A Study On 5 % And 10 % Bio-Blended Diesel Fuel Spray Deposition.
A STUDY ON 5 % AND 10 % BIO-BLENDED DIESEL FUEL SPRAY DEPOSITION
KELVIN THENG SERN LUNG
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SUPERVISOR DECLARATION
“I hereby declare that I have read this thesis and in my opinion this report is sufficient in terms of scope and quality for the award of the degree of Bachelor of
Mechanical Engineering (Automotive) with Honour”
Signature: ...
Supervisor: DR. YUSMADY BIN MOHAMED ARIFIN Date: JUNE 2012
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A STUDY ON 5 % AND 10 % BIO-BLENDED DIESEL FUEL SPRAY DEPOSITION
KELVIN THENG SERN LUNG
This project is submitted to Faculty of Mechanical Engineering
In partial fulfillment for
Bachelor Mechanical Engineering (Automotive) with Honour
Faculty of Mechanical Engineering Universiti Teknikal Malaysia Melaka
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DECLARATION
“I hereby declare that the work in this report is my own except for summaries and quotations which have been duly acknowledged”
Signature: ...
Author: KELVIN THENG SERN LUNG Date: JUNE 2012
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ACKNOWLEDGEMENT
First of all, I would like to express the gratitude to Dr. Yusmady bin Mohamed Arifin, as my supervisor who had given his expert guidance and full commitment throughout this project.
Gratitude also goes to Faculty of Mechanical Engineering (UTeM) for giving me the opportunity to undergo this final year project as part of my evaluation during Bachelor Degree. Special thanks to En Fudhail bin Abdul Munir for his commitment as Head of PSM which had guided all of the students following the proper procedures during PSM implementation.
Last but not least, a lot of thanks to my family and friends for providing encouragement and strength to me to always give the best. I would like to express gratitude to all of who may involve either directly or indirect for all the support, cooperation, guidance throughout this project.
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ABSTRACT
Deposit formation inside a combustion chamber is a phenomenon that contributes to various engine problems such as increase in emission, engine performance reduction as well as engine damage. Due to higher viscosity, density and distillation temperature compared to diesel fuel, utilization of bio-diesel fuel increase the tendencies of deposit formation. The aim of this study is to investigate the deposit formation for 5 % and 10 % Bio-Blended Diesel Fuel (B5 and B10) using Fuel Spray Deposition Test (FSDT) apparatus. The deposit formation on hot surface depends on spray interval, fuel types, wall surface temperature, chemical reaction effect, heat transfer effect and cooling effect. Existing FSDT apparatus had been improved and experiment had been conducted successfully for surface temperature of 300 °C. In this study, it was found that deposition mass of both tested fuels was increased. Deposition mass of B10 was found to be higher than B5, due to higher value of density and viscosity. Deposit formation rate for both fuels was decreasing as a function of time. However, B10 have higher deposit formation rate as compared to B5 over time. Fuel deposit pattern onto the hot surface for both fuels differs to each others, due to the atomization ability of the fuels. Hence, the utilization of lower blends percentage of bio-diesel fuels had greater potential in reducing deposit formation on a combustion chamber wall in an engine.
