Physicochemical, Performance, Combustion and

energies Article

Physicochemical, Performance, Combustion and Emission Characteristics of Melaleuca Cajuputi Oil-Refined Palm Oil Hybrid Biofuel Blend Sharzali Che Mat 1,2 , Mohamad Yusof Idroas 1, *, Yew Heng Teoh 1 and Mohd Fadzli Hamid 1 1

2

*

School of Mechanical Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal 14300, Malaysia; [email protected] (S.C.M.); [email protected] (Y.H.T.); [email protected] (M.F.H.) Faculty of Mechanical Engineering, Universiti Teknologi MARA Pulau Pinang, Permatang Pauh 13500, Malaysia Correspondence: [email protected]; Tel.: +604-5996-301

Received: 13 September 2018; Accepted: 28 September 2018; Published: 14 November 2018







Abstract: To reduce the economic impact caused by the fossil fuel crisis and avoid relying on existing biofuels, it is important to seek locally available and renewable biofuel throughout the year. In the present work, a new light biofuel—Melaleuca Cajuputi oil (MCO)—was introduced to blend with refined palm oil (RPO). The physicochemical properties, combustion characteristics, engine performance, and exhaust emissions were comprehensively examined. It was found that the higher the percentage of MCO, the lower the viscosity and density of the blends obtained. Calorific value (CV) was increased with the increase of MCO fraction in the blend. Regression analysis has suggested that the blend of 32% (v/v) of RPO and 68% (v/v) of MCO (RPO32MCO68) is optimal to obtain viscosity and density in accordance with ASTM 6751/EN 14214 standards. The experimental results show that the in-cylinder pressure, brake torque, and brake power of the optimal blend were slightly lower than those of baseline diesel fuel. Brake specific fuel consumption (BSFC), carbon monoxide (CO), and unburnt hydrocarbon (HC) were found to be slightly higher compared to diesel fuel. Notably, nitrogen oxides (NOx ) and smoke opacity were found to be decreased over the entire range of the test. Overall, the optimal blend of RPO32MCO68 has shown a decent result which marks it as a potential viable source of biofuel. Keywords: Melaleuca Cajuputi oil; refined palm oil; hybrid biofuel; viscosity; binary blend

1. Introduction The rising demand for global energy, depletion of fossil fuel, and concern over environmental issues has led to an intensive search for renewable and reliable biofuel. The fluctuation of crude oil price and currency exchange rate could affect the energy supply and economics of those countries that solely depend on imported oil from others. To reduce the economic impact caused by the fuel crisis, it is important to seek biofuel which is available locally and renewable throughout the year. Thus, continuous effort in the search for new energy resources is very important to ensure energy security for the future. Over the past decades, straight vegetable oils (SVOs) have gained interest among researchers as a potential fossil fuel replacement. Their comparable properties to diesel, nontoxicity, and the absence of sulfur content make them an attractive alternative biofuel. At present, the European Union is the major producer of rapeseed and sunflower oils, while soybean, palm, and coconut oils are largely produced in the United States, South East Asia, and Philippines, respectively [1]. At present, over 95% of biodiesel produced globally is from edible vegetable oil [2].

