This work is done as a part of graduate course in Air Quality in Spring 2017. The author was pursuing MS in Environmental Engineering Sciences at University of Florida during the making of this project. (description coming soon) Presentation: https://goo.gl/2MnAmG

1. Page - 1/22
GRADUATE PROJECT
TITLE: Performance of Biodiesel against Petroleum Diesel: Fuel
Properties, Engine Exhaust Emissions, Scenario Analysis
Author: Kalaivanan Murthy (Kal)
Purpose: Course Project
Date: April 20, 2017
Length: 21 pages
Presentation: https://goo.gl/2MnAmG

2. Page - 2/22
INDEX
TITLE ...........................................................................................................................................................1
[1] ABSTRACT............................................................................................................................................3
[2] OBJECTIVES .........................................................................................................................................4
[3] INTRODUCTION...................................................................................................................................5
[4] BIODIESEL PROPERTIES....................................................................................................................6
[4.1] Viscosity...........................................................................................................................................6
[4.2] Density. ............................................................................................................................................7
[4.3] Oxygen Content................................................................................................................................7
[4.4] Cetane Number.................................................................................................................................7
[4.5] Energy Content.................................................................................................................................8
[4.6] Brake Effective Power and Brake Specific Fuel Consumption (BSFC). .........................................8
[5] ENGINE EXHAUST EMISSIONS ........................................................................................................9
[5.1] NOx Emissions.................................................................................................................................9
[5.2] Particulate Matter. ............................................................................................................................9
[5.3] Hydrocarbons. ................................................................................................................................10
[5.4] Carbon Monoxide...........................................................................................................................11
[5.5] Sulfur..............................................................................................................................................11
[5.6] Polycyclic Aromatic Hydrocarbons (PAHs). .................................................................................11
[6] BIODIESEL TRENDS..........................................................................................................................12
[6.1] Timeline: Production and Consumption.........................................................................................12
[6.2] Scenario Analysis: Alternative (B20) and Hypothetical (B100) Scenarios ...................................14
[6.2.1] Alternative Scenario-1:............................................................................................................15
[6.2.2] Alternative Scenario-2.............................................................................................................15
[6.2.3] Alternative Scenario-3:............................................................................................................15
[7] CHALLENGES.....................................................................................................................................16
[8] CONCLUSION .....................................................................................................................................17
[9] ACKNOWLEDGEMENT.....................................................................................................................18
[10] REFERENCES....................................................................................................................................19

3. Page - 3/22
[1] ABSTRACT
Biodiesel is claimed to be a superior alternative to petroleum diesel. But the claim lacks
profound evidences because of two reasons. First – the performance of biodiesel is tested in
engines designed for petroleum diesel. Second – biodiesels are made from different biogenic
sources; and this variation introduces an uncertainty. This project contrasts the difference
between biodiesel and petroleum diesel; highlights the benefits of the former through three
aspects: fuel properties, engine exhaust emissions and urban scenario analysis. As a fuel,
biodiesel is viscous and contains oxygen. From an engine-exhaust perspective, biodiesel
emissions are cleaner than petroleum diesel with few limitations. It generates significantly lesser
amount of particulate matter (soot), hydrocarbons and carbon monoxide. In contrast, it generates
significantly higher amount of NOx compared to petroleum diesel. It is observed that the
maximum reduction in PM, HC and CO is between 40% to 60%, while the maximum increase in
NOx is found to be just 12%. In addition, biodiesel is considered as a carbon neutral fuel as the
emitted carbon dioxide is consumed back by the plants. Although there are strong evidences in
support of biodiesel from an environmental perspective, mechanical, thermodynamic and
hydraulic aspects of biodiesel poses challenges thwarting its commercial acceptance.

4. Page - 4/22
[2] OBJECTIVES
The primary objective is to highlight the emission differences between biodiesel and petroleum
diesel. This project focuses on engine exhaust emissions; not on post-treatment tail-pipe exhaust.
Diesel is used in various classes of automobiles – from light passenger cars to heavy duty trucks.
Since different vehicles have different engine technology, the emissions are found to vary
between different vehicle classes and engine technologies. This project highlights on commonly
observed differences. The specific objectives of the project are:
1. To study the fuel properties of biodiesel that are important to ambient air quality. The
fuel properties of biodiesel are enumerated with respect to that of petroleum diesel.
2. To study biodiesel emissions from compression ignited engines with respect to petroleum
diesel emissions. The emissions studied are engine exhaust emissions resulting from
compression ignited combustion engines.
3. To study the biodiesel consumption trends in United States and their impact on
environment. The air quality benefits of biodiesel are studied by forecasting alternative
and hypothetical scenarios.
These objectives are accomplished by understanding past research and inferring the common
observations with the evidences collected from renowned journals.