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ABSTRAK
Pemendapan dalam kebuk pembakaran ialah fenomena yang menyumbang kepada masalah terhadap enjin seperti peningkatan emisi terhadap persekitaran, pengurangan prestasi enjin dan kerosakan dalam enjin. Disebabkan bio-diesel mempunyai kelikatan, ketumpatan dan suhu penyulingan yang lebih tinggi daripada minyak diesel, penggunaan minyak bio-diesel dalam pasaran telah meningkatkan kecenderungan dalam pembentukan pemendapan. Tujuan kajian ini adalah untuk menyiasat pembentukan pemendapan bagi 5 % dan 10 % campuran bahan api Bio-Diesel (B5 dan B10) dengan menggunakan radas Ujian Pemendapan Semburan Bahan Api (FSDT). Pembentukan pemendapan terhadap permukaan panas bergantung kepada selang masa semburan, jenis bahan api, suhu permukaan, tindak balas kimia, kesan pemindahan haba dan kesan penyejukan. Radas FDST telah dibaik pulih dan ujikaji telah selesai dijalankan bagi suhu permukaan 300 °C. Dalam kajian ini, didapati bahawa jisim pemendapan bagi kedua-dua bahan api yang diuji menunjukkan peningkatan. Disebabkan ketumpatan dan kelikatan yang lebih tinggi, B10 menghasilkan jisim pemendapan yang lebih tinggi daripada B5. Kadar pembentukan pemendapan bagi kedua-dua bahan api berkurang dengan masa. Tetapi, B10 mempunyai kadar pembentukan pemendapan yang lebih tinggi daripada B5, berkadar dengan masa. Corak pemendapan bagi kedua-dua bahan api menunjukan perbezaaan disebabkan oleh keupayaan pengabusan bahan api tersebut. Maka, penggunaan bahan api yang mempunyai peratusan pencampuran bio-diesel yang lebih rendah mempunyai kecenderungan dalam pengurangan pembentukan pemendapan pada dinding kebuk pembakaran bagi sesuatu enjin.
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TABLE OF CONTENT
CHAPTER TITLE PAGE
SUPERVISOR DECLARATION ii
DECLARATION iii
AKNOWLEDGEMENT iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENT vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF ABBREVIATIONS xiii
LIST OF SYMBOLS xv
LIST OF APPENDICES xvi
CHAPTER 1 INTRODUCTION 1
1.1 Background 1
1.1.1 Bio-Diesel Fuel 2
1.1.2 Fuel Deposition 3
1.2 Problem Statement 4
1.3 Objectives 5
1.4 Scopes 5
CHAPTER 2 LITERATURE REVIEW 6
2.1 The Effect of Bio-Diesel Fuel Properties 6
2.1.1 Viscosity 7
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CHAPTER TITLE PAGE
2.2 Concerns Using Bio-Diesel Fuel 10
2.2.1 Emissions 10
2.2.2 Impact on Engine Performance 12 2.3 Engine Deposition Phenomena 13 2.3.1 Fuel Spray/Wall Impingement 13
2.3.2 Regime Transition 14
2.4 Deposits and Precipitate Formation 16
CHAPTER 3 METHODOLOGY 19
3.1 Introduction 19
3.2 Tested Fuel 20
3.3 Problems with Current Fuel Spray Apparatus 22 3.4 Modification of Current Fuel Spray Apparatus 24
3.4.1 Fuel Spray Chamber 24
3.4.2 Fuel Tank 26
3.5 Experimental Set Up and Procedures 28 3.5.1 Fuel Spray Deposition Test (FSDT)
Apparatus 28
3.5.2 Procedures 30
CHAPTER 4 RESULTS & DISCUSSIONS 33
4.1 Introduction 33
4.2 Experimental Results 33
4.2.1 Bio-Diesel Fuel Deposition on a Hot Surface 33 4.2.2 Deposition Characteristics of B5 and B10 35
4.2.2.1 Deposit Formation Characteristics
for B5 36
4.2.2.2 Deposit Formation Characteristics
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CHAPTER TITLE PAGE
4.3 Discussions 38
4.3.1 Deposit Formation Rate, R in Relation to
Tested Fuels 38
4.3.2 Deposit Formation Mechanisms 40 4.3.3 Fuel Properties on Deposit Formation
for Bio-Diesel Fuels 40
4.3.4 Deposition Pattern Due to Fuel Properties 41
4.4 Problems Faced 42
4.4.1 Fabrication of FDST Apparatus 42 4.4.2 Time Constraint During Experimental
Setup 42
4.4.3 Effect of Bio-Diesel Fuel Vapors to
