Journal of Sustainable Bioenergy Systems, 2013, 3, 272-286
Published Online December 2013 (http://www.scirp.org/journal/jsbs)
http://dx.doi.org/10.4236/jsbs.2013.34037
Open Access JSBS
Engine Performance and Exhaust Emissions of
Peanut Oil Biodiesel
Bjorn S. Santos*, Sergio C. Capareda, Jewel A. Capunitan
Department of Biological and Agricultural Engineering, Texas A&M University, College Station, USA
Received June 14, 2013; revised July 6, 2013; accepted August 5, 2013
Copyright © 2013 Bjorn S. Santos et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
The engine performance and exhaust emissions of biodiesel produced from peanut oil must be evaluated to assess its
potential as an alternative diesel fuel. In this study, two diesel engines rated at 14.2 kW (small) and 60 kW (large) were
operated on pure peanut oil biodiesel (PME) and its blends with a reference diesel (REFDIESEL). Results showed that
comparable power and torque were delivered by both the small and large engines when ran on pure PME than on REF-
DIESEL while brake-specific fuel consumption (BSFC) was found to be higher in pure PME. Higher exhaust concen-
trations of nitrogen oxides (NOx), carbon dioxide (CO2) and total hydrocarbons (THC) and lower carbon monoxide (CO)
emissions were observed in the small engine when using pure PME. Lower CO2, CO and THC emissions were obtained
when running the large engine with pure PME. Blends with low PME percentage showed insignificant changes in both
engine performance and exhaust emissions as compared with the reference diesel. Comparison with soybean biodiesel
indicates similar engine performance. Thus, blends of PME with diesel may be used as a supplemental fuel for steady-
state non-road diesel engines to take advantage of the lubricity of biodiesel as well as contributing to the goal of lower-
ing the dependence to petroleum diesel.
Keywords: Biodiesel; Peanut Oil; Engine Performance; Exhaust Emissions
1. Introduction
Growing concerns over possible scarcity in petroleum
fuel reserves as well as increasing awareness on global
environmental issues prompted the development and uti-
lization of non-petroleum based fuels that are clean, sus-
tainable and renewable [1,2]. Oils from biomass are a po-
tential alternative to petroleum-based fuels; however,
their high viscosity limits their application as engine fuel
and therefore must be modified prior to utilization [3].
Hence, transesterification of the oils should be done to
improve their properties, producing a product termed as
biodiesel.
Biodiesel is a mixture of monoalkyl esters of long
chain fatty acids (FAME) derived from a renewable lipid
feedstock, such as vegetable oil or animal fat [1,2,4]. It
can be produced from the transesterification of any
triglyceride feedstock, which includes oil-bearing crops,
animal fats and algal lipids [5]. The feedstock commonly
utilized for biodiesel production depends upon the coun-
try’s geographical, climatic and economic conditions.
Rapeseed and canola oil are mainly used in Europe, palm
oil in tropical countries and soybean oil and animal fats
in the US [6]. However, the supply of these feedstocks
may not be enough to displace all petroleum-based diesel
(petrodiesel) usage. In the US, soybean oil alone cannot
satisfy the demand of feedstock quantity for biodiesel
pro- duction since it accounts for only 13.5% of the total
production [7] and only an estimated 6% of petrodiesel
demand can be replaced if all US soybean production
were utilized as biodiesel feedstock [8]. Consequently,
alternative feedstocks were identified such as sunflower,
moringa, hazelnut and jatropha seed oils among others
[9-12]. Peanut is a potential oilcrop as it contains the
high amount of oil (40% - 50% of the mass of dried nuts)
[13] as compared to only about 15% - 20% for soybean
oil [14]. The US Department of Agriculture reports an
annual peanut yield of 4.70 metric tons per ha, which is
almost twice as that for soybean (2.66 metric tons per ha)
[15]. Thus, oil yield for peanuts can reach as much as
1059 L/ha while it is only 446 L/ha for soybean oil [14].
Biodiesel production from peanut oil has been studied
by few researchers. Nguyen et al. [3] studied peanut oil
*Corresponding author.

B. S. SANTOS ET AL. 273
extraction using diesel-based reverse-micellar microemul-
sions. Their product is a peanut oil-diesel blend which
was tested for peanut oil fraction, viscosity, cloud point
and pour point, all of which met the requirements for bio-
diesel fuel. Moser [16], on the other hand, prepared me-
thyl esters from high-oleic peanut oil using catalytic so-
dium methoxide and obtained 92% yield of peanut me-
thyl esters which exhibited excellent oxidative stability
but poor cold flow properties. A study by Kaya et al. [17]
showed ester conversion of 89% via sodium hydrox-
ide-catalyzed transesterification of solvent-extracted oil
from peanuts grown in Turkey. The obtained biodiesel
has a viscosity close to petrodiesel but has calorific value
6% less than that for petrodiesel. Important fuel proper-
ties such as density, flash point, cetane number, pour
point and cold point fall within the set standards.
