Energy Conversion and Management 87 (2014) 250–257

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Energy Conversion and Management

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Biodiesel production and performance evaluation of coconut, palmand their combined blend with diesel in a single-cylinder diesel engine

http://dx.doi.org/10.1016/j.enconman.2014.07.0060196-8904/� 2014 Elsevier Ltd. All rights reserved.

⇑ Corresponding author. Address: Department of Mechanical Engineering,University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +60 3 79674448;fax: +60 3 79675317.

E-mail address: habib63119@yahoo.com (M. Habibullah).

M. Habibullah ⇑, H.H. Masjuki, M.A. Kalam, I.M. Rizwanul Fattah, A.M. Ashraful, H.M. MobarakCentre for Energy Sciences, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

a r t i c l e i n f o

Article history:Received 6 March 2014Accepted 1 July 2014Available online 26 July 2014

Keywords:Palm biodieselCoconut biodieselPalm–coconut blendEngine performanceEngine emissions

a b s t r a c t

Biodiesel is a renewable and sustainable alternative fossil fuel that is derived from vegetable oils andanimal fats. This study investigates the production, characterization, and effect of biodiesel blends fromtwo prominent feedstocks, namely, palm and coconut (PB30 and CB30), on engines. To aggregate theadvantages of high ignition quality of palm and high oxygen content of coconut, combined blend of thistwo biodiesels (PB15CB15) is examined to evaluate its effect on engine performance and emissioncharacteristics. Biodiesels are produced using the alkali catalyzed transesterification process. Variousphysicochemical properties are measured and compared with the ASTM D6751 standard. A 10 kW,horizontal, single-cylinder, four-stroke, and direct-injection diesel engine is employed under a full loadand varying speed conditions. Biodiesel blends produce a low brake torque and high brake-specific fuelconsumption (BSFC). However, all emissions, except for NOx, are significantly reduced. PB15CB15improves brake torque and power output while reducing BSFC and NOx emissions when compared withCB30. Meanwhile, compared with PB30, PB15CB15 reduces CO and HC emissions while improving brakethermal efficiency. The experimental analysis reveals that the combined blend of palm and coconut oilshows superior performance and emission over individual coconut and palm biodiesel blends.

� 2014 Elsevier Ltd. All rights reserved.

1. Introduction

Global energy consumption has been increasing because oflifestyle changes and substantial population growth. The transpor-tation sector is one of the top consumers of energy and primarilyrelies on diesel engines. These engines are more efficient and costeffective than gasoline engines because of their higher energydensity, which provides higher mileage and lower emissions. Thediesel burning that occurs in transport vehicles results in seriousecological changes, which include the increase in global surfacetemperature (global warming), as well as changes in rainfallpatterns and in the frequency of extreme weather events. In addi-tion, the demand for sustainable alternatives for crude oil hasincreased because of limited fossil fuels resources, increasingprices of world crude oil, and environmental concerns [1]. Onesolution to this problem is the partial replacement of diesel withbiodiesel. Unlike diesel fuel, biodiesel has the potential to reduceatmospheric carbon dioxide and significantly decrease smoke, par-

ticulate matter (PM), hydrocarbon (HC), and carbon monoxide (CO)emissions because it is a clean burning fuel [2,3]. However, the dis-advantages of biodiesel use include high production cost, limitedfeedstock availability, food vs. fuel concern, inferior storage stabil-ity, low volumetric energy content, high specific fuel consumption,and high nitrogen oxide exhaust emission [4,5].

1.1. Objectives of the study

This experimental study examines the potential of using a com-bined blend of coconut and palm biodiesel as a partial replacementfor diesel fuel in a single-cylinder diesel engine. ASTM D7467enables the blending of biodiesel with diesel from 6% to 20%(B6–B20). B20 represents a good balance of cost, emission, materialcompatibility, and cold weather performance [6]. Biodiesel blendsof up to 20% with diesel (B20) can be easily used in the existing die-sel engines without the need for engine modification [7]. Thisstudy has particular relevance to Malaysia where the potentialexists for both increased palm and coconut oil production andthe establishment of economically viable application of biodieselsfrom these oils at a high percentage. Thus, this study examinesthe feasibility of using 30% diesel–biodiesel blend of palm–coconutand their combined blend in a single-cylinder engine.

