with load

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Fig.A21 Variation of CO emission with load

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Fig.A22 Variation of NO emission with load

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Fig.A23 Variation of CO2 emission with load

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Fig. A24 Variation of oxygen with load

APPENDIX: B

The Time waveforms recorded vertical on cylinder head at various loads & fuel combinations and not shown in results are appended for verification

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Fig.B1 Time wave form recorded vertical on cylinder head for neat diesel at no load

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Fig.B2 Time wave form recorded vertical on Cylinder head for neat diesel at 25% full load

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Fig.B3 Time wave form recorded vertical on cylinder head for neat diesel at 50%

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Fig.B4 Time wave form recorded vertical on full load cylinder head for neat diesel at 75% full load

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Fig.B5 Time wave form recorded vertical on cylinder head for pure biodiesel (BD)at no load

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Fig.B6 Time wave form recorded vertical on cylinder head for pure biodiesel at 25%full load

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Fig.B7 Time wave form recorded vertical oncylinder head for pure biodiesel at 50% full load

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Fig.B8 Time wave form recorded vertical on cylinder head for pure biodiesel at 75% full load

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Fig.B9 Time wave form recorded vertical on cylinder head for 95%BD+5%T at no load

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Fig.B10 Time wave form recorded vertical on cylinder head for 95%BD+5%T at 25% full load

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Fig.B11 Time wave form recorded vertical on cylinder head for 95%BD+5%T at 50% full load

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Fig.B12 Time wave form recorded vertical on cylinder head for 95%BD+5%T at 75% full load

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Fig.B13 Time wave form recorded vertical on cylinder head for 90%BD+10%T at no load

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Fig.B14 Time wave form recorded vertical on cylinder head for 90%BD+10%T at 25% full load

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Fig.B15 Time wave form recorded vertical on for 90%BD+10%T at 50% full load

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Fig.B16 Time wave form recorded vertical on cylinder head cylinder head for 90%BD+10%T at 75% full load

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Fig.B17 Time wave form recorded vertical on cylinder head for 85%BD+15%T at no load

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Fig.B18 Time wave form recorded vertical on cylinder head for 85%BD+15%T at 25% full load

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Fig.B19 Time wave form recorded vertical on cylinder head for 85%BD+15%T at 50% full load

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Fig.B20 Time wave form recorded vertical on cylinder head for 85%BD+15%T at 75% full load

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Fig.B21 Time wave form recorded vertical on cylinder head for 80%BD+20%T at no load

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Fig.B22 Time wave form recorded vertical on cylinder head for 80%BD+20%T at 25%full load

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Fig.B23 Time wave form recorded vertical on cylinder head for 80%BD+20%T at 50% full load

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Fig.B24 Time wave form recorded vertical on cylinder head for 80%BD+20%T at 75% full load

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Fig.B25 Time wave form recorded vertical on cylinder head for 75%BD+25%T at no load

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Fig.B26 Time wave form recorded vertical on cylinder head for 75%BD+25%T at 25% full load

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Fig.B27 Time wave form recorded vertical on cylinder head for 75%BD+25%T at 50% full load

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Fig.B28 Time wave form recorded vertical cylinder head for 75%BD+ 25%T at 75% full load

APPENDIX: C

Pressure verses crank angle and Ignition delay curves which are not mentioned in results are appended below for verification

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Fig.C1 Pressure plot for diesel run

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Fig.C2 Delay identification for diesel run

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Fig.C3 Pressure Vs CAD for 50% full load

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Fig.C4 Delay identification at 50% full load

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Fig.C5 Pressure Vs CAD for 25% full load

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Fig.C6 Delay identification at 25% full load

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Fig.C7 Pressure Vs CAD for no load

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Fig.C8 Delay identification at no load

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Fig.C9 Pressure plot for 80%BD+20%T run

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Fig.C10 Delay identification for80%BD+20%T run

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Fig.C11 Pressure plot for 85%BD+15%T run

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Fig.C12 Delay identification for 85%BD+15%T run

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Fig.C13 Pressure plot for 90%BD+10%T run

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Fig.C14 Delay identification for 90%BD+10%T run

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Fig.C15 Pressure plot for 95%BD+5%T run

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Fig.C16 Delay identification for 95%BD+5%T run

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Fig.C17 Pressure plot for biodiesel run

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Fig.C18 Delay identification for biodiesel run

APPENDIX:D

Derived Graphs of CHRR and NHRR are not mentioned in results are appended below for verification

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Fig.D1 CHRR plot at 80% BD+20%T blend fuel

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Fig.D2 CHRR plot at 85% BD+15%T blend fuel

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Fig.D3 CHRR plot at 90% BD+10%T blend fuel

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Fig.D4 CHRR plot at 95% BD +5%T blend fuel

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Fig.D5 CHRR plot for Biodiesel fuel

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Fig.D6 CHRR plot for Diesel fuel

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Fig. D7 NHRR plot for 80%BD+20%T run

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Fig.D8 NHRR plot for 85%BD+15%T run

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Fig.D9 NHRR plot for 90%BD+10%T run

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Fig.D10 NHRR plot for 95%BD+5%T run

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Fig.D11 NHRR plot for Biodiesel run

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Fig.D12 NHRR plot for Diesel run

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Fig.D13 CHRR plot at 50% full Load

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Fig. D14 CHRR plot at 25% full Load

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Fig. D15 CHRR plot at no Load

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Fig.D16 NHRR plot at 50% full Load

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Fig.D17 NHRR plot at 25% full Load

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Fig. D18 NHRR plot at no Load

109 of 109 pages

Details

Title
Some studies on a single cylinder Di-Diesel Engine with coconut biodiesel (come) and triacetin additive blends as alternate fuel
College
Andhra University  (AU College of Engineering)
Course
Mechanical
Author
Year
2010
Pages
109
Catalog Number
V280415
ISBN (Book)
9783656744962
File size
8484 KB
Language
English
Notes
Best Researcher awarde and Senior Professor
Tags
some, di-diesel, engine
Quote paper
Basava Venkata Appa Rao (Author), 2010, Some studies on a single cylinder Di-Diesel Engine with coconut biodiesel (come) and triacetin additive blends as alternate fuel, Munich, GRIN Verlag, https://www.grin.com/document/280415

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