Another important aspect in biodiesel research that
must be considered is the assessment of its performance
as an engine fuel. Studies involving the application of
peanut oil biodiesel in an engine are very limited in lit-
erature. A number of studies discussed the performance
of biodiesel from other feedstocks such as soybean, sun-
flower, canola, in an engine which specifically has the
effect of using biodiesel blends on engine power and fuel
economy [18]. However, engine performance may be
affected by the variation in biodiesel quality caused by
differences in the esterification process and the raw ma-
terials used, among others [19].
Aside from engine testing, emissions associated with
the use of biodiesel also need to be evaluated to assess its
cleanliness as a fuel. The Environmental Protection
Agency (EPA) reported that non-road diesel engines
have a substantial role in contributing to the nation’s air
pollution and therefore stricter emission standards were
imposed with regards to the amounts of particulate mat-
ter, nitrogen oxides and sulfur oxides [20]. This necessi-
tates the analysis of biodiesel emissions to ensure com-
pliance with current EPA regulations.
Hence, this study was conducted to investigate the ap-
plication of peanut oil biodiesel as an engine fuel and
compared it with those of soybean oil biodiesel and a ref-
erence petroleum diesel. This study aims to: 1) assess
fuel properties of the peanut oil biodiesel in accordance
with ASTM standards; 2) determine the effect of blend-
ing percentage of biodiesel on the characteristic engine
performance (i.e. net brake power, torque and specific
consumption); 3) determine the relationship between
pollutant concentrations (i.e. NOx, THC, CO and CO2) in
a diesel engine exhaust and the percentage of biodiesel in
fuel blends; and 4) compare performance with exhaust
emissions when using peanut oil methyl ester (PME),
soybean oil methyl ester (SME) and a reference diesel
(REFDIESEL).
2. Materials and Methods
2.1. Materials
PME was prepared from previously extracted and refined
oils at the Bio-Energy Testing and Analysis (BETA) La-
boratory at Texas A & M University, College Station,
TX. The following conventional biodiesel reaction con-
ditions were used: reaction time, 1 h; weight of catalyst,
0.4 wt%. of initial oil weight; vol. of methanol, 15%·vol.
of oil; reaction temperature: 50˚C. The biodiesel obtained
was then blended with a reference diesel (REFDIESEL-
ULSD standard no. 2 reference fuel). The test fuels were
analyzed to determine if they meet ASTM 6751-07 stan-
dard.
Fuels and fuel blends are as follows:
5% PME-95% REFDIESEL-B5 PME
20% PME-80% REFDIESEL-B20 PME
50% PME-50% REFDIESEL-B50 PME
100% PME-0% REFDIESEL-B100 PME
Soybean oil biodiesel (SME) and the reference diesel
were purchased commercially.
2.2. ASTM Characterization of Biodiesel Fuels
ASTM characterization of the biodiesel was done to en-
sure that the test fuel used in the study conforms to the
ASTM D6751-08 standard (ASTM, 2008). Some of the
referenced procedures in the ASTM 6751 standard were
conducted in the BETA lab. Such procedures were: cloud
and pour point (ASTM D2500), flash point (ASTM D93),
water and sediment (ASTM D2709), kinematic viscosity
(ASTM D445), acid number (ASTM D664) and gross
heating value (ASTM D4809).
2.3. Engine Performance and Exhaust Emissions
Testing
Engine performance and exhaust emissions testing were
conducted at the BETA Lab engine testing facility. In-
strumentation needed to measure some of the EPA regu-
lated emissions, such as CO, CO2, NOx, THC, and SO2
were in place.
2.3.1. Test Equipment
The BETA lab uses two (2) test engines with their own
respective test beds and dynamometer set-ups. One of the
test engines was a 3-cylinder Yanmar 3009D diesel en-
gine rated at 14.2 kW. Table 1 lists the general specifica-
tions of the small and large test engine. The engine load
was controlled by a water-cooled eddy current absorption
dynamometer with a Dynamatic® EC 2000 controller.
The maximum braking power of the dynamometer was
rated at 22.4 kW (30 hp) at 6000 rpm.
The large test engine used in the study was an in-line,
4-cylinder, 4.5 L, four stroke, naturally aspirated John
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B. S. SANTOS ET AL.
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Table 1. General specifications for Yanmar 3009D and
JD4045DF150 diesel engines.