M. Habibullah et al. / Energy Conversion and Management 87 (2014) 250–257 251

2. Literature review

This study investigates the effect of biodiesel comprising twopromising alternative feedstocks of Malaysian origin, namely, palmand coconut, and their combined blends on engine performanceand emission characteristics. Palm oil is the highest yielding oilcrop that produces an average of 4–5 tons of oil/ha annually, whichis approximately 10 times the yield of soybean oil [8]. Palm oil iscultivated abundantly in Malaysia. Meanwhile, the production ofcoconut oil is among the highest with 2260 kg of oil/ha [9]. Previ-ous studies have shown that coconut biodiesel offers good ignitionand combustion characteristics, low pollutant emission, and stableoperation with any diesel blend, which results in smooth operationwith longer maintenance intervals than other biodiesels [10,11].

2.1. Feedstocks

2.1.1. PalmAmong all plant families, palm (Elaeis guineensis Jacq.) is the

most popular and extensively cultivated. All tropical areas withhot and humid weather, such as Malaysia and Indonesia, are idealfor palm cultivation [12]. This particular variety can produce 10–35 t/ha of palm fruits. Oil is extracted from both the pulp and theseed. Palm oil trees are commercially cultivated to produce com-mercial edible oil [13].

2.1.2. CoconutCoconut (Cocos nucifera Linn) or coconut palm is one of the

most important nut crops and is a member of the family Arecaceae.Coconut is native to the tropical eastern regions. The crop is grownthroughout the Asian continent, in Central and South America, andin some parts of Africa. Large palms grow up to 30 m tall, with pin-nate leaves of 4–6 m long, and pinnae of 60–90 cm long. Palm has asingle trunk that is 20–30 m tall. The cultivation of coconutrequires sandy, saline soils with abundant sunlight and regularrainfall throughout the year. A coconut palm tree can yield up to75 fruits per year. Coconut palm is known for its versatility, as evi-denced by the numerous domestic, commercial, and industrial usesof its different parts.

2.2. Engine performance and emission study

Recent studies have been conducted on the production, physi-cochemical properties, engine performance, and emission charac-teristics of palm and coconut biodiesels and their blends asdiesel engine fuel [14–19]. Mofijur et al. [20] studied the proper-ties, performance, and emissions of 5% and 10% palm and Moringaoleifera biodiesel blends (PB5, PB10, MB5 and MB10) in a multi-cyl-inder diesel engine at various engine speeds. PB5, MB5, PB10, andMB10 produced 1.38%, 2.27%, 3.16%, and 4.22% lower brake powerand 0.69%, 2.56%, 2.02%, and 5.13% higher BSFC, respectively, thandiesel. PB5, MB5, PB10, and MB10 also showed a 1.96%, 3.99%,3.38%, and 8.46% increase in NOx; 14.47%, 3.94%, 18.42%, and9.21%, decrease in HC; and 13.17%, 5.37%, 17.36%, and 10.60%decrease in CO, respectively, compared with diesel. Liaquat et al.[21] investigated the effects of PB20 and diesel fuel during anendurance test and found 3.88% higher BSFC, 11.71% lower HC,11% lower CO, and 3.31% higher NOx emissions than diesel.Ndayishimiye and Tazerout [22] studied the engine performanceand emission characteristics of a palm oil-based biodiesel in a die-sel engine and found that a high percentage of palm biodieselblended with diesel fuel decreases the heating value while increas-ing brake thermal efficiency. NOx emissions and CO emissionswere higher at a low load, but lower at a full load for a high per-centage of palm oil methyl ester.

