Energy Conversion and Management 105 (2015) 617–629

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Energy Conversion and Management

journal homepage: www.elsevier .com/ locate /enconman

Review

Implementation of palm biodiesel based on economic aspects,performance, emission, and wear characteristics

http://dx.doi.org/10.1016/j.enconman.2015.08.0200196-8904/� 2015 Elsevier Ltd. All rights reserved.

⇑ Corresponding authors at: Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +60 3 79674448; fax: +60 3 796E-mail addresses: mosarof.hossain.rubel@gmail.com (M.H. Mosarof), kalam@um.edu.my (M.A. Kalam).

M.H. Mosarof ⇑, M.A. Kalam ⇑, H.H. Masjuki, A.M. Ashraful, M.M. Rashed, H.K. Imdadul, I.M. MonirulCentre for Energy Science, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

a r t i c l e i n f o

Article history:Received 30 April 2015Accepted 9 August 2015Available online 22 August 2015

Keywords:BiodieselPalm oilDiesel engineMalaysia

a b s t r a c t

Thehigh cost of energy supplies and the growing concern over the dependency on fossil fuels have impelledmany countries to search for renewable and alternative energy sources. The extensive use of fossil fuels fortransportation and power generation all over the world have caused the supply of fossil fuels to continu-ously decrease and have aggravated environmental pollution. Searching for alternative fuels has becomeimperative to reduce pollution and address the problems on fossil fuels. Vegetable oil fuels, such as palmoil biodiesel, serve as alternative forms of energy and are currently being studied, particularly as a dieselfuel substitute. The purpose of this study is to review the potential of palmoil as an energy source and alter-native diesel fuel in terms of its performance, environmental impact, wear characteristics, and economicconsiderations. Compared with other vegetable oils, palm oil is a relatively sustainable, environment-friendly, less expensive, and economically beneficial potential source of energy. Palm oil plantation andproduction is a major industry in Malaysia, contributing to the economic growth and development ofthe country. The properties of palm oil biodiesel, namely, high oxidation stability, good cold properties,cetane number, and higher viscosity, makes it a suitable diesel substitute. Compared with other vegetableoils and petroleum diesel fuels, palm oil is associated with better engine performance, higher specific fuelconsumption, and shorter ignition delay. Use of palmoil also reduces exhaust emission of hydrocarbon, car-bonmonoxide, carbondioxide, and smoke, but not oxide of nitrogen emissions. The higher viscosity of palmoil improves its lubricating properties and anti-wear characteristics, which are favorable for various enginecomponents. Therefore, the aimof this study is to reviewvarious studies on palmbiodiesel production fromdifferent countries and compare the findings of these studies with the situation in Malaysia. This studyexamines the economic aspects of using palm oil, as well as its effects on performance, emission, and wearcharacteristics. Palm biodiesel could be the candidate with the greatest potential in all aspects.

� 2015 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6182. Reasons for using palm vegetable oil fuel as alternative fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6183. Palm oil biodiesel as an alternative diesel fuel in Malaysia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6214. Characterization of palm oil biodiesel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622

4.1. Economic considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6224.2. Engine performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6234.3. Exhaust emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6254.4. Wear characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 625

5. Discussion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6266. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 626

Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627

75317.

618 M.H. Mosarof et al. / Energy Conversion and Management 105 (2015) 617–629

1. Introduction

The decrease in the amount of available fossil fuels and theincrease in air pollution from their combustion have prompted asearch for alternative fuels and better combustion technology.Since 1977, many countries have taken various steps to reduce theirdependency on imported oils. Numerous studies explored alterna-tive fuel resources and measures on how to use energy in the mostefficient way. In addition to the depletion of petroleum resources,the increasing stringency of environmental regulations toreduce emissions have accelerated the search for alternative fuels.Environmental pollution has been a growing concern and the effectof global warming has amplified [1–4]. Utilizing non-petroleum oiland domestic resources of energy has increased the self-reliance ofcountries. This strategy is adopted by the Malaysian government.Currently, energy conservation and the search for alternative fuelsare given high priority. In particular, biodiesel has been consideredin energy planning as a potential alternative diesel fuel [5,6]. Afterseveral years of finding ways to improve diesel engines, suchengines are almost fully developed and fuel economy has beenimproved considerably. Therefore, the exhaust emissions of green-house gases from diesel engines have been reduced. Comparedwithpetroleum fuel, alternative fuels are proven more effective whenused in diesel engines. Biodiesel is a greener alternative to fossil fuelbecause it can reduce emissions; thus, it is more beneficial to theenvironment and to human health [7,8].

Vegetable oils are converted into biodiesel, which is well suitedfor diesel engines. Its low impact on the environment and eco-nomic benefits are the major reasons for the use of biodiesel.Vegetable oils are nontoxic sources of renewable energy and donot contribute to global carbon dioxide (CO2) buildup. Therefore,vegetable oils as fuels have been studied extensively in recentyears [9–12]. Rahman et al. [13], investigated palm oil as one ofthe vegetable oils widely used as a diesel fuel alternative. Otherstudies on alternative fuels that investigated the use of coconut[14,15], moringa [16], peanut [17], soybean [18,19], and rapeseedoils generated positive results [20].

The possibility of utilizing biodiesel as a diesel fuel alternativehas been known since 1892. Vegetable oils have been studied as die-sel fuel substitutes and energy sources all over the world. In theEuropean Union (EU), methyl esters from vegetable oils are called‘‘biodiesel fuel.” Rapeseed oil methyl esters are produced and mar-keted as ‘‘biodiesel” vehicle fuel in the EU, especially in France,Austria, and Germany [21–23]. In Malaysia, the performance andtechnical aspects of soybean, rapeseed, jatropha, coconut, and palmoils as alternative fuels for diesel engines have been studied [24].

Rakopoulos et al. [25], observed that vegetable oils have highviscosity rates and are incompatible with lubricating oils normallyused in diesel–fueled engines. Pyrolysis products form and lead toinjector nozzle and piston fouling. Such fouling affects the fuelinjection system, engine compression, and fuel combustion andconsequently affects emissions. Compared with diesel fuels, veg-etable oil fuels have lower emissions of oxide of nitrogen (NOx),Carbon dioxide (CO2), and hydrocarbon (HC) [26]. Thus, the useof vegetable oils in existing diesel engines is highly expedient.Transesterification is conducted to produce biodiesel from veg-etable oil with alcohol [27]. The resulting vegetable oil methylesters are expected to increase in importance in the future andexhibit potential technological success; internal combustion (IC)engines using palm oil methyl esters have proven the efficiencyof this alternative fuel, under certain conditions, for transportand commercial vehicles [28,29].

Öztürk [30] studied biodiesel as fuel for indirect injection (IDI)diesel engines. However, the results showed that substitutingdiesel fuel with biodiesel without an engine substation cannot be

altered, used, or modified by the engine itself. Furthermore, envi-ronmental pollution levels are lower when biodiesel is usedinstead of diesel fuel. A study should be conducted to assess thesuitability palm oil fuel blends for IC engines. Fuel of 100% palmoil was also studied in Australia in 1982. The Primary EnergyInvestigation Unit of James University in Queensland investigatedthe thermal efficiency of palm oil and its products as compressionignition fuels in a petroleum diesel engine. In an industrial scale,diesel fuel made from palm oil blended with gas oil was preparedat the National Chemical Laboratories and generated satisfactoryresults [31]. In India, diesel engines are mostly used for transportand agriculture machinery. Palm oil methyl esters (POME) as a die-sel fuel blend was used in a direct ignition (DI) diesel engine andgenerated positive results as an alternative fuel [32].

