b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3

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Performance and emissions of a diesel tractor engine fueled

with marine diesel and soybean methyl ester

B. Gokalp b, E. Buyukkaya a,*, H.S. Soyhan a

a
Sakarya University, Engineering Faculty, Department of Mechanical Engineering, Esentepe Campus, 54187 Sakarya, Turkey
b
Kocaeli University, Engineering Faculty, Department of Mechanical Engineering, Izmit, Turkey

article info abstract

Article history: Biodiesel is an alternative fuel that is cleaner than petrodiesel. Biodiesel can be used
Received 23 June 2010 directly as fuel for a diesel engine without having to modify the engine system. It has the
Received in revised form major advantages of having high biodegradability, excellent lubricity and no sulfur
26 April 2011 content. This paper presents the results of investigations carried out in studying the fuel
Accepted 6 May 2011 properties of soybean methyl ester (SME) and its blend with marine diesel fuel from 5%,
Available online 12 June 2011 20% and 50% blends by volume and in running a diesel engine with these fuels. The results
indicate that the use of biodiesel produces lower smoke opacity (up to 74%), but higher
Keywords: brake specific fuel consumption (BSFC) (up to 12%) compared to marine fuel (MF). The
Diesel engine performance measured carbon monoxide (CO) emissions of B5 and B100 fuels were found to be 3% and
Emission 52% lower than that of the MF, respectively.
Marine fuel ª 2011 Elsevier Ltd. All rights reserved.
Soybean methyl ester

1. Introduction greenhouse gases to exceed which subsequently results in

temperature increase (global warming) and temperature
Recently, biodiesel has received significant attention both as decrease (global cooling) in the nature. The other major
a possible renewable alternative fuel and as an additive to the harmful emissions are CO, NOx and UHC. In addition, our
existing petroleum-based fuels. Biodiesel exhibits several energy reserves are decreasing proportionally to increasing
merits when compared to that of the existing petroleum fuels. energy demand [4]. So, in the last couple of decades alterna-
Many researchers have shown that particulate matter (PM), tive fuels have gained a great importance [5] and a lot of
unburned hydrocarbons (UHC), CO, and sulfur levels are researches have been made on this topic in this sense. Natural
significantly less in the exhaust gas while using biodiesel as gas, hydrogen, vegetable oil, alcohol and biogas are some of
fuel. However, an increase in the levels of oxides of nitrogen is the most important alternative fuels. The usage of bio-fuels
reported with biodiesel [1]. In addition, since biodiesel does and alcohols (ethanol, methanol) in the diesel fuels as
not contain carcinogens such as polyaromatic hydrocarbons a blend has been intensively researched in the last couple of
(HC) and nitrous polyaromatic hydrocarbons, it produces decades. The performance and exhaust emissions of diesel
pollutants that are less detrimental to human health [2]. engines using various biodiesels have been studied by many
According to Gokalp et al. [3] (2008) addition of biodiesel fuels investigators [6e8]. Marine engines account for about 30% of
to the standard diesel fuel enhances the emission character- nonroad engines, but as they tend to be concentrated in
istics of diesel engines. coastal areas (ports, recreational areas, lakes, rivers, etc.), the
Petroleum fuel emissions have harmful effects on the local levels of pollutants may become too concentrated.
nature. For example, uncontrolled CO2 increase causes Recreational sailboats powered by auxiliary diesel engines

* Corresponding author. Tel.: þ90 264 295 5864; fax: þ90 264 2955601.
E-mail address: ebkaya@sakarya.edu.tr (E. Buyukkaya).
0961-9534/$ e see front matter ª 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.biombioe.2011.05.015
3576 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3