In another study, Liaquat et al. [23] employed 5% and 15%blends of coconut biodiesel in a single-cylinder diesel engine tostudy its performance and emission characteristics. A 0.69% and2.58% torque reduction, 0.66% and 2.61% power reduction, 0.53%and 2.11% higher BSFC were found for the 5% and 15% blends,respectively. In the case of CO and HC emissions, a maximum of21.51% and 27.19% reduction was observed at different throttlepositions. How et al. [24] studied the effect of 10%, 30% and 50%blends of coconut biodiesel on performance and criterion-regulated emissions along with polycyclic aromatic hydrocarbons(PAHs) in a multi-cylinder diesel engine. They observed a 0.4–20% higher BSFC, 8.5–42.4% lower smoke, max. 37.6% lower HC,and 40.1% lower PAH emission than diesel fuel at different throttlesettings.

Ozawa et al. [25] studied the application of coconut oil methylester in diesel engines and found that the break mean effectivepressure was 11% lower for coconut oil methyl ester than dieselfuel because of the lower heating value. The combustion chamberwall temperature also rose quickly, and the ignition timing wasadvanced when the blending ratio of coconut oil methyl esterwas increased, thus exhibiting superior compression ignition char-acteristics in a cold start.

In a previous study, Sanjid et al. [26] evaluated the production,physicochemical properties, engine performance, and exhaustemission characteristics of palm, jatropha, and the combinationof palm–jatropha biodiesel (PBJB5 and PBJB10) in an unmodifieddiesel engine at engine speeds ranging from 1400 rpm to2200 rpm. PBJB5 and PBJB10 biodiesels showed 7.55% and 19.82%higher BSFC, slightly lower BP, 9.53% and 20.49% lower CO, and3.69% and 7.81% lower HC, respectively, than diesel fuel.

3. Materials and method

3.1. Biodiesel production

Both palm and coconut biodiesel were produced by using thealkali catalyzed transesterification process with methanol andpotassium hydroxide. The alcohol reacted with the triglyceridesto form the mono-alkyl ester or biodiesel and glycerol. The simpleequation of this process is shown below.

Triglycerideþ Alcohol! Estersþ Glycerol

In this process, crude coconut oil or crude palm oil were placed withmethanol (25 v/v% of oil) and potassium hydroxide (KOH) (1 w/w%of oil) in a jacket reactor at 60 �C using a circulating water bath. Thismixture was stirred at 1200 rpm by using a motor stirrer for 2 h andwas then poured in a separation funnel. Separation time of 12 h wasallotted for glycerin and methyl ester to separate. The lower layercontained glycerol and impurities, whereas the upper layer con-tained the methyl ester of vegetable oil. The methyl ester separatedfrom glycerol was washed with distilled water to remove theentrained impurities and glycerin. In this process, 50% (v/v) of dis-tilled water at 60 �C was sprayed over ester and shaken gently.The opaque lower layer containing water and impurities wasremoved. Biodiesel was then placed in a rotary evaporator (IKARV10) to reduce the moisture content. Biodiesel was then subjectedto under vacuum distillation at 65 �C for 1 h using a rotary evapora-tor to remove water and methanol. Finally, moisture was absorbedby using anhydrous sodium sulfate, and the final product was col-lected after filtration.

3.2. Determination of fatty acid composition

Fatty acids are of two types: saturated and unsaturated. Fattyacids without carbon–carbon double bonds are known as

252 M. Habibullah et al. / Energy Conversion and Management 87 (2014) 250–257

saturated, whereas those that contain double bonds are known asunsaturated fatty acids. Gas chromatography (GC) (Agilent 6890,USA) was used to test the fatty acid composition of palm andcoconut biodiesel. Table 1 shows the operating conditions of theGC analysis, whereas Table 2 shows the comparative fatty acidcomposition results of palm and coconut biodiesels. Palm biodieselwas found to contain 44.4% saturated and 55.6% unsaturated fattyacids, whereas coconut biodiesel contains 91.3% saturated and 8.7%unsaturated fatty acids.

3.3. Biodiesel characterization

The properties of all samples were assessed in the TribologyEngine Laboratory and Energy Laboratory, Department of Mechan-ical Engineering, University of Malaya. The major physicochemicalproperties, including density, kinematic viscosity, higher heatingvalue (HHV), acid value, oxidation stability, and flash point, weremeasured by using several methods. Table 3 shows the synopsisof equipment and test methods used to determine fuel properties.Table 4 shows the individual fuel properties along with standardbiodiesel properties.