Benjumea et al. [33] observed the following important combus-tion parameters: fuel injection timing, cylinder gas pressure, heatrelease, combustion temperature, and combustion duration. Astudy on the combustion characteristics of palm oil showed thatpoor ignition quality is due to the unacceptable atomization ofthe higher viscosity fuel. To overcome these problems, methodssuch as micro emulsion, transesterification, and improved engineand fuel system design have been proposed. The heating value ofpalm oil biodiesel is lower than that of conventional diesel fuelfor diesel engines. Palm oil allowed for shorter ignition delay whenthe biodiesel contents are increased in blends. The emissionparameters of greenhouse gases, except for NOx, decrease withthe addition of biodiesel in blend ratios; NOx increases becauseof a shorter ignition delay [34–36].

Numerous investigations on palm oil as a diesel fuel substitutehave presented the tribological, environmental, and economicaspects of using this type of oil. The objective of the current paperis to review the use of palm oil as an alternative fuel in Malaysia. Tothis end, the economic considerations, engine performance,exhaust emission, and wear characteristics of palm biodiesel arediscussed in this paper.

2. Reasons for using palm vegetable oil fuel as alternative fuel

The full utilization of fuel from vegetable oils as an alternativefuel is constrained by the following considerations:

� Vegetable oils can make only a marginal contribution to the fuelsupply worldwide.

� Vegetable oil fuels could only acquire a significant share of thefuel market under certain local conditions (e.g., in Malaysia,some EU countries, and the US).

� Fluctuations in the world market price of vegetable oil compli-cate the assessment of the economic viability and the availabil-ity of vegetable oil fuel compared with conventional fuels [37].

Misra and Murthy [37] noted that vegetable oil fuel can be usedfor diesel engines for the following reasons:

� Vegetable oil is biodegradable and nontoxic.� Knocking tendency is lower because of the reasonable cetanenumber of vegetable oil fuel.

� This type of fuel contains a low amount of sulfur; thus, it isenvironment-friendly.

� Modifying the major components of diesel engines is notrequired because of the enhanced lubricity of vegetable oil fuel.

� The flash point of vegetable oil is higher than that of diesel;thus, safety is improved.

� This type of oil is completely compatible with conventional die-sel and alternative fuel.

� It results in low emission and noise.

Table 1Palm oil production in different countries regions [40].

Rank Country Production (million ton)

1 Indonesia 33.0002 Malaysia 20.5003 Thailand 2.2504 Colombia 1.1085 Nigeria 0.9306 Papua New Guinea 0.6307 Ecuador 0.5758 Ghana 0.4959 Honduras 0.44010 Cote D’ivoire 0.40011 Guatemala 0.35512 Brazil 0.34013 Costa Rica 0.27014 Cameroon 0.27015 Congo 0.21516 Philippines 0.135

Coconut oil 2%

Co�onseed oil 3%

olive oil 2%

Palm oil 35%

Palm Kernel oil 4% Peanut oil

3%

Rapseed oil 16%

Soybean oil 26%

Sunflower oil 9%

Coconut oil Co�onseed oil olive oil

Palm oil Palm Kernel oil Peanut oil

Rapseed oil Soybean oil Sunflower oil

Fig. 2. Major vegetable oil producers [43].

M.H. Mosarof et al. / Energy Conversion and Management 105 (2015) 617–629 619

For the aforementioned reasons, many countries haveattempted to develop an alternative fuel based on their resources,such as palm oil, which has been explored in Malaysia. Severalinvestigations noted that palm oil biodiesel and conventional die-sel have nearly similar properties, such as calorific values, cetanenumber, viscosity, and density [38]. A large amount of palm oil isproduced in Malaysia. The country produces approximately 74.1%of the world’s palm oil. According to the Department of Statistics,Malaysia, currently 14% of the total land area of this countryproduces palm oil. At present, 19.667 million tonnes of palm oilis produced from 5.392 million hectares of land in Malaysia.Furthermore, 0.66 million kernel palm oil is produced from thisland area [39]. Other countries that produce palm oil areIndonesia, Thailand, and Colombia. Produces palm oil as analternative fuel in many countries, which are shown in Table 1.

Biodiesel production has been increased from 16 to 28 milliontonnes from 2009 to 2014 over the world. In particular, palm oilbiodiesel production increased from 3.2 to 8.3 million tonnes from2009 to 2014 [41]. According to the Economics and IndustryDevelopment Division of the Malaysian Palm Oil Board (MPOB),the production of crude palm oil in Malaysia in 2014 was 19.667million tonnes, increasing marginally by 3.04–24.29% from15.824 million tonnes in 2007; in 2014, the production of crudepalm kernel oil (CPKO) also rose to 2.278 million tonnes or

0

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n (1

000

MT)

Fig. 1. Palm oil production in M

19.39% from 1.908 million tonnes in the previous year. Fig. 1presents some data on palm oil production in Malaysia.

According to the Department of Statistics, Malaysia, the totalland area for palm oil in the country in 1975 was 641,791 hectares,which increased to 5,000,109 hectares in 2011. The monthly stockof palm oil in every year averaged about a million tonnes andended with a record high stock of 1.903 million tonnes in 2014,up 33.64% from 1.424 million tonnes in 2007 [42]. Fig. 2 mentionsthe major vegetable oil production in the world [43], and Fig. 3shows oil palm planted area distribution by category in Malaysia.As shown in Fig. 3, 66% of areas are private estates and only 6%is owned by the government.

Studies using palm oil fuel as diesel fuel have described manyspecies of oil palm are expedient as biodiesel feedstocks. In 1983,the Palm Oil Research Institute of Malaysia (PORIM) successfullyconducted transesterification process to produce crude palm oil(CPO) and crude palm stearin (CPS) and their correspondingmethyl esters. Petronas found the properties of methyl ester tobe analogous to those of diesel [31,44]. PORIM also evaluated thecar performance fitted with a CPO-fueled diesel engine. Elsbettet al. [45] observed that the car ran for more than 35,000 km

in Malaysia

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alaysia (1976–2014) [42].

62%15%

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13%

Palm Oil Planted Area, 5.34 Million Hectares

Private Estates Independent SmallholdersState Scheme/Govt. Agencies RISDAFELCRA FELDA

Fig. 3. Distribution of oil palm planted area by category, 2014 [43].0.75

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Dens

ity (g

cm

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Temperature (°C)

Diesel

Biodiesel

Rapseed

Sunflower

Soybean

Palm

Corn

Fig. 4. Densities of different biodiesel fuels and diesel fuel at different temperatures[55].