have proven to be a reliable and high profile market for Bio- vegetable oil blends get close to that of diesel fuel. It was found
diesel. In 1997, CytoCulture surveyed 100 recreational boaters that rubber seed oil diesel could be alternatively used instead
in the San Francisco Bay area and found that 97% of the of diesel fuel when it is preheated or diluted [18]. According to
vessels using biodiesel from 1993 to 1997 were sailboats. Most [3] diesel fuels and marine fuels are also shown with extensive
of the boats were in the 30 to 50 foot range, and most had emission analysis that the addition of biodiesel fuels to the
smaller diesel engines (12e50 HP) that consumed relatively standard diesel fuel enhances the emission characteristics of
little fuel [9]. diesel engines.
Although biodiesel has many advantages when it comes to Monyem et al. [19] reported that fuel properties of biodiesel
fuel properties, it still has several properties that need to be might be affected by oxidation after the biodiesel was stored
improved, such as its lower calorific value, lower horsepower for a period of time. They heated a commercial biodiesel while
output, and its comparatively higher emission of nitrogen bubbling oxygen through it to simulate storage conditions.
oxides. Rakopoulos et al. [10] examined the use of sunflower They revealed that after this process the commercial biodiesel
and cottonseed oil methyl esters (biodiesels) of Greek origin as had a shorter ignition delay and lower hydrocarbons (HC)
supplements in the diesel fuel at blend ratios of 10/90 and 20/ emission [20]. Dorado et al [21] tested a three cylinder, four
80, in a fully instrumented, six-cylinder, turbocharged and strokes and 2500 cc direct injection diesel engine with olive oil
intercooled, direct injection (DI), Mercedes-Benz, mini-bus methyl ester. They reported a significant reduction in CO (up
diesel engine. They measured the fuel consumption, exhaust to 58.9%), CO2 (up to 8.6%, excepting step no. 2, which pre-
smokiness and exhaust regulated gas emissions such as sented a 7.4% increase), NO (up to 37.5%) and NOx (up to 32%)
nitrogen oxides, carbon monoxide and total unburned hydro- for used olive oil methyl ester compared to Diesel fuel. Puhan
carbons. Here, it is shown that all the biodiesel blends tested et al [22] tested mahua oil ethyl ester in a four-stroke naturally
could be used safely and advantageously in conventional aspirated direct injection diesel engine and have reported
diesel engines, at least in small blending ratios [10]. Ghobadian that emission of carbon monoxide, hydrocarbon, oxides of
et al. [11] employed biodiesel produced from waste vegetable nitrogen and smoke were decreased by 58, 63, 12 and 70%,
cooking oil of a restaurant. They found that power and respectively, in comparison with diesel.Kaplan et al [23]
performance with fuel blends were similar to net diesel fuel. compared sunflower-oil biodiesel and diesel fuels at full and
The BSFC was also similar to net diesel fuel. Brake thermal partial loads (the latter defined by constant fuel mass delivery)
efficiency for biodiesel was slightly increased in B20; HC, CO and at different engine speeds in a 2.5 l and 53 kW engine. The
and CO2 emissions were decreased with biodiesel while NOx loss of torque and power ranged between 5% and 10%, and
emission were slightly increased [12]. Devan and Mahalakshmi particularly at full load, the loss of power was closer to 5% at
[13] demonstrated that CO, HC and smoke emissions decrease, low speed and to 10% at high speed. Baldassarri et al [24]
but NOx emission slightly increase with the biofuel blends. tested a six-cylinder 7.8 l engine following the ECE R49 test
They also showed that the lower heating value of the blends cycle with 20% blends of rapeseed-oil biodiesel (with a glyc-
were similar to diesel fuel. Ozsezen et al [14] found that erin content of 1.15%) in diesel fuel. They measured a mean
maximum torque obtained with the WPOME (Waste Palm Oil BSFC increase of 2.95% with 95% statistical confidence.
Methyl Ester) and COME (Canola Oil Methyl Ester) bio-fuels was Bata and Roan [25] observed that the CO concentration
lower than that of PBDF (petroleum-based diesel fuel), brake with ethanol addition to unleaded gasoline decreased close to
specific fuel consumption was higher than that of PBDF and 40%e50% at a lean mixture, which was near to stoichiometry.
peak cylinder gas pressure obtained with COME was similar to They found that 20% ethanol fuels gave the best results of the
PBDF. They also showed that lower smoke, HC, CO2 and CO engine performance and exhaust emissions. Abu-Qudais et.al
emissions were obtained with bio-fuels. [26] also found that the optimum ethanol addition to diesel
According to [15] sensible performance and emission was about 15%e20%. According to their studies, while the
results obtained in short-term operation with the vegetable brake thermal efficiency (BTE) increased 7.5% with 20%
oils while some problems such as filter clogging, carbon ethanol addition as a fumigant, smoke emission and soot
deposits occurred in long-term duration. In the same mass concentration decreased 48% and 51%, respectively.
research, it was found that brake thermal efficiency was 1.61% Also, while BTE increased 3.6% with 15% ethanol addition to
lower, BSFC was 50 g/kwh higher and brake specific energy diesel fuel smoke emission and soot mass concentration
consumption (BSEC) was 867.11 kJ/kWh higher with net dec- decreased 33.3% and 32.5%, respectively. According to Agar-
can hemp vegetable oil than that of diesel fuel. In another wal [27], methanol addition to diesel fuel exceeds brake tor-
experimental study [16] it was found that the engine power que, volumetric efficiency and better anti-knock behavior
output and and the fuel consumption of the engine obtained with the increasing methanol ratio in the blend. Buyukkaya
with vegetable oil and its blends were so close to the results [28] observed that The smoke opacity reduction was 45% with
obtained with pure diesel. It was also found that NOx, CO and B70 while it was 60% with pure biodiesel. In the same
HC emissions were lower with vegetable oil and its blends research, it was found that the brake specific fuel consump-
than that of pure diesel. According to [15] engine power and tion of the B5, B20, B70 and B100 fuels were observed to be
brake mean effective pressure (BMEP) decreased slightly and higher by 2.5%, 3%, 5.5% and 7.5% than that of the diesel fuel,
BSFC increased slightly with the increasing ratio of jojoba oil respectively while brake thermal efficiency BTE of the engine
in the fuel blend. Vegetable oils have high viscosity compared is improved with increasing concentration of the biodiesel in
to diesel fuel that may cause some problems. According to [17] the blend except for B70. Many researchers have tested the
heating or diluting with other fuels could reduce viscosity of diesel engine with biodiesel in varying proportions as listed in
oils and with the increasing temperature viscosity of Table 1 [29].
 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3 3577