Specification Yanmar 3009D JD 4045DF150
Rated power 14.2 kW (19 hp)
at 3000 rpm
60 kW (80 hp) at
2700 rpm
Number of cylinders 3 4
Bore 72 mm 106 mm
Stroke 72 mm 127 mm
Displacement 0.879 L 4.5 L
Compression ratio 22.6:1 17.6:1
Combustion system Indirect injection Direct injection
Aspiration Natural Natural
Deere diesel engine. It was connected to a 450 HP water-
cooled eddy current inductor dynamometer (Pohl Asso-
ciates Inc., Hatfield, PA). The engine’s rated power was
at 80 HP with rated speed of 2500 rpm. The engine’s ge-
neral specifications were listed in Table 1. The engine
load and throttle were controlled by a multi-loop Inter-
Loc V dynamometer and throttle controller (Dyne Sys-
tems Inc., Jackson, WI).
2.3.2. In strume ntation and Data Acquisition
Equipment
Figure 1 shows the schematics of the data acquisition
system for the Yanmar 3009D and JD 4045DF150 diesel
engines. Instrumentation includes measurement of test
cell ambient conditions (barometric pressure, tempera-
ture, and humidity), engine speed and torque, fuel flow
rates, engine manifold pressures and temperatures, and
engine exhaust gaseous emissions measurements. Fuel
flow was measured with an AW positive displacement
gear type flow meter with 50% ± 1% duty cycle. Mani-
fold pressure measurements were taken by strain gauge
pressure transducers positioned in the exhaust and intake
manifolds. Temperature measurements were measured
with shielded type-K thermocouples at roughly the same
aforementioned locations as pressure. Engine brake tor-
que and speed were acquired from the dynamometer.
National Instruments (NI) data acquisition equipment
(DAQ) was installed in different parts of the test engines
and the test cell. A fiber optic cable connects the remote
computer to the NI PCI-7831R FPGA module. Thermo-
couples and pressure transducers were connected to the
SCXI 1320 and SCXI 1326 signal conditioning units.
Torque and engine speed data are collected using a NI
Labview program developed for this research. Exhaust
emissions, such as CO, NOx, and SO2 were measured
with electrochemical SEM sensors, while CO2 and total
hydrocarbons (THC) were measured with NDIR sensors,
all assembled in an Enerac™ model 3000E emissions
analyzer.
The emissions analyzer has a capability of measuring
0 to 3500 ppm NOx concentrations, 0 to 2000 ppm CO
and SO2 concentrations, with an accuracy of ±2% of
reading; 0 to 5% by volume total hydrocarbon concentra-
tions, and 0 to 20% CO2 concentrations with an accuracy
of ±5% of reading. In addition, it also measures the am-
bient temperature, stack temperature, stack velocity, and
test cell O2 concentrations.
2.3.3. Experimental Method
Engine power tests are conducted in accordance with
SAE Standard Engine Power Test Code for diesel en-
gines (SAE J1349 Revised MAR2008). Baseline engine
performance and emissions tests are performed using
ULSD reference diesel fuel. Engine performance data for
ULSD reference diesel were corrected to the standard
atmospheric conditions using the compression ignition
engine correction formula according to SAE J1349 -
MARCH2008.
Variables such as air and relative humidity are care-
fully monitored. Fuel temperature is controlled as out-
lined in the test procedure. Tests were conducted in a
randomized complete block design (RCBD) to prove that
the fuel sequence is not significant to the results of the
study. Response variables were the following: net brake
power (kW), torque (N-m), fuel consumption (L/h), NOx
concentrations (ppm), unburned hydrocarbon concentra-
tions (ppm), CO concentrations (ppm), and CO2 concen-
trations (%).
The BETA lab is equipped with a NI Labview pro-
gram that can perform remote-based switching of fuel
source. This provides changing of test fuels without
turning off the engine. At each fuel change, the fuel filter
was replaced and then the engine was warmed at idle
speed on the new fuel for 15 minutes to purge remaining
previous test fuel from the engine’s fuel system. Then,
the engine was operated at full throttle and prepared for
the next performance testing. Also, a new set of sintered
filters for the exhaust emissions analyzer was installed
prior to the next emissions testing.
