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Elsevier Editorial System(tm) for Energy Conversion and Management Manuscript Draft Manuscript Number: Title: Particulate Emissions from Biodiesel Fuelled CI Engines Article Type: Review Article - by invitation only Keywords: Particulate; biodiesel; size-number distribution; toxic potential; soot morphology. Corresponding Author: Prof. Avinash Kumar Agarwal, PhD Corresponding Author's Institution: IIT Kanpur First Author: Avinash Kumar Agarwal, PhD Order of Authors: Avinash Kumar Agarwal, PhD; Tarun Gupta, PhD; Pravesh c Shukla, MTech; Atul Dhar, PhD Abstract: Compression ignition engines are the most popular prime-movers for transportation sector as well as for stationary applications. Petroleum reserves are rapidly and continuously depleting at an alarming pace and there is an urgent need to find alternative energy resources to control both, the global warming and the air pollution, which is primarily attributed to combustion of fossil fuels. In last couple of decades, biodiesel has emerged as the most important alternative fuel candidate to mineral diesel. Numerous experimental investigations have confirmed that biodiesel results in improved engine performance, lower emissions, particularly lower particulate mass emissions vis-à-vis mineral diesel and is therefore relatively more environment friendly fuel, being renewable in nature. Environmental and health effects of particulates are not simply dependent on the particulate mass emissions but these change with varying physical and chemical characteristics of particulates. Particulate characteristics are dependent on largely unpredictable interactions between engine technology, after-treatment technology, engine operating conditions as well as fuel and lubricating oil properties. This review paper presents an exhaustive summary of literature on the effect of biodiesel and its blends on exhaust particulate's physical characteristics (such as particulate mass, particle number-size distribution, particle surface area-size distribution, surface morphology) and chemical characteristics (such as elemental and organic carbon content, speciation of polyaromatic hydrocarbons, crustal and anthropogenic trace metals, sulfates, nitrates etc.) in order to comprehensively assess the effects of biodiesel usage on the environment as well as on the human health. Control of particulate emissions using various engine control parameters such as intake air boosting using turbocharging, high pressure fuel injections and multiple injections, exhaust gas recirculation (EGR), after-treatment devices etc. in combination with the use of biodiesel has also been critically reviewed and included in this review article. Suggested Reviewers: Suresh K Aggarwal PhD Professor, Department of Mechanical Engineering, University of Illinois@chicago, USA [email protected] Chang Sik Lee PhD Professor, Department of Mechanical Engineering, Hanyang University, South Korea [email protected]
Anirudh Gautam PhD Executive Director, Engine Development Directorate, Research Designs and Standards Organisation, Lucknow [email protected] Opposed Reviewers:
IIINNNDDDIIIAAANNN IIINNNSSSTTTIIITTTUUUTTTEEE OOOFFF TTTEEECCCHHHNNNOOOLLLOOOGGGYYY KKKAAANNNPPPUUURRR DEPARTMENT OF MECHANICAL ENGINEERING
KANPUR-208016, INDIA
Dr. Avinash Kumar Agarwal, Tel: + 91 512 2597982 (O), + 91 512 2598682 (R)
Poonam and Prabhu Goyal Endowed Chair Professor Fax: + 91 512 259 7408
Email:[email protected] http://home.iitk.ac.in/~akag
September 4th, 2014
Editor,
Energy Conversion and Management
Dear Sir,
I am submitting a manuscript entitled “Particulate Emissions from Biodiesel Fuelled CI Engines", by
Avinash Kumar Agarwal*, Tarun Gupta, Pravesh C Shukla, Atul Dhar for inclusion in “Energy
Conversion and Management”. This paper is being submitted against the invitation by Ms. Shannon
Qu on 14th March, 2014.
Submission of this article implies that the work described has not been published previously (except in
the form of an abstract or as part of a published lecture or academic thesis), that it is not under
consideration for publication elsewhere, that its publication is approved by all authors and that, if
accepted, it will not be published elsewhere in the same form, in English or in any other language,
without the written consent of the Publisher.
Looking forward to your kind consideration.
Best regards
Dr A K Agarwal
Cover letter
Energy Conversion and Management
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Particulate Emissions from 1
Biodiesel Fuelled CI Engines 2
3
Avinash Kumar Agarwal1*, Tarun Gupta2, Pravesh C Shukla2, Atul Dhar1 4
Engine Research Laboratory, 5
Departments of 1Mechanical and 2Civil Engineering 6
Indian Institute of Technology Kanpur, Kanpur-208016, India 7
*Corresponding author’s email: [email protected] 8
9
Abstract 10
Compression ignition engines are the most popular prime-movers for transportation 11
sector as well as for stationary applications. Petroleum reserves are rapidly and 12
continuously depleting at an alarming pace and there is an urgent need to find 13
alternative energy resources to control both, the global warming and the air pollution, 14
which is primarily attributed to combustion of fossil fuels. In last couple of decades, 15
biodiesel has emerged as the most important alternative fuel candidate to mineral 16
diesel. Numerous experimental investigations have confirmed that biodiesel results in 17
improved engine performance, lower emissions, particularly lower particulate mass 18
emissions vis-à-vis mineral diesel and is therefore relatively more environment friendly 19
fuel, being renewable in nature. Environmental and health effects of particulates are 20
not simply dependent on the particulate mass emissions but these change with varying 21
physical and chemical characteristics of particulates. Particulate characteristics are 22
dependent on largely unpredictable interactions between engine technology, after-23
treatment technology, engine operating conditions as well as fuel and lubricating oil 24
*ManuscriptClick here to view linked References
2
properties. This review paper presents an exhaustive summary of literature on the effect 25
of biodiesel and its blends on exhaust particulate’s physical characteristics (such as 26
particulate mass, particle number-size distribution, particle surface area-size 27
distribution, surface morphology) and chemical characteristics (such as elemental and 28
organic carbon content, speciation of polyaromatic hydrocarbons, crustal and 29
anthropogenic trace metals, sulfates, nitrates etc.) in order to comprehensively assess 30
the effects of biodiesel usage on the environment as well as on the human health. 31
Control of particulate emissions using various engine control parameters such as intake 32
air boosting using turbocharging, high pressure fuel injections and multiple injections, 33
exhaust gas recirculation (EGR), after-treatment devices etc. in combination with the 34
use of biodiesel has also been critically reviewed and included in this review article. 35
Keywords: Particulate; biodiesel; size-number distribution; toxic potential; soot 36
morphology. 37
1. Introduction 38
Fossil fuels have dominated transportation sector since the invention of internal 39
combustion engines in early nineteenth century. Conventional petroleum resources are 40
finite and they contribute enormously to the ever-rising green house gas emissions to 41
the atmosphere thus renewable alternative fuels are being globally developed and 42
explored frenetically by researchers. Depletion of fossil fuels is eminent in near future. 43
In addition, environmental pollution concerns due to combustion of fossil fuels provides 44
a unique and significant motivation for developing renewable alternative fuels, which 45
have the potential to sustain ever-growing fuel demand for transportation sector. In 46
order to effectively control environmental pollution and mitigate its harmful effects, 47
exhaust characterization at the engine outlet as well its impact of its transformational 48
products in the atmosphere is extremely essential [1]. Health effects of exhaust 49
particulates depend on chemical composition and physical characteristics, which 50
3
determines their true residence time and availability as sorption sites inside the human 51
respiratory system [2-6]. 52
Biodiesel has emerged as a strong diesel alternative, and comprises of fatty acid alkyl 53
esters derived from transesterification of triglycerides present in vegetable oils/ animal 54
fats. Biodiesel has been well accepted as renewable alternative to mineral diesel 55
globally. Large numbers of scientific studies have reported successful operation of 56
compression ignition (CI) engines with biodiesels derived from different feedstock. 57
Biodiesel can either be used as a full replacement of mineral diesel or it can also be 58
blended with mineral diesel in any proportion[7]. 59
Formation of particulates and gaseous emissions depend not only on physical and 60
chemical properties of the fuels but this process is also greatly influenced by complex in-61
cylinder processes such as air-fuel mixing, combustion chamber geometry and 62
temperature and pressure condition of cylinder charge during combustion [8, 9]. 63
Particulate formation in a diesel engine is very sensitive to relative air-fuel mixture 64
strength (λ) in rich, premixed reaction zones of the combustion chamber, where soot 65
precursors are initially generated [8]. Physical properties of biodiesel are also important, 66
which directly affect spray atomization, droplet size distribution and fuel-air mixing in 67
the combustion chamber. Injection delay and spray tip penetration is relatively longer 68
for biodiesel compared to mineral diesel, whereas spray cone angle, spray area and 69
spray volume are relatively smaller. Relatively higher viscosity and surface tension of 70
biodiesel is responsible for larger sauter mean diameter (SMD) of the spray droplets 71
[10]. In last two decades, advancements in diesel technology such as application of very 72
high fuel injection pressures, split injection, turbo-charging, after-treatment devices 73
have resulted in considerable reduction in engine-out emissions but these technologies 74
have also increased engine control complexities and sensitivity of engine towards 75
changes in fuel properties and lubricating oil properties. It is universally accepted that 76
4
biodiesel blend usage in CI engines reduces PM mass emission but mixed trends are 77
reported for the physical and chemical characteristics of biodiesel particulates 78
depending upon the engine technology, biodiesel feedstock, biodiesel blend 79
concentration, type of after-treatment device used, engine management system 80
optimization etc. Several toxicological studies [2, 3] reported that biodiesel use in engine 81
results in lower toxicity of particulates, especially lower mutagenic potential as 82
compared to mineral diesel. A review paper [11] on effect of diesel exhaust on human 83
health concluded that evidence from scientific studies so far is insufficient to adequately 84
validate the diesel particulate-lung cancer hypothesis. This further emphasizes the need 85
to study biodiesel vs. diesel exhaust critically under various engine operating conditions 86
typically encountered in real world situation. 87
This review is an attempt to present an exhaustive literature review of the effects of 88
biodiesel and biodiesel blends on the exhaust particulate’s chemical characteristics (such 89
as elemental and organic carbon, speciation of polyaromatic hydrocarbons, crustal and 90
anthropogenic trace metals, sulfates and nitrates) and physical characteristics (such as 91
particulate mass emission, particle number-size distribution, particle surface area-size 92
distribution, and particulate morphology). This review critically assesses the effect of 93
biodiesel on the environment as well as human health under varying engine operating 94
conditions, varying fuel injection parameters and strategies, using various after-95
treatment control technologies to assess the possible threat emanating from a large 96
scale biodiesel usage. 97
2 Chemical Characterization of Particulates 98
2.1 Chemical Composition of Particulates 99
Diesel engine undergoes heterogeneous combustion phenomenon. Fuel is injected into 100
the combustion chamber towards the end of the compression stroke in conventional CI 101
engines. Modern diesel engines are equipped with common rail direct injection system, 102
5
which have spit injection, i.e. fuel is injected in pilot injection, main injection and post 103
injection in the same engine cycle. When fuel is injected into the combustion chamber at 104
very high injection pressure, it breaks into large number of small droplets under the 105
influence of high combustion chamber pressure, prevailing at the end of compression 106
stroke. Compressed air in the combustion chamber offers resistance to the high pressure 107
fuel droplets, which results in further fragmentation of small droplets into further finer 108
droplets. When a relatively larger droplet breaks into several smaller droplets, total 109
surface area of the droplet increases significantly. This higher surface area provides 110
superior interaction between fuel droplets and surrounding hot high pressure 111
combustion chamber air, which eventually results in higher degree of completion of 112
combustion of the fuel injected. 113
Heywood [12] explained soot formation in the engine combustion chamber. By 114
considering a single fuel droplet inside the combustion chamber, soot formation process 115
can was explained. A single fuel droplet comes into contact with hot, high pressure air in 116
the combustion chamber (Figure 1). 117
118
(a) Diesel droplet (b) Biodiesel droplet 119
Figure 1: Evaporation of single diesel and biodiesel droplet inside combustion chamber 120
A small quantity of fuel evaporates from the fuel droplet surface and forms rich fuel-air 121
mixture closer to the surface of the droplet. Mixture composition becomes progressively 122
leaner as the distance from the surface of the droplet increases as seen in figure 1. 123
Wherever the air availability is good enough for combustion of fuel droplets, combustion 124
tends to be complete, resulting in low particulate formation. Near the droplet surface, 125
6