5. Page - 5/22
[3] INTRODUCTION
Biodiesel is an alternative fuel produced from biogenic sources, a vegetable or animal oil, by
transesterification, which separates ester from glycerin. The ester is then refined to extract
biodiesel. The calorific value of biodiesel lies between 36.5-38 MJ/kg, while the corresponding
range for petroleum diesel is 42.5-44 MJ/kg. Biodiesel is biodegradable, non-toxic, renewable
and carbon-neutral fuel. The annual consumption of biodiesel in United States in 2016 is 2.06
billion gallons which is 20, 500% higher than in 2001. The emissions generated by biodiesel is
found to be cleaner in aspects pertaining to carcinogenic compounds. In particular, particulate
matter, hydrocarbons and carbon dioxide are lesser in biodiesel combustion. Besides, it is free
from sulfur and aromatic compounds. Biodiesel also offers better lubricity which reduces the
reliance on lubricative additives. Yet, biodiesel is challenged by factors majorly related to engine
technology. This limits its wide-scale implementation in energy and transportation sector.
In general, diesel fuel outperforms gasoline on the basis of fuel economy, hauling capacity and
long range driving. Diesel emission has 60% lesser carbon dioxide than gasoline. It is seen as a
ecofriendly fuel with respect to greenhouse gas emissions. In 2014, 50% of automobile sales in
Europe are diesel powered, while it is just 3% in United States. It is interesting to note that diesel
vehicle has just 4% of US fleet but it accounts for more than half of the nation’s on-road NOx. [3]
Automobile engine emissions depend on two factors: fuel type and engine technology. As such,
same fuel can generate different emission patterns at different combustion environments. Given
this condition, the emission of biodiesel varies with the engine technology, loading condition and
engine speed. Yet, there are common patterns which are observed while using biodiesel in the
place of regular petroleum diesel.
Fuel properties play a key role in the exhaust emissions. The fuel properties which has
significant impact on engine power and emissions are viscosity, density, oxygen content, cetane
number, brake specific fuel consumption and the presence of characteristic chemical compounds
such as sulfur and aromatics. Likewise, the emissions which has significant impact on ambient
air quality are nitrogen monoxide, nitrogen dioxide, particulate matter, hydrocarbons, carbon
monoxide, carbon dioxide, sulfur and aromatic compounds. These two aspects – the properties
and the emissions – are discussed in this report.

6. Page - 6/22
The specifications for conventional diesels and biodiesels are developed by ASTM International.
ASTM D975 has specifications for conventional diesel, ASTM D7467-15ce1 for B20 and
ASTM D6751-15ce1 for B100. [4]
Blends are used to overcome the problem of engine power and
torque. Lower blends can be safely used in diesel engines but higher blends require engine
modification. Modern cars employ common-rail injection systems, which is found to have
cleaner emissions than archaic direct injection systems. Many studies show that the optimum
blend for a trade-off between NOx increase and PM-CO-HC decrease is B20. However, there are
challenges associated with using higher blends such as B60 or B80. Nevertheless, the demand for
biodiesel is inevitably increasing and given its environmental benefits, it can be asserted that
biodiesel is the fuel of the future.
[4] BIODIESEL PROPERTIES
The properties of biodiesel differ from petroleum diesel both by physical and chemical aspects.
Physically, biodiesels are denser and more viscous than petroleum diesel. Chemically, they
contain oxygen, and they are free from sulfur and aromatic compounds. Thermodynamically,
they have lesser heating value, hence lesser energy than petroleum diesel. This reduces power
and torque output. The properties of biodiesel are summarized in the following table.
Table 4.1 Properties of Biodiesel in comparison with Petroleum Diesel and SME biodiesel
Property Units Petroleum Diesel Biodiesel
Soy Methyl Ester
(SME)
Viscosity 40 °C, cSt 2-3.5 3.5-5.5 4.7
Density 15 °C, g cm-3
0.81-0.86 0.87-0.895 0.88
Oxygen % mass ≈0 10-11 NA
Cetane Number 40-45 45-55 56.4
Energy MJ/kg 42.5-44 36.5-38 37.1
Sulfur % mass 0.0015-0.05 ≈0 NA
Aromatics % mass 30 ≈0 NA
Flash Point °C 64 NA 169
[4.1] Viscosity. Viscosity is a measure of fluid’s resistance to flow. It is an important factor for
design of fuel injection systems. Biodiesels have viscosities in the range of 3.5-5.5 centi-Stoke at
40 °C. Petroleum diesels have viscosities in the range of 2.0-3.5 centi-Stoke at 40 °C. It can be
seen that biodiesel has higher viscosity than petroleum diesel. Soy Methyl Ester (SME) has