620 M.H. Mosarof et al. / Energy Conversion and Management 105 (2015) 617–629

without any technical problem, and the fuel was safe to handle andwas cheaper in price. When CPO is used with any fossil fuel, burn-ing CPO produces CO2. However, released CO2 is consumed byplants during their life cycles, thereby resulting in zero net emis-sion of CO2 to the environment. Vegetable oil biodiesels arepredicted to be the fuels of the future as they offer renewableand environment-friendly energy, and in the case of CPO, sustain-able energy, because CPO is produced all year round, thus ensuringa stable supply.

The test by PORIM on CPO-fueled engine provides evidence forthe potential of CPO as an alternative fuel. In the future, diesel-powered vehicles will gain more popularity because diesel con-tains approximately 15% more energy than an equal volume ofgasoline does. In addition to fuel economy, fuel supply and vehiclecost are other factors that show the higher efficiency of diesel thanthat of gasoline.

Palm biodiesel properties are maintained on the basis of ASTMdiesel and biodiesel specifications [46,47]. However, producers andrefiners have to pay more attention to meet the requirements. Oneof the important requirements is a sulfur-free diesel or diesel oilwith 0.05% sulfur content, which is very expensive. With theseconsiderations, many studies have searched for an alternative fuelfrom renewable sources, which could substitute the conventionaldiesel oil.

The suitability of vegetable oil fuels in diesel engines arisesfrom their similarities to HC-based diesel fuel in molecular struc-ture and carbon-to-hydrogen ratio (C:H). However, compared withdiesel fuel, vegetable oil fuels have higher relative molecularmasses and viscosities as well as contain oxygen in the molecularformula; other related disadvantages need to be considered [48].According to Ziejewski and Kaufman [49], most researchers haveconcluded that vegetable oils can burn safely during short-timecombustion in diesel engines.

The disadvantages of using vegetable oil in diesel engines forprolonged periods of time include severe engine deposits,piston-ring sticking, injector coking, and lubricating-oil thickening

Table 2Physical properties of diesel and some vegetable oils [53,54].

Properties Diesel Soybean Palm Cotto

Density (kg/m3) at 15 �C 820–890 914 918 915Kinematic Viscosity (mm2/s) 3–7.5 58–63 95–106 73Flash point (�C) 93 330 280 243Cetane number 50 37 40 35–4Pour point (�C) <�5 �4 31 �1Iodine Value (gl2/g) – 109 48–58 103–Sulfur (wt%) <1.0 0.01 0.01 0.01Carbon residue (%wt) <0.15 0.24 0.23 0.24

[50]. The high viscosity of vegetable oil reduces the atomization offuel and increases the penetration in fuel spray. High spray pene-tration is responsible for such problems as engine deposit growthand thickening of lubricating oil. However, these effects can bereduced or eliminated by the transesterification of oil to methylester [51].

According to Laforgia and Ardito [52], the physical and chemicalproperties of crude vegetable oil are improved by transesterifica-tion; they suggest the following:

� In the injection system, pumping problems and nozzle wear arecaused by reducing the viscosity (ASTM D445-74).

� Cetane Test Method (ASTM D-613) is used to measurethe cetane number, which is slightly increased bytransesterification.

� Transesterification causes the heating value of crude vegetableoil to be almost equal to that of diesel fuel.

Nevertheless, diesel engines using vegetable oils as fuels andtheir by-products are potentially very attractive. Engines that pro-duce energy with the use of palm oil and other low-cost vegetableoils are likely to be relatively economical compared with virtuallyall other energy sources. Vegetable oils are typically denser thangas oil and have slightly lower caloric values and normally higherviscosities than diesel oil [53]. Blin et al. [53] and Sidibé et al. [54]compared diesel oil and some alternative fuels, as shown inTable 2; they observed numerous physical properties of dieseland vegetable oils, including density, viscosity, flash point, pourpoint, cloud point, cetane number, sulfur content, and iodine value.

As seen from Fig. 4, the densities of different fuels vary atdifferent temperatures. The density of each fuel decreases as thetemperature increases, and every biodiesel shows a higher densitythan diesel at different temperatures.

n Jatropha Corn Rapssed Sun-flower Linssed

940 910 912 916 92455 60–64 77 55–61 31–35240 277 320 316 241

0 39 38 32–36 37 353 �1.1 �11 �5 �15

115 82–98 103–128 105 125–140 1800.01 0.01 0.01 0.01 –– 0.24 0.3 0.27 0.22

0

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10 20 30 40 50 60 70 80 90 100 110 120 130 140

Kin

emat

ic V

isco

sity

(mm

²s-1)

Temperature (°C)

Diesel

Biodiesel

Rapseed

Sunflower

Soybean

Palm

Corn

Fig. 5. Kinematic viscosities of different biodiesel fuels and diesel fuel at differenttemperatures [55,56].

Indonesia51%

Malaysia34%

Thailand4%

Colombia2%

Nigeria1%

others8%

ig. 6. Corresponding percentages of palm oil production of different countriesilseeds: World Markets and Trade, 2013/14) [43].

M.H. Mosarof et al. / Energy Conversion and Management 105 (2015) 617–629 621

As shown in Fig. 5, viscosity is a function of temperature, that is,when temperature changes, the kinematic viscosity changes aswell [57–59]. Yilmaz [60] observed that vegetables oils, comparedwith standard diesel fuel, are highly viscous. Oils from soybean,sunflower, rapeseed, corn, and palm exhibit similar trend lines athigh temperatures.

As mentioned, environmental problems have impelled manycountries to search for suitable alternative fuels based on theirresources. Numerous studies have shown that vegetable oil gener-ates low emission when used in diesel engines. Therefore, Malaysiahas increasingly produced palm oil, which is the primary commod-ity in the country, and many researchers have investigated thepotential of palm oil as an alternative diesel fuel.

3. Palm oil biodiesel as an alternative diesel fuel in Malaysia

Palm oil has been studied thoroughly as a diesel substitute inMalaysia; being a country rich in palm oil and a major exporterof the commodity, Malaysia has been trying to introduce palmoil as an alternative diesel fuel in the world [61]. According tothe Overview of the Malaysian Oil Palm Industry 2014, the totalexports of Malaysian palm oil products decreased to 25.07 milliontonnes or by 2.5% in 2014 from 25.70 million tonnes exported in2013; however, the total export revenue increased by 3.7% to RM63.618 billion in 2014 from RM 61.363 billion in 2013 as a resultof higher export prices. MPOB has developed a method of convert-ing free fatty acids in CPO, CPS, and CPKO to methyl esters undermild conditions [62]. As shown in Fig. 6, 34% of the total palm oilin the world is from Malaysia. A large amount of the worldwidedemand for palm oil, about 51%, is exported by Indonesia.

According to the Overview of the Malaysian Oil Palm Industry2014, the total exports of palm oil decreased by 4.6% from18.146 million tonnes in 2013 to 17.306 million tonnes in 2014;the largest export market for palm oil is China. The exports of palmkernel oil decreased by 4.6% to 1.116 million tonnes in 2014 from1.170 tonnes in 2013 because of the lower demand for palm oil inChina PR, the US, and Japan. Palm kernel cake exports alsodecreased by 3.5% to 2.574 million tonnes in 2014 from 2.668 mil-lion tonnes in 2013 because of the lower demand for palm oil inSouth Korea, Turkey, China PR, and the EU [62]. Other reasons forthe decrease in the exports of palm oil include the use of other veg-etable oils and the increase in the number of palm oil producingcountries, such that many countries imported oils from neighbor-ing countries because of lower prices.