where rich mixture formed (λ <1.0), combustion tends to be relatively incomplete, which 126
results in higher particulate formation. Similarly, there is no air/ oxygen available 127
inside the core of the droplet. Under the influence of hot burning droplets, fuel closer to 128
the droplet surface and the fuel present inside the droplet is either not able to burn or 129
burn partially, thus forming pyrolyzed fuel remnants, which act as precursors for soot 130
formation. Biodiesel has slightly higher temperature required of vaporization therefore 131
it can be assumed that the vaporization of biodiesel droplet is slightly lower as compared 132
to mineral diesel droplet. On the other hand, there is absolutely no oxygen present 133
inside diesel droplet (Figure 1a). Absence of oxygen molecules inside the fuel droplet 134
results in unburned hydrocarbons and pyrolyzed carbonaceous compounds. In case of 135
biodiesel, combustion is aided partially inside the droplet (Figure 1b) by the oxygen 136
atoms present in the biodiesel molecules (~11% w/w) [13]. 137
Diesel particulate mainly comprise of four components, namely (i) elemental carbon 138
(EC), (ii) organic carbon (OC), (iii) sulfate and (iv) ash, which mainly includes trace 139
metals [14]. Figure 2 shows typical composition of particulate emitted by CI engines. 140
141
142
Figure 2: Typical diesel particulate composition [15] 143
Elemental carbon is known as 'soot' and it mainly comprises of 'carbon'. Elemental 144
carbon is crystalline in structure and mostly forms central part of particulate [16]. 145
Organic carbon mainly consists of hydrocarbons, which either remained unburned 146
during combustion, primarily originating from fuel or lubricating oil or form due to 147
Carbon 41%
Unburned Oil
25%
Unburned fuel 7%
Ash and Others
14%
Sulphate and Water
13%
7
condensation of organic vapors as a left-over of incomplete combustion. Organic fraction 148
of the particulate is of great concern due to its harmful effects on humans. Diesel and 149
biodiesel exhaust particulates both consists of significant amount of organic fraction. 150
However, scientific studies have shown that biodiesel exhaust particulates have 151
significantly lower organic fraction. 152
In a study, Rounce et al. [17] reported that concentration of acetaldehyde, formaldehyde, 153
benzene, and 1,3-butadiene was lower for rapeseed methyl ester (RME) in comparison to 154
ultra-low sulfur diesel (ULSD). RME produced relatively lower solid particulate and 155
higher liquid particulate as compared to ULSD. Particulate number concentration 156
reduced for the entire size range. However, RME produced a higher proportion of nano-157
particulates of smaller size range and such nano-particulates had higher soluble organic 158
fraction (SOF), which is a marker of toxicity. They reported that DPF captured ~99% 159
solid particulates in terms of mass and particle number for both ULSD and RME. 160
Similarly, DPF reduced~88% and ~80% liquid portion of particulates for ULSD and 161
RME. In another study, Zhu et al. [18] reported significantly reduced smoke opacity 162
with increase in biodiesel proportion in the test fuel, while the total particle number 163
concentration actually increased. It was observed that sulfate and SOF increased in 164
particulates with increasing biodiesel blend concentration, whereas solid particulates 165
actually reduced in number. Nucleation mode particle number concentration was 166
observed to be higher for biodiesel and total particle number concentration reduced with 167
ULSD. The contribution of lubricating oil was suggested to be as high as 80- 90% in 168
the SOF portion of the particulate [19]. 169
Chuepeng et al. [20] did experiments with B30 and reported that B30 produced lower 170
particulates on a mass basis at all engine operating conditions compared to ULSD. They 171
also observed lower EC content in particulate of B30 as compared to ULSD. They 172
suggested that presence of oxygen in biodiesel limits the in-cylinder particle formation 173
8
by influencing both the carbon chain formation and its oxidation. At a high engine load, 174
higher amount of fuel-borne oxygen leads lower EC formation for biodiesel. Young et al. 175
[21] reported that non-volatile particulate concentration emitted by heavy-duty diesel 176
engine increased with increasing load from 25% to 75% and it decreased with increasing 177
biodiesel blend from 2- 20%. Williams et al. [19] measured particulate mass for different 178
engine operating conditions and determined volatile mass fraction of the particulates 179
using thermo-gravimetric analysis (TGA) from a CRDI V6 engine fuelled with RME 180
blended with ULSD (B30). They reported higher volatile organic fractions for idle and 181
low load conditions. EC fraction was lower for B30 compared to ULSD. Li et al. [22] 182
compared exhaust emissions and particulate size distribution for diesel, fresh cooking oil 183
(FCO) and waste cooking oil (WCO) at two engine operating conditions (23 kW and 47 184
kW). PM emission was almost equal to diesel at lower load however it reduced 185
significantly when engine was operated at higher loads. FCO showed higher PM 186
emissions at both conditions and both fuels showed lower nuclei mode particles after 187
DOC compared to mineral diesel. This suggested that DOC was not very effective in 188
reducing nano-particles emanating from diesel as compared to those from biodiesel. 189
Schönborn et al. [23] studied the effect of different molecular structures of fatty esters 190
on NOx and soot formation. They concluded that different biodiesels have different 191
physical and chemical properties depending on the fatty ester composition, which affect 192
the combustion in diesel engines. Lapuerta et al. [24] evaluated the effect of 193
unsaturation level of biodiesel on NOx and PM emissions. They reported significant 194
reduction in PM mass and smoke opacity for biodiesel (B100) however PM mass 195
decreased by ~20% and NOx increased by ~10%, as biodiesel became more unsaturated. 196
They also reported smaller mean diameter particulates from unsaturated biodiesel. 197
Zhang et al. [25] investigated the particle size distribution in a biodiesel blend fuelled 198
CRDI engine exhaust and found that B100 resulted in no emission of nucleation mode 199
9
particles. Soewono et al. [26] investigated particulate morphology and microstructure 200
using diesel and B20 by employing transmission electron microscopy (TEM) and Raman 201
spectroscopy. B20 particulates showed higher structural disorder compared to diesel 202
particulates for the same engine operating conditions and structural order of soot 203
improved for higher engine loads. Tan et al. [27] tested five test fuels namely mineral 204
diesel, B10, B20, B50 and B100 for particle size-number distribution and reported that 205
the nucleation mode particles increased with increasing biodiesel blends concentration 206
vis-a-vis mineral diesel. Number of accumulation mode particles decreased with 207
increasing biodiesel content in the test fuel. They explained that higher number of 208
nucleation mode particles emitted with biodiesel may be a result of higher degree of 209
saturation of condensed matter in presence of lesser number of soot nuclei. Evaporation 210
and mixing characteristics of biodiesel is worse than mineral diesel, which leads to an 211
increase in SOF, which form nucleation mode particles. Biodiesel's fuel oxygen content 212
helps in producing higher number of ultra-fine and nano-particles. Tinsdale et al. [28] 213
investigated the impact of biodiesel on particle numbers, sizes and mass emissions from 214
a diesel engine. Accumulation mode particles and carbonaceous mass decreased and 215
organic mass in particulate increased by using B30. FAME (B30) led to increased 216
nucleation mode particles as compared to mineral diesel. Song et al. [29] studied 217
particulate emissions from oxidized and heated biodiesel and compared the results with 218
non-oxidized biodiesel and ULSD. They reported that particle mass and particle number 219
reduced with the use of biodiesel for heated and oxidized biodiesel. 220
2.2 Elemental and Organic Carbon (EC/OC) 221
Elemental carbon and organic carbon are the two main components exhaust 222
particulates. A large number of studies have investigated the EC and OC content of 223
diesel and biodiesel particulates. As a result of heterogeneous combustion in CI engines, 224
unburned and partially burnt hydrocarbons are emitted. Under high temperature and 225
10
pressures encountered in the combustion chamber, a fraction of hydrocarbons, which are 226
present in locally rich regions, undergo pyrolysis. Most of the hydrogen atoms get 227
striped off the hydrocarbon chain and only carbon atoms remain. This result in the 228
formation of carbon core, which is also called as 'soot' (also known as EC). Carbon 229
undergoes cyclization, sheet like structure formation and eventually nano-tube like 230
structures called spherules are formed. Volatile organic materials usually condense over 231
the solid and dry soot and the particles grow. This condensed organic material is 232
extremely harmful for humans. This condensed organic matter contain hundreds of 233
organic compounds formed as a result of complex organic species formation pathways 234
during fuel pyrolysis in the engine combustion chamber. Some of the organic compounds 235
are known carcinogens such as polyaromatic hydrocarbons (PAHs), Benzene-Toluene-236
Xylene (BTX). A detailed discussion on PAHs emissions has been included in later part 237
of this review. Poitras et al. [30] observed a significant reduction in PM as well as 238
OC/EC ratio upon using biodiesel blends during an experimental study conducted to 239
study the impact of B0 (Diesel), B2, B5, B10, B20, B50 and B100 on particulate 240
emissions. Gangwar et al. [31] performed comparative study of diesel and biodiesel PM 241
mass and chemical composition. They reported that OC/ EC ratio decreased with 242
increasing engine load. BSOF was higher for B20 compared to mineral diesel for same 243
engine operating condition and it decreased with increasing engine load for both test 244
fuels. Although PM emission was lower for B20, PAHs emissions were same for both 245
fuels. Schauer et al. [32] analysed chemical composition of PM from four gasoline 246
vehicles under three driving cycles namely; cold-cold unified driving cycle (UDC), hot 247
UDC and steady-state driving cycle. They analyzed particulate composition for EC, OC, 248
sulfates, nitrates, organic compounds etc. using gas chromatography-mass spectroscopy 249
(GC-MS). The average mass emission rates varied from <0.1 to 1.3 mg/km for a hot UDC 250
and steady-state driving cycles, while it ranged between 1.0 to 7.1 mg/km for cold-cold 251
11
UDC. EC was the main component in particulates for cold-cold UDC cycle and OC 252
consisted of different types of compounds for different cycles. Pabkin et al. [33] also 253
investigated physical, chemical and toxicological characteristics of particulates emitted 254
from a heavy-duty diesel engines equipped with advanced after-treatment devices. They 255
reported significant reduction in particle bound organics in the vehicles equipped with 256
advanced emission control devices. They observed insignificant reduction in hopanes 257
and steranes. Liu et al. [34] used two engine models (2004 model with EGR and 2007 258
model with EGR) crankcase condenser and a DPF and analyzed the particulate samples 259
for C1, C2 and C10-13 particle (EC, OC) phase and semi-volatile organic species. In 2004 260
model, formaldehyde, acetaldehyde and naphthalene were the major fractions out of 150 261
analyzed organic species. The concentration of the above compounds reduced 262
significantly in the 2007 model engine. In another study, Agarwal et al. [6] evaluated 263
comparative toxicity of nano-particles emitted from diesel and B20 fuelled engine. OC, 264
EC content of the particulates was determined for primary and secondary emissions 265
from diesel and B20 fuelled engine. 266
267
Figure 3: EC/OC ratio for diesel and biodiesel (primary and secondary emissions) [6] 268
A photochemical chamber was used for generating secondary emissions. It was found 269
that EC was higher for diesel for both primary and secondary emissions. EC/OC ratio 270
12
was also higher for diesel at higher engine loads. Figure 3 shows the EC/OC ratio 271
obtained for diesel and B20 exhaust [6]. 272
2.3 Trace Metals in Particulates 273
Trace metal emissions from compression ignition engines is of a major environmental 274
and health concern. Lubricating oil, fuel and engine friction/ wear generated debris are 275
major source of trace metal emitted as a part of particulates from the engines. 276
Concentration of trace metals in the fuels such as mineral diesel varies depending upon 277
various factors namely type of crude oil used for production of diesel, synthesis processes 278
and catalysts used in refining process etc. Trace metals are categorized as 279
'anthropogenic metal emissions' and 'crustal metal emissions'. Fe, Ca, Mg, Na are the 280
major crustal metal emissions. Several studies have been performed for trace metal 281
emission evaluation from diesel engines. Transition metal containing particulates can 282
even penetrate deep into the human body. These trace metals raise the level of reactive 283
oxygen species (ROS) activity in cell structures, which in-turn elevates the oxidative 284
stress [35-39]. Pillay et al. [40] compared the trace metals in Neem biodiesel vis-à-vis 285
two commercial grade biodiesels and concluded that Neem biodiesel has relatively lower 286
trace metal content compared to the other two. Some metals like Mn, Cu, Pb etc. were 287
observed to be in higher concentration in Neem biodiesel though. They suggested that 288
further refinement of biodiesel for de-metallization need to be undertaken for 289
sustainable biodiesel usage. Betha et al. [41] characterized trace metal emissions from 290
waste cooking oil-derived biodiesel (B100), ultra-low sulfur diesel and B50 blend. Mg, K, 291
and Al were present in significantly higher concentration in diesel as well as biodiesel. 292
In biodiesel, Zn, Cr, Cu, Fe, Ni, Mg, Ba and K were observed to be in higher 293
concentration compared to biodiesel. However, Co, Pb, Mn, Cd, Sr, and As were observed 294
to be higher in mineral diesel. They carried out risk assessment study and found that 295