3.4. Engine tests

The experiment was performed in the Heat Engine Laboratoryof the Mechanical Engineering Department, University of Malaya,in a naturally aspirated single-cylinder diesel engine. The enginedetails are given in Table 5. This engine is commonly used forsmall-scale power generation. The test engine was directly coupledwith the SAJ SE-20 eddy current dynamometer. Fuel flow was mea-sured by using a Kobold ZOD positive-displacement type flowmeter. Engine oil, cooling water, exhaust gas, and inlet air temper-atures were measured by using a K-type thermocouple. A DASTEP8Data Acquisition System collected the data. The brake torque,brake power (BP), BSFC, and brake thermal efficiency (BTE) werecalculated according to Eqs. (1)–(3), respectively. The engine fuelsystem was modified by adding separate tanks with two-wayvalves, which enabled rapid fuel switching. Fig. 1 shows the testsetup. A gas analyzer (AVL DiCom4000) measured the exhaustgas composition of CO, HC, and NOx emissions. Details of differentmeasuring equipment are shown in Table 6.

For the tests using biodiesel blends, the engine was run withdiesel until a steady operating condition was achieved. The fuelwas then changed to a biodiesel blend. After running the enginefor five minutes, data acquisition commenced to ensure theremoval of residual diesel in the fuel line. After each test, theengine was again run with diesel to drain all of the remainingblend in the fuel line. This procedure was followed for each blend.The test fuels were diesel, 30% coconut biodiesel (CB30), 30% palmbiodiesel (PB30), and blend of 15% palm and 15% coconut biodiesel

Table 1GC operating conditions.

Property Specifications

Carrier gas HeliumLinear velocity 24.4 cm/sFlow rate 1.10 mL/min (column flow)Detector temperature 260.0 �CColumn head pressure 56.9 kPaColumn dimension BPX 70, 30.0 m � 0.25 lm � 0.32 mm IDInjector column oven 240.0 �C

Temperature ramp 140.0 �C (hold for 2 min)8 �C/min 165.0 �C8 �C/min 192.0 �C8 �C/min 220.0 �C (hold for 5 min)

(PB15CB15) in diesel. The fuels were blended by using a homoge-nizer device at a speed of 3000 rpm for 10 min. Table 4 shows someimportant characteristics of the tested fuels. The engine was oper-ated between 1400 and 2400 rpm with a step of 200 rpm under100% load conditions. Statistical analysis was conducted by apply-ing two-sided Student’s t-test for independent variables to test forthe significant differences between samples set means usingMicrosoft Excel 2013. Differences between mean values at a levelof p = 0.05 (95% confidence level) were considered statisticallysignificant.

BP ¼ 2pN60� T ð1Þ

BSFC ¼_m

BPð2Þ

BTE ¼ 3600BSFC � HHV

� 100% ð3Þ

where N is the engine speed in rpm, _m is the fuel flow in g/h, andHHV is the higher heating value of fuel in MJ/kg.

4. Results and discussion

4.1. Performance analysis

4.1.1. Brake torqueThe engine torque variation with respect to engine speed at full

load for all fuels is presented in Fig. 2. The torque values of theengine were first increased and then decreased at medium enginespeeds. The maximum torque values were obtained at 1800 rpmengine speed for all fuels. Beyond this speed, the torques of theengine decreased mainly because of two main factors, namely,decreased volumetric efficiency attributed to the increase in speedand augmentations in the mechanical losses [27]. The maximumtorque generated by the engine was 31.67 Nm when diesel wasused. With the use of biodiesel blends, the brake torque slightlydropped. The maximum torque levels of the engine using PB30,CB30 and PB15CB15 were 30.47, 30.24, and 30.44 Nm, respectively.These results can be attributed to the fact that diesel fuel hashigher HHV than biodiesel blends [23]. The average brake torquesfor diesel, PB30, CB30, and PB15CB15 over the entire engine speedrange were 31.32, 30.08, 29.83, and 30.03 Nm, respectively. Thus,the overall reductions in brake torque for PB30, CB30, andPB15CB15 compared with diesel were 3.94%, 4.74%, and, 4.11%respectively. These changes were significant at a level of p < 0.02.Other than lower HHV, the higher density and viscosity of biodieselblends resulted in lower velocity of the air fuel mixtures, lack ofturbulence, and lack of mixing of the air and fuel particles in thecombustion chamber, which affect combustion efficiency whencompared with diesel [28]. These factors reduce brake torqueand brake power output. PB30 exhibits the highest brake torqueamong the biodiesel blends because it has the highest HHV(Table 3). PB15CB15 shows a slight improvement in brake torquecompared with CB30.