The marine diesel emissions of greatest concern are accuracies of the measured parameters and the uncertainties
released from large commercial and military ships because in the calculated parameters are given in Table 3.
they represent the largest source of marine emissions. Main The engine specifications are given in Table 4. The test
aim of this study is to investigate the effects of SME inclusion engine was coupled to a Schenk hydraulic dynamometer
on the performance and exhaust missions, fuel consumption providing a maximum engine power of 45 kW with a 0.1 kW
measurements, exhaust gas temperatures of direct injection of uncertainty to control engine speed and load. Engine speed
diesel engine fueled with soybean metyhl ester (SME), marine was measured by a digital tachometer with a resolution of
fuel and their fuel blends and all the experiments were per- 1 rpm. Full load characteristics of the DI diesel engine fueled
formed without any modification on the engine. It is also with SME, its blends and marine diesel fuels were at the
hoped that the new data presented here will help in devel- constant engine speeds, ranging from 1000 to 2400 rpm with
oping new predictive methods or procedures for this actual an interval of 200 rpm. In each speed, the maximum engine
problem. torque was reached for each fuel. In other words, the test
engine was operated at different torques when different fuels
were tested.
2. The biodiesel production and All load characteristics were taken of the engine perfor-
specifications mance on marine diesel fuel and SME. The three blends were
prepared by a splash mixing technique, which consists of
The biodiesel used in this study was provided from a local pouring the SME into a diesel container in the following
producer that uses a transesterification process together with proportions by volume; 50% marine fuel and 50% SME (B50),
methanol, which was catalyzed by potassium hydroxide. It is 80% marine fuel and 20% SME (B20), and 95% marine fuel and
crucially important to know how much potassium hydroxide 5% SME (B5). The each mixture separately was stored in the
is needed to neutralize the free fatty acids in soybean crude fuel tank. Before each fuel test, the fuel tank of 16-L capacity
oil. Through a titration analysis, it was found that 10.2 g of and fuel lines were drained, and the engine was operated at
potassium hydroxide per 1 L of soybean crude oil. It was least 15 min to stabilize on the new fuel. At each speed, the
pointed out that 250 ml of CH3OH and required amount of KOH engine was operated 5 min to achieve steady-state conditions,
were added into soybean crude oil and the reactions were and the data were collected in sixth minutes. Each test was
taken place at 42  C. A water spray system was used to wash repeated 3 times and the results of the three repetitions were
process and the equal amount of water and biodiesel mixture averaged. In each test, coolant and exhaust temperatures, fuel
was then thoroughly agitated for 12 min allowing the water to consumption, airflow rate, and exhaust emissions were
settle out of the biodiesel. The technical specifications of the recorded systematically. The fuel injection angle of the fuel
biodiesel purchased from the producer are given in Table 2. injection system was kept constant at 14 BTDC.
The exhaust gas temperature was measured using a ther-
mocouple connected to the exhaust pipe just downstream of
3. Experimental setup and procedure the exhaust manifold. The cooling water temperatures at the
inlet and outlet of the engine block were measured using “Pt
Tests have been conducted on a four-stroke, naturally aspi- 100” thermocouples. The fuel consumption of the engine was
rated four cylinder and direct injection diesel engine. The test determined by measuring the fuel level decrease in a measure-
engine and experimental set up are shown in Fig. 1. The ment container in a given period of time. The volumetric flow