The total palm oil-planted area increased by 3.1% from 5.229million hectares in 2013 to about 5.392 million hectares in 2014.

F(O

The plantation areas are located in peninsular Malaysia (P.Malaysia), Sabah, and Sarawak. Currently, the largest oil palm plan-tation, which is about 1.511 million hectares or 28% of the total oilpalm plantation area, is located in Sabah. Sarawak has 1.263 mil-lion hectares of oil palm plantation area (23%), and P. Malaysiahas 2.617 million hectares of oil palm plantation area (49%).Fig. 7 shows the areas where oil palms are cultivated in Malaysiafrom 1975 to 2014 [42].

The patented biodiesel production process essentially consistsof two steps: esterification of free fatty acids present in the oil intomethyl esters and transesterification of the neutral glyceride mix-ture directly into methyl esters [63]. A study on palm oil diesel(POD) fuel identified the characteristics of POD. A laboratory eval-uation of palm oil methyl esters was conducted including thedetermination of cetane number [64]. Table 3 shows the composi-tion of fatty acids in POME, and Table 4 shows the properties ofPOME, which performs better than petroleum oil does.

In a field trial program in Malaysia, palm oil was used as fuel formany vehicles, including a tractor, a truck, a Land Cruiser, and amotorized cutter. In 1983, promising results were obtained andengendered numerous experimental works, especially on a labora-tory scale. Within a period of approximately two years, the LandCruiser and truck covered 96,000 km and 98,000 km, respectively,and the tractor was used for 1100 h; all of them were still perform-ing well [31,69]. The preliminary field trial was also performed oneight taxis. They were fueled with methyl esters of refined,bleached, and deodorized (RBD) palm oil, and each covered a totaldistance of 70,000 km; an additional taxi ran on methyl ester ofRBD palm oil and was evaluated using a rolling road dynamometer.The results of the test showed that the power developed by the taxiwas highly similar to that developed when using diesel [70]. Arecent study investigated an Isuzu 4FBI four-cylinder IDI enginefueled with 100% POD, POD blends, and POD emulsions of 10% byvolume with water. The specific fuel consumptions of POD andits emulsions were slightly higher [71]. The University ofTechnology Malaysia (UTM) examined the temporary performanceof Ricardo E-6 and Lister diesel engines fueled with palm oil andfound that palm oil was technically favorable for use in dieselengines. The power output of diesel engines using palm oil wasthe same or higher than the power output when diesel fuel wasused; this finding was ascribed the higher specific gravity of palmoil [72].

At the University of Malaya, palm oil was used as fuel in anIsuzu 4FBI multicylinder diesel engine. However, ordinary dieselwas blended with palm oil at percentages of 25%, 50%, and 75%by volume. The engine performed smoothly, had no startup

0

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Fig. 7. Total area of oil palm plantations in P. Malaysia, Sabah, and Sarawak from 1975 to 2014 [42].

Table 4Fuel characteristics of CPO, CPS, POME, and Malaysian diesel [2,67,68].

Property Units ASTM test method Methyl esters of CPO Methyl esters of CPS POME Malaysian diesel

Density at 40 �C kg/m3 D 4052 855 857 870 823Viscosity at 40 �C mm2/s D 445 4.4 4.5 4.5 4Flash point �C D 93 178 165 174 80Pour point �C D 97 15 18 17 15Cloud point �C D 2500 16 19 18 18Distallation �CI.B.P. �C 313 320 22810% �C 321 331 25820% �C D86 322 332 27050% �C 325 335 29890% �C 332 343 376F.B.P. �C 345 349 400Final Recovery mL 99 98.5 98 –Sulfur content %wt IP 242 <0.04 <0.04 0.04 0.20Gross heat of combustion kJ/kg D 2382 39,700 39,900 40,135 45,800Conradson carbon Residue %wt D 189 0.02 0.05 0.02 0.14

Table 3Fatty acid composition of palm oil, CPO, CPS, CPKO, and palm kernel olein [55,59,65–67].

Carbon number Acid name Chemical formula Biodiesel Palm oil CPO CPS CPKO Palm kernel olein

C8:0 Caprylic C9H10O2 – – – – 4.4 5.4C10:0 Capric C11H22O2 – – – – 3.7 3.9C12:0 Lauric C13H26O2 0.3 1.15 0.3 0.4 48.3 41.5C14:0 Myristic C15H30O2 18.6 2.74 0.8 1.9 15.6 11.8C16:0 Palmitic C16H34O2 0.8 26.18 44.3 52 7.8 8.4C18:0 Stearic C19H38O2 4.5 11.97 5 4.1 2.0 2.4C18:1 Oleic C19H36O2 32.0 35.49 39.1 32.7 15.1 22.8C18:2 Linoleic C19H34O2 39.7 12.76 10.1 7.9 2.7 3.3C20:0 Arachidic C21H42O2 – 1.74 – – 0.2 0.1

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problems, and did not experience any audible knock; comparedwith conventional diesel, palm oil allowed for lower specific fuelconsumption [73].

4. Characterization of palm oil biodiesel

4.1. Economic considerations

Although engine manufacturers have studied the possibility ofusing palm oil as diesel substitute, economic conditions are not

yet deemed favorable and have inhibited development work [74].In Malaysia, the major economic player is the palm oil industry.The economics of palm oil is mostly dependent on the world pricesof methanol, crude petroleum oil, glycerol, and palm oil [36]. Theproduction of oil palm is five times and ten times higher than thatof rapeseed and soybean in the same land, and its total productioncost per unit is lower than those of other oil crops [75]. The cost ofsoybean oil is almost 20% higher than that of palm oil, and rape-seed oil production cost is considerably higher than those of othervegetable oils [24].

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The approximate price of palm oil in the world market is USD607.5 per metric ton in March 2015 [76]. In the EU, almost 41%used palm oil in 2012, with Netherlands and Germany as the lar-gest palm oil-using countries [77]. The cost of palm oil is predictedto decrease in the long run because of the current excess supply inthe market. The actual cost of producing palm oil for fuel in devel-oping countries depends on local factors, mainly the costs of landand labor. Typically, 4–5 tonnes of palm oil can be produced perhectare in a year [78]. An absolute economic comparison betweenpalm oil and mineral oil is difficult and the result varies from onecountry to another.

According to Picken et al. [68], factors that affect cost includethe following:

� Local cost of mineral oil and refining per liter.� Annual cost of a unit area of land for cultivation.� Fuel used in cultivating and harvesting of the land per unit area.� Fuel used as fertilizer on the land per unit area.� Labor cost for the cultivation of a unit area.� Cost processing of vegetable oil per litter.� Taxation system.

For the aforementioned reasons, the use of palm oil fuel is notyet economical. These reasons also affect the economic aspect ofusing palm oil.