13
B100 exhaust has possibly higher health risk compared to ULSD. Figure 4 shows the 296
emission of anthropogenic trace metal emissions from ULSD, B50 and B100 [41]. 297
298
Figure 4: Concentration of carcinogenic trace metals in diesel and biodiesel exhaust [41] 299
Gangwar et al. [31] evaluated trace metal content in diesel and Karanja biodiesel (B20) 300
particulates. They observed that Si, Cu, and Mg were present in higher concentration in 301
diesel particulate as compared to biodiesel particulate. However, Na, Fe, Ca, Pb, Mn and 302
Cr were found to be higher in biodiesel particulate as compared to diesel particulate. 303
Table 1 shows the metal concentration in diesel and Karanja biodiesel particulates. 304
Table 1: Trace metals concentration in diesel and biodiesel exhaust particulates [31] 305
Metals in
particulate
(mg/g)
No Load Full Load
1800 rpm 2400 rpm 1800 rpm 2400 rpm
DE B20 DE B20 DE B20 DE B20
Na 29.4-29.8 34.6-35.0 51.55-51.59 20.25-20.29 5.50-5.54 11.0-11.4 1.91-1.95 1.37-1.41
Ca 6.22-6.26 11.60-11.64 24.44-24.48 31.70-21.74 1.80-1.84 2.27-2.31 0.39-0.43 0.22-0.26
Fe 12.40-12.44 8.81-8.85 9.62-9.66 8.27-8.31 0.82-0.86 3.26-3.30 0.74-0.78 0.32-0.36
Pb 6.51-6.55 2.31-2.35 2.57-2.61 5.11-5.15 0.61-0.65 1.00-1.04 0.33-0.37 0.61-0.65
Si 6.75-6.79 2.04-2.08 2.40-2.44 0.63-0.67 1.01-1.05 0.84-0.88 1.14-1.18 0.04-0.08
Cu 2.60-2.64 1.81-1.85 2.13-2.17 2.07-2.11 1.89-1.93 1.93-1.97 0.31-0.35 0.11-0.13
Mg 1.89-1.93 0.81-0.85 1.74-1.78 2.23-2.27 1.52-1.56 0.57-0.61 0.27-0.31 0.04-0.08
B 4.30-4.34 3.31-3.35 0.32-0.36 0.07-0.11 0.37-0.41 1.50-1.54 0.14-0.18 0.01-0.03
Mn 0.23-0.27 0.56-0.6 0.057-0.061 0.27-0.31 0.01-0.03 0.17-0.21 0.01-0.05 0.01-0.03
14
Cr 0.40-0.44 0.05-0.09 0.15-0.19 0.13-0.17 0 0.01-0.03 0.01-0.03 0.01-0.03
306
Agarwal et al. [7] have also determined trace metal concentrations in diesel and Karanja 307
oil and reported relatively higher concentration of Ca, Co, Cr, Cu, Fe, Mg, Ni, Pb and Zn 308
in mineral diesel compared to Karanja oil. 309
310
2.4 Significance of Desulphurized Fuel 311
Diesel is a petroleum product derived from crude oil. Crude oil contains significant 312
amount of sulfur ranging from 0.5 to 5.0% (w/w) [42]. For automotive applications, 313
sulfur content of diesel should be very low therefore diesel is refined in such a manner 314
that sulfur content is reduced significantly. Several studies show that sulfur content of 315
diesel increases formation of particulate matter. Sulfur leads to formation of sulfur 316
dioxide, which results in formation of sulfates. Sulfate acts as nuclei for the 317
condensation of volatile organic compounds present in the diesel exhaust. The process, 318
in which condensed matter get adsorbed on to the existing nuclei is called heterogeneous 319
nucleation. On the other hand, main advantage of biodiesel is that it has no sulfur [13] 320
hence sulfate origin particulates are formed. Modern diesel vehicles equipped with after-321
treatment devices like diesel oxidation catalyst (DOC), diesel particulate filter (DPF) 322
etc. are vulnerable to sulfur content of the fuel. Catalysts like platinum (Pt) promote 323
formation of sulfate particulates in diesel exhaust, which is undesirable. 324
2.5 Unregulated Emissions 325
The current emission regulations are based on controlling emission of regulated gases 326
(CO, THC and NOx) and particulate matter (PM). Vehicles/ engines also emit large 327
number of other emissions, most of which are in very small quantities except CO2 and 328
moisture, also are currently categorized as unregulated emissions. In some regulations, 329
CO2 is now included as regulated emission. Unregulated emissions are important from 330
health stand point. Ravindra et al. [43] indicated in their research that there should be 331
15
emission regulations for carcinogenic compounds like PAHs. PAHs, carbonyl compounds 332
and BTEX are harmful species emitted in diesel exhaust in traces. It is important to 333
perform chemical speciation of these organic species being emitted by the engine. 334
2.5.1 Carbonyl Compounds 335
Diesel engines emit large number of different harmful compounds and many compounds 336
are still unknown. The term carbonyl refers to the carbonyl functional group, which is a 337
divalent group consisting of a carbon atom double-bonded to oxygen. Carbonyls are such 338
compounds, which have significant presence in engine exhaust. Most studies have 339
measured carbonyl emissions by derivatives of 2,4- di-nitro-phenyl-hydrazine (DNPH) 340
[44-48]. Carbonyl emissions lead to formation of secondary organic aerosols (SOA) by 341
forming oligomers [49]. Contribution of carbonyls in diesel particles also enhances its 342
responses physiologically [50]. Figure 5 shows the basic structures of carbonyl group and 343
carbonyl compounds such as Aldehydes and Ketones. 344
345
Figure 5: Carbonyl Group, Aldehyde and Ketone 346
Pang et al. [51] investigated characteristics of carbonyl emissions from a diesel engine 347
fuelled with biodiesel-ethanol-diesel blend. They reported that acetaldehyde was the 348
carbonyl compound in highest concentration emitted, followed by formaldehyde, acetone, 349
propaldehyde and benzaldehyde respectively. They reported 1-12% higher total carbonyl 350
emissions with biodiesel-ethanol-diesel blend depending on engine operating condition. 351
They also observed that carbonyl emissions increased with increasing engine speed 352
while minimum carbonyl emissions were found at 50% engine load, when the engine 353
was operated at a constant speed [52]. Ho et al. [52] measured and quantified 15 354
16
different carbonyl emissions and formaldehyde was found to be the most dominant 355
compound, followed by acetaldehyde and acetone. They reported that formaldehyde was 356
54.8- 60.8% of the total carbonyl compounds present in the exhaust. They took samples 357
at various locations in city of Hong Kong and reported that formaldehyde concentration 358
was quite high compared to theoretical value expected in summer, which suggests 359
significant effect of photochemical reactions in formaldehyde production in ambient. 360
2.5.2 Benzene, Toluene, Ethyl-Benzene and Xylene (BTEX) 361
Petroleum derivatives such as gasoline contain these compounds (BTEX), which have 362
harmful effects on humans. Cheung et al. [53] investigated BTEX emission from a diesel 363
engine fuelled with mineral diesel, biodiesel and biodiesel blends with methanol (5%, 364
10%, and 15%) at constant engine speed 1800 rpm for five different loads. They reported 365
that biodiesel had lower BTEX emissions compared to mineral diesel and higher blends 366
of methanol in biodiesel further reduced BTEX emissions. Higher oxygen content in the 367
fuel leads to oxidation of BTEX. They observed that higher engine load results in lower 368
BTEX emission in the engine exhaust. Di et al. and Takada et al. [54, 55] also reported 369
lower BTEX emissions at higher engine loads. Ballesteros et al. [56] used biodiesel and 370
reported relatively lower aromatic emissions. Correa and Arbilla [57] found a strong 371
correlation between carbonyl emissions and biodiesel content (r2 > 0.96). They reported 372
that esters in biodiesel may be a main source of these carbonyl emissions. On the other 373
hand, Liu et al. and Cheung et al. [34, 53] indicated that carbonyl emissions increase 374
with increasing biodiesel content at lower engine load, however it decreases at higher 375
engine loads. Xue et al. [58] summarized that biodiesel reduces the emission of aromatic 376
and poly-aromatic compounds. They also suggested that carbonyl emissions increase in 377
general with biodiesel content because biodiesel provides extra oxygen in the fuel 378
molecules. 379
2.5.3 Polycyclic Aromatic Hydrocarbons (PAHs) 380
17
PAHs are well known carcinogens and are produced as a result of incomplete 381
combustion of fuel in diesel engines. Ravindra et al. [43] prepared a database to identify 382
and characterize the PAHs emissions in their study. They also discussed factors 383
affecting PAHs emissions. Most of the probable human carcinogenic PAHs are found to 384
be adsorbed on the particulate matter surface. There are no strict regulations for PAH 385
emissions but these pollutants should get high priority due to their huge negative 386
impact on human health. Figure 6 shows the priority listed PAHs. Some of compounds 387
shown in Figure 6 are considered as 'probable human carcinogen' (B2), while some are 388
not listed as 'human carcinogens' (D) [43]. The toxicity of these PAH compound is highly 389
dependent on their molecular structure. Two isomers of PAHs with different structure 390
show quite different toxicity. Therefore EPA has divided these PAH compounds into 391
different categories. 392
393
Figure 6: Priority list PAHs [43] 394
* (Not included in priority list); D (not listed as to human carcinogens); B2 (probable human carcinogen) 395
18
Lea-Langton et al. [59] collected particulate samples for diesel, biodiesel and cooking oil 396
for comparing and analyzing particulate bound PAH emissions from a heavy duty DI 397
diesel engine. Most of the particulate bound PAH were found to be lower in both biofuels 398
compared to mineral diesel, especially at low load conditions and most of the larger 399
PAHs such as benzo(a)anthracene, chrysene, benzo(b)fluoranthene and 400
benzo(k)fluoranthene were oxidized by DOC. They also reported that flouranthene was 401
absent in mineral diesel but was present in particulates, which was an evidence of 402
pyrolytic formation of flouranthene in engine combustion chamber. Zielinska et al. [1] 403
reviewed physical and chemical transformations of primary diesel emissions. They 404
concluded that transformation of primary diesel emissions in atmosphere is very 405
important in the context of human health. Primary diesel exhaust reacts mainly with 406
OH radicals, ozone, NOx radicals and sunlight. Monocyclic aromatics of primary diesel 407
exhaust reacts with OH radicals and form various aromatic compounds such as phenols, 408
glyoxal, quinones, nitro-PAHs, and aromatic aldehydes etc. Agarwal et al. [6] compared 409
the toxic potential of diesel and biodiesel (B20) fuels for primary and secondary 410
emissions. By measuring particulate size-number distribution, size-surface area 411
distribution, elemental and organic carbon content, particle bound PAHs and toxic 412
equivalent factor, toxicity and potential health hazards of these emissions were 413
assessed. They reported that toxicity of biodiesel exhaust was comparatively lower than 414
mineral diesel exhaust. Lu et al. [60] reported that waste cooking biodiesel resulted in 415
reduction of PAH emissions in comparison to LSD and ULSD. They reported that ULSD 416
resulted in nearly 8.6% lower PAH emissions compared to LSD. Biodiesel significantly 417
reduces the PAH emissions in the particulate as compared to ULSD and LSD and it was 418
reported to be lower by 32.5% and 38.1%, respectively compared to LSD and ULSD. 419
In recent decades, it is reported that PAHs presents in the diesel particulates are one of 420
the main factor, which adversely affect human health. PAHs include various kinds of 421
19
poly-aromatic compounds, which manifest different toxic properties. EPA has listed 16 422
PAHs as carcinogenic, probable carcinogenic and possible carcinogenic and the 423
molecular structure of these is shown in Figure 6 [43]. Researchers [61, 62] have 424
performed speciation of PAHs adsorbed on to the diesel particulates. Each PAH has a 425
different toxic potential for carcinogenic effects therefore speciation of PAHs is 426
important [63]. There are some studies, which report the toxic potentials of individual 427
PAH species. 428
429
Figure 7: Total toxic equivalent potential of PAHs emitted by diesel and biodiesel (B20) 430
fuelled engine [6] 431
Agarwal et al. [6] calculated individual PAH content from the total PAH load by using 432
procedure given by Pan et al. [62] (Figure 7). They also evaluated the toxic equivalent 433
factors (TEFs) of 8 PAHs and 2 nitro-PAHs. They performed this experimental study on 434
diesel and biodiesel (B20) for primary and secondary emissions from a CRDI engine. For 435
secondary emissions, they used a UV light illuminated photo-chemical chamber with a 2 436
hours residence time. They observed that the trend of total toxic equivalent potential 437
was similar to the particle bound PAH emissions. Slightly higher toxic potential for 438
diesel was observed compared to biodiesel. Similarly, primary particulates showed lower 439
toxicity compared to secondary emissions in terms of PAH toxicity. 440
20
441
Figure 8: Toxicity equivalent factors (TEFs) for diesel and biodiesel blends [65] 442
Karavalakis et al. [64] studied the impact of five biodiesels on PAHs, nitro-PAHs and 443
oxy-PAHs emissions. 10% (v/v) Biodiesels were blended with mineral diesel. A Euro-3 444
CRDI engine was tested on New European Driving Cycle (NEDC) and results were 445
compared with Artersias Driving Cycle (ADC). They observed that biodiesel addition to 446
mineral diesel leads to increase in emission of lower molecular weight PAHs. This 447
indicated relatively lower toxicological potential of biodiesel blends. However, higher 448
molecular weight PAHs showed both increasing and decreasing trends. It was observed 449
that nitro-PAHs were higher for biodiesel blends and oxy-PAHs increased with 450
increasing biodiesel blend concentration. Increasing engine speed and load reduced 451
emission of most of PAHs. Karavalakis et al. [61] tested Euro-2 diesel engine with diesel 452
and different biodiesel blends (B5, B10 and B20) for two vehicle driving cycle (ADC and 453
NEDC). They reported 11 PAHs and 5 nitro-PAHs emissions in the exhaust from diesel 454
and biodiesel blends. Lower molecular weight PAHs like phenanthrene, anthracene, 455
pyrene were the dominating PAHs, when biodiesel was blended with diesel. In general, 456
biodiesel blending resulted in lower emission of PAHs and nitro-PAHs. Bakeas et al. [65] 457
investigated PAH emissions from a Euro-4 CRDI engine fitted with DOC under NEDC 458
and ADC driving cycles (Figure 8). They used soyabean biodiesel, a palm-based biodiesel 459
and an oxidised biodiesel obtained from used frying oils, which were blended with ULSD 460
21
(B30, B50 and B80). They observed that all types of biodiesel reduced overall PAHs 461
toxicity except waste frying oil, which offsets the advantage of using waste frying oil as 462