Energies 2018, 11, 3146; doi:10.3390/en11113146

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Typical edible SVOs, such as sunflower, soybean, rapeseed, and palm oils, have been numerously studied and short-term tests revealed that those SVOs can be used directly on a compression ignition (CI) engine [3–7]. Notably, SVOs have slightly lower engine performance compared to diesel fuel. In general, nitrogen oxide (NOx ) emission was lower whereby carbon monoxide (CO) and hydrocarbon (HC) emissions were higher than diesel fuel. Nonetheless, the brake specific fuel consumption (BSFC) of all tested fuels is higher than diesel fuel. Higher BSFC is associated with high viscosity and low calorific value of the vegetable oil [8,9]. However, due to the concern over competition between food supply and fuel, extensive studies on non-edible vegetable oil have been carried out for the past decade. Jatropha, mahua, linseed, rubber, karanja, and cottonseed oil are among the non-edible oils that receive attention from many researchers [10–14]. Various blends of non-edible oil with diesel or biodiesel were found to have comparable engine performance and combustion as compared to diesel fuel. In addition, it was reported that the biodiesel fuels have demonstrated a better tribological performance than the diesel fuels [15]. Even though non-edible oils have the potential as an alternative to edible oil, they are yet to reach commercial scales for feedstock production. As a comparison, palm oil yielded an average 4000–5000 kg/hectare/year, while oil yielded for jatropha and karanja is less than 2500 kg/hectare/year [16]. With this consideration, palm oil was chosen in the present study. Recently, new light biofuels such as eucalyptus, pine, and camphor oils have been studied by a few researchers as a new source of biofuels [17–19]. In contrast to SVO, these light biofuels have relatively lower viscosity and high volatility. Unlike SVO, which is produced from the seed or kernel, eucalyptus oil is obtained mostly by a steam distillation process of leaves and twigs of the plants (Eucalyptus globulus) while camphor oil is extracted by steam from the chipped wood of the camphor tree (Cinnamomum camphora). Meanwhile, pine oil is derived from the resin of the pine tree (Pinus sylvestris). Back in 1981, Hoki et al. [20] studied various gasoline–eucalyptus oil blends on engine performance. They found that the performance of blended fuel is similar to gasoline fuel. Blended fuel also provides better anti-knocking compared to gasoline, due to its high octane number. Later, Poola et al. [21] found that a blend of 20% eucalyptus oil with gasoline provides better engine performance than gasoline fuel at a higher compression ratio. Hydrocarbons and carbon monoxide were also found to be lower compared to gasoline fuel. Despite eucalyptus oil being tested on a spark ignition engine, Devan and Mahalakshmi [22] studied a blend of paradise oil methyl ester and eucalyptus oil as the fuels for a diesel engine. Notable reductions of CO, HC, and smoke, but a slight increase of NOx emission compared to diesel fuel, were observed. The blend of 50% eucalyptus oil exhibited similar performance to that of diesel fuel. A blend of camphor oil [18] and pine oil [23] has also been reported to produce better performance, combustion, and emission characteristics. Recently, a blend of eucalyptus oil with palm kernel methyl ester has been reported to enhance engine performance and reduce certain emissions, especially at high load conditions [24]. In the present study, a new light biofuel—Melaleuca Cajuputi oil (MCO)—has been introduced and blended with refined palm oil (RPO) as a strategy to reduce the viscosity, density, and enhance the volatility of the blend. MCO is highly volatile and has low viscosity as compared to RPO, which has relatively low volatility and very high viscosity. The physicochemical characteristics of RPO-MCO blends are analyzed and compared to ASTM 6751/EN 14214 standards to see its potential as a new source of biofuel. In this study, a regression analysis method was employed to determine the optimal blend ratio. The optimized blend is further tested on a single cylinder diesel engine to investigate its performance, combustion, and emission characteristics. Overview of Melaleuca Cajuputi Oil and Refined Palm Oil Melaleuca cajuputi is a local tree species found in northern Australia, Indonesia, Malaysia, Thailand, Vietnam, Cambodia, and Papua New Guinea. Different terms are used in different countries to refer to the Melaleuca cajuputi tree, such as Kayu Putih (Indonesia) and Gelam (Malaysia). The Cajuputi