Table 1 e Studies with various blends of diesel and biodiesel.

Author Fuel used Engine performance Emission values

Babu et al. Blends of soybean methyl ester Reduction of 20.2% for CO, 6.1% for
and diesel PM and 4.5% increase for NOx
emission. 16.7% reduction in THC.
Schumacher Blends of soybean methyl ester Recommendation for 20:80 blend Increase in NOx and reduction in other emissions
et al. and diesel
Kalligeros Blends of marine diesel and two Slight reduction in SFC Reduction in CO, HC, NOx and particulate
et al. types of biodiesel (sunflower and matter emissions
olive oil)
Ramadhas Blends of rubber seed oil and 50e80% rubber seed oil resulted in better
et al. diesel performance. Acceptable BTE,
SFC noticed for
blend with 80% rubber seed oil
Huzayyin Blends of jojoba oil and gas oil Negligible power loss, slight Reduction in NOx and soot emissions
et al. increase in BSFC as compared to gas oil.
Baldassarri Blend of 20% biodiesel and diesel Small reduction in emissions of most of the
et al. aromatic and polyaromatic compounds
Ali et al. Blends of diesel and methyl soyate Up to 30% methyl soyate, Reduction in exhaust emissions except NOx
in varying proportions no reduction in power
3578 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3

unburned hydrocarbons (HC) and smoke opacity were

Table 2 e Properties marine fuel and soybean methyl
ester (SME) oil. determined.

Fuel property Method Marine Fuel SME

(ASTM test) (MF)