7. Page - 7/22
57.53% higher viscosity than No.2 petroleum diesel and Rapeseed Methyl Ester (RME) has
25.5% higher viscosity than SME. Higher viscosities are both beneficial and perilous. It is
beneficial for they facilitate better controllability of fuel; hence leakage is reduced and fuel is
efficiently utilized. In addition, they provide better lubrication. This reduces wear and the need
for lubrication additives. In contrast, higher viscosities are disadvantageous for its potential to
form sediments and deposits. They also have lesser back flow across piston clearance; hence,
biodiesel encounters higher fuel consumption when used in diesel vehicles. The fuel
consumption for biodiesel is higher by 2.38%, 4.35% and 6.05%, by volume, for B10, B20 and
B30 blends respectively. [11]
[4.2] Density. Density is a dominant factor for fuel controllability. It is associated with fuel
compressibility. The density of biodiesel is 0.87-0.89 g cm-3
, while the density of petroleum
diesel is 0.81-0.86 g cm-3
. It can be seen than biodiesel is denser than petroleum diesel. Fuels
having higher densities have higher mass per unit volume. Since fuel injection is based on
volume; and density is inversely proportional to volume, the mass of fuel consumed is higher for
denser fuels. As a result, biodiesels have higher bulk modulus, lesser combustion delay and
advanced combustion, which results in higher peak pressure.
[4.3] Oxygen Content. Oxygen is crucial for combustion, particularly for compression ignited
fuels, which include diesel. The oxygen content of biodiesel is 10-11%, while it is negligible in
petroleum diesel. Rapeseed Methyl Ester (RME) has 10.8% oxygen by mass. Presence of oxygen
enhances the oxidation of combustion products. It reduces soot, which is an unburned carbon
particle, and thus results in lesser particulate matter emission. But it increases the flash point,
which increases the peak pressure in combustion cylinder. [13]
[4.4] Cetane Number. Cetane number is a measure of diesel’s ignition delay, the time between
the start of ignition and the pressure increase. Cetane number has an inverse relation with
ignition delay. The cetane number of biodiesel is 45-60[14]
, while for petroleum diesel, it is 40-
55. [14]
Soy Methyl Ester (SME) has a cetane number of 56.4. [15]
It can be seen that biodiesels
have higher cetane number than petroleum diesel. This results in quicker ignition delay and
advanced combustion. The higher cetane number is due to presence of long-chain carbon
compounds and absence of aromatic hydrocarbons. [15]

8. Page - 8/22
[4.5] Energy Content. The energy content is represented by heating value. It is the measure of
amount of energy released per unit mass of fuel combusted. The higher heating value of
biodiesel is 127, 960 Btu/gal[24]
, while for petroleum diesel it is 138, 490 Btu/gal.[24]
It can be
seen that biodiesel has 7.6% lesser energy than petroleum diesel. Some studies report a 9%
reduction in energy for biodiesel. [14]
The lesser energy reduces engine power and torque.
However, this reduction in engine power is significant only at full-loading condition. A full
loading condition occurs when the accelerator is fully pressed.
Biodiesels fail to deliver power as much as petroleum diesel because of its lower energy content.
For a six-cylinder, four-stroke, turbo charged, direct injection diesel engine, it was observed
engine power was 3.7% and 6.1% lesser for B20 and B100, respectively, with respect to
petroleum diesel. Similarly, torque is lesser by 3.7% and 6.1% N-m for B20 and B100
respectively [5]
. However, the power loss is not significant for B5. Indeed, one study reports a
power increase of 2 N-m for B5. [14]
Optimizing blend percent and power reduction, it is found
that B17 is the ideal blend since it had least power loss per unit volume of biodiesel percent. One
study claims higher viscosity as the reason for power loss. It finds that the 3-8% power loss in
cottonseed biodiesel is not due to its 5% lower heating value but due to its atomization difficulty.
Another study by Southwest Research Institute reports a power loss of 1.5-2% and 8% for B20
and B100 respectively. As mentioned above, many studies have an agreement that the power loss
is significant only at full-loading condition. [14]
[4.6] Brake Effective Power and Brake Specific Fuel Consumption (BSFC). Brake effective
power is the ability to control fuel flow during injection. Fuels with higher viscosity, such as
biodiesels, results in improved brake effective power. Brake Specific Fuel Consumption (BSFC)
is a measure of fuel efficiency. It is the ratio of mass rate of fuel to brake effective power. In
regard to loading condition and blend ratio, BSFC is lower at lower loads and higher blends. [25]
BSFC for biodiesel is found to be higher by 2.5%, 3.0% and 7.5% for B5, B20 and B100
respectively. [5]
This is due to higher fuel consumption and lower heating value. [26] [14]
In another
case, when temperature was adjusted to make the viscosities equal for both fuel, petroleum diesel
has higher fuel consumption. One study reports that BSFC of biodiesel is 13.8% higher than
petroleum diesel. [17]