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(also spelt cajuput or cajeput) is possibly referring to the Indonesian name for the tree [25,26]. Energies 2018, 11, x 3 of 20 Melaleuca Cajuputi oil (MCO) is categorized as an essential oil commercially used as a home remedy for stomach headaches, colds, and relief ofrelief itching caused caused by insect mosquito bites [26]. remedy for aches, stomach aches, headaches, colds, and of itching by or insect or mosquito bites Trees of these species can typically reach up to 25 m in height. Figure 1 shows the tree and [26]. Trees of these species can typically reach up to 25 m in height. Figure 1 shows the tree andleaves leaves ofofMelaleuca Melaleucacajuputi cajuputiwhile whileFigure Figure2 2shows showsthe theneat neatMCO MCOand andrefined refinedpalm palmoil oil(RPO). (RPO).The Theworld world production of MCO is estimated to be more than 600,000 kg annually where Indonesia and Vietnam production of MCO is estimated to be more than 600,000 kg annually where Indonesia and Vietnam produce producemore morethan thanhalf halfofofthe thetotal totaloil. oil.Indonesia Indonesiaisisestimated estimatedtotoproduce producemore morethan than350,000 350,000kgkgofofoil oil annually, and Vietnam produces an average of 100,000 kg of oil per year [27,28]. This oil is extracted annually, and Vietnam produces an average of 100,000 kg of oil per year [27,28]. This oil is extracted from fromthe theleaves leavesand andtwigs twigsmostly mostlythrough throughwater-steam water-steamdistillation. distillation.This Thisextraction extractionmethod methodisischeap, cheap, simple, and not hazardous. An alternative process, like supercritical fluid extraction, simple, and not hazardous. An alternative process, like supercritical fluid extraction,isisseldom seldomused used because it is more expensive compared to the water-steam distillation process. Figure 3 shows because it is more expensive compared to the water-steam distillation process. Figure 3 showsthe the schematic schematicdiagram diagramofofthe thewater-steam water-steamdistillation distillationmethod methodtotoextract extractMCO. MCO. This complexmixture mixture volatile components extracted the leaves andthrough twigs Thisoil oil is is aacomplex of of volatile components extracted fromfrom the leaves and twigs through water-steam distillation. can be intogroups two main which are water-steam distillation. MCO can MCO be divided intodivided two main whichgroups are monoterpenes monoterpenes (monoterpenes hydrocarbon and oxygenated monoterpenes) and sesquiterpenes (monoterpenes hydrocarbon and oxygenated monoterpenes) and sesquiterpenes (sesquiterpenes (sesquiterpenes hydrocarbon and oxygenated sesquiterpenes) [29]. As previously the majorof hydrocarbon and oxygenated sesquiterpenes) [29]. As previously reported, the reported, major constituent constituent of MCO is 1,8-cineole comprising 30% to 70% of the oil [25,30]. In addition, MCO comprises MCO is 1,8-cineole comprising 30% to 70% of the oil [25,30]. In addition, MCO comprises lipophilic lipophilic compound; this lipophilicity MCO solubility SVOs andrange a wideofrange compound; this lipophilicity propertyproperty enhancesenhances MCO solubility in SVOs in and a wide liquid ofhydrocarbons liquid hydrocarbons without the presence of a surfactant [26]. without the presence of a surfactant [26]. Refined product from from the thefractionation fractionationprocess processofofcrude crude palm which Refinedpalm palmoil oil(RPO) (RPO) is is aa product palm oil,oil, which has has better flow properties comparedtotocrude crudeoil. oil.InIngeneral, general,crude crude palm palm oil oil is better flow properties compared is aa semi-solid semi-solidfat fatatat ◦ temperatures temperatureslower lowerthan than2020 C. °C.Palm Palmoil oilwas waschosen chosenininthis thisstudy studybecause becauseofofits itsabundantly abundantlyavailable available feedstock and some of its properties are similar to diesel fuel [31]. In comparison, feedstock and some of its properties are similar to diesel fuel [31]. In comparison,palm palmoil oilyields yieldsthe the highest oil compared to soybean, sunflower, rapeseed, or even other non-edible vegetable oils. Palm oil highest oil compared to soybean, sunflower, rapeseed, or even other non-edible vegetable oils. Palm can an average of 4 to oil of every year for every of landof[32]. high yield oil produce can produce an average of54tons to 5of tons oil every year for hectare every hectare landThe [32]. The high ofyield palmofoilpalm is making it a promising feedstock for an alternative biofuel. Despite numerous research oil is making it a promising feedstock for an alternative biofuel. Despite numerous conducted on non-edible oils, those oils, non-edible oils are still unable to compete palmwith oil inpalm terms research conducted on non-edible those non-edible oils are still unable towith compete oil ofinoil yielded. terms of oil yielded.