the Surrounding 42
CHAPTER 5 CONCLUSION & RECOMMENDATIONS 44
5.1 Conclusions 44
5.2 Recommendations 45
5.2.1 Hot Plate Design and Dimensions with
Types of Heater Plate Used 45 5.2.2 Filtering System to Reduce the Effect
of Fuel Vapors 46
REFERENCES 48
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LIST OF TABLES
NO. TITLE PAGE
2.1 ASTM Standards of Bio-Diesel and Petro-Diesel Fuels 12
2.2 Regime Transition Conditions 15
3.1 Properties of Tested Fuels 21
3.2 Summarized Comparison of FSDT Apparatus Before
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LIST OF FIGURES
NO. TITLE PAGE
1.1 Basic Transesterification Process 2
1.2 Transesterification of Triglycerides with Alcohol 2 1.3 Fuel Deposition Phenomena inside Combustion Chamber 3 2.1 Bio-Diesel Fuel Properties and Their Associated Impact on
Engine Operation, Storage and Transportation as Compared
to Fossil Diesel 6
2.2 Bio-Diesel Kinematic Viscosity Variations with Temperature 8 2.3 Kinematic Viscosity Variations with Bio-Diesel Blend
Percentage 8
2.4 Specific Gravity of Bio-Diesel and Its Blends with No. 2
Diesel Fuel 9
2.5 Direct Impact and Corresponding Interactions of Bio-Diesel
Fuel Properties on Emissions as Compared to Fossil Diesel 10 2.6 Diesel Engine Emission Characteristics for Operation
with Bio-Diesel 11
2.7 Schematic of Different Impact Regimes 14 2.8 The Amount of Precipitates Formed by SBO, CSO and PF
Based Bio-Diesel as Function of Bio-Diesel Fraction and
Temperature 18
3.1 Flow Chart of Methodology 20
3.2 Fuel Density Comparisons for Diesel and Bio-Diesel Fuels 21 3.3 Existing Fuel Spray Deposition (FSDT) Apparatus 22
3.4 Current Fuel Tank without Cover 22
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NO. TITLE PAGE
3.6 Improper Fuel Spray Chamber Design 23 3.7 Comparison of Fuel Spray Chamber Between Before
and After Modification 24
3.8 Fuel Spray Chamber with Acrylic Cover and Sliding
Mechanism 25
3.9 Fuel Spray Chamber with Exhaust Fan and Aluminium Hoses 25 3.10 Jack System Use to Support and Adjust the Heater Plate
Position 26
3.11 Comparison of Fuel Tank between Before and After
Modification 27
3.12 Modified Fuel Spray Deposition Test (FSDT) Apparatus 28 3.13 Schematic Diagram of Fuel Spray Deposition (FSDT)
Apparatus 29
3.14 Dimension of the Aluminium Hot Plate 29 3.15 Distances between the Fuel Injector and Center of the Hot Plate 31 3.16 Hot Plate Placement onto the Support 32 3.17 Weight of Hot Plate Measurement Using Microbalance After
Cooled Down 32
4.1 Deposition Mass, M of B5 and B10 34
4.2 Visual Comparison for B5 and B10 Deposits 35 4.3 Deposit Formation Rate, R versus Time, T for Tested Fuels 38
4.4 General Features for the Single and Non-Single Droplet States during Diesel and Bio-Diesel Fuel Droplet Evaporation 39 4.5 Evaporation Characteristics for Diesel Fuel, B100 and
Bio-Blended Diesel Fuels 39
4.6 Fuel Vapors Emitted from Exhaust Fan of the Spray Chamber 43 5.1 Charcoal Canister Used in Carburetor System 46 5.2 Fuel Vapor Canister Filter Made of Polyester Fibers 47
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LIST OF ABBREVIATIONS
ASTM American Society for Testing and Material BHA Butylated Hydroxyanisole
BHT Butylated Hydroxytoluene CI Compression Ignition
CN Cetane Number
CO Carbon Monoxide
CO2 Carbon Dioxide CSO Cottonseed Oil
CSOME Cottonseed Oil Methyl Ester D2 No.2 Type Diesel Fuel DC Direct Current
FAME Fatty Methyl Esters
FSDT Fuel Spray Deposition Test
HC Hydrocarbon
HCCI Homogeneous Charge Compression–Ignition
HP Horsepower
HSDI High Speed Direct Injection ID Ignition Delay
La Laplace Number
max Maximum
MEP Maximum Evaporation Rate Point