The important sources of uncertainty in this study are:
1) Supply of consistent quality of fuel; 2) proper con-
trol over relevant engine parameters (e.g. speed and load);
and 3) proper use and calibration of the measurement
instruments. To minimize the first source of uncertainty,
test fuels were processed in such a way that it will match
up ASTM 6751 standard. Fresh batch of biodiesel was
used to ensure consistency of the fuel quality in the ex-
periment. The uncertainty associated with the second
source was minimized by depending on the proper con-
trol and use of engine instrumentation and controller
equipment. Parameters, such as engine speed, fuel flow
rate, and load accuracy were matched to within ±5 RPM,
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275
±1% of the reading, and ±0.05% of the rated output, re-
spectively. Finally, the uncertainty associated with the
third source was minimized by calibrating emissions
equipment each day prior to start of testing, and all other
instruments (pressure transducers, thermocouples, flow
rate meters, etc) on routine basis.
both PME and SME than that for REFDIESEL, an indi-
cation of good fuel quality in terms of safety during
transport, handling and storage [2]. Water and sediment
are below the maximum limit but the kinematic viscosity
for PME is higher by around 14% over the maximum
specified limit. Acid numbers are also below the speci-
fied limit. PME has higher cloud point than both SME
and REFDIESEL. Gross heating values are lower for
both biodiesels than that for REFDIESEL, with PME
having slightly higher value than SME. These differences
in fuel properties can lead to differences in engine per-
formance, as will be discussed in the succeeding para-
graphs.
In order to understand the effect of the biodiesel on en-
gine combustion efficiency, the brake specific fuel con-
sumptions (BSFC) for the test fuels and each fuel blend
were measured at peak torque condition. This condition
was chosen since it is the point of minimum air/fuel ratio
and maximum smoke [21]. Results were compared to
those of the control fuel using statistical analysis pro-
cedures (ANOVA and LSD).
3.2. Engine Performance
3. Results and Discussion
The performances of the engines at full load (the fuel
pump is at the maximum delivery setting) using test fuels
(PME, SME and PME-REFDIESEL blends) were deter-
mined in accordance to SAE J1349 Power test code pro-
cedures. Baseline engine performance and emissions
3.1. Characteristics of Test Fuels
Table 2 shows the characteristics of the test fuels PME,
SME and REFDIESEL as determined following ASTM
standards. The values of the flash point are higher for
Figure 1. Schematics of the data acquisition system for the Yanmar 3009D and JD 4045DF150 diesel engines.
Table 2. Properties of test fuels and the reference diesel according to ASTM standards.
Property Method Specifications Reference Diesel Peanut ME Soybean ME
Flash Point, ˚C D93 130 min. 128 190 199
Water and Sediment, vol% D2709 0.050 max <0.01 <0.05 <0.01
Kinematic Viscosity, 40˚C, mm2/s D445 1.9 - 6.0 2.3 7.0 4.7
Sulfur, ppm D5453 15 max Unknown Unknown 4
Cetane Number D613 47 min Unknown Unknown 55
Cloud Point, ˚C D2500 Report −35 15 −6
Carbon Residue, %mass D4530 0.050 max Unknown Unknown 0.01
Acid Number, mg KOH/g sample D664 0.50 max 0.04 0.13 0.19
Distillation temperature, ˚C D1160 360 max Unknown Unknown 329
Oxidation Stability, hours EN14112 3 min Unknown Unknown 7.2
Gross Heating Value, MJ/kg D4809 Report 42.7 39.2 38.8

B. S. SANTOS ET AL.
276
tests were performed using standard no. 2 ULSD fuel
(REFDIESEL). Corrected values of the net brake power
and brake-specific fuel consumption for ULSD, as de-
scribed earlier, were also presented in the following sec-
tions.
3.2.1. Net Brake Power
3.2.1.1. Small Engine
The net brake power at different engine speeds and fuel
blends during the operation of the 14.2-kW Yanmar
3009D engine is presented in Figure 2. At different en-
gine speeds, there is an initial gradually increasing trend
in power until a maximum is reached and then it falls
rapidly as the engine speed is further increased (Figure
2(a)). Power decreases after a maximum is reached due
to increase in friction at higher speeds. The net brake po-
wer, as defined by the Society of Automotive Engineers
[22], is a measure of the engine’s horsepower delivered
directly to the engine’s crankshaft without the loss in po-
wer caused by the accessories such as the gearbox, alter-
nator, differential, water pump, and other auxiliary com-
ponents such as power steering pump, muffled exhaust
system, etc.
(a)
(b)
Figure 2. Net brake power of the Yanmar engine at various
(a) engine speeds and (b) PME-REFDIESEL fuel ble nds.
Comparison of the engine brake power at different fuel
blends shows that there is negligible power loss when
using the different proportion of PME and REFDIESEL
(Figure 2(b)). There was even a slight increase of around
2.3% for B100 PME to a net brake power of 13.8 kW.