As mentioned, the economics of palm oil methyl esters dependconsiderably on the world prices of palm oil, methanol, and fossilfuel. However, in Malaysia, which is a major producer of palmoil, using such oil as an alternative energy source or alternative die-sel fuel is favorable; substantial research has provided evidence forthis assertion [79]. By contrast, developing countries still dependon mineral fuels that produce high levels of pollutants. TheMalaysian government has inspired the development of aneconomic and environmental policy adopting palm oil as analternative fuel in the country, at least for transportation andagricultural vehicles [76].

According to national economics, a country depends on oil rev-enue to survive in the world. At least 90% of government revenuecomes from oil exports. Oil is important and profitable for develop-ing and Middle Eastern countries [80]. Palm oil is widely used ascooking oil in food-processing industries. The higher price of CPOhas an impact on local residents who use this product regularlyin food. In the past few years, cooking oil prices have doubled; suchan increase may be caused by the higher demand in China andIndia [81]. In Malaysia, palm oil production has increased the areaof palm oil plantations through rainforest clearing, and refining ofbiodiesel has been adopted to address the shortage of palm oil.According to a report published in the New York Times on 19January 2008, cooking palm oil prices increased by 75% as theend of 2007. Studies have shown that street vendors in Malaysiaare having difficulty selling cooking oil [82]. Refined palm oil con-tains 50% saturated fat, 39% monosaturated fat, and 11% unsatu-rated fat, making it more suitable for use as cooking oil. Bycontrast, CPO and CPKO are suitable for biodiesel production[83]. According to global estimates, 74% of palm oil is used for foodproducts and 24% is used for industrial purposes [84]. Palm oil is akey to earning foreign currency; providing local and foreign jobs;reducing poverty; improving power generation; and acceleratingnational development, industrialization, and GDP growth [84].

Fuel is in high demand in rich countries, whereas food is in highdemand in developing and poor countries. In most developingcountries, high food prices pose a major challenge to the survivalof poor people and may be caused by political disorder in recentyears [85]. Approximately 85% of the changes in food prices inthe world are caused by unreliable weather patterns, rising energyprices, and increasing food demand, whereas 15% of the changes

are caused by ethanol production [86]. Poor people spend 75% oftheir income on food, but food prices are most volatile in develop-ing countries [87]. Most poor people living below the poverty lineand lived in rural areas. Reduced poverty among small-scale farm-ers, sustainability, and improved nutritional awareness couldresult from palm oil production. Biodiesel production from veg-etable oils offers new sources of income to poor farmers and tothe smallholder sector [88]. Poor and developing countries haveincreased their profits as a consequence of biofuel production.According to theWorld Watch Institute, biofuel production is morebeneficial to the rural poor because global agriculture prices haveincreased as a result of its production. Biofuel production benefits800 million undernourished individuals in rural areas [89]. Fortypercent of the total food production is wasted because of badweather and flooding. As food prices continue to rise, the effectof escalating food prices may be felt even by the urban poor andmay cause food scarcity and poverty. Food security is driven bylower prices of agricultural products, which could hurt more thanit could help people [90]. Corn oil production converted 15% of thetotal corn production in the world supposedly for food into fuel.Many economists have suggested that the conversion from foodinto fuel may be caused by speculations of flood and plunges infood prices [91,92]. Farmers earn more from the higher prices ofbiofuel than from food production. Smallholder average incomefrom palm oil production is seven times more than food productionincome [93]. The main objective of using food for biofuel produc-tion has been pushed to the curb demand. Biofuel must be pro-duced economically, socially, and environmentally in feasibleareas and can be traded freely. Palm biodiesel could be providinggreat benefits; it is more producible in low agriculture lands andlow energy is required for conversion [82]. Food productionrequires many factors, such as useful land, investment, water,infrastructure support, fertilizers, and labor [86]. CPO biodieselcan reduce 41% of exhaust emission than fossil fuel and worksmore efficiently as a carbon sink than rainforests [94]. A smalleramount of fertilizers, fuels, and pesticides are required in palmoil production compared with food production [95]. Palm oilreduced 535,995 USD worth of CO2 per year, and avoided defor-estation worth 21,373 USD per ha. CPO is a cheaper alternativeto fossil fuel; in terms of price, the benefits of using palm biodieselis approximately 11,832 USD per ha per year [96]. Palm oil plantsare more productive and have a life cycle of 20–25 years [97]. Theadvantages of palm in the world market including productivity,volume, versatility, and price. Implementation of Malaysian palmoil as biodiesel may put pressure on certain types of vegetableoil, stabilize food prices, lift the tax burden on biofuel subsidies,and improve the food provision program.

4.2. Engine performance

The relationship among fuel properties, such as viscosity, calori-fic value, specific density, and surface tension are affected byengine performance [30]. Fuel consumption increases withincreasing biodiesel oil in blends and results in better combustionwhen injected into a combustion chamber. The performance of adiesel engine operating on sunflower oil as an alternative dieselfuel was examined for higher fuel consumption and lower torquegeneration. The low percentage of biodiesel (20% or less) blendsprovides higher brake power for completed combustion with lowerfuel consumption. Engine performance has improved by havinghigher calorific value and lower viscosity in biodiesel [98].However, according to the results at maximum fuel delivery ratesof the injection pump with standard calibration, this engine pro-duced equivalent power or minor power increases when operatingon biodiesel oils and biodiesel oil or a diesel fuel mixture.

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Masjuki et al. [99], used coconut oil-blended diesel fuel to oper-ate an IDI diesel engine. The brake power output per specific den-sity was observed at speeds between 800 r/min and 3200 r/min forthe various combinations of fuel. The coconut oil blends developedpower per specific density similar to that of ordinary diesel (OD).Fuel consumption increases with an increasing amount of coconutoil in blended fuels. Overall lubricating oil analysis has shown thatthe results for 10–30% coconut oil blends are better than those for40–50% blended fuels and comparable with the results from OD.Thus, the use of coconut oil blend in diesel engines is expected tobecome a reality in the near future.

A stationary engine test was conducted at the UTM. The testemployed a Ricardo E-6 and a traditional slow-speed single-cylinder Lister stationary engine. The short-term performance ofboth engines fueled with palm oil have shown that palm oil is tech-nically suitable for use in diesel engines [72]. Studies have shownthat POME is much safer because of its high-storage ability. Whenpalm oil was stored for about 12 months in a storage tank, palm oilmethyl ester showed a high flash point. The properties of kine-matic viscosity increased, oxidative stability decreased, and acidvalue, iodine value, cloud point, and pour point were unaffectedduring extended storage of palm oil methyl ester [100]. Whenpalm oil methyl ester was stored for around three months, theproperties of acid value and viscosity increased and the inductionperiod decreased [101]. Palm oil also has higher specific fuel con-sumption; thus, it reduced emission from another fossil fuel usedin light-duty diesel engines [102].

