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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

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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

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[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.

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[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.

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[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.

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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

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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]

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[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]

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[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.

𝑁𝑂𝑥𝐵𝐷

𝑁𝑂𝑥𝑃𝐷= 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

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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.

𝑃𝑀𝐵𝐷

𝑃𝑀𝑃𝐷= 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.

𝑇𝐻𝐶𝐵𝐷

𝑇𝐻𝐶𝑃𝐷= exp ( − 11195 ∗ 10−6 ∗ 𝑓𝐵𝐷)

Variables: THCBD – total hydrocarbon emissions from biodiesel; THCPD – total

hydrocarbon emissions from petroleum diesel; fBD – biodiesel blend percent (in %).

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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.

𝐶𝑂𝐵𝐷

𝐶𝑂𝑃𝐷= 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.

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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

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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

An

nu

al A

mo

un

t (m

illio

n g

al)

Time

BIODIESEL TRENDS

Consumption (Mgal) Production (Mgal) Poly. (Consumption (Mgal))

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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

An

nu

al In

crea

se

Year

ANNUAL GROWTH RATE

Annual Increase (Production) Annual Increase (Consumption)

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[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.

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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.

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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.)

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.

Page - 19/22

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