min Minimum
NOx Nitrogen Oxides PF Poultry Fat Based PM Particulate Matter PME Palm Methyl Ester PrG Propyl Gallate
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LIST OF ABBREVIATIONS
PSM Projek Sarjana Muda
SAE Society of Automotive Engineers SBO Soybean Oil
SG Specific Gravity SP Spray Penetration TBHQ Tert-Butylhydroquinone USA United States of America
UTeM Universiti Teknikal Malaysia Melaka
vol Volume
We Weber Number
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LIST OF SYMBOLS
L Length [m]
Characteristic Length [m]
μ Viscosity [mm2/s]
t Time [s]
ρ Density [kg/m3][g/ml]
v Velocity [m/s]
σ Surface Tension [kg/s2]
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LIST OF APPENDICES
NO. TITLE PAGE
A Gantt Chart of PSM Implementation 54
B Density Measurement of Diesel and Bio-Diesel Fuels 55
C Fuel Properties of D2 and B5 56
D Electric Motor Specification Used in FSDT Apparatus 57 E Experimental Result of Deposition Mass, M for B5 at 300 °C 58
F Experimental Result of Deposition Mass, M for B10 at 300 °C 59
G Slope Calculation for Deposit Formation Rate, R of B5 and
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CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
Development of diesel engine had been evolved dramatically since its invention around 1900’s. Throughout the industrial revolution era, diesel engine had made its important roles and been widely used especially in transportation fields such as heavy trucks, heavy machineries and most importantly, commercial vehicles. Diesel engine had many advantages than gasoline type engines: high power-to-weight ratio, higher thermal efficiencies, better fuel economies, simpler construction and most importantly lower hydrocarbons (HC) emission.
However, emission from burned diesel fuel had brought major drawbacks since it produce particulate emissions such as sulfates from sulfur contents inside the fuel [1], as much as 20 to 50 times higher than conventional petrol-diesel [2]. This had brought major concerns since it is harmful to the environments and most importantly to publics. Typical proposed low-emissions fuel should have high cetane number (CN), low boiling range, low aromatic compound and addition of oxygenates [1]. Hence, some of the researchers had started to developing new alternatives fuels from vegetable oils and cooking oils to produce bio-diesel. Bio-diesel, an alternative fuel from diesel, is known as fatty acid methyl or ethyl esters formed from vegetable oils or animal fats with alcohols through transesterification process [3]. It is renewable, bio-degradable and oxygenated compared to conventional diesel fuel [4]. With the implementation of bio-diesel into the market, this had eventually reduced the needs from fossil fuels which is depleting throughout the years.
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1.1.1 Bio-Diesel Fuel
Bio-diesel (chemical name: fatty acid methyl esters (FAME), C14-C24 methyl esters, is defined as a fuel comprised of mono-alkyl esters of long–chain fatty acids derived from renewable lipid feedstock, such as vegetable oils or animal fats, for used in compression-ignition (CI) diesel engine [5]. It is a type of alternative fuel that had the potential to reduce emissions and green house effect. It is known as “advanced bio-fuel” through the Energy Independence and Security Act of 2007 [3].
Bio-diesel is produced from transesterification process by reaction of fatty acids such as glyceride with alcohol in presence of catalyst. The produced product, which is long chain fatty acids that comprise of alkyl esters and glycerol.