Palm oil blends and diesel fuel are used in KIR-LOSKAR TV-1, afour-stroke diesel engine at varying loads. The maximum output ofthe engine is 5.2 KW with a varying load of 20–100% by maintain-ing constant speed at 1500 rpm. The brake thermal efficiency of25%, 50%, 75%, and 100% of palm biodiesel were 30.895%, 30.56%,29.22%, 29.58%, and 28.65%, respectively. At full load, the brakespecific fuel consumption (BSFC) for 100% palm oil and diesel were274.90 g/KW h and 314.91 g/KW h, respectively. The BSFC for 25%,50%, and 75% of palm oil were observed to be 2.59%, 8.93%, and9.25% higher than that of diesel respectively [32]. When the engineis operated by palm oil or palm oil blends, the BSFC is slightlyhigher at 2–6% for palm oil blends, 14–17% for preheated palmoil, and 17–25% for palm oil methyl ester [103].

Nagi and Nagi [104] tested a four-cycle diesel engine model(DWE-47-50-HS-AV) by using palm oil and the engine has a max-imum torque of 3200 rpm. The test was observed at 650, 1000,1350, 1700, and 2050 rpm, and time was measured for every100 mL fuel consumption. Based on the test, more time is requiredby palm oil for consumption and specific fuel consumption of palmoil is lower compared with that of diesel. Torque and thermal effi-ciency of palm oil biodiesel is lower than that of diesel fuel at var-ious loads [105]. The bsfc has to be found for palm oil blend exceptfrom another biodiesel at 2000 rpm [106]. Based on another study,the BSFC of palm biodiesel for 6.0-L Ford Cargo DI diesel engine has8–10% lower than that of petroleum-based diesel fuel (PBDF), andthe maximum brake torque for waste palm oil methyl ester(WPOME) is 320.24 Nm at 1500 rpm. Brake thermal efficiencyhas decreased by 4%. The brake power of WPOME was obtainedat 50.78 KW at 1500 rpm, indicating an almost 2.5% decrease intotal power [107]. The brake power of WPOME decreased by3.7%, about 65.8 KW at 2000 rpm [108]. Therefore, the brake powerof WPOME is less than that of PBDF.

At low speeds, CPO-OD blends produced higher torque andengine brake power compared with OD fuel; however, at above2000 rpm speeds, CPO-OD blends produced less brake power thanOD fuel. The bsfc for 25%, 50%, and 75% CPO-OD blends were 10%higher than that of OD fuel at engine speeds of 2200–2500 rpm[109]. The average fuel consumption was 8 L per 100 km for urban

and 7 L per 100 km for extra urban when palm oil was used on anElsbett diesel engine running for 80,000 km [110]. Benjumea et al.[33] investigated the combustion and performance of palm biodie-sel fueled in an HSDI engine operating at 2000 rpm and 100 Nm, aswell as the effect of altitudes at 500–2400 m above sea level. Fuelconsumption increased with increasing altitude and the brakethermal efficiency of biodiesel decreased in these altitudes.Moreover, palm biodiesel led to better performance and the brakethermal efficiency was slightly lower than diesel for the altitudes.If the percentage of palm biodiesel increased in biodiesel blends,BSFC also increased because of a lower amount of heating valuein palm biodiesel [111].

Colombian Oil Palm Research Center conducted a challenginglong-term performance evaluation of transit buses fromTransmilenio to the capital of Bogota. Buses were scheduled to tra-vel 100,000 km and PME blends varied from B5 to B50. Specific fuelconsumption, maintenance costs, and emissions were evaluatedand these tests were challenging for PME performance in Bogota.Climate conditions are irregular in Bogota and temperatures rangefrom �8 �C to 20 �C; the city is located at 2600 m above sea level.According to the test, B5 showed improved performance in theseweather conditions [112].

The performance of an Isuzu 4FBI diesel engine was studiedusing palm oil fuel with conventional diesel at percentages of25%, 50%, and 75% by volume [73]. The brake power output atspeeds between 900 rpm and 3000 rpm for various combinationsof fuel were examined. Pure palm oil fuel and its blends developedpower similar to that of pure conventional diesel. The maximumpower for all fuels was observed at 1250 rpm, with conventionaldiesel fuel producing 9.2 kW, followed by fuel blends of 25%,50%, and 75% for palm oil, and 8.79%, 7.75%, and 7.25% for purepalm oil fuel. The brake power of palm oil blends was 0.83% higherthan that of canola blends [113]. The lower viscosity of preheatingCPO did not affect the injection system and also provided smoothfuel even at 100 �C heating. CPO has shown high peak pressure ofapproximately 6% and low period ignition delay of about 2.6�; alower amount of heat was released compared with petroleum die-sel [114]. Various engine problems such as engine deposit, stickingof piston ring, and injector conking were found by using high-viscosity and low-volatility raw vegetable oils in diesel engines.The higher viscosity of palm biodiesel can be caused by pooratomization in fuel, which leads to injector deposits and conkingof valves [115]. Bari et al. [114] observed the performance anddurability of diesel engines with fueled CPO. A longer period ofcombustion was observed in CPO than in diesel fuel. Accordingto the study, CPO showed a heavy amount of carbon deposits fromthe combustion chamber; piston ring wear, scuffing of fuel con-sumption in the cylinder, and irregular spray formed when palmoil biodiesel was used in the diesel engine. Palm oil reduced theamount of unsaturated molecules that could cause oxidation sta-bility to engine performance. Oxidation stability can be causedby harmful effects of filter plugging, deposits, and corrosion[112,116]. Injector deposits of PB20 blend was higher than thoseof diesel fuel at the end of the 150 h endurance test. PB20 blendshowed that overlapping deposits were relatively thick at the tipand the injector hole exit along the shrinkage of the injector holediameter [117].

A four-stroke DI diesel engine, model Kubota ASK-R3100-50-B,operates at a constant speed of 1500 rpm. The brake thermalefficiency of 20% palm oil blends is 0.2% higher than that ofdiesel. Compared with diesel, palm oil blends have less brakethermal efficiency because of lower calorific values at 40%, 60%,and 100% [118]. Therefore, the average power output of palm oilbiodiesel and blends is almost the same as that of petroleum diesel[119].

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4.3. Exhaust emissions

When a diesel engine is operated with fossil fuel, it emitsexhaust gases such as hydrocarbon (HC), carbon monoxide (CO),carbon dioxide (CO2), particulate matter (PM), and nitrogen oxide(NOx) [120].

Based on numerous studies conducted in the last 20 years, veg-etable oils derived from fuel can be used in a diesel engine toreduce engine-exhaust emission components, such as unburnedfuel, HC, CO, and PM emissions. However, unlike petroleum diesel,biodiesel or vegetable oil contains oxygen, which can contribute tolower levels of PM emissions [121]. The ability of biodiesel toreduce emissions was recognized by the national biodiesel board,which developed a program to commercialize biodiesel as an alter-native fuel [122].

In the study conducted by Shehata [123], exhaust temperaturewas recorded for diesel, palm oil, cotton oil, and flax oil with orwithout exhaust gas recirculation (EGR) for a Deutz F1L511-typediesel engine. The gaseous emissions were measured at full loadat the speed of 1600 rpm without EGR and at 75% load at the speedof 1400 rpmwith EGR. Exhaust gas temperature increased with theincrease in engine speed and also decreased with the increase inEGR for diesel, palm, cotton oil, and flax oil. The highest exhaustgas temperature was found from palm oil at high engine speedwithout EGR and the exhaust gas temperature decreased by 7%for palm oil with the increase in EGR by 0–15% at 1400 rpm speedcompared with diesel, cotton, and flax. The higher ignition delayand unburnt portion to burn at the later diffusion combustionphase causes higher exhaust-gas temperature [124].