Several studies also observed a slight increase in po-
wer; one of which is reported by Usta et al. [23], where
the power slightly increased for the 5% sunflower oil
biodiesel (SFME)-diesel blend but decreased by about
2% - 3% for the 30% blend. Also, Moreno et al. [19]
showed no noticeable power loss when using 25, 50 and
75% blends of SFME and diesel, and even slightly
gained around 3% for the 25% blend. However, when
pure SFME was used, a slight loss was observed (~1.5%).
Song and Zhang [24] also observed that the engine brake
power and torque increased with the increase in biodiesel
percentage in the blends. Finally, Al-Widyan et al. [25]
found that the engine power was higher when using bio-
diesel than diesel.
The net brake power when using PME was also com-
pared to that when using SME, as shown in Figure 3.
SME followed a similar trend in net brake power at in-
creasing engine speed. It also had similar value of net
brake power with REFDIESEL (13.5 kW at engine speed
of 2940 rpm) and thus, slightly lower than PME (13.8
kW).
Some researchers explained that the increase in engine
power when using biodiesel can be attributed to the
higher viscosity of biodiesel, which enhances fuel spray
penetration, and thus improves air-fuel mixing [26-28].
Also, the high lubricity of biodiesel might result in re-
duced friction loss and thus improve the brake effective
power, as was proposed by Ramadhas et al. [29].
3.2.1.2. Large Engine
For the 4-cylinder-80-hp John Deere engine, the net
brake power at different engine speeds as shown in Fig-
Figure 3. Net brake power of the Yanmar engine using
PME, SME and REFDIESEL at varying engine spe ed.
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B. S. SANTOS ET AL. 277
ure 4(a) follows the same trend as with the small engine.
Comparison of the different fuel blends, however, showed
that there was a slight loss of power for B5 PME com-
pared to REFDIESEL (Figure 4(b)). B5 PME has 0.81%
less power than REFDIESEL (55.7 kW). An improve-
ment was also observed as the percentage of PME was
increased to 50% peanut oil biodiesel and 50% diesel
fuel. B50 PME obtained the highest peak power of 55.9
kW, which was 1% higher than REFDIESEL (not sig-
nificant). However, this improvement gradually disap-
pears as the percentage of PME in the blend was increas-
ed to B100 PME. A slight loss in power was observed for
B100 PME with 54.8 kW.
The net brake power for of PME at different engine
speeds in comparison with SME and REFDIESEL are
also presented in Figure 5. The corrected peak net brake
power using REFDIESEL was observed to be the highest
compared to the biodiesel fuels, although the differences
are not quite significant. Hence, PME yields as much as
the same power as SME and REFDIESEL.
3.2.2. Engine Torque
3.2.2.1. Small Engine
The engine torque at varying engine speed and fuel blends
were also obtained and shown in Figure 6. The torque is
a good indicator of an engine’s ability to do work and is
a function of engine speed. Similar to engine power, the
torque was gradually increasing at low speed and de-
creased rapidly after a maximum value was reached. Tor-
que decreases because the engine is unable to ingest a full
charge of air at higher speeds [30].
There was a slight variation in peak torque values for
PME-REFDIESEL blends compared to REFDIESEL.
The peak torque values for B5, B50 and B100 fuel blends
were higher than that for REFDIESEL. B20 PME obtained
the least peak torque value with 47.37 N-m, while B50
PME obtained the highest with 49.9 N-m.
3.2.2.2. Large Engine
The plots of peak torque values for the different fuel
blends and engine speeds for the large John Deere engine
are shown in Figure 7. The peak torque values for most of
the PME blends increased by as much as 2%. Peak tor-
que was measured from 287.1 N-m for B5 PME to 294.5
N-m for B50 PME at a speed of 800 rev/min. Torque va-
lues for B20 PME and B100 PME were observed at 289.3
N-m and 289.8 N-m, respectively.
The peak torque values in comparison with SME are
presented in Figure 8 and indicate similar values for PME
(289.8 N-m at 868.5 rpm) and SME (288.7 N-m at 854
rpm). A similar decrease in peak torque values as the en-
gine speed increased was observed just as seen in the small
engine performance study.
(a)
(b)
Figure 4. Net brake power of the John Deere engine at var-
ious (a) engine speeds and (b) PME-REFDIESEL fuel
blends.
Figure 5. Net brake power of the John Deere engine using
PME, SME and REFDIESEL at varying engine spe ed.
3.2.3. Brake Specific Fuel Consumption (BSFC)
3.2.3.1. Small Engine
The brake specific fuel consumption (BSFC) is a meas-
ure of fuel efficiency within the crankshaft of an internal
combustion engine and can be obtained by dividing the
rate of fuel consumption of the engine by the net brake
power [30]. Figure 9 shows the BSFC in relation to
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278
(a) (b)
Figure 6. Engine torque of the Yanmar engine at various (a) engine speeds and (b) PME-REF DIESEL fue l blends.