Density (kg/m3), D1298 830 881 4. Results and discussions

15  C
Viscosity at D445 3.7 4.173 The effects of pure SME and its blends compared to those of
40  C (mm2/s) marine fuel on engine performance (engine power, torque,
Calorific value D4809 44.308 37.388
brake specific fuel consumption, brake thermal efficiency,
(MJ/kg)
Sulfur (wt. %) D 4294 0.29 e
mechanical efficiency) and emission (NOx, CO and soot
Flash point ( C) D93 75 105 opacity) have been studied for an unmodified diesel engine.
Cetane Index D976 45 e Fig. 2a shows the variation in engine power at full load for
Cetane number D613 e 50 different fuels. The results show that there are no noticeable
Cloud Point ( C) D97 6 e differences in the measured engine power output between
D2500 e 3
marine and B5 fuels. However, the measured engine power for
Particulate D5452 3 e
other blends is lower than that of the diesel fuel. Maximum
Matter (mg/L)
reduction in engine power for B20, B50 and B100 fuels is 2.35%,
3% and 5%, respectively. Lower heating value of the SME is
rate of the intake air was measured using a rotary type flow responsible for this reduction. Similar results were reported
meter. A surge tank located between the air flow meter and by Kaplan et al [23], who compared sunflower-oil biodiesel and
intake manifold was used for damping out the pulsations diesel fuels at full and partial loads and at different engine
produced by the engine, thus obtaining a steady airflow. After speeds in diesel engine. Their results showed a power reduc-
the engine reached the stabilized working condition, parame- tion between 5% and 10%. They also explained this power
ters like the speed of operation, fuel consumption and torque reduction with lower heating value of the biodiesel.
were measured. The brake power, brake specific fuel Fig. 2b shows the variation in engine torque at full load for
consumption and brake thermal efficiency were computed. All different fuels. Maximum torque was obtained at 1600 rpm for
observations recorded were replicated thrice to get a reasonable each kind of fuel. At 1600 rpm, power and torque of the diesel
value. A Bosch GMBH-ETD02050A model smoke meter was used and B5 fuels were almost imperceptible. At higher speeds, the
to measure the opacity in the exhaust gas by drawing 1.80 l of torque delivered with B5 fuel was a few higher than the torque
exhaust gas through a paper filter. delivered by marine fuel. But, a more pronounced torque drop
The exhaust emissions, namely CO, CO2 and NOx, were was observed for B20, B50 and B100 fuels, and the average
measured using Horiba gas analyzer. Further details of the torque drop between diesel and B20, B50 and B100 fuels is 2.29
instrumentation are summarized in Table 1. Nm, 3.68 Nm and 6.72 Nm, respectively.
First, marine fuel was used as fuel at the diesel engine. The higher viscosity and surface tension of biodiesel
Then, the engine was tested with soybean oil methyl ester prevent sufficient breaking of the biodiesel during injection
(SME). Then, 5%, 20% and 50% volumetric proportions of SME process. Various reasons, most of them related to viscosity,
with marine fuel named as B5, B20 and B50 were also tested, have been reported in the literature to explain the torque and
respectively. Physical characteristics of the tested fuels are power recovery (with respect to the loss of heating value) at
given in Table 2. All tests were performed under steady-state full load with respect to that obtained with diesel fuel. Kaplan
conditions. The brake thermal efficiencies (BTE) of the [23] compared pure soybean oil biodiesel with conventional
engine, the specific fuel consumption (BSFC), exhaust gas diesel in a turbocharged engine at 1400 rpm and full load
temperature, and exhaust emissions, such as nitrogen oxide equipped with two different injection pumps. He found that
(NOx), carbon monoxide (CO), carbon dioxide (CO2) and not only the mass of fuel but also the volume injected was

Fig. 1 e The schematic layout of the experimental setup.