9. Page - 9/22
[5] ENGINE EXHAUST EMISSIONS
Biodiesel, due to its biogenic origin and oxygen possession, has cleaner emissions than fossil
based fuels. Emissions of particulate matter (PM), carbon monoxide (CO) and hydrocarbons
(HC) are significantly lesser in biodiesel exhaust. However, biodiesel has higher emission of
nitrogen oxides (NOx) than its counterpart, petroleum diesel. This is discussed in the following
section.
[5.1] NOx Emissions. In diesel engines, NOx is generated thermal NOx and to a lesser extent by
prompt NOx. Biodiesel emits higher NOx than petroleum diesel. This is due to higher volumetric
efficiency and faster air-fuel mixing. The latter is associated with increased peak pressure, which
is a result of advanced combustion. It reduces ignition delay and increases the chamber
temperature. In addition, lesser soot generation leaves much of the radiation unabsorbed and
results higher temperature. [5]
The increase in NOx is 12% for B100 and 6% for B20, with respect to petroleum diesel. This
difference increases with engine speed. Another study reports that on average, NOx were higher
by 2.1%, 5.9% and 9.3% for B10, B20 and B100 respectively. [11]
US-EPA gives the following
empirical equation for determining NOx from biodiesel relative to petroleum diesel. It is
expressed as a function of biodiesel blend percent.
𝑁𝑂𝑥 𝐵𝐷
𝑁𝑂𝑥 𝑃𝐷
= exp ( 979.4 ∗ 10−6
∗ 𝑓𝐵𝐷)
Variables: NOxBD – NOx emissions from biodiesel; NOxPD – NOx emissions from
petroleum diesel; fBD – biodiesel blend percent (in %).
According the equation, NOx emissions has linear and inverse relationship against biodiesel
blend percent. In other words, NOx increases with biodiesel content in the fuel. The linear
relationship implies that the relative reduction in NOx (relative reduction = gross
reduction/biodiesel percent) remains same for all blends. Shorter ignition delay, higher
temperature and higher oxygen content are the factors resulting in higher NOx. [15]
Another study
claims higher NOx is due to higher surface tension. [7]
[5.2] Particulate Matter. Biodiesel emits particulate matter in form of soot, which is an
unoxidized carbon particle. Biodiesel emits lesser particulate matter than petroleum diesel. This

10. Page - 10/22
reduction is due to the presence of oxygen, which oxidizes the otherwise formed soot. In
addition, absence of sulfur and aromatic hydrocarbons promotes this reduction.
The reduction in particulate matter emissions was 60% for B100 and 20% for B20. It was found
that the reduction is higher in indirect injection engines. Another study reports a reduction of
0.73%, 3.42% and 5.78% for B10, B20 and B30 respectively. US-EPA gives the following
empirical equation for determining the PM reduction as a function of biodiesel blend percent.
𝑃𝑀 𝐵𝐷
𝑃𝑀 𝑃𝐷
= exp ( − 6384 ∗ 10−6
∗ 𝑓𝐵𝐷)
Variables: PMBD – particulate matter emissions from biodiesel; PMPD – particulate
matter emissions from petroleum diesel; fBD - biodiesel blend percent (in %).
The equation when plotted shows a non-linear proportional relationship against biodiesel blend
percent. It is found that the relative reduction was higher for B20-B25 blends. A supporting
observation was that particulate matter reductions were 20% for B20 but only 60% for B100,
when it must linearly correspond to 100%. [14]
It was also found that the reduction of particulate
matter increases against the engine load.
[5.3] Hydrocarbons. Biodiesel generates lesser hydrocarbons than petroleum diesel. The
reduction was up to 70% for B100 and 32% for B20. This is due to higher oxygen content,
higher cetane number and formation of peroxides. It is found that this reduction shrinks with
speed. At 2100 rpm, it is equal to 15% and 7.5% respectively. This implies that the reduction of
hydrocarbons decreases against engine speed. Another study reports a hydrocarbon reduction of
3.43%, 8.13% and 12.73% for B10, B20 and B30 respectively. [11]
Hydrocarbon emissions are
found to be inversely proportional to oxygen content and directly proportional to engine speed.
US-EPA gives the following empirical equation for determining the total hydrocarbon reduction
as a function of biodiesel blend percent.
𝑇𝐻𝐶 𝐵𝐷
𝑇𝐻𝐶 𝑃𝐷
= exp ( − 11195 ∗ 10−6
∗ 𝑓𝐵𝐷)
Variables: THCBD – total hydrocarbon emissions from biodiesel; THCPD – total
hydrocarbon emissions from petroleum diesel; fBD – biodiesel blend percent (in %).