feedstock for biodiesel production (Figure 8). Ravindra et al. [43] reported that larger 463
molecular weight PAHs formed by pyro-synthesis of lower molecular weight PAHs in 464
addition to contributions from lubricating oil. Rhead and Hardy [66] explained that 465
PAHs are complex organic molecules, which include hydrogen and carbon atoms and at 466
least two benzene rings. PAH formation takes place because of the incomplete fuel 467
combustion, and unburned lubricating oil [43, 67]. Riddle et al. [68] explained that PAHs 468
are mutagenic and carcinogenic. PAHs are widely spread compounds in the atmosphere. 469
According to USEPA, 16 PAHs are classified as priority pollutants. Miet et al. [69] 470
explained that nitro-PAHs are formed in the engine as precursor PAHs due to 471
incomplete combustion. Nitro-PAHs can also be formed as a result of radical reactions of 472
OH and NO3 with PAHs. Heeb et al. [70] explained that Nitro-PAHs contribute to 473
mutagenicity and genotoxicity of diesel particulates. Nisbet et al. [63] reported the toxic 474
equivalent factor of different PAHs species. Pan et al. [62] compared the PAHs and 475
nitro-PAHs emissions from diesel, biodiesel (B100,soy methyl ester), and B20. They 476
performed experiment on a Cummins B5.9 engine. The values for PAHs and nitro-PAHs 477
emissions for diesel and biodiesel blends were obtained by using gas chromatography 478
(GC) coupled with mass spectrometry (MS). Bagley et al. [71] reported that particle-479
bound PAHs and 1-nitropyrene reduced by use of biodiesel. 480
2.5.5 Effect of Biodiesel on Unregulated Emissions 481
Karavalakis et al. [61] carried out investigations on regulated and unregulated 482
emissions from a Euro-2 IDI diesel passenger vehicle (Toyota Corolla 2.0 TD CR: 23:1, 483
61 kW @ 4000 rpm 174 Nm @ 2000 rpm, 1998 model) using LSD and soy methyl ester 484
blends and compared the results of experiments performed under ADC and NEDC test 485
cycles. Unregulated emissions of PAHs, Nitro-PAHs and carbonyl compounds were 486
22
measured. For PAH analysis, glass fiber filters were used for particulate phase 487
sampling. Gas chromatograph mass spectrophotometer (GC-MS) was used for PAHs and 488
nitro-PAHs determination. They identified and quantified 13 carbonyl compounds in the 489
exhaust and reported relatively higher concentration of carbonyl compound in ADC 490
compared to NEDC. Formaldehyde was the major compound in both cases, followed by 491
acetaldehyde, butylaldehyde, benzaldehyde, valeraldehyde and p-tolualdehyde. 492
Formaldehyde mainly originated from incomplete combustion of saturated aliphatic 493
hydrocarbons. Lower saturated aromatic hydrocarbons in the biodiesel blends were 494
responsible for lower Formaldehyde emissions for higher blends. Thus, carbonyl 495
emissions were affected by biodiesel blending ratio. 496
Tan et al. [72] performed experiment on a light duty diesel engine using five different 497
fuels having different sulfur content and investigated effect of sulfur on regulated and 498
unregulated emissions. The investigations were conducted for three unregulated 499
emissions namely formaldehyde, acetaldehyde and SO2. They found that formaldehyde 500
emission was not detected by their instruments. Acetaldehyde emission decreased with 501
increasing load and decreased with increasing fuel sulfur content. SO2 emission 502
increased continuously with increasing engine load and decreased with lowering sulfur 503
content of the fuel. Concentration of formaldehyde was so low that it could be measured 504
only at low engine loads. This suggested that low combustion chamber temperature, 505
prevailing at low engine load conditions has higher formaldehyde emissions. 506
Formaldehyde is an intermediate combustion product. Formaldehyde emission 507
decreases with increasing engine load and combustion chamber temperature [72]. 508
Cheung et al. [73] conducted an experiment on a four cylinder DI engine with ULSD and 509
four different ethanol blends (blend-1, blend-2, blend-3 and blend-4 containing 6.1%, 510
12.2%, 18.2% and 24.2% ethanol v/v i.e. oxygen content 2%, 4%, 6% and 8% w/w). 511
Ethanol is an oxygenated compound, and can be blended with diesel. The objective of 512
23
this study was to investigate regulated and unregulated emissions from ULSD-ethanol 513
blends. They found that unburnt ethanol and acetaldehyde emissions in exhaust 514
increased but formaldehyde, ethene, ethyne, 1,3-butadiene and BTX decreased with 515
increasing load. They observed that formaldehyde emission decreased with increasing 516
alcohol content in ULSD, possibly because of increased H/C ratio [74]. However, 517
emissions depend on several factors such as fuel blends composition, fuel's oxygen 518
content, engine technology, test cycles, etc. They also measured BTX emissions. BTX 519
emissions reduced with increasing engine load. This was because at higher combustion 520
chamber temperature, benzene and its derivatives oxidize. At low engine load, higher 521
benzene emissions were observed. Toluene and xylene also showed the same trend as 522
benzene. Combustion chamber temperature and oxygen content of fuel are therefore 523
very important factors for BTX emissions. 524
525
2.6 Effect of After-treatment Devices (DOC and DPF) 526
Biodiesel is an alternate fuel for mineral diesel however it has some properties, which 527
are different from diesel. Some studies [6, 75] showed that particulate characteristics of 528
biodiesel are different than that of mineral diesel. Several researchers performed 529
studies on the effect of biodiesel exhaust on the after-treatment devices. Biodiesel 530
contains some trace metals, which result in catalytic activity in the exhaust. 531
Composition of biodiesel particulates is quite different compared to ones from diesel. 532
Agarwal et al. [6] suggested that biodiesel contain complex compounds, which are 533
relatively more difficult to oxidize during combustion process. Shi et al. [76] investigated 534
effect of diesel oxidation catalyst (DOC) on exhaust from engine fuelled with mineral 535
diesel and B20 and reported that DOC reduces CO and HC emissions by 90-95% and 36-536
70% respectively (Table 2). Total carbon emission decreases by ~22-32% with use of 537
DOC. OC reduction was ~35-97% and EC reduction was ~3-65%. OC/ EC ratio of PM2.5 538
24
from mineral diesel slightly increased at lower loads after DOC, however this parameter 539
showed an opposite trend for B20. 540
Table 2: Effect of DOC on fuel based emission factors (EF) of TC, EC and OC in PM2.5, 541
diesel fuel [76] 542
Speed
(rpm)/load
%
EC/(mg/g) OC/(mg/g) TC/(mg/g)
Diesel
Diesel +
DOC
Diesel
Diesel +
DOC
Diesel
Diesel +
DOC
2125/25 0.016 0.007 0.15 0.108 0.165 0.115
2125/50 0.05 0.037 0.148 0.118 0.198 0.155
2125/75 0.084 0.082 0.144 0.073 0.229 0.155
2690/25 0.032 0.029 0.306 0.228 0.337 0.258
2690/50 0.135 0.12 0.23 0.162 0.365 0.282
2690/75 0.206 0.134 0.221 0.182 0.427 0.317
543
Zhu et al. [77] evaluated particulate and unregulated emissions with and without DOC 544
in a Euro-5 diesel engine fuelled with biodiesel and biodiesel-ethanol blends. DOC was 545
found to be quite effective in reducing particle mass emissions, particle numbers as well 546
as unregulated emissions. However, DOC was not equally effective in emission 547
reduction for hydrocarbon compounds. They concluded that combination of biodiesel-548
ethanol with DOC is effective in reducing particulate emission and unregulated 549
emissions. Bagley et al. [71] tested an IDI diesel engine for emission reduction with 550
oxidation catalytic converter fuelled with diesel and soy biodiesel. They reported that 551
vapor phase PAH emissions reduced up to 90% by the use of oxidation catalytic 552
converter for both fuels. Particle and vapor phase mutagenic compounds reduced up to 553
50% by use of oxidation catalytic converter. Williams et al. [78] investigated adverse 554
effects of trace metals present in biodiesel on the after-treatment devices, which 555
included several diesel particulate filter (DPF) substrates, DOC and selective catalytic 556
reduction (SCR) catalysts. They observed no thermal-mechanical degradation of 557
25
cordierite, aluminum titanate or silicon carbide DPFs with 150,000 miles equivalent 558
exposure to biodiesel ash and thermal aging. Performance of DOC was adversely 559
affected at 150,000 miles equivalent aging, and resulted in increased level of HC and CO 560
emissions after DOC. Vertin et al. [79] conducted tests to observe the impact of soy 561
biodiesel blend (B20) and two kinds of ULSD on a cordierite DPF. They observed that 562
B20 particulates were more reactive to DPF compared to diesel particulates. DPF 563
showed 80% higher efficiency with B20 and pressure drop was also not very high. Austin 564
et al. [80] performed active regeneration experiment on a B20 fuelled diesel engine 565
equipped with DOC and DPF. B20 particulates showed five times greater reaction ratio 566
in active regeneration compared to ULSD. The researchers concluded that due to the 567
higher reaction rate of B20 particulates, lower amount of fuel is required for 568
regeneration. Asti et al. [81] studied the effect of biodiesel on particulates during active 569
and passive DPF regeneration and found that particulate emissions decreased with 570
increasing biodiesel content in the fuel. They observed temperature gradient in DPF 571
during active regeneration with biodiesel however, no appreciable temperature gradient 572
was observed during passive regeneration with biodiesel. Ash content of DPF was also 573
higher with biodiesel. Parihar et al. [82] focused on physical characterization of diesel 574
and biodiesel particulates from a CRDI engine using MOUDI (10 stages) and observed 575
that submicron particle mass concentration was higher for higher loads. PM2.5 576
contributes approximately 75-90% of the total particulate mass. Di Iorio et al. [83] 577
analyzed the impact of biodiesel on particulate emissions and DPF regeneration and 578
observed that biodiesel leads to lower particulate emissions, which require less frequent 579
regeneration. On the other hand, regeneration of DPF with biodiesel require higher 580
quantity of fuel to be injected due to biodiesel's lower calorific value. They suggested 581
that using a 'flexible management system' is required for optimum regeneration, which 582
can take care of differences in fuel properties. Pidgeon et al. [84] investigated the effect 583
26
of biodiesel blend on catalyzed particulate filter (CPF) performance and observed that 584
the soot reactivity of the CPF increases with increasing blend ratio of biodiesel. They 585
also reported that the PM oxidation increases with increasing biodiesel blend ratio at 586
constant CPF temperature. 587
3 Physical Characterization of Particulates 588
Biodiesel is a good alternative fuel for mineral diesel. As a partial or complete 589
replacement of mineral diesel, biodiesel needs to be critically evaluated for its physical, 590
chemical and thermal properties as well as its combustion products/ emissions. Physical 591
characterization of emissions includes measurement of the emitted particulate’s mass 592
and size-number distribution. Section 3.1 and 3.2 provide insights into particulate mass 593
and number emissions from diesel engine fueled with biodiesel and its blends with 594
mineral diesel. 595
3.1 Particulate Mass Emissions 596
Diesel engines are one of the biggest source of carbonaceous particulate emissions in the 597
environment. These primary particulate emissions cause several adverse effects in the 598
environment as well as on human health. These particles are formed due to incomplete 599
combustion of fuel in fuel-rich regions of the diesel engine. Formation of particulate 600
occurs mainly due to the insufficient oxygen availability in fuel-rich regions during 601
heterogeneous combustion. It is therefore essential to optimize the fuel injection 602
parameters in order to reduce particulate formation. Biodiesel is an oxygenated fuel and 603
some of its properties are different than mineral diesel, causing lower particulate 604
formation in an engine. Particulate mass emission is very important from regulated 605
emission control point of view and has been explained in two different aspects. First, the 606
effect of fuel injection strategy, and second, the effect of biodiesel blend composition of 607
particulate emission is summarized here. Most studies on biodiesel particulate show 608
lower particulate mass emissions compared to mineral diesel. Biodiesel fuel's molecular 609
27
oxygen helps in improving combustion in the engine combustion chamber thus lower 610
particulate emissions are reported [24, 85] however some studies have also reported 611
identical or increased PM mass emissions with biodiesel usage [86, 87]. An EPA report 612
encompassing 39 scientific studies on heavy duty engines concluded that use of B100 613
and B20 leads to ~50% and 10% PM mass reduction respectively vis-a-vis mineral diesel 614
[85]. A scientific study suggested that reduction in smoke from Neem oil methyl ester 615
(NOME)-diesel and castor oil methyl ester (COME)-diesel blends was mainly due to 616
additional oxygen present in biodiesel, which reduced PM formation [88]. Biodiesel 617
blended with LSD emitted lower PM mass emission as compared to LSD, however no 618
concrete trend was reported for biodiesel blended with ULSD as compared to ULSD [89]. 619
Another scientific study reported relatively lower PM mass emissions from 100% 620
biodiesel and biodiesel blends in comparison to mineral diesel in a DI engine equipped 621
with electronically controlled fuel pump [90]. They also suggested that fuel oxygen in 622
biodiesel/ blends was the main reason for reduced PM mass emission [90]. Another 623
study reported that Soy biodiesel usage resulted in 77% lower PM mass emission in 624
comparison to mineral diesel [91]. Correlations derived from several test fuels suggested 625
that PM mass emission decreased with increasing fuel oxygen content as well as 626
adiabatic flame temperature [91]. Another study on RME reported that particulate 627
emissions significantly depend upon engine operating conditions. At low engine loads, 628
relatively higher PM mass emissions were observed with biodiesel compared to mineral 629
diesel. Interestingly, at higher engine loads, a reduction in PM mass emission was 630