(a)

(b)

Figure1.1.(a) (a)Melaleuca Melaleucacajuputi cajuputitree treeand and(b) (b)Melaleuca Melaleucacajuputi cajuputileaves. leaves. Figure

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Figure 2. (a) Melaleuca Cajuputi oil and (b) refined palm oil. Figure 2. (a) (a) Melaleuca Cajuputi oil and (b) refined palm oil.

Figure 3. Water-steam distillation method.

2. Materials and Methods

Figure 3. Water-steam distillation method. Figure 3. Water-steam distillation method.

2. Materials and Methods 2.1. Materialsand 2. Materials Methods

Melaleuca Cajuputi oil (MCO) used in this study was purchased from a local supplier who 2.1. Materials 2.1. Materials imports it from Indonesia. In Indonesia, most of the Cajuputi trees are found in the Maluku islands. Melaleuca Cajuputi oil (MCO) used in this study was purchased from a local supplier who MCOMelaleuca is highly volatile andoilhas a clearused greenish color. Meanwhile, the refined palm oil (RPO) usedwho was Cajuputi (MCO) in this study was purchased from a local supplier imports it from Indonesia. In Indonesia, most of the Cajuputi trees are found in the Maluku islands. purchased from Indonesia. the local market. imports it from In Indonesia, most of the Cajuputi trees are found in the Maluku islands. MCO is highly volatile and has a clear greenish color. Meanwhile, the refined palm oil (RPO) used MCO is highly volatile and has a clear greenish color. Meanwhile, the refined palm oil (RPO) used wasHybrid purchased from the local market. 2.2. Biofuel Preparation was purchased from the local market. HybridBiofuel biofuelPreparation of RPO-MCO blends was prepared on a volume basis (v/v). Two samples of straight 2.2. Hybrid 2.2. Hybrid Biofuel Preparation oil of 100% RPO and 100% MCO, as well as three blends at a mixing ratio of 25% (MCO25RPO75), Hybrid biofuel of RPO-MCO blends was prepared on a volume basis (v/v). Two samples of 50% Hybrid (MCO50RPO50), 75% (MCO75RPO25) MCO with werebasis prepared. Duesamples to MCO’s biofuel of and RPO-MCO blends was prepared on aRPO, volume (v/v). Two of straight oil property, of 100% RPO and 100% MCO, as well as three blends at a mixing ratio of 25% lipophilicity is able to blend RPO any ratio without the presence of a surfactant [26]. straight oil of 100% itRPO and 100% with MCO, as atwell as three blends at a mixing ratio of 25% (MCO25RPO75), 50% (MCO50RPO50), and 75% (MCO75RPO25) MCO with RPO, were prepared. This advantage leads to simplicity of the blend at minimum cost and fast preparation. Each blend was (MCO25RPO75), 50% (MCO50RPO50), and 75% (MCO75RPO25) MCO with RPO, were prepared. Due to MCO’s mixed lipophilicity property, it is able to gravitational blend with RPO at any ratio without the presence homogenously with aproperty, magnetic it stirrer. stability [33]without was conducted for a Due to MCO’s lipophilicity is ableThe to blend with RPO at anytest ratio the presence of a surfactant [26]. This advantage leads to simplicity of the blend at minimum cost and fast month to observe anyThis signsadvantage of phase separation. A stable blend important to ensure cost the quality of of a surfactant [26]. leads to simplicity of theis blend at minimum and fast preparation. Each blend was homogenously mixed with a magnetic stirrer. The gravitational stability the fuel and make it commercially usable. preparation. Each blend was homogenously mixed with a magnetic stirrer. The gravitational stability test [33] was conducted for a month to observe any signs of phase separation. A stable blend is test [33] was conducted for a month to observe any signs of phase separation. A stable blend is 2.3. Physicochemical Analyses important to ensureProperties the quality of the fuel and make it commercially usable. important to ensure the quality of the fuel and make it commercially usable. The kinematic viscosity of RPO, MCO, and their blends were measured according to American 2.3. Physicochemical Properties Analyses 2.3. Physicochemical Properties Analyses Society for Testing and Materials (ASTM) D445. Calibrated glass capillary viscometer (Cannon-Fenske The kinematic viscosity of RPO, MCO, and their blends were measured according to American The kinematic viscosity of RPO, MCO, and their blends were measured according to American Society for Testing and Materials (ASTM) D445. Calibrated glass capillary viscometer (CannonSociety for Testing and Materials (ASTM) D445. Calibrated glass capillary viscometer (Cannon-