4.1.2. Brake powerThe brake power of an engine is directly proportional to torque

and engine speed. Fig. 3 shows the variation of break power outputwith engine speed for different biodiesel blends. For all the testedfuels, break power steadily increased with engine speed until2400 rpm. The maximum break power output values obtained fordiesel, PB30, CB30, and PB15CB15 were 7.70, 7.40, 7.35, and7.38 kW, respectively. As previously discussed, the brake poweroutput for biodiesel blends was lower because of low brake torque.The average brake power values for diesel, PB30, CB30, andPB15CB15 over the entire engine speed range were 6.23, 5.98,

Table 2Fatty acid composition results of palm biodiesel and coconut biodiesel.

FAME name Structure Molecular weight Formula PBD (wt.%) CBD (wt.%)

Methyl octanoate 8:00 158.24 CH3(CH2)6COOCH3 n.d. 8.2Methyl decanoate 10:00 186.29 CH3(CH2)8COOCH3 n.d. 6.6Methyl laurate 12:00 214.34 CH3(CH2)10CO2CH3 n.d. 48.3Methyl myristate 14:00 242.4 CH3(CH2)12COOCH3 n.d. 16.4Methyl palmitate 16:00 270.45 CH3(CH2)14CO2CH3 40.1 9.3Methyl palmitoleate 16:01 268.43 CH3(CH2)5CH@CH(CH2)7COOCH3 n.d. n.d.Methyl stearate 18:00 298.5 CH3(CH2)16CO2CH3 4.3 2.4Methyl oleate 18:01 296.49 CH3(CH2)7CH@CH(CH2)7CO2CH3 43.1 7.0Methyl linoleate 18:02 294.47 CH3(CH2)3(CH2CH@CH)2(CH2)7CO2CH3 12.5 1.7Saturated 44.4 91.3Monounsaturated 43.1 7.0Polyunsaturated 12.5 1.7Total 100 100

n.d. = not detected.

Table 3List of equipment used for testing fuel properties.

Property Standard method Equipment Manufacturer Model Accuracy

Density ASTM D 7042 Stabinger viscometer Anton Paar SVM 3000 ±0.1 kg/m3

Kinematic viscosity ASTM D445 Stabinger viscometer Anton Paar SVM 3000 ±0.1 mm2/sDynamic viscosity ASTM D 7042 Stabinger viscometer Anton Paar SVM 3000 ±0.35%Higher heating value ASTM D 240 Automatic calorimeter IKA, UK C2000 ±0.1%Flash point ASTM D 93 Pensky-martens flash point tester Normalab, France NPM440 ±0.1 �COxidation stability EN ISO 4112 Biodiesel rancimat Metrohm, Switzerland 873 Rancimat ±0.01 hAcid value ASTM D 664 Automated titration system Mettler Toledo, Switzerland G-20 Rondolino ±0.001 mg KOH/g

Table 4Major physicochemical properties of tested fuels.