Figure 1.1 Basic Transesterification Process [6]
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Bio-diesel usually blended with petroleum diesel to make bio-diesel blends; B100 is pure FAME, while B20, B5 and B2 are fairly common blend levels [3]. Bio-diesel blends are classified through the letter B with followed numbers that denotes the percentage of bio-diesel in the blend. For example, B20 of bio-diesel is consists of 20 % of bio-diesel blends inside the fuel. However, for the conventional and unmodified diesel engine, it can only operate with maximum of 20 % bio-diesel blended fuel [7].
1.1.2 Fuel Deposition
Inside combustion chamber, large amount of fuel droplet was produced during fuel injection process. This droplet will experience atomization and eventually burned inside combustion chamber. However, due to some properties inside engine such as ignition delay (ID) or excessive amount of fuel droplet, some of the fuel droplet will not eventually burned up and cause impingement onto the wall surface of combustion chamber and piston head. This repeating process will in turn produce liquid fuel films [8], where deposit formation will produce onto combustion chamber wall surface. Figure 1.3 below shows the common fuel deposits on top of the piston bowl inside common diesel engine.
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According to Werlberger and Cartellieri [10], they discovered that for small bore direct injection diesel engine, more than 50 % of the fuel will impinged on the top of piston bowl at high load conditions.
Inside small diesel engine, probability of impingement onto wall surface was higher, due to factors such as higher injection pressure that leads to higher spray penetration of fuel droplet [11], longer ID as compared to injection period [12], small engine with smaller stroke between injector nozzle and piston head [13], and incomplete combustion causing unburned fuel droplets, especially in the case for bio-diesel fuel [2].
Wall surface temperature plays major role in fuel impingement. Higher wall surface temperature will have less fuel impinge onto it than lower wall surface temperature as discovered by Tang et al. in the case for bio-diesel [14]. Higher
volatility and heavier molecular mass fuel (density) will more likely to produce more impingement on wall surface as experimental results discovered by Tat and Gerpen [15].
1.2 PROBLEM STATEMENT
Engine deposition is the phenomena where deposit forms from unburned fuels inside the combustion chamber. This in turns leads to increase in emission and reduce engine performance [16]. Wall surface temperature was found to be one of the main factors that affect the amount of deposit accumulated [14].
In this study, Fuel Spray Deposition Test (FSDT) was used to conduct an experiment to investigate the deposit formation of B5 and B10 due to fuel spray impingement on a hot surface.
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1.3 OBJECTIVES
The main objective of this research is to investigate the deposit formation tendency for bio-blended diesel (B5 and B10) fuel spray on a hot surface plate.
1.4 SCOPES
This study was focused on the investigation of deposit formation for B5 and B10 on a hot surface due to fuel spray impingement. At first, the current design of FSDT apparatus, fabrication method, as well as properties and behavior of fuel are studied. Then, the current apparatus was improved and experiments were conducted for further investigation.
The main scopes of this study are summarized as below:
i. Modify the existing fuel spray apparatus.
ii. B5 and B10 were used as the tested fuel for fuel spray deposition investigation.
iii. Fuel injection pump was set at constant speed of 1450 rpm which is corresponding to constant engine speed.
iv. Hot surface temperature was set at 300 °C corresponding to the wall surface temperature that is before the MEP temperature of diesel fuel [17].
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CHAPTER 2
LITERATURE REVIEW
2.1 THE EFFECT OF BIO-DIESEL FUEL PROPERTIES
Through the transesterification process, bio-diesel fuel had experienced some changes to its properties such as high density, high viscosity, high CN, lower heat content and etc, as compared to conventional diesel fuel. Thus, this difference in fuel properties will prone to have several impacts on engine operation as well as to the environment. Figure 2.1 below shows the general impact of bio-diesel as compared to diesel fuels.
Figure 2.1 Bio-diesel fuel properties and their associated impact on engine operation, storage and transportation as compared to fossil diesel [18]
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2.1.1 Viscosity
Viscosity of the blended bio-diesel plays major role in operation of CI engine. It is an important factor in predicting the performance of potential alternatives diesel fuel sources [3]. This is because minimum amount of viscosity from fuel is needed due to possible of power loss caused by injection pump and injector leakage inside engine. However, higher viscosity of fuels will cause poor combustion rate, due to poor fuel injection atomization [16] that leads to deposit formation and high fuel spray penetration (SP) inside cylinder. This in turn will causing engine oil diluted with fuel itself that changing the engine oil properties [6].