observed with biodiesel [92]. Table 3 summarizes several scientific studies showing the 631
effect of different biodiesels on PM mass emission vis-a-vis baseline mineral diesel. 632
Table 3: Summary of effect of biodiesel on PM mass emissions 633
Test fuel Change in
PM (% w/w)
Reference
28
B35 (Soybean oil biodiesel) -25 Wang et al., 2000 [93]
B100 (Soybean oil biodiesel) -55* Canaki, 2007[94]
B100 (Soybean oil biodiesel) -60* Canaki and Van Gerpen 2003 [95]
B100 (Soybean oil biodiesel) -77 Sharp et al., 2005 [91]
B100 (Soybean oil biodiesel) -52* Qi et al., 2009 [96]
B10 (Rapeseed oil biodiesel) -24 Kousoulidou et al., 2010 [97]
B20 (Rapeseed oil biodiesel) ~0 Turrio-Baldassarri et al., 2004 [86]
B100 (Rapeseed oil methyl ester) -50 Krahl et al., 2007 [98]
B100 (mixture of Rapeseed and Recycled
Cooking oil methyl ester)
-80 to -65* Grimaldi et al., 2002 [99]
B100 (Karanja oil biodiesel) -50* Raheman et al., 2004 [100]
B10 (Palm oil biodiesel) -17 Kousoulidou et al., 2010 [97]
Ethanol: Methyl soyate: Diesel (5:20:75) blend Shi et al., 2006 [101]
B100 (Yellow grease biodiesel) -64* Canaki et al., 2003 [95]
B50 -12* Xiaoming et al., 2005 [102]
B20 -13* Xiaoming et al., 2005 [102]
*: Change in smoke opacity 634
Another study reported that both, B100 and B20 reduced PM emissions, and PM 635
reduction is generally independent of the feedstock used for biodiesel production. Even 636
lower blends of biodiesel were effective in reducing PM mass emissions [103]. Lower 637
particulate emissions were also seen for biodiesel fuelled engine fitted with an oxidation 638
catalyst [104]. Reduction in smoke was also reported with increasing blend 639
concentration of Linseed oil biodiesel in another study [105] and higher reduction in 640
smoke level was reported at higher engine loads [106]. Lower PM mass emissions were 641
also reported for 100% Palm oil biodiesel vis-a-vis mineral diesel [107]. 642
29
643
Figure 9: Effect of biodiesel blending on PM emissions [108] 644
A review article on criteria pollutants from biodiesel engines concluded that increased 645
biodiesel concentration in test fuel in a heavy-duty diesel engine application reduces 646
HC, CO, and PM emissions substantially, along with slightly increased NOx emissions 647
[108]. Figure 9 shows these findings for heavy-duty and medium-duty engines. Results 648
from light-duty engines were more fluctuating, and showed some increase in CO, PM 649
and NOx emissions with increasing biodiesel concentration in the test fuel. Another 650
scientific study reported that PM mass emissions mostly decreased with increasing 651
biodiesel content in the test fuel at all test modes, reaching peak reduction of ~49-62% 652
with 100% biodiesel vis-a-vis baseline diesel [30]. Saanum et al. [109] reported that PM 653
emissions were slightly higher for biodiesel than diesel (marine gas oil: MGO) at low 654
engine loads, but the trend reverses at higher engine loads and biodiesel emits lower PM 655
mass emissions compared to mineral diesel. The filter smoke number (FSN) was 656
significantly lower for biodiesel at all loads tested. 657
3.1.1 Effect of Injection Strategies 658
It is desirable to have superior combustion in diesel engines to have lower particulate 659
emissions. This can be achieved by optimizing injection parameters such as fuel 660
injection pressure, injection timing etc. A diesel engine with mechanical pump system 661
does not provide flexibility in injection therefore modern diesel engines are equipped 662
30
with CRDI system, which provides excellent flexibility for fuel injection such as high 663
pressure (up to 2000 bar) injection, split and multiple injections, injection duration 664
control and injection timing control. PM mass emissions can be drastically reduced by 665
optimizing fuel injection parameters [110]. Many studies have reported significant 666
reduction in PM mass emissions upon using modern high pressure flexible fuel injection 667
systems. This section provides insights into the effect of different injection strategies on 668
particulate emission from CI engines fuelled with mineral diesel and biodiesel. 669
Suryawanshi et al. [111] reported that for various blends of Karanja oil methyl ester, 670
smoke opacity was lower compared to mineral diesel operation. Smoke was further 671
reduced by retarded injection timings. Corgard et al. [112] observed that utilization of 672
biodiesel blends resulted in lower smoke emission from a HSDI diesel engine. They 673
retarded the injection timings for reducing increased NOx levels due to use of biodiesel. 674
Nearly two-third reduction in smoke produced by mineral diesel was achieved by 30% 675
biodiesel blend with retarded injection timings [112]. 676
Combustion chamber visualization and computational studies on soot formation 677
confirmed that it gets accumulates in the spray tip region [113-116]. In single injection 678
pulses, high momentum of injected spray droplets for longer duration continuously 679
results in supply of fuel droplets to relatively low temperature region of the combustion 680
chamber in comparison to split injection, which results in higher soot formation [113]. In 681
a split-injection mode, the fuel injected in the second pulse, wherein fuel droplets enter 682
into a relatively fuel-lean and high-temperature region formed due to the combustion of 683
the fuel injected during the first injection pulse. In split injection, soot formation is 684
considerably reduced because the fuel injected is rapidly consumed in combustion 685
process before it starts accumulating in a fuel-rich soot-producing zone [113]. For 686
achieving effective reduction in soot formation, split injection, and optimization of time 687
interval between the two injection pulses is very critical. Separation between two 688
31
injection pulses should be long enough so that the soot formation zone of the first 689
injection pulse is not replenished with the incoming fuel from the second injection pulse. 690
Separation between the two injection pulses should be short enough to ensure that high 691
temperature and pressure conditions are available to the incoming fuel droplet for its 692
rapid combustion, resulting in lower soot formation [113]. 693
Yamane et al. [117] observed that PM emissions from biodiesel showed a high level of 694
SOF compared to mineral diesel (gas oil) at lower engine loads. They investigated spray 695
jet penetration of biodiesel and mineral diesel corresponding to injection conditions 696
prevailing at lower engine loads. They observed shorter spray penetration for biodiesel 697
due to its higher kinematic viscosity and density, which resulted in inferior air-fuel 698
mixing [117]. Inferior air-fuel mixing was reported to be the main reason for higher PM 699
mass emissions. Ye et al. [118] concluded that impact of injection strategy and biodiesel 700
fueling on PM mass emissions strongly depends on the engine load in a CRDI engine. 701
They also suggested that use of biodiesel and increased fuel injection pressure 702
effectively reduced PM emissions at low load conditions, however biodiesel didn't show 703
significant effect at moderate and higher engine loads on PM mass emissions. Yehliu et 704
al. [119] reported increased brake specific PM emissions with B100 vis-a-vis diesel at 705
some operating conditions but reduction at other conditions for both single and split 706
injection mode in a CRDI engine. At some operating conditions, increased PM mass was 707
attributed to increase in SOF fraction of particulates due to relatively lower volatility of 708
biodiesel in comparison to mineral diesel. Particulates from B100 mainly consisted of 709
condensed organics, because the particle number concentration dropped dramatically in 710
comparison to particle concentration for mineral diesel, when a thermo-denuder was set 711
to 400°C. instead of 30°C, in order to remove organics [119]. Kegl et al. [120] reported 712
50% reduction in smoke along with other regulated pollutants for a B100 fuelled bus 713
32
engine at a retarded fuel injection timing (19° bTCD) in comparison to mineral diesel 714
engine at a normal fuel injection timing (23° bTDC) in an ESC test-cycle. 715
3.1.2 Effect of Fuel Composition 716
After 1970's energy crisis, many researchers started exploring a suitable alternative fuel 717
for mineral diesel. Biodiesel was considered as one of the potential alternative fuels for 718
diesel. One major advantages of biodiesel is that it has inherent oxygen content in the 719
fuel molecule itself, which enhances the probability of complete combustion. On the 720
other hand, biodiesel's evaporative property are not as good as mineral diesel, therefore 721
it has low evaporation rate at relatively lower engine loads, because of lower in-cylinder 722
temperatures. Shi et al. [101] reported significant reduction in PM emissions from blend 723
of ethanol:methylsoyate:diesel (5:20:75) compared to that from mineral diesel [101]. Zhu 724
et al. [18] observed that PM emissions from biodiesel fuelled engine operation were 725
lower than mineral diesel fuelled engine. PM emissions further reduced with an 726
increasing ethanol/ methanol concentration in biodiesel-alcohol blend at medium and 727
high engine loads. PM reduction by addition of alcohols to biodiesel was due to higher 728
oxygen content of alcohol-biodiesel blend in comparison to biodiesel, which improved the 729
combustion process and reduced PM emissions. Also, alcohol in the blended fuel reduced 730
the cetane number hence increased ignition delay period therefore higher fuel quantity 731
burned in premixed combustion phase, resulting in lower PM emissions [18]. However, 732
15% alcohol blends lead to higher PM emissions than biodiesel (B100) and mineral 733
diesel at low loads [18]. Yoon et al. [121] observed significantly lower filter smoke 734
number (FSN) for biodiesel-ethanol blend (90:10) in comparison to mineral diesel in 735
double injection strategy. Lower soot emissions were primarily due to higher oxygen 736
content of the blended fuel and absence of soot precursors (sulfur and aromatics 737
contents) [121]. Particle number concentration of larger particles, which contribute 738
dominatingly to PM mass for biodiesel-ethanol blend, were significantly lower than 739
33
mineral diesel [121]. Lu et al. [122] reported that in his experiments of port injection of 740
ethanol in a biodiesel fuelled engine, CO and HC emissions increased compared to 741
biodiesel (B100) operated engine, and 35–85% reduction in NOx and smoke was 742
observed. Kohoutek et al. [123] used ULSD and got 30% lower PM mass and number 743
emissions in comparison to 410 ppm sulfur containing diesel in a modern DI diesel 744
engine. At high engine load, specific emission of PM1.8 from biodiesel decreased by 68.4% 745
and 50.3%, compared with LSD and ULSD respectively [60]. PM mass emission reduced 746
by 20.6% upon using biodiesel compared to LSD and was slightly on the higher side as 747
compared to ULSD at lower engine loads. 748
Dwivedi et al. [124] reported that total PM mass reduced by ~20% with B20 in 749
comparison to mineral diesel in a CIDI engine. Due to better lubricity of biodiesel, trace 750
metal content in the particulate also reduced for B20. Benzene soluble organic fraction 751
(BSOF) was found to be higher for B20. Kim et al. [125] also found 20% lower PM mass 752
for B20 fuelled engine in comparison to mineral diesel. 15% biodiesel and 5% ethanol 753
blended with mineral diesel reduced PM mass further. Important observation was that 754
total number of particles reduced for biodiesel but number of nuclei mode particles was 755
higher for biodiesel compared to mineral diesel. Rakopoulos et al. [126] reported that 756
peak value of smoke opacity reduced by 40% and 73% respectively for the biodiesel and 757
n-butanol blends during transient tests in a CI engine. Relative fuel-bound oxygen plays 758
dominant role here. In a review, Graboski et al. [127] concluded that PM mass emission 759
reduction was proportional to the fuel oxygen content as long as cetane number was 760
higher than 45 or density was lower than 0.89 kg/ l. 761
34
762
Figure 10: Effect of carbon chain length on total PM mass emissions (450 bar injection 763
pressure, 4 bar IMEP, 7.1°bTDC SOI) [23] 764
Schönborn et al. [23] studied the effect of carbon chain length and degree of 765
unsaturation on PM mass emissions. Total particulate mass emitted by mineral diesel 766
was higher than biodiesel (Figure 10). Lower particulate mass emission from biodiesel 767
are attributed to higher fuel oxygen content, which helps in oxidation of soot particles 768
and soot precursors. The behenic acid methyl ester (22 carbon atoms fatty acid chain) 769
showed a distinctively higher emission of PM mass than other lower fatty acid chain 770
length molecules. It is possibly due to spray formation and fuel-air mixing being affected 771
by fuel's high viscosity and low volatility. 772
3.2 Particulate Size-Number Distribution 773
Most emission regulations globally prescribe PM mass measurement and control. Size 774
affects the behavior of particulates in the engine as well as in the environment [15]. 775
Adverse health effects due to particulates are more severe for smaller nuclei mode 776
particulates. This fact has been recognized and new emission legislations, beyond Euro-777
5 also prescribe limit on total particle number concentration along with particulate 778
mass. Table 4 shows typical contribution of different size particles emitted by diesel 779
engines to PM mass and total numbers. Almost 90% particulate emitted from diesel 780
engines originates as nuclei mode particles. Parihar et al. [82] suggested that 781
contribution made by PM2.5 particles to the total PM mass varies from 75-95%, 782
35
depending on engine load, for mineral diesel as well as B20. Particles larger than 10 µm 783
contributed up to 10-15% to cumulative mass whereas particles in size range 2.5-10 µm 784
contribute up to 20-30% of the total PM mass. Li et al. [22] reported that densities of 785
particles smaller than 50 nm varied from 1.1 g/cm3 to 1.6 g/cm3. For particles having 786
mobility diameter closer to 1 µm, particle densities varied from 0.2 to 0.6 g/cm3. Hence, 787
methods employed to control PM mass do not necessarily result in particulate number 788
reduction. In this scenario, it is important to characterize the effect of biodiesel on 789