Properties Unit Diesel PB30 CB30 PB15CB15 PB100 CB100

Density kg/m3 829.6 841.8 838.2 840.0 870.2 858.2Kinematic viscosity mm2/s 3.0738 3.5366 3.3793 3.4580 4.6175 4.0927Dynamic viscosity mPa s 2.5501 2.9752 2.8491 2.9123 3.9672 3.5469Higher heating value MJ/kg 45.238 43.869 43.152 43.396 39.910 38.284Flash point �C 68 75 75 72 140.5 118.5Oxidation stability h 58.51 9.53 6.33 6.21 6.59 8.10Acid value mg KOH/g 0.10 0.26 0.18 0.24 0.40 0.35

Table 5Summary of engine specification.

Specification Description

Model TF 120 MType 1-cylinder, horizontal, water-cooled,

4-cycle diesel engineCombustion system Direct injectionAspiration Natural aspirationCylinder bore � stroke 92 mm � 96 mmDisplacement 638 ccContinuous rated output 2400 rpm, 10.5 Ps, 7.7 kWMaximum rated output 2400 rpm, 12 Ps, 8.8 kWDimension Length (695.5 mm) �Width

(348.5 mm) � Height (530 mm)Cooling system Radiator cooling systemLubrication system Completed enclosed forced lubricating system

M. Habibullah et al. / Energy Conversion and Management 87 (2014) 250–257 253

5.93, and 5.97 kW, respectively. Thus, the average brake poweroutputs were lower than that of diesel fuel by 3.92%, 4.71%, and4.10% for PB30, CB30, and PB15CB15, respectively. These changeswere significant at a level of 0.01 < p < 0.02. The reduced powerfor biodiesel blends can be attributed to their lower energy contentper unit volume than diesel fuel. Moreover, the high viscosity anddensity of biofuels result in uneven combustion and poor atomiza-tion, thus producing low power [29]. The brake power for PB30was 0.83% higher than that of CB30 because of the higher HHV of

palm biodiesel. Engine performance with fuel blend PB15CB15was better than that of the CB30 fuel blend under all tested enginespeeds.

4.1.3. BSFCThe variation of BSFC for all tested fuels with respect to engine

speed is depicted in Fig. 4. BSFC is the ratio between mass fuel con-sumption and brake power. For a given fuel, BSFC is inversely pro-portional to thermal efficiency. Biodiesel usually possesses lowHHV because of its fuel-borne oxygen. High fuel consumptioncan be attributed to the volumetric effect of a constant fuel injec-tion rate, along with the high viscosity of biodiesel blends[30,31]. The average BSFCs for diesel, PB30, CB30, and PB15CB15over the entire engine speed range were 258.35, 280.53, 281.69,and 280.45 g/kW h, respectively. Thus, the average BSFCs were8.58%, 9.03%, and 8.55% higher than that of diesel fuel for PB30,CB30, and PB15CB15, respectively. These changes were found tobe significant at a level of p < 0.01. The graph reveals that BSFC firstdecreased and was the lowest at 1800 rpm and then increasedalong with engine speed for all test fuels. With the increase inspeed from 1400 rpm to 1800 rpm, the BSFC for all the fuelsdecreased because of the increase in atomization ratio. The fuelconsumption increased from 1800 rpm to 2400 rpm because ofthe decreasing volumetric efficiency, whereas the lowest BSFCoccurred at 1800 rpm [32]. CB30 showed the highest BSFC on

Laptop

BiodieselDiesel

Gas analyzer

Fuel flow meter

Radiator

Battery

Controller

Test engine

Muffler

Dynamometer

Fig. 1. Engine test setup.

Table 6Details of different measuring instrument.

Equipment Component Measurement principle Measurement range Resolution

SAJ SE20 Dynamometer Torque Strain gauge load cell 0–80 Nm ±0.25 NmKobold ZOD flow meter Engine speed Pulse pickup 0–6000 rpm ±1 rpmThermocouple Temperature K-Type �200 �C to +1000 �C ±1 �CAVL DiCom 4000 CO Non-dispersive infrared (NDIR) 0–10 vol.% 0.01 vol.%

CO2 NDIR 0–20 vol.% 0.1 vol.%HC NDIR 0–20,000 ppm vol. 1 ppmNOx Electrochemical 0–5000 ppm vol. 1 ppmO2 Electrochemical 0–25 vol.% 0.01 vol.%

Fig. 2. Variation of brake torque with respect to engine speed at full load. Fig. 3. Variation of brake power with respect to engine speed at full load.