Ndayishimiye and Tazerout [103] observed minimal differenceamong HC, CO, and NOx emissions when running on any of thesefuels. The emission results for the CI engine (Model Lister–PetterTS1 at maximum speed of 3500 rpm) illustrated minimal differ-ence in the level of emissions from the combustion of these fuels.Palm oil fuel gives nearly constant HC emissions over light loadrange, whereas petroleum-based fuel exhibited worsening lightload emissions. At middle and full loads, HC emission was signifi-cantly reduced with the edition of methyl esters in biodiesel. Thehigher viscosity and lower cetane number of palm oil comparedwith diesel fuel leads to higher HC emission. In another study byLiaquat et al. [125] using palm oil fuel in a four-stroke direct injec-tion (DI) diesel engine, exhaust emissions were measured with aBosch exhaust gas analyzer (model ETT 0.08.36) for emission char-acteristics and Bacharach (Model CA300NSX) for emission concen-trations. The test was conducted for about 250 h at an engine speedof 2000 rpm. Both CO and CO2 emissions indicated decreasingtrends as the percentage of palm oil fuel increased in various fuelblends compared with diesel. These observations showed thatpalm oil fuel was environment-friendly as far as the two gaseswere concerned.

Canakci et al. [126] reported that exhaust gas emission wasmeasured using a Bilsa MOD 500 exhaust gas analyzer as an emis-sion device. Percentages of CO2, CO, and O were determined. Thisstudy was conducted only on a 1.8 VD Diesel BMC diesel engine.The result showed that CO2 decreased with increasing speed.With palm oil, the percentage of CO2 was higher compared withthat of conventional diesel. However, the percentage of CO wasnegligible because improved combustion took place in the enginefueled with palm oil. In general, palm oil fuel is not expected tocause environmental problems because results gathered from thetrial had shown that the levels of pollutant concentrations andsmoke were generally comparable or less and were lower at highengine speed [127,128].

Investigations around the world were conducted to study theeffects of fuel properties, such as cetane number, aromatic content,and viscosity on emission characteristics. Cetane number is mostly

generated for NOx emission from diesel engines. However, theeffect of each property is difficult to observe separately becauseeach property affects the others [129]. Lower cetane number withkeeping aromatic content, particulate emissions decrease, and NOx

emission increases at high load. As aromatic content increases,both NOx and particulate emissions also increase at high load,although overall combustion characteristics are not sensitive toaromatic content and high-pressure injection produces high NOx

concentration but less particulate emissions [130].De Almeida et al. [131] reported that NOx emissions were lower

for palm oil compared with diesel fuel at 1800 rpm. When thespeed range is 2500 rpm to 3500 rpm, palm oil and diesel fuel indi-cate almost the same NOx emissions. The NOx emission is mainlycaused by higher combustion temperatures. NOx emissionsincreased with increasing engine loads [32]. Abedin et al. [132]observed that based on the emission characteristics of palm oil bio-diesel compared with jatropha, lower CO and HC emissions pro-duced an average of 8.8% and 2.2% than the jatropha blends,respectively. Lower CO and HC emissions were caused by shorterignition delay and oxygen contents in blends. The emission ofNOX decreased with about 3.3% of palm oil biodiesel. Higher cetanenumber, lower viscosity, and density were the most physical prop-erties with lower NOx emission.

4.4. Wear characteristics

When two contact surfaces slide against each other, some wearand friction at the contact surface are produced, which generallydepends on load, speed, temperature, lubricant, and additive for-mulation. Nowadays, design of wear is a major challenge formechanical engineers. Every object wears out because enginesand machines operate continuously, and their moving parts aredamaged by wear and friction. Continuous operation may causecatastrophic failure of pistons or cylinder liners, and may lead toa sudden and costly breakdown of the engine [133]. Therefore, atribological evaluation of palm oil fuel is important. Fazal et al.[134] concluded that because an engine was designed for use withconventional diesel fuel, some defects were anticipated, such asclogging in the fuel filter, nozzle deposits, and corrosion when run-ning on palm oil. To study these effects, an engine must be runningfor several hundred hours. Moreover, the effects of palm oil fuelson boundary-lubricated wear of cast iron and mild steel wereinvestigated by Masjuki and Maleque [135]. The pin-on-disc andtri-pin-on-disc friction and wear apparatus were used to studythe effects of different concentrations of palm oil fuel contami-nated lubricants on the characteristics of cast iron and mild steel.For comparison, base diesel engine lubricating oil and pure palmoil fuel were used as lubricants. In the case of cast iron, the exper-iments were performed for a sliding speed of 0.2 m/s, specific loadof 1 MPa, and at room temperature. In the case of mild steel, theapparatus was fabricated to give a projected contact stress byapplying loads of 57 N and 80 N per pin. The amount of wearwas measured as the weight losses of the cast iron and mild steeltest specimens. In the former case, the addition of about 5% in theweight of palm oil fuel into the engine lubricant improved the wearresistance of the specimens. In the latter case, increasing the per-centage of contamination of the lubricant increased the wear rate.For the same percentage contamination, the wear rate because ofthe addition of palm oil fuel was less drastic than that for conven-tional diesel.

Basically, engine oil was contaminated because of the wear ofvarious engine components such as the piston and piston pins, pis-ton rings, cylinder liner, cam bearing, tappet, valve guides, crank-shaft, and valve systems, which are the critical wear componentsof diesel engines [136]. Fuel contains oxygen, which leads to morewear with high sulfur contents. Metal surfaces come into contact

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through the chemical reaction between oxygen and unsaturatedfatty acid, which consists of biodiesel [137]. Problems such aschanging lubricating properties, carbon deposits, and sticking ofpiston ring were observed in diesel engines after long-termoperation with biodiesel [138].

During the 150 h endurance test, the metallic particle concen-trations of PB20 were higher than those of diesel fuel [117]. Inthe lubrication analysis, when a diesel engine was running forabout 100 h with RPO biodiesel, the metal contents such as Cr,Al, Cu, and Si were higher than that of diesel fuel. According tothe engine wear evaluation, the weight loss of fuel pump, fuelvalve, exhaust valve, inlet valve, and piston engine componentsare almost the same for diesel and palm biodiesel. The highestamount of weight loss was observed in a compression ring whenthe engine was fueled with palm biodiesel compared with diesel.The weight loss of the compression ring for refined palm biodieselwas 6.1 times higher during the first 500 h and 4.4 times higherduring the second 500 h compared with the weight loss in a die-sel–fueled engine. When the engine was running for about1000 h, the piston ring gap increased for the refined palm oil andthe gap also increased if the engine was running at 2000 h [139].