(a) (b)
Figure 7. Engine torque of the John Deere engine at various (a) engine speeds and (b) PME-REFDIESEL fuel blends.
Figure 8. Engine torque of the John Deere engine using
PME, SME and REFDIESEL at varying engine spe ed.
varying engine speed and fuel blends. The BSFC is shown
to decrease with an increase in engine speed until it rea-
ches a minimum value and further increases at higher
speeds. Greater friction losses at higher speeds contribute
to the increase in fuel consumption while at low speed,
the longer time per cycle results in higher heat loss, al-
lowing for more fuel consumption.
At peak torque conditions, the BSFC was found to in-
crease when using pure PME but has no significant dif-
ference among the REFDIESEL, B5 and B20 fuel blends.
REFDIESEL obtained a corrected brake-specific fuel
consumption of 270.2 g/kW-h. An increase in BSFC was
also observed by Moreno et al. [19], when they fueled a
four-cylinder, turbocharged, indirect injected Isuzu en-
gine with pure sunflower oil biodiesel. The BSFC in-
creased by approximately 12% higher than with pure die-
sel fuel. Kaplan et al also observed similar results [31].
Fuel consumption increases when using biodiesel due to
its low heating value, as well as high density and viscos-
ity as compared to a regular diesel [18].
The BSFC for PME was also compared with that for
SME and REFDIESEL as presented in Figure 10 at dif-
ferent engine speeds. At peak torque conditions, both
B100 SME and B100 PME have higher BSFC than
REFDIESEL at 14% and 9%, respectively. Statistical ana-
lysis showed significant diffrences among the values, e

B. S. SANTOS ET AL. 279
(a) (b)
Figure 9. Brake specific fuel consumption (BSFC) of the Yanmar engine at various (a) engine speeds and (b)
PME-REFDIESEL fuel blends.
Figure 10. BSFC of the Yanmar engine using PME, SME
and REFDIESEL at varying engine speed.
with SME having higher BSFC than PME.
3.2.3.2. Large Engine
The trends in BSFC when running the large John Deere
engine with different blends of PME and REFDIESEL and
engine speeds are shown in Figure 11. Results showed
that the BSFC increases as the percentage of PME in the
mixture increases (Figure 11(b)). B50 PME obtained the
highest BSFC with 325.3 g/kW-h, compared to only 248.8
g/kW-h for REFDIESEL.
Comparison of PME with SME and REFDIESEL in
Figure 12 shows that REFDIESEL obtained the lowest
BSFC with a value of 248.78 g/kW-h. Statistical analysis
showed that there is no strong evidence of difference
between the BSFC of PME and SME. A 17.2% increase
in BSFC was observed from SME compared to REF-
DIESEL. Similar explanation as with the small engine
can be applied in these observations.
3.2.4. Engine Performance Summary
To summarize, PME delivered similar power and torque
(a)
(b)
Figure 11. BSFC of the John Deere engine at various (a)
engine speeds and (b) PME-REFDIESEL fue l blends.
as compared with pure REFDIESEL and SME when
used in both small and large engines. Power is a function
of the engine geometry, speed, air/fuel ratio, efficiencies
and fuel properties. Assuming mechanical losses are sim-
ilar, and since there were no modifications made in
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B. S. SANTOS ET AL.
280
Figure 12. BSFC of the John Deere engine using PME, SME
and REFDIESEL at varying engine speed.
the injection rates or duration for an individual test fuel,
similar performance of PME with REFDIESEL may be
attributed to the positive effects of its properties such as
higher viscosity and lubricity.
Moreover, the rise in mass flow for all biodiesel fuels
as observed from both engines can be attributed to the
lower heating values of the test fuels. The heating value
affects the torque being produced and in order to match
that torque with REFDIESEL, pure biodiesel and its
blends with REFDIESEL will have to put more energy in
the engine, resulting to higher fuel consumption. The
BSFC at peak torque conditions for both engines were
higher when using both PME and SME than the REF-
DIESEL.
3.3. Exhaust Emissions
Since the composition of the fuel affects the emissions of
an engine, emissions from biodiesel fuel are also differ-
ent as compared to those of petroleum diesel. Due to its
higher oxygen content (~10 - 12 wt·%), biodiesel has less
heating value and yields less particle emissions. Addi-
tional advantage is the absence of sulfur in biodiesel,
thus removing the typical aerosols derived from sulfuric
acid formed during diesel fuel combustion. However, it
should be noted that the results can also be affected by
the type of engine and its condition [32]. Some of the EPA
regulated emissions determined in this research were CO,
CO2, NOx, SO2, and total hydrocarbons.