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viscometer) was used to measure the viscosity values at 40 ◦ C. Kinematic viscosity was obtained by multiplying the time taken for MCO flowing to pass through a viscometer with the tube constant provided by the manufacturer. The density was obtained by dividing mass over the volume of the biofuel sample. The volume was measured using a 25 mL Gay-Lussac pycnometer at an ambient temperature (27 ◦ C) and weighed using a high precision Shimadzu ATX224 analytical balance. The pycnometer used was certified according to ISO 3507. The calorific value was measured according to ASTM D240. An adiabatic oxygen bomb calorimeter (Nenken 1013-B, Japan) was used to measure the energy available from the biofuel. RPO fatty acids and MCO constituents were analyzed using the Perkin Elmer, Clarus 600 gas chromatography mass spectrometry (GC-MS). The GC-MS used helium gas as a carrier with a column size of 30 m × 250 µm. The initial temperature was 50 ◦ C and then increased to 230 ◦ C at 3 ◦ C/min. The chemical compositions were confirmed by comparing their retention times and mass spectra with data from library databases and published literature. The flash point value was measured according to ASTM D3828. A closed cup flash tester (K16500, Koehler instrument company, USA) was used to measure the flash point value of the MCO. The acid value of MCO was measured according to ASTM D664. A 785 DMP Titrino (Metrohm, Switzerland) was used to measure the amount of acidic substance in the oil. Generally, a high acid value will cause corrosion to the fuel system and parts of the internal combustion engine. The water content of MCO was measured according to European Standards (EN) 12937 and carried out on a 787 Karl Fisher titrator (Metrohm, Switzerland). High water content will likely promote the corrosion of the engine parts and injection system. Boiling point was determined using the Melting Point M-565 (BUCHI, Switzerland). The measurement method was performed according to the manufacturer’s standard. 2.4. Hybrid Biofuel Optimization and Selection In the present study, a high viscosity RPO and low viscosity MCO were used to formulate a hybrid biofuel, aiming to study its potential as a new source of biofuel. This hybrid biofuel is totally 100% neat oil, which does not include any biodiesel or fossil fuel in its preparation. Somehow, at present, there is no specific biofuel standard for such a blend. Therefore, in this work, the newly developed hybrid biofuel will be benchmarked against the ASTM D6751/EN 14214 standards as guidelines. It is renowned that RPO is the promising biofuel alternative to fossil diesel. However, the main reasons why RPO cannot directly be used as diesel engine fuel are its relatively high viscosity and density, which lead to poor atomization, low volatility, and excessive carbon deposit inside the combustion chamber in the long term. Thus, in this study, only the selected and optimized hybrid biofuel blend will be chosen to be tested on a diesel engine to investigate its performance and emission characteristics. Obviously, viscosity and density have enormous influence on fuel spray characteristics, fuel atomization, flow properties, engine performance, and exhaust emissions [34–36]. Therefore, in this study, these two key properties were thoroughly optimized to meet the ASTM D6751/EN 14214 standards before the fuel was introduced to the engine. The data of physicochemical properties were analyzed using the regression method to generate a mathematical model that presented the correlation between blending ratio and its effect on viscosity or density. The mathematical model obtained was used to predict the optimum blend proportion for a desirable viscosity and density according to ASTM D6751/EN 14214. This optimization method was very beneficial to expedite the experiment and reduce cost and waste of materials compared to the trial and error experiment. 2.5. Experimental Setup and Measurement Procedure In this study, a single-cylinder air-cooled four-stroke diesel engine manufactured by Yanmar (Italy) was used for the experiment. The specifications of the engine are tabulated in Table 1. The engine