Even though high fuel SP properties cause problems as above, it is found that this properties leads to enhancing of power and torque produced onto the engine by some researchers [6, 7]. Meanwhile, the higher viscosity and surface tension of bio-diesel than bio-diesel fuel prevent sufficient breaking of the bio-bio-diesel during fuel injection process.
However, according to Aydin and Bayindir [19], they reported that engine torque was decreased when percentage of blends in CSOME (cottonseed oil methyl ester) increased due to higher viscosity and lower heating value of CSOME. This in turn raise up the probability of different feedstock has different properties throughout percentages of bio-diesel blended.
High viscosity properties from vegetable oils and animal fats tends to cause engine problems when used directly in common diesel engines [20-23], if the oils and fats are transesterified using short-chain alcohols, the produced monoesters will have viscosities that are almost identical to petroleum-based diesel fuel [24]. These monoesters have come to be known as bio-diesel.
Tesfa et al. [4] studies the effect of temperature on density and viscosity on
three types of bio-diesel fuel – corn oil based, rapeseed oil and waste oil based for various blended percentage. Figure 2.2 below summarize his findings of relationship between different feedstock and bio-diesel blended.
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1.1.1 Bio-Diesel Fuel
Bio-diesel (chemical name: fatty acid methyl esters (FAME), C14-C24 methyl esters, is defined as a fuel comprised of mono-alkyl esters of long–chain fatty acids derived from renewable lipid feedstock, such as vegetable oils or animal fats, for used in compression-ignition (CI) diesel engine [5]. It is a type of alternative fuel that had the potential to reduce emissions and green house effect. It is known as “advanced bio-fuel” through the Energy Independence and Security Act of 2007 [3].
Bio-diesel is produced from transesterification process by reaction of fatty acids such as glyceride with alcohol in presence of catalyst. The produced product, which is long chain fatty acids that comprise of alkyl esters and glycerol.
Figure 1.1 Basic Transesterification Process [6]
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Bio-diesel usually blended with petroleum diesel to make bio-diesel blends; B100 is pure FAME, while B20, B5 and B2 are fairly common blend levels [3]. Bio-diesel blends are classified through the letter B with followed numbers that denotes the percentage of bio-diesel in the blend. For example, B20 of bio-diesel is consists of 20 % of bio-diesel blends inside the fuel. However, for the conventional and unmodified diesel engine, it can only operate with maximum of 20 % bio-diesel blended fuel [7].
1.1.2 Fuel Deposition
Inside combustion chamber, large amount of fuel droplet was produced during fuel injection process. This droplet will experience atomization and eventually burned inside combustion chamber. However, due to some properties inside engine such as ignition delay (ID) or excessive amount of fuel droplet, some of the fuel droplet will not eventually burned up and cause impingement onto the wall surface of combustion chamber and piston head. This repeating process will in turn produce liquid fuel films [8], where deposit formation will produce onto combustion chamber wall surface. Figure 1.3 below shows the common fuel deposits on top of the piston bowl inside common diesel engine.
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According to Werlberger and Cartellieri [10], they discovered that for small bore direct injection diesel engine, more than 50 % of the fuel will impinged on the top of piston bowl at high load conditions.
Inside small diesel engine, probability of impingement onto wall surface was higher, due to factors such as higher injection pressure that leads to higher spray penetration of fuel droplet [11], longer ID as compared to injection period [12], small engine with smaller stroke between injector nozzle and piston head [13], and incomplete combustion causing unburned fuel droplets, especially in the case for bio-diesel fuel [2].