particulate number emissions. 790
Table 4: Size based classification of engine exhaust particulates [1, 15] 791
Size (nm) % Number % Mass
Nuclei mode 5-50 ~90 1-20
Accumulation mode 50-700 1-10 60-94
Coarse mode 700-10000 0-2 5-20
792
Kawano et al. [128] reported that particle size distribution of both diesel and RME was 793
mono-modal, and this distribution mostly covered accumulation mode particles for all 794
engine loads. The size distribution of accumulation mode particles of RME shifted 795
towards smaller sizes compared to diesel, and peak position of particle size distribution 796
was almost constant for varying engine loads. An increase in engine load increased the 797
peak number concentration in case of diesel and reduced the peak concentration for 798
RME [128] and these findings were in line with the other studies which suggested that 799
biodiesel particulates are mostly comprised of SOF, which gets destroyed in engine in 800
high temperature conditions prevailing at higher engines loads. Raahede [129] reported 801
a decreasing trend for particle number concentration, when moving from reference 802
diesel to biodiesel (B20) and this trend was attributed to higher fuel bound oxygen. 803
Puzun et al. [130] studied the particle size-number distribution of rapeseed biodiesel 804
blends and mineral diesel in a high-pressure CRDI engine. They reported that 805
36
particulate sizes emitted from this engine were mostly smaller than 300 nm [130]. For 806
diesel, particle number concentrations showed single peak distributions dominating 807
accumulation mode particles [130]. For biodiesel blends at lower and intermediate loads, 808
double peak in particle size-number distribution was seen with increasing concentration 809
of biodiesel in the fuel and nuclei mode particle numbers increased significantly; 810
particles with sizes more than 50 nm (accumulation mode) decreased and peak of 811
number concentration shifted towards smaller particles [130]. Tan et al. [27] reported 812
that peak value of nucleation mode particles below 30 nm increased with increasing 813
biodiesel concentration in fuel blend. Nucleation mode particle size peak becomes larger 814
with increasing biodiesel blend ratio, and accumulation mode particle size peak value 815
becomes smaller. Three mechanisms were thought to lead to greater nucleation mode 816
particle formation: (i) high super-saturation encourages formation of new particles by 817
nucleation at less solid soot surface, (ii) increased viscosity and lower volatility of 818
biodiesel causes higher SOF, and (iii) oxygen content of biodiesel causes carbonaceous 819
particle to transform from fine particles to ultra-fine particles or nano-particles. 820
Agarwal et al. [5] reported that particulate number emissions for B100 were higher than 821
mineral diesel however, these were comparable for B20 and diesel at lower loads. Jung 822
et al. [13] investigated the effect of biodiesel on oxidation of particulates using soy 823
methyl ester (SME) and diesel (#2) at 1400 rpm engine speed and 75% load. 824
Accumulation mode particle number concentration and particle volume distribution 825
were lowered by 38% and 82%, respectively for SME. They also reported lower particle 826
numbers than mineral diesel in large particle size range above 50 nm, but very similar 827
numbers was observed in nuclei region below 50 nm. This indicated towards lower PM 828
mass for B100 because of lower soot pyrolysis due to presence of fuel oxygen. High 829
numbers of engine out nuclei mode particles with B100 are considered to be due to 830
presence of large number of condensed droplets of high boiling point hydrocarbons, 831
37
which are also responsible for high VOF. They reported that rate of oxidation of SME 832
particulates was 6 times faster than diesel particulates [13], which verified the above 833
hypothesis. 834
3.2.1 Effect of Injection Strategy 835
Most modern engines are now equipped with advanced fuel injection systems controlled 836
by electronic control unit (ECU). These injection systems are designed in order to reduce 837
total PM mass emissions. However there is strong need to investigate the particle 838
number emissions also for varying injection parameters because it is proved beyond a 839
reasonable doubt that finer diesel particulates have higher toxicity. Several studies have 840
been carried out to study the particle number emissions from different types of engines, 841
fuels and engine operating conditions and some of them are discussed in this section. 842
Desantes et al. [131] investigated the effect of fuel injection pressure, SOI timings and 843
EGR on engine exhaust particle size-number distribution from a heavy-duty diesel 844
engine [131]. Increasing fuel injection pressure reduced number of accumulation mode 845
particle and favored nuclei mode particle formation. Increasing fuel injection pressure 846
improved air-fuel mixing, which reduced the spread of fuel-rich zones responsible for 847
formation of carbonaceous soot particles. Reduction in the concentration of carbonaceous 848
particles resulted in reduction in number of accumulation mode particles. Application of 849
EGR suppressed the nucleation mode particles and increased number of accumulation 850
mode particles. Advanced injection timings slightly reduced number of accumulation 851
mode particles without shifting the position peak concentration [131]. 852
38
853
Figure 11: Effect of fuel injection pressure on number of nuclei mode particles (2-67nm) 854
for biodiesel blends [132] 855
Sinha et al. [132] reported increase in total number concentration of nuclei mode 856
particles with increasing fuel injection pressure for diesel as well as biodiesel blends 857
(Figure 11). As biodiesel percentage increases in the blend, it increases fuel's oxygen 858
content, leading for formation of fewer number of carbonaceous accumulation mode 859
particles. Since lower number of carbonaceous particles are available for adsorption of 860
SOF, the partial pressure of these organic fractions increases, leading to higher 861
numbers of nuclei mode particles. Also, biodiesel produces higher soluble organic 862
fractions, which add to the partial pressure of gaseous hydrocarbons forming SOFs, 863
further enhancing nucleation process. Sinha et al. [132] also reported reduced 864
accumulation mode particle numbers (50-1000 nm) at all fuel injection pressures except 865
600 bar from Soybean biodiesel (B100) vis-à-vis ULSD. 866
3.2.2 Effect of Fuel Composition 867
Several studies showed that biodiesel and mineral diesel have different particle size-868
number distributions [18,23,133]. It is important from regulatory norms stand point to 869
evaluate the particle number emission for biodiesel. Pham et al. [133] reported that 870
saturated short-chain length FAMEs reduce NOx and particulate number concentration, 871
39
but led to higher BSFC as well as higher reactive oxygen species (ROS) emissions. 872
Unsaturated FAMEs emit lower particulate and ROS, but higher NOx. 873
Higher particulate mass (Figure 10) for diesel originated from larger number of 874
accumulation mode particles (Figure 12). 875
876
Figure 12: Effect of carbon chain length on particulate size distribution (450 bar 877
injection pressure, 4 bar IMEP, 7.1°bTDC SOI) [23] 878
Progressively higher number of nucleation mode particles was seen for fatty acid esters 879
with longer fatty acid chains (Figure 12). It is possible that the nuclei mode particles 880
consist of high boiling point constituents of fuel which remains unburned and condenses 881
in the exhaust gas [23]. Schönborn et al. also reported that increase in alcohol chain 882
length from 1 to 2 carbon atoms reduced NOx emissions, but increased total PM mass 883
emission, even under constant ignition delay and similar heat release conditions [23]. 884
Zhu et al. [18] compared the particulate size-number distribution for biodiesel and 885
biodiesel-alcohol blends with mineral diesel [18]. At all engine loads, total particulate 886
number concentration from biodiesel was higher than that from mineral diesel. Addition 887
of ethanol/ methanol in biodiesel reduced the total number concentration of particles 888
dramatically below the level of mineral diesel fuelled engine operation [18]. They also 889
suggested like many other researchers that blending alcohols with biodiesel decreases 890
carbon content and increases oxygen content of the fuel, leading to reduction in number 891
40
of nuclei mode particles and total particulate number concentration [18,134]. Lapuerta 892
et al. [135] reported that higher unsaturation level of biodiesel led to retarded start of 893
combustion, higher NOx emissions, higher heat release rate, lower smoke opacity, lower 894
particulate mass emissions and lower particulate size distribution. Song et al. [29] 895
reported that number of nucleation mode particles decreased or remained constant, and 896
number of accumulation mode particles above 30 nm increased for oxidized biodiesel 897
blends compared to non-oxidized biodiesel blend. The particulate mass-size distribution 898
for oxidized biodiesel blend reduced by 5 - 23.4% compared to non-oxidized biodiesel 899
blend at all engine loads. Total particle number concentration for oxidized biodiesel 900
blend compared with non-oxidized biodiesel blend was found to be strongly dependent on 901
test conditions. Nuszkowski et al. [136] reported that use of cetane improving additives 902
resulted in lower number of particulates in entire particle size range measured in the 903
study. The reduced particle number concentrations were in the diameter range of 6-56 904
nm and 100-205 nm, respectively. Addition of biodiesel reduced the particle number 905
concentration in the diameter range of 6-56 nm and 100-487 nm and was not affected in 906
other size ranges during transient engine operation [136]. Sinha et al. [132] investigated 907
the effect of using biodiesel on particulate emissions from a HSDI engine. They observed 908
that particle number density increased and particle size-mass distribution decreased 909
with increasing blending ratio of biodiesel. Zhang et al. [25] studied particle size-number 910
distribution of diesel (1135 ppm sulfur) and biodiesel (64 ppm sulfur) blends. Number 911
concentration of nuclei mode particles were three orders of magnitude higher for B60 912
and other lower biodiesel blends including mineral diesel in comparison to B100. They 913
gave the hypothesis that in case of high sulfur containing fuel, hydrated H2SO4 nuclei 914
acts as precursor for nuclei mode particulate formation (when the blend concentration 915
was lower than B60). For B100, nuclei mode particulate concentration was low due to its 916
extremely low sulfur content (64ppm). 917
41
4. Summary 918
It is essential to evaluate the effect of biodiesel on the particulate emissions from diesel 919
engines before it can be implemented on a large scale worldwide. Diesel particulate 920
consists of elemental carbon, organic carbon, trace metals, and organic compounds. Most 921
of the diesel particles are nano-particles. Their composition varies and depends strongly 922
upon engine operating conditions. A large number of researchers characterized biodiesel 923
particles for their physical and chemical characteristics and these studies are 924
summarized below: 925
1. Biodiesel has an advantage and emits lower particulate mass emissions compared to 926
mineral diesel for most engine technologies and all engine load-speed conditions. Most 927
studies suggested that there is a large reduction in total particulate mass emissions by 928
using biodiesel or biodiesel blends with mineral diesel. 20% blend of biodiesel with diesel 929
showed good result in terms of lower particulate mass emission. B100 further reduced 930
particulate emissions but not in the same proportion as that of B20. 931
2. Total particle number emissions also reduced with use of biodiesel but particle 932
number emissions near the nano-size range were higher for biodiesel. 933
3. Biodiesel is an oxygenated fuel, and fuel oxygen helps in improving combustion inside 934
the combustion chamber, resulting in lower PM mass emissions. Presence of fuel oxygen 935
reduces pyrolysis reactions in the combustion chamber. Pyrolysis of fuel and lubricating 936
oil in oxygen deficient regions of the combustion chamber is the main reason for 937
particulate formation in the engine. 938
4. Biodiesel shows lower organic carbon (OC) content of the particulate emitted by an 939
order of magnitude compared to mineral diesel. No significant reductions were observed 940
for elemental carbon (EC) content of the particulate. For biodiesel, most studies reported 941
higher EC/ OC ratio along with lower total particulate mass emissions, which indicated 942
to its lower environmental toxicity compared to mineral diesel. 943
42
5. For biodiesel, generally PAH emissions were found to be relatively lower but some of 944
the specific PAHs adsorbed by particulate were slightly higher compared to mineral 945
diesel. This indicates towards presence of structurally strong PAHs in biodiesel. Possibly 946
these PAHs are difficult to oxidize in the engine combustion chamber, even under higher 947
temperature and pressure conditions. 948
6. Biodiesel helps particulate oxidation in DOC/ DPF. Biodiesel inherently contains 949
some trace metals, which possibly act as catalysts in the after-treatment devices and 950
lower particulate emissions. Lower particulate emissions from biodiesel also result in a 951
longer useful life of after-treatment devices. 952
Overall, Biodiesel emits relatively lower particulate mass emissions which have lesser 953
environmental and health related toxicity, and impacts the exhaust gas after-treatment 954
devices life positively, in addition to protecting the environmental, being a green fuel. 955
References 956
[1] B. Zielinska. Atmospheric transformation of diesel emissions. Experimental and 957
Toxicologic Pathology. 57 (2005) 31-42. 958
[2] O. Schroeder, J. Krahl, J. Bünger. Environmental and health effects caused by the 959
use of biodiesel. SAE Technical Paper 1999-01-3561 (1999). 960
[3] J. Krahl, A. Munack, O. Schröder, H. Stein, J. BüNGER. Influence of biodiesel and 961
different designed diesel fuels on the exhaust gas emissions and health effects. SAE 962
Technical Papers 2003-01-3199 (2003). 963