11. Page - 11/22
The equation shows that the reduction is non-linearly proportional to biodiesel blend percent. It
was also found that the relative reduction was higher for B25 blends.
[5.4] Carbon Monoxide. Biodiesel emits lesser carbon monoxide than petroleum diesel. The
reduction was up to 50% for B100 and 15% for B20. Another study reports a reduction of 7.5%,
16.9% and 22.6% for B10, B20 and B30 respectively. These reductions were due to higher
oxygen content, poorer atomization and uneven distribution of fuel within the combustion
cylinder, which results in local oxygen deficiency and incomplete combustion. [5] [11]
Soy Methyl
Ester (SME), a soy based biodiesel, emits 15.29% less CO than petroleum diesel (No.2 Diesel).
[16]
US-EPA gives the following empirical equation for determining carbon monoxide reduction
as a function of biodiesel blend percent.
𝐶𝑂 𝐵𝐷
𝐶𝑂 𝑃𝐷
= exp ( − 6561 ∗ 10−6
∗ 𝑓𝐵𝐷)
Variables: COBD – carbon monoxide emissions from biodiesel; COPD – carbon
monoxide emissions from petroleum diesel; fBD – biodiesel blend percent (in %).
The equation shows that the reduction is non-linearly proportional to the biodiesel blend percent.
It was found that CO emissions decreases with engine speed. [5]
[5.5] Sulfur. Presence of sulfur in fuel results in emission of sulfur dioxide. It also generates
particulate matter in form of sulfate aerosols. Petroleum diesel has 0.0015-0.05% of sulfur by
mass and the corresponding sulfur dioxide emission is 10-150 ppmv. [14]
Modern diesel engines
emits lesser sulfur compounds, approximately10 ppmv, and older diesel engines produce higher
sulfur emissions, close to 150 ppmv. [27]
Biodiesels are free from sulfur compounds. Hence sulfur
dioxide emissions can be reduced by using biodiesel.
[5.6] Polycyclic Aromatic Hydrocarbons (PAHs). PAHs are hydrocarbons containing two or
more benzene rings. PAHs are carcinogenic; hence, it is toxic to humans. Biodiesels are free
from PAHs compounds. Petroleum diesel has 30% PAH by mass. [14]
Hence it is evident that
biodiesel has zero PAH emissions and is much safer than its fossil based counterpart.
The relative emissions of biodiesel with respect to petroleum are summarized in the following
table.

12. Page - 12/22
Table 5.1 Relative emissions with respect to petroleum diesel
B100 (% v/v) B20 (% v/v)
Nitrogen Oxides (NOx) 12 % 6 %
Particulate Matter (PM) – 60 % – 20 %
Hydrocarbons (HC) – 70 % – 32 %
Carbon Monoxide (CO) – 50 % – 15 %
Sulfur ≈ 0 ≈ 0
PAH ≈ 0 ≈ 0
The ‘–’ sign indicates reduction with respect to the baseline fuel (petroleum fuel).
[6] BIODIESEL TRENDS
[6.1] Timeline: Production and Consumption
The economics of biodiesel has grabbed overwhelming attention in the last ten years (2006-
2015). During this period, the average annual consumption of biodiesel has increased from
260.93 MGal to 1494.15 MGal. This corresponds to an increase of over 472% in a span of ten
years. It corresponds to 50% annual biodiesel consumption growth rate. The total biodiesel
consumed since 2001 is 9842.59 million gallons. In other words, close to one billion gallons of
petroleum diesel, was saved during this period.
Table 6.1: Annual production and consumption of biodiesel in United States
Year Production
(MGal)
Annual Increase
in Production (%)
Consumption
(MGal)
Annual Increase
in Consumption
(%)
2001 8.58 - 10.27
2002 10.48 22.23 16.36 59.34
2003 14.21 35.54 13.51 – 17.43
2004 27.98 96.92 26.84 98.68
2005 90.79 224.45 90.83 238.39
2006 250.44 175.85 260.93 187.27
2007 489.83 95.59 353.71 35.56
2008 678.11 38.44 303.56 – 14.18
2009 515.81 – 23.93 321.83 6.02
2010 343.45 – 33.42 260.08 – 19.19
2011 967.48 181.70 886.17 240.74

13. Page - 13/22
2012 990.71 2.40 899.05 1.45
2013 1359.46 37.22 1428.84 58.93
2014 1278.98 – 5.92 1416.86 – 0.84
2015 1263.34 – 1.22 1494.15 5.46
2016 1555.54 23.13 2059.62 37.85
Total Production
(since 2001):
9845.17 MGal
Total Increase
(since 2001):
18036.20 %
Total
Consumption
(since 2001):
9842.59 MGal
Total Increase
(since 2001):
19958.68 %
Source: U.S. Energy Information Administration
MGal stands for Mega Gallon. 1 MGal = 1,000,000 gallon
The above data is plotted in the following figure. It is evident that consumption of biodiesel
steeply increases over time. The trend (orange broken line) is rampantly upward and indicates a
high potential for biodiesel in near future.
Figure 6.1 Biodiesel trends in United States: Annual production and consumption
The following figure shows the annual growth rate of biodiesel consumption. The maximum rate
of growth was observed at two time points 2004-2005 and 2010-2011, which is six years apart. If
this follows the same trend, 2016-2017 must have had a peak. But data shows it did not. A
0.00
500.00
1000.00
1500.00
2000.00
2500.00
2001 2003 2005 2007 2009 2011 2013 2015
AnnualAmount(milliongal)
Time
BIODIESEL TRENDS
Consumption (Mgal) Production (Mgal) Poly. (Consumption (Mgal))