254 M. Habibullah et al. / Energy Conversion and Management 87 (2014) 250–257

M. Habibullah et al. / Energy Conversion and Management 87 (2014) 250–257 255

account of its lowest HHV. PB15CB15 showed the lowest BSFCamong all the biodiesel blends because of the combined effect ofimproved viscosity and HHV compared with PB30 and CB30.

Fig. 5. Variation of brake thermal efficiency with respect to engine speed at fullload.

4.1.4. BTEThe BTE for all the tested fuels with respect to the engine speed

is presented in Fig. 5. The BTE increased until 1800 rpm and thendecreased, with the lowest engine speed at 2400 rpm for all testedfuels because of poor spray characteristics and air–fuel mixing athigh engine speed [33]. The highest BTE values for diesel, PB30,CB30, and PB15CB15 at 1800 rpm were 31.97%, 30.25%, 30.65%,and 30.61%, respectively. The average BTE values for diesel, PB30,CB30, and PB15CB15 were 30.83%, 29.28%, 29.64%, and 29.61%,respectively. The overall BTE reductions for PB30, CB30, andPB15CB15 were respectively found to be 5.03%, 3.84%, and 3.97%lower than diesel fuel. The higher viscosity, density, and HHV thanthe diesel fuel was the primary cause of lower BTE. Higher viscositydecreases atomization and fuel vaporization, which results in amore uneven combustion than that of diesel fuel [34,35]. As aresult of its higher oxygen content and lower HHV, CB30 showedthe highest BTE, which was 1.23% higher than that of PB30.PB15CB15 showed a 1.12% higher BTE than PB30 and a slightlylower BTE than CB30.

4.2. Emission analysis

4.2.1. NOx emissionThe NOx emission from the engine for all testing fuels at

constant load is illustrated in Fig. 6. The thermal mechanism andprompt mechanism are the dominant mechanisms of a NOx forma-tion in biodiesel combustion [36]. The graph shows that NOx for-mation increased with the increase in speed for all tested fuels.The average NOx emissions for diesel, PB30, CB30, and PB15CB15were 643.83, 664, 680.33, and 672.16 ppm, respectively. Thus,the average NOx emissions for PB30, CB30, and PB15CB15 wererespectively 3.13%, 5.67%, and 4.40% higher than that of diesel fuel.These changes were found to be significant at p < 0.02. The higherbulk modulus of biodiesel resulted in the earlier opening of thenozzle and a more advanced injection than fossil diesel [37]. Thebiodiesel blends are expected to combust earlier with an improvedcombustion efficiency because biodiesel is an oxygenated fuel thatpossesses short ignition delay because of high CN. Thus, biodieselsform more NOx than diesel. NOx emission of CB30 was 2.40%higher than that of PB30, which can be attributed to its higher

Fig. 4. Variation of BSFC with respect to engine speed at full load.

CN. PB15CB15 showed a 1.22% higher NOx than PB30 and 1.20%NOx lower than the CB30 fuel blend.

4.2.2. CO emissionThe variation of CO emissions for different tested fuels at differ-

ent engine speeds is shown in Fig. 7. CO is formed as a result of theinadequate burning and partial oxidation of carbon atoms in thefuel [38]. Changes in CO emission depend on the fuel/air ratioinside the cylinder. When this ratio is high, the amount of COincreases. However, the fuel/air equivalence ratio increases withengine speed, which results in increased gas temperature in theengine cylinder. This increase in temperature likewise increasesthe conversion rates of CO to CO2, which results in low CO emissionat high engine speeds, as evident in the results. The average COemissions for PB30, CB30, and PB15CB15 were reduced by13.75%, 17.97%, and 15.84%, respectively, compared with dieselfuel. The significant decrease in CO emissions when running onbiodiesel blends compared with that when running on diesel fuelcan be attributed to the fact that the carbon content of biodieselwas lower than that of diesel fuel [38]. The presence of oxygenin biodiesel blends also enabled complete combustion, whichensured the formation of less CO compared with that in diesel.The average CO emission for PB30 was 5.15% higher than that ofCB30 because of its higher density and viscosity. Higher density

Fig. 6. Variation of NOx emissions with respect to engine speed at full load.