[4] J. Krahl, A. Munack, Y. Ruschel, O. Schröder, J. Bünger. Exhaust gas emissions and 964
mutagenic effects of diesel fuel, biodiesel and biodiesel blends. SAE Technical Papers 965
2008-01-2508 (2008). 966
[5] A.K. Agarwal, T. Gupta, A. Kothari. Particulate emissions from biodiesel vs diesel 967
fuelled compression ignition engine. Renewable and Sustainable Energy Reviews. 15 968
(2011) 3278-300. 969
43
[6] A.K. Agarwal, T. Gupta, N. Dixit, P.C. Shukla. Assessment of toxic potential of 970
primary and secondary particulates/aerosols from biodiesel vis-a-vis mineral diesel 971
fuelled engine. Inhalation toxicology. 25 (2013) 325-32. 972
[7] A.K. Agarwal, T. Gupta, A. Kothari. Toxic potential evaluation of particulate matter 973
emitted from a constant speed compression ignition engine: A comparison between 974
straight vegetable oil and mineral diesel. Aerosol Science and Technology. 44 (2010) 724-975
33. 976
[8] P.F. Flynn, R.P. Durrett, G.L. Hunter, A.O. zur Loye, O. Akinyemi, J.E. Dec, et al. 977
Diesel combustion: an integrated view combining laser diagnostics, chemical kinetics, 978
and empirical validation. SAE Technical Paper 1999-01-0509 (1999). 979
[9] A. Dhar, A.K. Agarwal. Effect of Multiple Injections on Particulate Size-Number 980
Distributions in a Common Rail Direct Injection Engine Fueled with Karanja Biodiesel 981
Blends. SAE Technical Paper 2013-01-1554 (2013). 982
[10] X. Wang, Z. Huang, O.A. Kuti, W. Zhang, K. Nishida. Experimental and analytical 983
study on biodiesel and diesel spray characteristics under ultra-high injection pressure. 984
International journal of heat and fluid flow. 31 (2010) 659-66. 985
[11] J.F. Gamble, M.J. Nicolich, P. Boffetta. Lung cancer and diesel exhaust: an updated 986
critical review of the occupational epidemiology literature. Critical reviews in toxicology. 987
42 (2012) 549-98. 988
[12] J.B. Heywood. Internal combustion engine fundamentals. Mcgraw-hill New York 989
1988. 990
[13] H. Jung, D.B. Kittelson, M.R. Zachariah. Characteristics of SME biodiesel-fueled 991
diesel particle emissions and the kinetics of oxidation. Environmental science & 992
technology. 40 (2006) 4949-55. 993
[14] P. Eastwood. Particulate emissions from vehicles. John Wiley & Sons 2008. 994
44
[15] D.B. Kittelson. Engines and nanoparticles: a review. Journal of Aerosol Science. 29 995
(1998) 575-88. 996
[16] R. Stevenson. The morphology and crystallography of diesel particulate emissions. 997
Carbon. 20 (1982) 359-65. 998
[17] P. Rounce, A. Tsolakis, A. York. Speciation of particulate matter and hydrocarbon 999
emissions from biodiesel combustion and its reduction by aftertreatment. Fuel. 96 (2012) 1000
90-9. 1001
[18] L. Zhu, C. Cheung, W. Zhang, Z. Huang. Emissions characteristics of a diesel engine 1002
operating on biodiesel and biodiesel blended with ethanol and methanol. Science of the 1003
Total Environment. 408 (2010) 914-21. 1004
[19] P. Williams, M. Abbass, G. Andrews, K. Bartle. Diesel particulate emissions. 1005
Combust Flame. Combustion and Flame. 75 (1989) 1-24. 1006
[20] S. Chuepeng, H. Xu, A. Tsolakis, M. Wyszynski, P. Price, R. Stone, et al. Particulate 1007
Emissions from a Common Rail Fuel Injection Diesel Engine with RME-based Biodiesel 1008
Blended Fuelling Using Thermo-gravimetric Analysis. SAE Technical Paper 2008-01-1009
0074 (2008). 1010
[21] L.H. Young, Y.J. Liou, M.T. Cheng, J.H. Lu, H.H. Yang, Y.I. Tsai, et al. Effects of 1011
biodiesel, engine load and diesel particulate filter on nonvolatile particle number size 1012
distributions in heavy-duty diesel engine exhaust. Journal of hazardous materials. 199 1013
(2012) 282-9. 1014
[22] H. Li, A. Lea-Langton, G. Andrews, M. Thompson, C. Musungo. Comparison of 1015
exhaust emissions and particulate size distribution for diesel, biodiesel and cooking oil 1016
from a heavy duty DI diesel engine. SAE Technical Paper 2008-01-0076 (2008). 1017
[23] A. Schönborn, N. Ladommatos, R. Allan, J. Williams, J. Rogerson. Effect of the 1018
molecular structure of individual fatty acid alcohol esters (biodiesel) on the formation of 1019
45
NOx and particulate matter in the diesel combustion process. SAE International 1020
Journal of Fuels and Lubricants. 1 (2009) 849-72. 1021
[24] M. Lapuerta, O. Armas, J. Rodriguez-Fernandez. Effect of biodiesel fuels on diesel 1022
engine emissions. Progress in energy and combustion science. 34 (2008) 198-223. 1023
[25] X. Zhang, H. Wang, L. Li, Z. Wu. Characteristics of Particulates and Exhaust Gases 1024
Emissions of DI Diesel Engine Employing Common Rail Fuel System Fueled with Bio-1025
diesel Blends. Fuel. 2013 (2008) 03-19. 1026
[26] A. Soewono, S. Rogak. Morphology and microstructure of engine-emitted 1027
particulates. Diesel Engine. SAE Techinical Paper 2009-01-1906 (2009). 1028
[27] P.Q. Tan, D.M. Lou, Z.Y. Hu. Nucleation mode particle emissions from a diesel 1029
engine with biodiesel and petroleum diesel fuels. SAE Technical Paper 2010-01-0787 1030
(2010). 1031
[28] M. Tinsdale, P. Price, R. Chen. The impact of biodiesel on particle number, size and 1032
mass emissions from a Euro4 diesel vehicle. SAE Technical Paper 2010-01-0796 (2010). 1033
[29] H. Song, M.H. Lee, H. Kang, K. Kim. The effects of oxidation deterioration biodiesel 1034
on particulate emission from heavy duty diesel engine. SAE Technical Papers 2012-01-1035
1600 (2012). 1036
[30] M.-J. Poitras, D. Rosenblatt, T.W. Chan, G. Rideout. Impact of Varying Biodiesel 1037
Blends on Direct-Injection Light-Duty Diesel Engine Emissions. SAE Technical Paper 1038
2012-01-1313 (2012). 1039
[31] J.N. Gangwar, T. Gupta, A.K. Agarwal. Composition and comparative toxicity of 1040
particulate matter emitted from a diesel and biodiesel fuelled CRDI engine. Atmospheric 1041
Environment. 46 (2012) 472-81. 1042
[32] J. Schauer, C. Christensen, D. Kittelson, J. Johnson, W. Watts. Impact of ambient 1043
temperatures and driving conditions on the chemical composition of particulate matter 1044
46
emissions from non-smoking gasoline-powered motor vehicles. Aerosol Science and 1045
Technology. 42 (2008) 210-23. 1046
[33] P. Pakbin, Z. Ning, J.J. Schauer, C. Sioutas. Characterization of particle bound 1047
organic carbon from diesel vehicles equipped with advanced emission control 1048
technologies. Environmental science & technology. 43 (2009) 4679-86. 1049
[34] Y.Y. Liu, T.C. Lin, Y.J. Wang, W.L. Ho. Carbonyl compounds and toxicity 1050
assessments of emissions from a diesel engine running on biodiesels. Journal of the Air 1051
& Waste Management Association. 59 (2009) 163-71. 1052
[35] L.K. Limbach, P. Wick, P. Manser, R.N. Grass, A. Bruinink, W.J. Stark. Exposure of 1053
engineered nanoparticles to human lung epithelial cells: influence of chemical 1054
composition and catalytic activity on oxidative stress. Environmental science & 1055
technology. 41 (2007) 4158-63. 1056
[36] K. Donaldson, L. Tran, L.A. Jimenez, R. Duffin, D.E. Newby, N. Mills, et al. 1057
Combustion-derived nanoparticles: a review of their toxicology following inhalation 1058
exposure. Particle and Fibre Toxicology. 2 (2005) 10. 1059
[37] N. Künzli, I.S. Mudway, T. Götschi, T. Shi, F.J. Kelly, S. Cook, et al. Comparison of 1060
oxidative properties, light absorbance, and total and elemental mass concentration of 1061
ambient PM2. 5 collected at 20 European sites. Environmental health perspectives. 114 1062
(2006) 684. 1063
[38] A. Baulig, M. Garlatti, V. Bonvallot, A. Marchand, R. Barouki, F. Marano, et al. 1064
Involvement of reactive oxygen species in the metabolic pathways triggered by diesel 1065
exhaust particles in human airway epithelial cells. American Journal of Physiology-1066
Lung Cellular and Molecular Physiology. 285 (2003) L671-L9. 1067
[39] B. González-Flecha. Oxidant mechanisms in response to ambient air particles. 1068
Molecular aspects of medicine. 25 (2004) 169-82. 1069
47
[40] A. Pillay, M. Elkadi, S. Fok, S. Stephen, J. Manuel, M. Khan, et al. A comparison of 1070
trace metal profiles of neem biodiesel and commercial biofuels using high performance 1071
ICP-MS. Fuel. 97 (2012) 385-9. 1072
[41] R. Betha, R. Balasubramanian. Emissions of particulate-bound elements from 1073
stationary diesel engine: Characterization and risk assessment. Atmospheric 1074
Environment. 45 (2011) 5273-81. 1075
[42] M. Carrales, R.W. Martin. Sulfur content of crude oils. US Department of the 1076
Interior, Bureau of Mines 1975. 1077
[43] K. Ravindra, R. Sokhi, R. Van Grieken. Atmospheric polycyclic aromatic 1078
hydrocarbons: source attribution, emission factors and regulation. Atmospheric 1079
Environment. 42 (2008) 2895-921. 1080
[44] J.D. McDonald, E.B. Barr, R.K. White, J.C. Chow, J.J. Schauer, B. Zielinska, et al. 1081
Generation and characterization of four dilutions of diesel engine exhaust for a 1082
subchronic inhalation study. Environmental science & technology. 38 (2004) 2513-22. 1083
[45] J.J. Schauer, M.J. Kleeman, G.R. Cass, B.R. Simoneit. Measurement of emissions 1084
from air pollution sources. 2. C1 through C30 organic compounds from medium duty 1085
diesel trucks. Environmental science & technology. 33 (1999) 1578-87. 1086
[46] J.J. Schauer, M.J. Kleeman, G.R. Cass, B.R. Simoneit. Measurement of emissions 1087
from air pollution sources. 5. C1-C32 organic compounds from gasoline-powered motor 1088
vehicles. Environmental science & technology. 36 (2002) 1169-80. 1089
[47] D. Grosjean, E. Grosjean, A.W. Gertler. On-road emissions of carbonyls from light-1090
duty and heavy-duty vehicles. Environmental science & technology. 35 (2001) 45-53. 1091
[48] A. Kristensson, C. Johansson, R. Westerholm, E. Swietlicki, L. Gidhagen, U. 1092
Wideqvist, et al. Real-world traffic emission factors of gases and particles measured in a 1093
road tunnel in Stockholm, Sweden. Atmospheric Environment. 38 (2004) 657-73. 1094
48
[49] K.W. Loeffler, C.A. Koehler, N.M. Paul, D.O. De Haan. Oligomer formation in 1095
evaporating aqueous glyoxal and methyl glyoxal solutions. Environmental science & 1096
technology. 40 (2006) 6318-23. 1097
[50] M.C. Madden, L.A. Dailey, J.G. Stonehuerner, D.B. Harris. Responses of cultured 1098
human airways epithelial cells treated with diesel exhaust extracts will vary with the 1099
engine load. Journal of Toxicology and Environmental Health Part A. 66 (2003) 2281-97. 1100
[51] X. Pang, X. Shi, Y. Mu, H. He, S. Shuai, H. Chen, et al. Characteristics of carbonyl 1101
compounds emission from a diesel-engine using biodiesel–ethanol–diesel as fuel. 1102
Atmospheric Environment. 40 (2006) 7057-65. 1103
[52] S.S.H. Ho, K.F. Ho, S.C. Lee, Y. Cheng, J.Z. Yu, K.M. Lam, et al. Carbonyl 1104
emissions from vehicular exhausts sources in Hong Kong. Journal of the Air & Waste 1105
Management Association. 62 (2012) 221-34. 1106
[53] C. Cheung, L. Zhu, Z. Huang. Regulated and unregulated emissions from a diesel 1107
engine fueled with biodiesel and biodiesel blended with methanol. Atmospheric 1108
Environment. 43 (2009) 4865-72. 1109
[54] Y. Di, C. Cheung, Z. Huang. Experimental investigation on regulated and 1110
unregulated emissions of a diesel engine fueled with ultra-low sulfur diesel fuel blended 1111
with biodiesel from waste cooking oil. Science of the Total Environment. 407 (2009) 835-1112
46. 1113
[55] K. Takada, F. Yoshimura, Y. Ohga, J. Kusaka, Y. Daisho. Experimental study on 1114
unregulated emission characteristics of turbocharged DI diesel engine with common rail 1115
fuel injection system. SAE Technical Paper 2003-01-3158 (2003). 1116
[56] R. Ballesteros, J. Hernandez, L. Lyons, B. Cabanas, A. Tapia. Speciation of the 1117
semivolatile hydrocarbon engine emissions from sunflower biodiesel. Fuel. 87 (2008) 1118
1835-43. 1119
49
[57] S. Machado Corrêa, G. Arbilla. Carbonyl emissions in diesel and biodiesel exhaust. 1120
Atmospheric Environment. 42 (2008) 769-75. 1121
[58] J. Xue, T.E. Grift, A.C. Hansen. Effect of biodiesel on engine performances and 1122
emissions. Renewable and Sustainable Energy Reviews. 15 (2011) 1098-116. 1123
[59] A. Lea-Langton, H. Li, G.E. Andrews. Comparison of particulate PAH emissions for 1124
diesel, biodiesel and cooking oil using a heavy duty DI diesel engine. SAE Technical 1125
Paper 2008-01-1811 (2008). 1126
[60] T. Lu, Z. Huang, C. Cheung, J. Ma. Size distribution of EC, OC and particle-phase 1127
PAHs emissions from a diesel engine fueled with three fuels. Science of the Total 1128
Environment. 438 (2012) 33-41. 1129
[61] G. Karavalakis, S. Stournas, E. Bakeas. Effects of diesel/biodiesel blends on 1130
regulated and unregulated pollutants from a passenger vehicle operated over the 1131
European and the Athens driving cycles. Atmospheric Environment. 43 (2009) 1745-52. 1132
[62] J. Pan, S. Quarderer, T. Smeal, C. Sharp. Comparison of PAH and nitro-PAH 1133
emissions among standard diesel fuel, biodiesel fuel, and their blend on diesel engines. 1134
Proceedings of the 48 th ASMS Conference on Mass Spectrometry and Allied Topics, 1135
Long Beach, CA 2000. 1136
[63] I.C. Nisbet, P.K. LaGoy. Toxic equivalency factors (TEFs) for polycyclic aromatic 1137
hydrocarbons (PAHs). Regulatory toxicology and pharmacology. 16 (1992) 290-300. 1138
[64] G. Karavalakis, G. Fontaras, D. Ampatzoglou, M. Kousoulidou, S. Stournas, Z. 1139
Samaras, et al. Effects of low concentration biodiesel blends application on modern 1140
passenger cars. Part 3: Impact on PAH, nitro-PAH, and oxy-PAH emissions. 1141
Environmental Pollution. 158 (2010) 1584-94. 1142
[65] E. Bakeas, G. Karavalakis, G. Fontaras, S. Stournas. An experimental study on the 1143
impact of biodiesel origin on the regulated and PAH emissions from a Euro 4 light-duty 1144
vehicle. Fuel. 90 (2011) 3200-8. 1145
50
[66] M. Rhead, S. Hardy. The sources of polycyclic aromatic compounds in diesel engine 1146
emissions. Fuel. 82 (2003) 385-93. 1147
[67] H. Richter, J. Howard. Formation of polycyclic aromatic hydrocarbons and their 1148
growth to soot—a review of chemical reaction pathways. Progress in energy and 1149
combustion science. 26 (2000) 565-608. 1150
[68] S.G. Riddle, C.A. Jakober, M.A. Robert, T.M. Cahill, M.J. Charles, M.J. Kleeman. 1151
Large PAHs detected in fine particulate matter emitted from light-duty gasoline 1152
vehicles. Atmospheric Environment. 41 (2007) 8658-68. 1153
[69] K. Miet, K. Le Menach, P.-M. Flaud, H. Budzinski, E. Villenave. Heterogeneous 1154
reactivity of pyrene and 1-nitropyrene with NO2: Kinetics, product yields and 1155
mechanism. Atmospheric Environment. 43 (2009) 837-43. 1156
[70] N.V. Heeb, P. Schmid, M. Kohler, E. Gujer, M. Zennegg, D. Wenger, et al. 1157