14. Page - 14/22
convincing reason for this is hydraulic fracturing (fracking), which shifted the demand for oil to
natural gas.
Figure 6.2 Annual growth rate of biodiesel consumption
[6.2] Scenario Analysis: Alternative (B20) and Hypothetical (B100) Scenarios
The emission savings achieved by using biodiesel instead of petroleum diesel for different
scenarios is estimated below. On a side note; the following emission estimations are for an ideal
case and at 70% engine loading.
Amount of CO2 emitted in Diesel = 161.3 lb/MBtu
Amount of Energy per unit Diesel combusted = 138490 Btu/gal
Amount of CO2 per unit volume Diesel combusted = 22.33 lb/gal
Density of Petroleum Diesel = 6.94 lb/gal
Amount of CO2 per unit mass Diesel combusted = 3.21 lb/lb
Amount of CO2 per unit volume Diesel combusted = 1487.60 m3/m3
Diesel B20 B100
Fraction of CO2 in total emissions (Diesel) = 0.055 0.037 0
Fraction of NOx in total emissions (Diesel) = 0.000535 0.000565 0.000685
Fraction of CO in total
emissions (Diesel) = 0.00024 0.00022 0.00014
Fraction of HC in total
emissions (Diesel) = 0.000028 0.000025 0.000013
(The above fractions are based on volume.)
-50
0
50
100
150
200
250
300
2001 2003 2005 2007 2009 2011 2013 2015
AnnualIncrease
Year
ANNUAL GROWTH RATE
Annual Increase (Production) Annual Increase (Consumption)

15. Page - 15/22
[6.2.1] Alternative Scenario-1: If petroleum diesel had been used instead of biodiesel during the
period, 2001-2016. This is a hypothetical scenario.
The total biodiesel consumed during 2001-2016 is approximately 9.8 billion gallons. During this
period, instead of biodiesel, had petroleum diesel been used, it would have resulted in emission
excess of all emissions but NOx. The negative sign for NOx shows biodiesel has resulted in
emission of approximately 10.2 million tons of NOx (emission excess).
Alternative Scenario-1: Petroleum diesel instead of biodiesel during 2001-2016
Amount of Emissions for 9842590.00 x1000 gallons of fuel
Unit D-
Emissions
(m3/m3)
Unit D-
Emissions
(kg/gal)
Unit BioD-
Emissions
(kg/gal)
Million
Metric Tons
(If Diesel)
Million
Metric
Tons (If
B100
used)
Million
Metric Tons
Savings B100
Million
Metric Tons
Savings B20
CO2 81.8182 0.3794 0.0000 3734.2934 0.0000 3734.2934 746.8587
NOx 0.7959 0.0037 0.0047 36.3245 46.5089 – 10.1844 – 2.0369
CO 0.3570 0.0017 0.0010 16.2951 9.5055 6.7896 1.3579
HC 0.0417 0.0002 0.0001 1.9011 0.8827 1.0184 0.2037
[6.2.2] Alternative Scenario-2: Emission savings in near future, if biodiesel consumption is same
as the average consumption in the past five years (2011-2015).
The average annual rate of consumption of biodiesel during 2011-2015 is 1.2 billion gallons. If
the consumption follows the same rate in the following years, there would be significant savings
in emissions as shown in the following table.
Alternative Scenario-2: Annual average biodiesel consumption during 2011-2015
Amount of Emissions for 1225000.00 x1000 gallons of fuel
Unit D-
Emissions
(m3/m3)
Unit D-
Emissions
(kg/gal)
Unit BioD-
Emissions
(kg/gal)
Million
Metric Tons
(If Diesel)
Million
Metric
Tons (If
B100
used)
Million
Metric Tons
Savings B100
Million
Metric Tons
Savings B20
CO2 81.8182 0.3794 0.0000 464.7668 0.0000 464.7668 92.9534
NOx 0.7959 0.0037 0.0047 4.5209 5.7885 – 1.2675 – 0.2535
CO 0.3570 0.0017 0.0010 2.0281 1.1830 0.8450 0.1690
HC 0.0417 0.0002 0.0001 0.2366 0.1099 0.1268 0.0254
[6.2.3] Alternative Scenario-3: If biodiesel completely replaces petroleum diesel in near future.

16. Page - 16/22
The average annual rate of petroleum diesel consumption during 2011-2015 is approximately
37.2 billion gallons. Instead, had B100 or B20 is used in place of petroleum diesel, it would have
resulted in significant emission savings as shown in the following table.
Alternative Scenario-3: Annual average petroleum diesel consumption during 2011-2015.
Amount of Emissions for 37171980 x1000 gallons of fuel
Unit D-
Emissions
(m3/m3)
Unit D-
Emissions
(kg/gal)
Unit BioD-
Emissions
(kg/gal)
Million Metric
Tons (If
Diesel)
Million
Metric
Tons (If
B100
used)
Million
Metric Tons
Savings B100
Million
Metric Tons
Savings B20
CO2 81.8182 0.3794 0.0000 14103.1050 0.0000 14103.1050 2820.6210
NOx 0.7959 0.0037 0.0047 137.1847 175.6478 – 38.4630 – 7.6926
CO 0.3570 0.0017 0.0010 61.5408 35.8988 25.6420 5.1284
HC 0.0417 0.0002 0.0001 7.1798 3.3335 3.8463 0.7693
From the above analysis, it is evident that biodiesel generates significantly lesser emissions than
petroleum diesel, except NOx. Biodiesel is highly recommended considering the magnitude of
savings achieved. This further validates that biodiesel is a superior alternative to petroleum diesel
and a promising fuel of the future.
[7] CHALLENGES
Biodiesel as a fuel do not have any limitations, but biodiesel as an automobile fuel has some
challenges because the existing diesel engines are targeted for petroleum diesel. The higher
viscosity of biodiesel is likely to result in sedimentation and deposition. At the same time, it is
beneficial in lubricating the cylinder walls.
The experimental results with respect to biodiesel emissions is influenced by fuel injection,
engine speed and loading condition. These are factors associated with engine type. For example,
emission of particulate matter is higher at full-loads and at higher engine speeds. Hence it is
challenging to compare the performance of biodiesel between different biodiesel sources when
there is a high variation associated with engine factors.
Though biodiesel ‘blends’ are found to be an ideal choice for trading-off emission benefits and
engine power drawbacks, it cannot be used as such. While B5 can be used in place of petroleum
diesel, moderate and higher blends such as B20 and B70 respectively, cannot be used without the
manufacturer’s assurance.