 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3 3579

rapeseed-oil methyl. Consequently, fuel economy is lower on

Table 3 e The accuracies of the measurements and the
uncertainties in the calculated results. biodiesel as stated by Graboski et al. [2] it is observed that MF
appears to have a lower BSFC value than other blends.
Parameters Accuracy
The difference between the energy content of the fuel
Engine speed 1 rpm consumed and the useful power extracted from the engine is
Temperatures 1  C known as Thermal Efficiency (TE). The BTE of the test engine
CO 0.05%
as a function of engine speed at full load is shown in Fig. 2d. It
HC 10 ppm
is observed that pure SME yields maximum BTE, which is
CO2 0.1%
NOx 300 ppm  1% followed by the other blends in diminishing order. It is noticed
Smoke meter 0.1% that the use of oxygen-rich biodiesel promote a better
Calculated results Uncertainty combustion, thus improving the thermal efficiency compared
BSFC max. 2% to the other blends because of less heat transfer or less
BTE max. 2% exhaust loss.
At full load, brake thermal efficiency decreases with
increasing engine speed up to 2400 rpm. At 2400 rpm, the BTE
values are 0.348, 0.3522, 0.358, 0.378 and 0.423 for MF, B5, B20,
higher (1.2e3.2%) in the case of biodiesel. The higher viscosity B50 and B100, respectively. That is, BTE of the engine is
reducing the back flow across the piston clearance of the improved with increasing concentration of the biodiesel. The
injection pump was used to responsible for this reduction. possible reason for this is the additional lubricity provided by
Moreover, the difference in fuel delivery was reduced as the the biodiesel. Labeckas et al. [35] tested a 4750 cc engine under
injection temperature was increased, in accordance with the different steady modes using 5%, 10%, 20%, 35% blends with
corresponding decrease in viscosity. By contrast, when injec- diesel and pure rapeseed-oil biodiesel. They obtained higher
tion temperatures for diesel and biodiesel were adjusted to BTEs with 5e10% blends compared to the others. On the other
give close viscosities, then the diesel fuel delivery by volume hand, Ramadhas et al. [36] obtained higher BTEs with 10% and
was slightly higher as a consequence of its lower density 20% blends. This improved efficiency was explained by
enhancing the flow rate through orifices. authors as follows. The mixing of biodiesel in diesel oil yields,
The BSFC of the test engine as a function of engine speed at in general, good thermal efficiency curves. Initially the
full load is shown in Fig. 2c. At 1600 rpm, the BSFCs MF and thermal efficiency of the engine is improved with increasing
B100 fuels were 214 g/kWh and 240 g/kWh, respectively. BSFCs concentration of the biodiesel in the blend. The possible
of the B5, B20, B50 and B100 fuels were observed to be higher reason for this is the additional lubricity provided by the bio-
by 2.2%, 2.7%, 4% and 10.8% than that of the diesel fuel, diesel. The molecules of biodiesel contain some amount of
respectively. The higher fuel consumption of the B100 and oxygen, which takes part in the combustion process. Ram-
their blends could be primarily related to lower heating value adhas et al. observed that after a certain limit with respect to
of the B100. In this experiment, the SME’s lower heating value diesel ester blend, the thermal efficiency trend is reverted and
(LHV) is lower than the MF (LHVSME ¼ 37388 kJ/kg and it starts decreasing as a function of the concentration of blend.
LHVMARINE FUEL ¼ 44308 kJ/kg), it yields higher BSFC values. It is As seen in Fig. 2e, mechanical efficiency (ME) of the engine
generally accepted that fuel consumption is proportional to is decreasing by increased engine speed because of the
volumetric energy density of the fuel based upon the lower increase in friction loses. It is also seen that pure MF yields
and net heating value [2]. A large majority of authors reported maximum ME values while SME results in minimum ME.
that they found increases in biodiesel fuel consumption in The exhaust gas temperature of the engine as a function of
proportion to the biodiesel content in the blends and to the engine speed at full load is shown in Fig. 3a. It can be seen
loss of heating value [31e34]. Labeckas et al. [30] claimed that from the figure that biodiesel fuel and its blends give higher
the higher fuel consumption of the blends could be related to exhaust gas temperatures than MF for all of the engine speeds.
the lower, on average by 12.5% of net heating value of The increase in exhaust gas temperature increased with
increasing SME content and reached maximum at B100. Bio-
diesel that has a slightly lower cetane rating results in longer
ignition delay and slower burning rate [8]. This means late
Table 4 e Engine specifications. combustion in the expansion stroke, resulting in higher
Type of engine MR40 Basak tractor, direct exhaust and lubrication oil temperatures. In addition, a bio-
injection diesel may contain some constituents having higher boiling
points that are not sufficiently evaporated during the main
Cylinder number 4
combustion phase and continue to burn in the late combus-
Cylinder diameter (mm) 100
Stroke (mm) 100 tion phase [37]. This causes higher exhaust temperature.
Compression ratio 16.8/1 Higher ignition delay results in a delayed combustion and
Maximum engine power 40 (2400 rpm) higher exhausts gas temperatures. The gas temperature also
(kW) presented variations when the injection system was inspec-
Maximum engine torque 205 (1600 rpm) ted due to improved performance of diesel engine [5].
(Nm)
The emission characteristics of biodiesel are of special
Injection advance (CA) 14
Cylinder volume 3.14 l
interest regarding compliance with environmental standards.
The NOx emissions of the engine as a function of engine speed
3580 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3

at full load are shown in Fig. 3b. In a diesel engine, since the the high activation energy needed for the reactions involved.
formation of mixing fuel is heterogeneous, formation of NOx Hence the most significant factor that causes NOx formation is
was reached maximum level in regions where stoichiometric high combustion temperatures.
conditions exist. Resulting from the oxidation of atmospheric In order to get a full scale view of the total NOx behavior,
nitrogen at the high temperatures inside the combustion the maximum NOx values were showed as a function of mass
chamber of the engine, the NOx emissions depend on the percent of fuel oxygen and engine speed as shown Fig. 3b.
speed and load as well as the fuel type. It is observed that SME The increase in NOx emissions was proportional to the
yields higher NOx emission compared with other fuel blends. amount of biodiesel. In the case of pure biodiesel, the increase
This can be attributed to the higher oxygen content in the in NOx emission was 15.5% compared to the MF, on average.
SME. A recent work from Pitz and Mueller [38], showing that There were also 4.5% and 10% increase in NOx emissions for
NOx increase with bio-fuels is due to an increase of air/fuel B20 and B50, respectively. Similar conclusions were drawn by
zones very near to stoichiometric conditions thus resulting in other authors in the literature [39e41]. However, Dorado et al.
higher temperature and higher NOx. This phenomenon is [21] indicated a decrease in NOx emissions using waste olive
more visible when the heating value of the biofuel is much oil methyl ester instead of diesel fuel.
lower than the heating value of diesel or gasoline. The The use of biodiesel significantly reduced smoke opacity.
formation of NOx emissions increases with the use of bio- Biodiesel had the greatest effect on smoke in the lugging mode
diesel and its blends. The mechanism of NOx formation from where B10 reduced smoke by 28.6% and B20 reduced smoke by
atmospheric nitrogen has been studied extensively and it is 50% [2]. In this study, biodiesel addition reduced particulate
accepted that it is highly dependent upon temperature, due to emission in all stage as seen in Fig. 3c. It is observed that pure