Secondary effects of catalytic diesel particulate filters: conversion of PAHs versus 1158
formation of nitro-PAHs. Environmental science & technology. 42 (2008) 3773-9. 1159
[71] S.T. Bagley, L.D. Gratz, J.H. Johnson, J.F. McDonald. Effects of an oxidation 1160
catalytic converter and a biodiesel fuel on the chemical, mutagenic, and particle size 1161
characteristics of emissions from a diesel engine. Environmental science & technology. 1162
32 (1998) 1183-91. 1163
[72] P.Q. Tan, Z.Y. Hu, D.M. Lou. Regulated and unregulated emissions from a light-1164
duty diesel engine with different sulfur content fuels. Fuel. 88 (2009) 1086-91. 1165
[73] C. Cheung, Y. Di, Z. Huang. Experimental investigation of regulated and 1166
unregulated emissions from a diesel engine fueled with ultralow-sulfur diesel fuel 1167
blended with ethanol and dodecanol. Atmospheric Environment. 42 (2008) 8843-51. 1168
[74] E. Zervas. Regulated and non-regulated pollutants emitted from two aliphatic and a 1169
commercial diesel fuel. Fuel. 87 (2008) 1141-7. 1170
51
[75] P.C. Shukla, T. Gupta, A.K. Agarwal. A Comparative Morphological Study of 1171
Primary and Aged Particles Emitted from a Biodiesel (B20) vis-à-vis Diesel Fuelled 1172
CRDI Engine. Aerosol and Air Quality Research. 14 (2014) 934-42. 1173
[76] X. Shi, K. He, W. Song, X. Wang, J. Tan. Effects of a diesel oxidation catalyst on 1174
gaseous pollutants and fine particles from an engine operating on diesel and biodiesel. 1175
Frontiers of Environmental Science & Engineering. 6 (2012) 463-9. 1176
[77] L. Zhu, C. Cheung, W. Zhang, J. Fang, Z. Huang. Effects of ethanol–biodiesel blends 1177
and diesel oxidation catalyst (DOC) on particulate and unregulated emissions. Fuel. 113 1178
(2013) 690-6. 1179
[78] A. Williams, R. McCormick, J. Luecke, R. Brezny, A. Geisselmann, K. Voss, et al. 1180
Impact of Biodiesel Impurities on the Performance and Durability of DOC, DPF and 1181
SCR Technologies. SAE International Journal of Fuels and Lubricants. 4 (2011) 110-24. 1182
[79] K. Vertin, S. He, A. Heibel. Impacts of B20 Biodiesel on Cordierite Diesel 1183
Particulate Filter Performance. SAE Technical Paper 2009-01-2736 (2009). 1184
[80] G. Austin, J. Naber, J. Johnson, C. Hutton. Effects of Biodiesel Blends on 1185
Particulate Matter Oxidation in a Catalyzed Particulate Filter during Active 1186
Regeneration. SAE International Journal of Fuels and Lubricants. 3 (2010) 194-218. 1187
[81] M. Asti, E.M. Borla, F. Parussa, C.R.F. Scpa. Biodiesel Influence on Particulate 1188
Matter Behavior during Active and Passive DPF Regeneration. SAE Technical Paper 1189
2011-24-0204 (2011). 1190
[82] A. Parihar, V. Sethi, P. Parikh, D. Radhakrishna. Physical Characterization of 1191
Particulate Emissions from Compression Ignition Engine Operating on Diesel and 1192
Biodiesel Fuels. SAE Technical Paper 2011-26-0026 (2011). 1193
[83] S. Di Iorio, C. Beatrice, C. Guido, P. Napolitano, A. Vassallo, C. Ciaravino. Impact 1194
of Biodiesel on Particle Emissions and DPF Regeneration Management in a Euro5 1195
Automotive Diesel Engine. SAE Technical Paper 2012-01-0839 (2012). 1196
52
[84] J. Pidgeon, J. Johnson, J. Naber. An Experimental Investigation into Particulate 1197
Matter Oxidation in a Catalyzed Particulate Filter with Biodiesel Blends on an Engine 1198
during Active Regeneration. SAE Technical Paper 2013-01-0521 (2013). 1199
[85] EPA. A comprehensive analysis of biodiesel impacts on exhaust emissions. 1200
Assessment and Standards Division (Office of Transportation and Air Quality of the US 1201
Environmental Protection Agency). Report EPA420-P-02-001 (2002). 1202
[86] L. Turrio-Baldassarri, C.L. Battistelli, L. Conti, R. Crebelli, B. De Berardis, A.L. 1203
Iamiceli, et al. Emission comparison of urban bus engine fueled with diesel oil and 1204
‘biodiesel’blend. Science of the Total Environment. 327 (2004) 147-62. 1205
[87] Y.-f. Lin, Y.-p.G. Wu, C.-T. Chang. Combustion characteristics of waste-oil produced 1206
biodiesel/diesel fuel blends. Fuel. 86 (2007) 1772-80. 1207
[88] M.N. Nabi, M.M.Z. Shahadat, M.S. Rahman, M.R.A. Beg. Behavior of diesel 1208
combustion and exhaust emission with neat diesel fuel and diesel-biodiesel blends. SAE 1209
Technical Paper 2004-01-3034 (2004). 1210
[89] M. Alam, J. Song, R. Acharya, A. Boehman, K. Miller. Combustion and emissions 1211
performance of low sulfur, ultra low sulfur and biodiesel blends in a DI diesel engine. 1212
SAE Technical Paper 2004-01-3024 (2004). 1213
[90] R. McGill, J. Storey, R. Wagner, D. Irick, P. Aakko, M. Westerholm, et al. Emission 1214
performance of selected biodiesel fuels. SAE Technical Paper 2003-01-1866 (2003). 1215
[91] C.A. Sharp, T.W. Ryan, G. Knothe. Heavy-duty diesel engine emissions tests using 1216
special biodiesel fuels. SAE Technical Paper 2005-01-3671 (2005). 1217
[92] B.M. Spessert, I. Arendt, A. Schleicher. Influence of RME and Vegetable Oils on 1218
Exhaust Gas and Noise Emissions of Small Industrial Diesel Engines. SAE Technical 1219
Paper 2004-32-0070 (2004). 1220
53
[93] W. Wang, D. Lyons, N. Clark, M. Gautam, P. Norton. Emissions from nine heavy 1221
trucks fueled by diesel and biodiesel blend without engine modification. Environmental 1222
science & technology. 34 (2000) 933-9. 1223
[94] M. Canakci. Combustion characteristics of a turbocharged DI compression ignition 1224
engine fueled with petroleum diesel fuels and biodiesel. Bioresource technology. 98 1225
(2007) 1167-75. 1226
[95] M. Canakci, J.H. Van Gerpen. Comparison of engine performance and emissions for 1227
petroleum diesel fuel, yellow grease biodiesel, and soybean oil biodiesel. Transactions of 1228
the ASAE. 46 (2003) 937-44. 1229
[96] D. Qi, L. Geng, H. Chen, Y. Bian, J. Liu, X. Ren. Combustion and performance 1230
evaluation of a diesel engine fueled with biodiesel produced from soybean crude oil. 1231
Renewable Energy. 34 (2009) 2706-13. 1232
[97] M. Kousoulidou, G. Fontaras, L. Ntziachristos, Z. Samaras. Biodiesel blend effects 1233
on common-rail diesel combustion and emissions. Fuel. 89 (2010) 3442-9. 1234
[98] J. Krahl, A. Munack, O. Schröder, H. Stein, L. Herbst, A. Kaufmann, et al. The 1235
influence of fuel design on the exhaust gas emissions and health effects. SAE Technical 1236
Paper 2005-01-3772 (2005). 1237
[99] C.N. Grimaldi, L. Postrioti, M. Battistoni, F. Millo. Common rail HSDI diesel 1238
engine combustion and emissions with fossil/bio-derived fuel blends. Evaluation. 2011 1239
(2002) 12-20. 1240
[100] H. Raheman, A. Phadatare. Diesel engine emissions and performance from blends 1241
of karanja methyl ester and diesel. Biomass and Bioenergy. 27 (2004) 393-7. 1242
[101] X. Shi, X. Pang, Y. Mu, H. He, S. Shuai, J. Wang, et al. Emission reduction 1243
potential of using ethanol–biodiesel–diesel fuel blend on a heavy-duty diesel engine. 1244
Atmospheric Environment. 40 (2006) 2567-74. 1245
54
[102] L. Xiaoming, G. Yunshan, W. Sijin, H. Xiukun. An experimental investigation on 1246
combustion and emissions characteristics of turbocharged DI engines fueled with blends 1247
of biodiesel. SAE Technical Paper 2005-01-2199 (2005). 1248
[103] R.L. McCormick, C. Tennant, R.R. Hayes, S. Black, J. Ireland, T. McDaniel, et al. 1249
Regulated emissions from biodiesel tested in heavy-duty engines meeting 2004 emission 1250
standards. SAE Technical Paper 2005-01-2200 (2005). 1251
[104] E. Verhaeven, L. Pelkmans, L. Govaerts, R. Lamers, F. Theunissen. Results of 1252
demonstration and evaluation projects of biodiesel from rapeseed and used frying oil on 1253
light and heavy duty vehicles. SAE Technical Paper 2005-01-2201 (2005). 1254
[105] A.K. Agarwal, L. Das. Biodiesel development and characterization for use as a fuel 1255
in compression ignition engines. Journal of engineering for gas turbines and power. 123 1256
(2001) 440-7. 1257
[106] D. Qi, H. Chen, L. Geng, Y. Bian. Experimental studies on the combustion 1258
characteristics and performance of a direct injection engine fueled with biodiesel/diesel 1259
blends. Energy Conversion and Management. 51 (2010) 2985-92. 1260
[107] Y.-C. Lin, W.-J. Lee, T.-S. Wu, C.-T. Wang. Comparison of PAH and regulated 1261
harmful matter emissions from biodiesel blends and paraffinic fuel blends on engine 1262
accumulated mileage test. Fuel. 85 (2006) 2516-23. 1263
[108] C. Robbins, S.K. Hoekman, E. Ceniceros, M. Natarajan. Effects of biodiesel fuels 1264
upon criteria emissions. SAE Technical Paper 2011-01-1943 (2011). 1265
[109] I. Saanum, M. Bysveen, J.E. Hustad. Study of particulate matter-, NOx-and 1266
hydrocarbon emissions from a diesel engine fueled with diesel oil and biodiesel with 1267
fumigation of hydrogen, methane and propane. SAE Technical Paper 2008-01-1809 1268
(2008). 1269
55
[110] A.K. Agarwal, V. Chaudhury, P.C. Shukla. Macroscopic Spray Parameters of 1270
Karanja Oil and Blends: A Comparative Study. SAE Technical Paper 2012-28-0028 1271
(2012). 1272
[111] J.G. Suryawanshi, N. Deshpande. Effect of injection timing retard on emissions 1273
and performance of a Pongamia oil methyl ester fuelled CI engine. SAE Technical Paper 1274
2005-01-3677 (2005). 1275
[112] D.D. Corgard, R.D. Reitz. Effects of Alternative Fuels and Intake Port Geometry 1276
on HSDI Diesel Engine Performance and Emissions. Development. 1 (2001) 0652. 1277
[113] R. Reitz. Controlling DI diesel engine emissions using multiple injections and 1278
EGR. Combustion science and technology. 138 (1998) 257-78. 1279
[114] A. Uludogan, J. Xin, R. Reitz. Exploring the use of multiple injectors and split 1280
injection to reduce DI diesel engine emissions. SAE Technical Paper 962058 (1996). 1281
[115] Z. Han, A. Uludogan, G.J. Hampson, R.D. Reitz. Mechanism of soot and NOx 1282
emission reduction using multiple-injection in a diesel engine. SAE Technical Paper 1283
960633 (1996). 1284
[116] J.E. Dec, C. Espey. Ignition and early soot formation in a DI diesel engine using 1285
multiple 2-D imaging diagnostics. Presented at the Society of Automotive Engineers 1286
International Congress and Exposition, Detroit, MI, 27 Feb-2 Mar 19951995. 1287
[117] K. Yamane, A. Ueta, Y. Shimamoto. Influence of physical and chemical properties 1288
of biodiesel fuels on injection, combustin and exhaust emission characteristics in a direct 1289
injection compression ignition engine. International Journal of Engine Research. 2 1290
(2001) 249-61. 1291
[118] P. Ye, A.L. Boehman. An investigation of the impact of injection strategy and 1292
biodiesel on engine NOx and particulate matter emissions with a common-rail 1293
turbocharged DI diesel engine. Fuel. 97 (2012) 476-88. 1294
56
[119] K. Yehliu, A.L. Boehman, O. Armas. Emissions from different alternative diesel 1295
fuels operating with single and split fuel injection. Fuel. 89 (2010) 423-37. 1296
[120] B. Kegl. Effects of biodiesel on emissions of a bus diesel engine. Bioresource 1297
technology. 99 (2008) 863-73. 1298
[121] S.H. Yoon, J.W. Hwang, C.S. Lee. Effect of injection strategy on the combustion 1299
and exhaust emission characteristics of a biodiesel-ethanol blend in a di diesel engine. 1300
Journal of engineering for gas turbines and power. 132 (2010). 1301
[122] X. Lu, J. Ma, L. Ji, Z. Huang. Simultaneous reduction of NOx emission and smoke 1302
opacity of biodiesel-fueled engines by port injection of ethanol. Fuel. 87 (2008) 1289-96. 1303
[123] P. Kohoutek, N. Metz, K. Richter, A. Volkswagen, M. AG. Particulate matter 1304
emissions from modern diesel engines, impact of fuel quality and PM-development from 1305
road transport in Germany. ILSI-Symposium vom1999. 1306
[124] D. Dwivedi, A.K. Agarwal, M. Sharma. Particulate emission characterization of a 1307
biodiesel vs diesel-fuelled compression ignition transport engine: A comparative study. 1308
Atmospheric Environment. 40 (2006) 5586-95. 1309
[125] H. Kim, B. Choi. The effect of biodiesel and bioethanol blended diesel fuel on 1310
nanoparticles and exhaust emissions from CRDI diesel engine. Renewable Energy. 35 1311
(2010) 157-63. 1312
[126] C.D. Rakopoulos, A.M. Dimaratos, E.G. Giakoumis, D.C. Rakopoulos. 1313
Investigating the emissions during acceleration of a turbocharged diesel engine 1314
operating with bio-diesel or n-butanol diesel fuel blends. Energy. 35 (2010) 5173-84. 1315
[127] M. Graboski, R. McCormick, T. Alleman, A. Herring. The effect of biodiesel 1316
composition on engine emissions from a DDC series 60 diesel engine. National 1317
Renewable Energy Laboratory (Report No: NREL/SR-510-31461). (2003). 1318
[128] D. Kawano, H. Ishii, Y. Goto, A. Noda. Application of biodiesel fuel to modern 1319
diesel engine. Training. 2012 (2006) 09-5. 1320
57
[129] C. Raahede. Particle characteristics - PAH and Gaseous emission from light duty 1321
CI engines fueled with biodiesel and biodiesel blends. SAE Technical Paper 2010-01-1322
1277 (2010). 1323
[130] A. Puzun, S. Wanchen, L. Guoliang, T. Manzhi, L. Chunjie, C. Shibao. 1324
Characteristics of particle size distributions about emissions in a common-rail diesel 1325
engine with biodiesel blends. Procedia Environmental Sciences. 11 (2011) 1371-8. 1326
[131] J. Desantes, V. Bermúdez, J. García, E. Fuentes. Effects of current engine 1327
strategies on the exhaust aerosol particle size distribution from a heavy-duty diesel 1328
engine. Journal of Aerosol Science. 36 (2005) 1251-76. 1329
[132] A. Sinha, J. Chandrasekharan, J. Nargunde, W. Bryzik, K. Acharya, N. Henein. 1330
Effect of biodiesel and its blends on particulate emissions from HSDI diesel engine. SAE 1331
Technical Paper 2010-01-0798 (2010). 1332
[133] P. Pham, T. Bodisco, S. Stevanovic, M. Rahman, H. Wang, Z. Ristovski, et al. 1333
Engine performance characteristics for biodiesels of different degrees of saturation and 1334
carbon chain lengths. SAE International Journal of Fuels and Lubricants. 6 (2013) 188-1335
98. 1336
[134] Y. Di, C. Cheung, Z. Huang. Comparison of the effect of biodiesel-diesel and 1337
ethanol-diesel on the particulate emissions of a direct injection diesel engine. Aerosol 1338
Science and Technology. 43 (2009) 455-65. 1339
[135] M. Lapuerta, O. Armas, J. Rodríguez-Fernández. Effect of the degree of 1340
unsaturation of biodiesel fuels on NOx and particulate emissions. SAE International 1341
Journal of Fuels and Lubricants. 1 (2009) 1150-8. 1342
[136] J. Nuszkowski, K. Flaim, G. Thompson. The effect of cetane improvers and 1343
biodiesel on diesel particulate matter size. SAE International Journal of Fuels and 1344
Lubricants. 4 (2011) 23-33. 1345