17. Page - 17/22
Regarding engine exhaust emissions, biodiesel generates higher NOx than petroleum diesel. This
can be overcome by installing appropriate control technologies before releasing it into the
atmosphere. Selective catalytic reduction is one way to control automobile NOx.
[8] CONCLUSION
Based on the above discussion, following three points can be concluded.
1. The properties of biodiesel significantly differ from that of petroleum diesel. Those which
have pronounced effect are viscosity, oxygen content and heating value. The properties that
are favorable to biodiesel is oxygen content. The properties that are unfavorable to biodiesel
are viscosity, heating value, brake specific fuel consumption, flash point and cetane number.
However, it is with respect to engine performance this becomes unfavorable.
2. The emissions generated by biodiesel are cleaner than petroleum diesel. The emissions that
are favorable to biodiesel are particulate matter, hydrocarbons and carbon monoxide. It was
observed that B20 results in reduction of these pollutants by 20%, 32% and 15%
respectively. In addition, biodiesel emissions are free from sulfur and aromatic compounds.
However, with respect to NOx emissions, biodiesels are unfavorable.
3. The timeline of biodiesel consumption shows a strong increasing trend. The consumption in
2016 is more than 200 times of the consumption in 2001. Assuming the consumption of
petroleum diesel in near future is not less than the average of past five years (2011-2015),
replacing conventionally used petroleum diesel by biodiesel could save a net annual
emissions of 2820.6 million metric tons of carbon dioxide. The corresponding reduction in
carbon monoxide and hydrocarbons are 5.1 and 0.8 million metric tons respectively. It is
highly certain that an enormous amount of particulate matter emissions could be reduced. (At
the time of making this document, it could not be quantified due to insufficient data.)

18. Page - 18/22
[9] ACKNOWLEDGEMENT
The author would like to acknowledge two people who were instrumental in making of this
project.
1. Dr. Myoseon Jang
Associate Professor, Department of Environmental Engineering Sciences, University of
Florida.
Atmospheric and Air Quality Scientist (Specialty: Heterogeneous Chemistry of Organic
Compounds, Air Pollutant Characterization and Modeling)
2. Mr. Trevor Tilly, PhD Student (Advised by Professor Dr. Myoseon Jang)
Graduate Student Research Assistant, Department of Environmental Engineering Sciences,
University of Florida.

19. Page - 19/22
[10] REFERENCES
[1] Energy Information Administration - United States, Monthly Energy Review, Biodiesels and
other renewable fuels overview, Retrieved: April 10, 2017.
https://www.eia.gov/totalenergy/data/monthly/index.php#renewable
[2] Environmental Protection Agency - United States, A comprehensive analysis of biodiesel
impacts on exhaust emissions, Retrieved: April 10, 2017.
https://www3.epa.gov/otaq/models/analysis/biodsl/p02001.pdf
[3] Bureau of Transportation Statistics, Diesel-powered Passenger Cars and Light Trucks,
Retrieved: April 10, 2017.
https://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/bts_fact_sheets/oct_2015/htm
l/entire.html
[4] Alternative Fuels Data Center, Biodiesel Blends, Retrieved on April 10, 2017,
http://www.afdc.energy.gov/fuels/biodiesel_blends.html
[5] Buyukkaya, E. (2010). Effects of biodiesel on a DI diesel engine performance, emission and
combustion characteristics. Fuel, 89(10), 3099-3105.
[6] Szybist, J.P., Song, J., Alam, M., Boehman, A.L. (2007).Biodiesel combustion, emissions
and emission control. Fuel processing technology, 88(7), 679-691.
[7] Palash, S. M., Kalam, M. A., Masjuki, H. H., Masum, B. M., Fattah, I. R., & Mofijur, M.
(2013). Impacts of biodiesel combustion on NO x emissions and their reduction approaches.
Renewable and Sustainable Energy Reviews, 23, 473-490.
[8] Schumacher, L. G., Marshall, W., Krahl, J., Wetherell, W. B., & Grabowski, M. S. (2001).
Biodiesel emissions data from series 60 DDC engines. Transactions-American Society of
Agricultural Engineers, 44(6), 1465-1468.
[9] Zou, L., & Atkinson, S. (2003). Characterising vehicle emissions from the burning of
biodiesel made from vegetable oil. Environmental technology, 24(10), 1253-1260.
[10] Dincer, K. (2008). Lower emissions from biodiesel combustion. Energy Sources, Part A,
30(10), 963-968.