Fig. 7. Variation of CO emissions with respect to engine speed at full load.

Fig. 8. Variation of HC emissions with respect to engine speed at full load.

256 M. Habibullah et al. / Energy Conversion and Management 87 (2014) 250–257

and viscosity caused poor fuel atomization and spray formation,which resulted in incomplete combustion and increased CO emis-sion [39]. PB15CB15 produced 2.43% lower CO than PB30 and 2.60%higher CO than CB30 fuel. Thus, the addition of CB in PB clearlyresulted in a significant improvement in CO emission reduction.

4.2.3. HC emissionHydrocarbon emission is affected by engine operating condi-

tions, fuel properties, and fuel spray characteristics [40]. Fig. 8shows the variation of HC emission in ppm for all the tested fuelsat various engine speeds. The average HC emissions for diesel,PB30, CB30, and PB15CB15 in the entire engine speed range were78.50, 64.17, 54.00, and 58.17 ppm, respectively. Thus, the averageHC emission was reduced by 18.26%, 31.21%, and 25.90% for PB30,CB30, and PB15CB15, respectively, compared with diesel fuel. Thisresult can be attributed to the better conversion of HC resultingfrom higher CN together and oxygen content. An earlier combus-tion timing attributed to higher CN with advantageous conditions(post flame oxidation, higher flame speed, etc.) during air–fuelinteractions that resulted from the fuel borne oxygen, particularlyin the fuel-rich regions, enhanced the oxidation of unburned HC,thus reducing HC significantly [18,41]. PB30 showed 18.83% higherHC emission than that of CB30. This variation can be attributed tothe variation of density and viscosity values among the fuels, as

explained in the case of CO emission [42]. PB15CB15 produced9.35% lower HC than PB30 and 7.72% higher HC than CB30 fuel.Thus, the addition of CB in PB clearly resulted in a significantimprovement in HC emission reduction.

5. Conclusion

This study was conducted in two phases. In the first phase,biodiesel was obtained. In the second phase, the blend properties,engine performance, and emission of palm, coconut and their com-bined blend with diesel were investigated. The results of this workcan be summarized as follows:

� The average engine brake power values for PB30, CB30, andPB15CB15 were respectively 3.92%, 4.71%, and 4.10% lower,whereas BSFC values were higher (8.55–9.03%) than that of die-sel fuel. The BTE values were much (3.84–5.03%) lower thanthat of diesel fuel due to their much lower HHV. PB15CB15showed slightly higher BTE (1.12%) than PB30 and slightlylower BP and BTE (0.20% and 0.12%, respectively) than CB30fuel. By contrast, BP decreased by 0.20% compared with thatof PB30 and increased by 0.63% compared with that of CB30.� The average NOx emissions were 3.13–5.67% higher for all the

tested biodiesel blends compared with that of diesel fuel. TheNOx emission of CB30 was 2.40% higher than that of PB30,whereas PB15CB15 showed a 1.22% higher NOx emission thanthat of PB30 and 1.20% lower NOx emission than that of CB30.� CO and HC emissions were reduced to a great extent at 13.75–

17.97%, compared with those of diesel fuel operation. PB30showed 5.15% and 18.83% higher CO and HC emission, respec-tively, compared with the values for CB30. Meanwhile,PB15CB15 showed lower CO and HC emission (2.43% and9.35%, respectively) than PB30 and slightly higher emissions(2.60% and 7.72%, respectively) than CB30 fuel.� Combined blend of palm and coconut biodiesel shows superior

performance and emission over individual coconut and palmbiodiesel blends depending on performance and emissionparameters.

Acknowledgements

The authors would like to appreciate the University of Malayafor financial support through High Impact Research Grant titled:Clean Diesel Technology for Military and Civilian TransportVehicles having Grant Number UM.C/HIR/MOHE/ENG/07.

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