Fig. 2 e Variations of the power output (a), the engine torque (b), the BSFC (c), the BTE (d) and the ME (e) with engine speed at
full load.
 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3 3581

Fig. 3 e Variations of the exhaust gas temperature (a), the NOx emissions (b), the smoke opacity (c) and the CO emissions (d)
with engine speed at full load.

SME yields minimum smoke opacity, which is followed by the and its 5%, 20% and 50% blends with MF. The experimental
other blends in diminishing order. Higher BTE indicates better results are described as follows:
and complete combustion of fuel. That is, lesser amount of
unburned hydrocarbons present in the engine exhaust gases. i. The substitution of MF with biodiesel (SME) led to
So, lower smoke opacity values are achieved with biodiesel a combination of positive and negative outcomes. The
blends as compared to that of the diesel fuel. The smoke only low concentration blends in terms of performance
opacity reduction was 62% with B50 while it was 74% with efficiency and environmentally friendly emissions
pure biodiesel. (particularly for B20 and lower blends) could be recog-
The CO emission of engine at full load is shown in Fig. 3d. nized as the potential candidates to be certificated for
The CO emission level decreased with increasing SME full scale usage in unmodified diesel engines. B5 gives
percentage in MF. At low engine speeds, the CO emissions of the best brake thermal efficiency of engine.
the B5, B20, B50 and B100 are 3%, 13%, 27% and 39% lower than ii. The addition of biodiesel in MF fuel improves the emis-
that of MF, respectively. This decrease may be due to the sions of PM, which comprise a serious disadvantage of
oxygen content of the blends and pure biodiesel. Poor atom- the diesel engine, especially in polluted areas such as
ization and uneven distribution of small portions of fuel port and beach.
across the combustion chamber, along with a low gas iii. CO emissions were dropped (COMF ¼ 725 ppm;
temperature, may cause local oxygen deficiency and incom- COSME ¼ 475ppm at 1800 rpm at full load. There was 52%
plete combustion [42]. The highest CO emission of 1050 ppm drop) when running on SME and its blends.
was measured for MF at 1000 rpm. The CO emissions are iv. The main reason of increasing fuel consumption is that
shown to decrease more rapidly for all fuels from 1000 rpm SME’s lower heating value (37388 kJ/kg) is smaller than
to1800 rpm. Reduced CO emissions were maintained, prob- marine fuel’s lower heating value (44308 kJ/kg). Any way
ably, thanks to the oxygen inherently present in the biofuel, a lower fuel consumption rate is required for a fuel with
which makes it easier to be burnt at higher temperature in the a higher heating value. The marine fuel has the highest
cylinder. Similar results can be found in other studies [42,43]. heating value among four fuel blends. All blends under
same load, the lower calorific value of the fuels that
contain biodiesel, this behavior was expected.
5. Conclusions v. BSFC of the four different kinds of fuels decreased
slightly with the increase the proportion of fuel blends.
In this paper, fuels under constant engine torque at full load On the other hand, the use of SME as a blend has not any
and varied engine speeds have been tested in a four-stroke positive effect on BSFC of the engine. 100% MF appeared
four cylinders diesel engine. Engine tests were done for SME to have a lower BSFC value than the other B100 (dropped
3582 b i o m a s s a n d b i o e n e r g y 3 5 ( 2 0 1 1 ) 3 5 7 5 e3 5 8 3

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