Fazal et al. [140] investigated the wear and friction of palm oilbiodiesel. The friction and wear characteristics were investigatedusing a four-ball machine (IP 239/45) operated with palm oilmethyl esters. The test conducted at speed speed which was600 rpm to 1500 rpm and instead at 1200 rpm and ASTM D4172standard. The variation of the friction coefficient calculated fromtorque has two parts. The average friction coefficient increaseswith rotating speed and the average friction coefficient of dieselis much higher than that of biodiesel. The wear and friction is alsohigher at high speed. Wear and friction decreased with the increasein palm oil concentration. Higher concentration of biodiesel leadsto a consistent reduction of wear at almost 20% lower than thatof diesel at 1500 rpm. At above 20% biodiesel concentration, thelubricity in terms of wear and friction decreases with high speed.

Ashraful et al. [141] observed the use of palm oil fuel in an Isuzu(model 4 FBI), multicylinder IDI diesel engine, and the researchersmonitored engine wear by analyzing the lubricating oil for metalwear levels. The metallic wear debris analysis in the lubricanttaken during the running hours of the engine for all metals (Al,Pb, Fe, and Cu) except lead was studied, which indicates that theirconcentration in the lubricant sump decreased significantly whenpalm oil fuel and its blends were used as fuel compared with ordi-nary fuel alone. Tribologically, palm oil fuel blended with conven-tional diesel offered an appealing fuel alternative for small dieselengines, especially those that run at low speeds. The engine wasrun and sent to a laboratory for wear debris, total base numberor total acid number (TAN), and viscosity analysis. The results fromthis analysis indicated that no substantial changes were foundwhen burning pure conventional diesel, pure palm oil, or one ofthe blends. Fuel injector polymerization and carbon deposits wereinspected after every run. It was observed that the metal-wearlevels inspection results at the end of each test run for all the var-ious fuels showed minimal polymerization of the fuels.Correspondingly, the amount of carbon deposit is also comparable[142].

Haseeb et al. [143] investigated the effect of temperature on thefriction and wear of palm oil biodiesel. The friction and weardecreased with the increase in temperature by the lubricity ofpalm biodiesel. The oxidative products that increase TAN are sig-nificant in reducing wear, whereas the corrosive effect is minor.The wear and deformation on the surface increases the tempera-ture as the biodiesel concentration increased. Palm oil biodieselhave better lubricity at even higher temperatures.

Palm oil methyl ester was also used in blended lubricant for atwo-stroke, single cylinder engine at the University Malaya. A

Yamaha 100 sports gasoline engine without any modificationwas also used. The engine specification and lube-oil blendedconfiguration are given in reference [144]. In this case, thepiston-ring wear rate reduced slightly in the oils blended withPOME, notably with 5% POME compared with oils without POME.Carbon deposits on the piston, spark plug, and cylinder headsincrease as the percentage of POME increased in the lubricatingoil blends [145]. At the University Malaya, a small amount of palmoil diesel (POD) was also used as a lubricant additive and theresults indicate that POD can help reduce the wear because itcontains fatty acids, which are additives in a commercial enginelubricant [146].

5. Discussion

Nowadays, globalization and industrial developments in theworld require more fossil fuel while aiming to reduce environmen-tal pollution through green technology. Production and consump-tion of fossil fuel has increased by about 5–6% every year. Palmbiodiesel is one alternative fuel that can reduce environmental pol-lution and meet the demand for fossil fuel. Compared with othervegetable oils, palm oil is a more sustainable and affordable fuelthat is environment friendly and has greater potential energy andeconomic benefits. Malaysia is a developing country that is also thesecond highest producer of palm oil in the world, with major mar-kets in Europe and the US. Palm oil is also used as cooking oil andmany food manufacturing factories use about 74% of palm oil forfood processing. Developing countries spend most of their moneyon imported petroleum diesel. According to MPOB economic statis-tics in 2014, Malaysia produced 19.667 million tonnes of palm oil,which was approximately 5.392 million ha. Malaysia earned RM63.618 billion revenue by exporting 25.07 million tonnes of palmoil in 2014. In low-temperature countries, palm oil is very suitablefor diesel engines and can be used under �21 �C to 0 �C tempera-ture conditions. Many studies illustrate that better diesel engineperformance is achieved by using palm oil biodiesel. Higher speci-fic fuel consumption was observed in palm oil biodiesel and itsblends is higher than in diesel fuel. In diesel engines, exhaust emis-sions, such as HC, CO, CO2, smoke, and PMwere reduced because ofpalm oil biodiesel compared with diesel. Engine fouling compo-nents, such as fuel injector, fuel pump, piston ring, filter plugging,and various sliding engine parts are required for lubrication. Palmoil and blends have better lubrication properties than diesel in ashort-term engine run. When an engine has been running for longperiods, palm oil does not provide better lubrication and can be acause of carbon deposits, piston-ring sticking, and changing lubric-ity problems of the engine. Palm oil contains a lower amount ofmetal compositions, such Fe, Pb, Cr, and Si, compared with diesel.Production of palm oil biodiesel is more profitable for farmers andsmall holders and also develops livelihood, education, and medicalfacilities in developing countries. In summary, palm oil and itsblends have better engine performance, lower exhaust emission,good lubrication properties, and economical sustainability.

6. Conclusions

Diesel engine using vegetable oil as alternative fuel (e.g., palmoil methyl esters) is potentially highly attractive and performsmuch better than other types of fuel. The properties of palm oil fuelare not significantly different from those of conventional dieselexcept that the former has a higher specific gravity and viscosityand a slightly lower cetane index. According to the present study,performance and exhaust emissions using palm oil fuel and itsblends with conventional diesel fuel in stationary diesel enginesare comparable to those of conventional diesel fuel. Moreover,

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palm oil fuel is environment-friendly and exhaust emission ismuch cleaner with reduced black smoke, CO, HC, and absence ofSO2 excluding NOX. Wear analysis also showed that palm oil doesnot seriously affect engine and bearing components, does notdegrade lubricating oil, and produce comparable amounts ofcarbon deposits. Palm oil and its blends improve the anti-wearcharacteristics of the engine components. Compared with pureconventional diesel fuel, palm oil and its emulsion with ordinarydiesel fuel show a slightly higher specific fuel consumption. Thehigh fuel consumption of palm oil fuel and its blends can counter-act the lower heating values such that the engines consume anequal amount of energy. The ignition delays for palm oil fuel areshorter than those for diesel fuel.

Generally, economic prospects for this fuel are not yet promis-ing because of factors such as production cost and fuel economy.However, if research to reduce production cost is intensified, thenenergy produced by engines using palm oil are likely to becomeeconomically competitive with virtually all other forms of energy.Such a development is expected to reduce global dependence onmineral oil for the transportation and industrial sectors. In sum-mary, Malaysia has attempted to introduce palm oil as an alterna-tive fuel for diesel engines because it can enable communities inthis country and elsewhere to produce their own fuel, therebyfreeing them from their dependence on petroleum fuels that aresubject to price fluctuations and supply problems. More impor-tantly, money that would otherwise be spent on fuel can be savedto support the needs of the community.

Acknowledgement

The authors would like to appreciate University of Malaya forfinancial assistance by means of High Impact Research grant titled:‘‘Clean Diesel Technology for Military and Civilian TransportVehicles” of grant number UM.C/HIR/MOHE/ENG/07.

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