3.3.1. Small Engine Emissions
The emission concentrations for PME and its blends at
peak torque conditions are shown in Figure 13. The NOx
concentration was found to increase as the percentage of
PME biodiesel in a blend is increased, reaching as high
as 30% when using pure PME (Figure 13(a)). The same
was observed by many other researchers concerning the
NOx emissions when using biodiesel. A maximum of
15% increase in NOx emissions for B100 was observed
by Nabi et al. [33] at high load condition which was at-
tributed to the 12% oxygen content of the B100 and
higher gas temperature in combustion chamber. A greater
increase in NOx emissions (22.1%) was observed by
Ozsezen et al. [34] when they employed waste palm oil
biodiesel on a 6-cylinder WC, NA, DI diesel engine while
canola biodiesel produced NOx emissions higher than
petrodiesel by 6.5%. The increase in NOx emissions
could have been affected by the differences in the fuel
properties between diesel and biodiesel. According to
Moser et al. [35], the higher density and viscosity of the
biodiesel imply that the differential pressure at the ad-
vance piston contained in the distributor pump is slightly
increased, which in turn advances injection. Also, the
amount of fuel injected per cycle could also be affected
by variations in density in the fuel. In addition, the fuel
spray properties might also be modified due to increases
in the size of the droplets of the fuel, thus affecting
burning of the fuel [35]. The increase in NOx emissions
could also be related to the higher oxygen content of bio-
diesel, as it may provide additional oxygen for NOx for-
mation [21].
For the CO2 emissions, as shown in Figure 13(d),
REFDIESEL had the least CO2 concentration (7%) while
PME has approximately 18% more emissions. Other re-
searchers also report that the CO2 emissions increase
when an engine is ran on biodiesel due to more efficient
combustion [29,36-40]. Nevertheless, others reason out
that this can be offset by planting and raising biodiesel
crops as supported by life-cycle assessment of CO2 emis-
sions from biodiesel [39,41]. About 50% - 80% reduction
in CO2 emissions can be obtained when using biodiesel
[42].
THC concentrations also increased by as much as 30%
when B100 PME (14 ppm) was used as compared with
REFDIESEL (10.78 ppm). However, there is no definite
trend that can be seen for the fuel blends (Figure 13(c)).
A similar increase in hydrocarbon emissions was observed
by Munoz [32] at high engine speed and load. They ex-
plained that hydrocarbon emissions increased since the
higher density and viscosity of biodiesel changes the cha-
racteristics of the fuel jet, i.e. size of droplets, penetration,
etc., liberated by the injector. It also increases the amount
of fuel retained in the interior of the injector nozzle, and
therefore cannot be incorporated in the combustion cham-
ber immediately, causing an increase in the hydrocarbons
without burning.
The CO concentration was found to decrease with an
increase in the percentage of PME in the fuel blends
(Figure 13(b)). A decrease of 29% in CO concentrations
where observed as the mixture increase from 0 to 50%
PME fuel. Similar decrease (around 30%) as compared to
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B. S. SANTOS ET AL.
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281
(a) (b)
(c) (d)
(e)
Figure 13. Various exhaust emission concentrations using different PME-REFDIESEL fuel blends for the Yanmar diesel
engine.
petrodiesel was observed by Puhan et al. [43] when they
used Mahua oil biodiesel. Utlu et al. [44] observed a
17.1% decrease when using waste frying oil biodiesel
and Wu et al. [45] reports an average of 4% - 16% CO
reduction for five biodiesels. The lower CO emissions
can be attributed to the higher oxygen content of bio-
diesel as compared to petrodiesel which promotes com-
plete combustion and thus, reduction in CO emissions
[40,46-48].
Finally, there were no noticeable increase in the SO2
concentrations produced using PME and its blends with
REFDIESEL (Figure 13(e)). At peak torque conditions,
the SO2 concentrations stayed below 10 ppm levels, a
proof of the advantage of using biodiesel due to its low
sulfur content as compared with petroleum diesel.
The emissions of PME were also compared with those
when using SME as shown in Figure 14. SME has Higher
NOx concentrations than REFDIESEL while PME has clo-
ser values, but still higher (Figure 14(a)). CO and CO2
concentrations tend to decrease as the engine speed in-
creased and were relatively similar for both SME and
PME (Figures 14(b) and (c)). REFDIESEL, as expected,
has higher CO concentrations than the biodiesel fuels.