Wall surface temperature plays major role in fuel impingement. Higher wall surface temperature will have less fuel impinge onto it than lower wall surface temperature as discovered by Tang et al. in the case for bio-diesel [14]. Higher
volatility and heavier molecular mass fuel (density) will more likely to produce more impingement on wall surface as experimental results discovered by Tat and Gerpen [15].
1.2 PROBLEM STATEMENT
Engine deposition is the phenomena where deposit forms from unburned fuels inside the combustion chamber. This in turns leads to increase in emission and reduce engine performance [16]. Wall surface temperature was found to be one of the main factors that affect the amount of deposit accumulated [14].
In this study, Fuel Spray Deposition Test (FSDT) was used to conduct an experiment to investigate the deposit formation of B5 and B10 due to fuel spray impingement on a hot surface.
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1.3 OBJECTIVES
The main objective of this research is to investigate the deposit formation tendency for bio-blended diesel (B5 and B10) fuel spray on a hot surface plate.
1.4 SCOPES
This study was focused on the investigation of deposit formation for B5 and B10 on a hot surface due to fuel spray impingement. At first, the current design of FSDT apparatus, fabrication method, as well as properties and behavior of fuel are studied. Then, the current apparatus was improved and experiments were conducted for further investigation.
The main scopes of this study are summarized as below:
i. Modify the existing fuel spray apparatus.
ii. B5 and B10 were used as the tested fuel for fuel spray deposition investigation.
iii. Fuel injection pump was set at constant speed of 1450 rpm which is corresponding to constant engine speed.
iv. Hot surface temperature was set at 300 °C corresponding to the wall surface temperature that is before the MEP temperature of diesel fuel [17].
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CHAPTER 2
LITERATURE REVIEW
2.1 THE EFFECT OF BIO-DIESEL FUEL PROPERTIES
Through the transesterification process, bio-diesel fuel had experienced some changes to its properties such as high density, high viscosity, high CN, lower heat content and etc, as compared to conventional diesel fuel. Thus, this difference in fuel properties will prone to have several impacts on engine operation as well as to the environment. Figure 2.1 below shows the general impact of bio-diesel as compared to diesel fuels.
Figure 2.1 Bio-diesel fuel properties and their associated impact on engine operation, storage and transportation as compared to fossil diesel [18]
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2.1.1 Viscosity
Viscosity of the blended bio-diesel plays major role in operation of CI engine. It is an important factor in predicting the performance of potential alternatives diesel fuel sources [3]. This is because minimum amount of viscosity from fuel is needed due to possible of power loss caused by injection pump and injector leakage inside engine. However, higher viscosity of fuels will cause poor combustion rate, due to poor fuel injection atomization [16] that leads to deposit formation and high fuel spray penetration (SP) inside cylinder. This in turn will causing engine oil diluted with fuel itself that changing the engine oil properties [6].
Even though high fuel SP properties cause problems as above, it is found that this properties leads to enhancing of power and torque produced onto the engine by some researchers [6, 7]. Meanwhile, the higher viscosity and surface tension of bio-diesel than bio-diesel fuel prevent sufficient breaking of the bio-bio-diesel during fuel injection process.
However, according to Aydin and Bayindir [19], they reported that engine torque was decreased when percentage of blends in CSOME (cottonseed oil methyl ester) increased due to higher viscosity and lower heating value of CSOME. This in turn raise up the probability of different feedstock has different properties throughout percentages of bio-diesel blended.
High viscosity properties from vegetable oils and animal fats tends to cause engine problems when used directly in common diesel engines [20-23], if the oils and fats are transesterified using short-chain alcohols, the produced monoesters will have viscosities that are almost identical to petroleum-based diesel fuel [24]. These monoesters have come to be known as bio-diesel.
Tesfa et al. [4] studies the effect of temperature on density and viscosity on
three types of bio-diesel fuel – corn oil based, rapeseed oil and waste oil based for various blended percentage. Figure 2.2 below summarize his findings of relationship between different feedstock and bio-diesel blended.