20. Page - 20/22
[11] Bakeas, E., Karavalakis, G., & Stournas, S. (2011). Biodiesel emissions profile in modern
diesel vehicles. Part 1: Effect of biodiesel origin on the criteria emissions. Science of the total
environment, 409(9), 1670-1676.
[12] Karavalakis, G., Boutsika, V., Stournas, S., & Bakeas, E. (2011). Biodiesel emissions
profile in modern diesel vehicles. Part 2: Effect of biodiesel origin on carbonyl, PAH, nitro-PAH
and oxy-PAH emissions. Science of the total Environment, 409(4), 738-747.
[13] Rounce, P., Tsolakis, A., Leung, P., & York, A. P. E. (2010). A comparison of diesel and
biodiesel emissions using dimethyl carbonate as an oxygenated additive. Energy & Fuels, 24(9),
4812-4819.
[14] Lapuerta, M., Armas, O., & Rodriguez-Fernandez, J. (2008). Effect of biodiesel fuels on
diesel engine emissions. Progress in energy and combustion science, 34(2), 198-223.
[15] Wang, W. G., Lyons, D. W., Clark, N. N., Gautam, M., & Norton, P. M. (2000). Emissions
from nine heavy trucks fueled by diesel and biodiesel blend without engine modification.
Environmental Science & Technology, 34(6), 933-939.
[16] Monyem, A., & Van Gerpen, J. H. (2001). The effect of biodiesel oxidation on engine
performance and emissions. Biomass and bioenergy, 20(4), 317-325.
[17] McCormick, R. L., Graboski, M. S., Alleman, T. L., Herring, A. M., & Tyson, K. S. (2001).
Impact of biodiesel source material and chemical structure on emissions of criteria pollutants
from a heavy-duty engine. Environmental science & technology, 35(9), 1742-1747.
[18] Ireland, J., McCormick, R., Yanowitz, J., & Wright, S. (2009). Improving biodiesel
emissions and fuel efficiency with fuel-specific engine calibration (No. 2009-01-0492). SAE
Technical Paper.
[19] Hoekman, S. K., & Robbins, C. (2012). Review of the effects of biodiesel on NOx
emissions. Fuel Processing Technology, 96, 237-249.
[20] Nabi, M. N., Akhter, M. S., & Shahadat, M. M. Z. (2006). Improvement of engine
emissions with conventional diesel fuel and diesel–biodiesel blends. Bioresource Technology,
97(3), 372-378.

21. Page - 21/22
[21] Fontaras, G., Karavalakis, G., Kousoulidou, M., Tzamkiozis, T., Ntziachristos, L., Bakeas,
E., ... & Samaras, Z. (2009). Effects of biodiesel on passenger car fuel consumption, regulated
and non-regulated pollutant emissions over legislated and real-world driving cycles. Fuel, 88(9),
1608-1617.
[22] He, C., Ge, Y., Tan, J., You, K., Han, X., Wang, J., ... & Shah, A. N. (2009). Comparison of
carbonyl compounds emissions from diesel engine fueled with biodiesel and diesel. Atmospheric
Environment, 43(24), 3657-3661.
[23] Chai, M., Lu, M., Liang, F., Tzillah, A., & Dendramis, N. (2013). The use of biodiesel
blends on a non-road generator and its impacts on ozone formation potentials based on carbonyl
emissions. Environmental pollution, 178, 159-165.
[24] Alternative Fuels Data Center, Fuel Properties Comparison, Retrieved: April 14, 2017.
http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf
[25] Guider, T. P. (2008). Characterization of Engine Performance with Biodiesel Fuels
(Doctoral dissertation, Masters Thesis, Lehigh University).
[26] Xue, J., Grift, T. E., & Hansen, A. C. (2011). Effect of biodiesel on engine performances
and emissions. Renewable and sustainable energy reviews, 15(2), 1098-1116.
[27] Nett Technologies Inc., What are diesel engines, Retrieved: April 13, 2017,
https://www.nettinc.com/information/emissions-faq/what-are-diesel-emissions
[28] Dieselnet, Emission Standards, Retrieved: April 13, 2017,
https://www.dieselnet.com/standards/
[29] Shirneshan, A. (2013). HC, CO, CO2 and NOx emission evaluation of a diesel engine
fueled with waste frying oil methyl ester. Procedia-Social and Behavioral Sciences, 75, 292-297.
[30] Reşitoğlu, İ. A., Altinişik, K., & Keskin, A. (2015). The pollutant emissions from diesel-
engine vehicles and exhaust after treatment systems. Clean Technologies and Environmental
Policy, 17(1), 15-27.