Total hydrocarbon concentrations seemed to be not af-
fected by the engine speed, but were slightly higher in
SME than in PME emissions (Figure 14(d)).
3.3.2. Large Engine Emissions
The emissions were also determined for the large
John-Deere engine as shown in Figure 15. Similar to the
observations in the small engine, the NOx concentration
increased as the percentage of PME in the blend in-
creased. The maximum increase was observed with B100
PME which has 18% highr NOx concentrations than
e

B. S. SANTOS ET AL.
282
(a) (b)
(c) (d)
(e)
Figure 14. Various emission concentrations of the Yanmar engine using PME, SME and REFDIESEL at varying engine
speeds.
REFDIESEL. CO2 and THC emissions have similar
trends in that they were observed to increase with B5
PME but decreased when the percentage of PME in the
fuel blend is increased. The trend in CO emissions, on
the other hand, was found to be similar to that for the
small engine. The lowest CO concentration was observed
with B50 PME at 98 ppm, while B100 PME (8% higher
than B50 PME) has 109 ppm of CO concentrations. Fi-
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B. S. SANTOS ET AL. 283
(a) (b)
(c) (d)
(e)
Figure 15. Various exhaust emission concentrations using different PME-REFDIESEL fuel blends for the John Deere diesel
engine.
nally, SO2 concentrations, yields no definite trend and did
not seem to be affected by the changes in percentage of
PME in the test fuel.
Comparison of the emissions of PME with those of
SME is also presented in Figures 16. Generally, NOx
emissions tend to decrease as the speed of the engine is
increased (Figure 16(a)). REFDIESEL obtained the low-
est peak NOx concentrations with 454 ppm at 1203
rev/min and has slightly lower value than SME (522
ppm). PME has similar NOx emissions (521 ppm) with
SME.
CO2 concentrations were observed to gradually in-
crease as the speed was increased up to a certain point
(2050 rev/min) only and then decreased rapidly up to
peak power conditions (Figure 16(b)). CO2 emissions
were slightly higher for PME as compared with those of
SME but lower than those of REFDIESEL at intermedi-
ate engine speeds. CO and THC concentrations, on the
other hand, tend to peak as they approach peak power
conditions (Figures 16(c) and (d)). SME has higher THC
concentrations than PME but lower CO concentrations.
3.3.3. Exhaust Emissions Summary
Generally, NOx emissions were found to be higher when
using pure biodiesel (PME) than with the reference diesel
for both small and large engines. It also increases with
the increase in the percentage of PME in the fuel blends.
CO2 concentrations were also observed to increase in the
small engine when using pure PME but decreased in the
large engine. A notable increase in THC for the pure
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284
(a) (b)
(c) (d)
Figure 16. Various exhaust emissions of the John Deere engine using PME, SME and REFDIESEL at varying engine speed.
PME in the small engine was observed while an increas-
ing trend with an increase in PME in the blend was ob-
served for the large engine. Similar trends in CO and SO2
emissions were observed in both small and large engines,
with CO decreasing in concentration with the increase in
PME in the blend and SO2 being lower than 10 ppm.
Differences in exhaust emission concentrations in PME
and PME-REFDIESEL blends were observed due to
changes in properties such as density, viscosity and hea-
ting values, as well as the composition of the fuel. These
altogether affect the fuel injection characteristics and the
mechanism of fuel burning, thus resulting in variation in
emission concentrations of the EPA regulated pollutants.
4. Conclusion
The engine performance and exhaust emissions were
evaluated for a small and large engine operated on pure
PME and its blends with a reference diesel. SME was
also tested for comparison purposes. Results showed that
comparable power and torque were delivered by both the
small and large engines when ran on pure PME while
BSFC was found to be higher as compared to the refer-
ence diesel. Analyses of the exhaust emissions of the
small engine when ran on pure PME showed higher NOx,
CO2 and THC but lower CO emissions. The fuel blends
at the lower end showed insignificant changes in the ex-
haust emissions. The large engine also produced higher
NOx emissions but lower CO2, CO and THC emissions
when ran on pure PME. SO2 remained below 10 ppm and
lower than that produced by the reference diesel. Based
on these observations, biodiesel may be used as a sup-
plemental fuel for steady-state non-road diesel engines.
Using small percentage of fuel blends, such as B5 and
B20, resulted in insignificant changes in peak power and
BSFC as compared to that of pure diesel fuel. Hence,
consumers may choose to use these blends in order to
take advantage of the lubricity of biodiesel as well as
contributing to the goal of lowering the dependence to
petroleum diesel.
5. Acknowledgements
We gratefully acknowledge the Houston Advanced Re-
search Center (HARC) for financial support of this pro-
ject.
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