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power. The fuel mass consumption was measured using an electronic scale with a 0.1 gram accuracy. was coupled to the 20 kW eddy current dynamometer to measure the brake torque and brake power. In order to measure the air flow rate, a mass air flow sensor (hot wire type) was used. In addition, The fuel mass consumption was measured using an electronic scale with a 0.1 gram accuracy. In order the exhaust gas temperature was measured using a K-type thermocouple. to measure the air flow rate, a mass air flow sensor (hot wire type) was used. In addition, the exhaust The in-cylinder pressure was measured using a Kistler 6051A piezoelectric pressure transducer gas temperature was measured using a K-type thermocouple. mounted at the top of the cylinder head and the signal was transmitted to a Kistler 5027A12 charge The in-cylinder pressure was measured using a Kistler 6051A piezoelectric pressure transducer amplifier. Furthermore, the crankshaft rotation angle was measured using an incremental type rotary mounted at the top of the cylinder head and the signal was transmitted to a Kistler 5027A12 charge encoder. amplifier. Furthermore, the crankshaft rotation angle was measured using an incremental type In this study, the exhaust emissions and smoke opacity were measured using a SPTC Autocheck rotary encoder. (Korea) emissions and smoke analyzer. The emissions analyzer measured nitrogen oxides (NOx) at a In this study, the exhaust emissions and smoke opacity were measured using a SPTC Autocheck range of 0–5000 ppm, hydrocarbon (HC) at a range of 0–10,000 ppm, carbon monoxide (CO) at a range (Korea) emissions and smoke analyzer. The emissions analyzer measured nitrogen oxides (NOx ) at of 0–10% vol., carbon dioxide (CO2) at a range of 0–20% vol., and oxygen (O2) at a range of 0–25% vol. a range of 0–5000 ppm, hydrocarbon (HC) at a range of 0–10,000 ppm, carbon monoxide (CO) at a Meanwhile, the smoke analyzer measured smoke opacity at a range of 0–100% with a resolution of range of 0–10% vol., carbon dioxide (CO2 ) at a range of 0–20% vol., and oxygen (O2 ) at a range of 0.1%. 0–25% vol. Meanwhile, the smoke analyzer measured smoke opacity at a range of 0–100% with a In this work, only optimized hybrid biofuel which has the viscosity and density that meet ASTM resolution of 0.1%. D6751/EN 14214 standards was selected for the engine test and compared with the baseline diesel In this work, only optimized hybrid biofuel which has the viscosity and density that meet fuel. The experiment was performed at the wide-open throttle (WOT) with engine speed ranging ASTM D6751/EN 14214 standards was selected for the engine test and compared with the baseline from 2000 to 3500 rpm. Before the experiment started, the engine was initially running for 10 minutes diesel fuel. The experiment was performed at the wide-open throttle (WOT) with engine speed to allow the engine to attain the optimum operating condition. For in-cylinder pressure ranging from 2000 to 3500 rpm. Before the experiment started, the engine was initially running for measurement, 100 continuous engine cycles were recorded, and the average pressure trace was 10 minutes to allow the engine to attain the optimum operating condition. For in-cylinder pressure calculated. The schematic diagram of the experimental setup is presented in Figure 4. measurement, 100 continuous engine cycles were recorded, and the average pressure trace was calculated. The schematic diagram ofTable the experimental setup is presented in Figure 4. 1. Engine specifications. Model/make Table 1. Engine specifications. Yanmar L70N Fuel injection system Direct injection Model/Make Yanmar L70N Maximum output (kW) 4.9 Fuel injection system Direct injection Rated speed (rpm) 3600 Maximum output (kW) 4.9 Displacement (litre) 0.320 Rated speed (rpm) 3600 Bore × stroke (mm) 78 × 67 Displacement (litre) 0.320 Bore × stroke (mm) 78 × 67 Cylinder single Cylinder single Compression ratio 20:1 Compression ratio 20:1 Cooling system Forced air Cooling system Forced air LubricationLubrication system system Forced lubricating Forced lubricating

Figure 4. Schematic diagram of engine dynamometer setup.

3. Results

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3.1. Gravitational Stability Test All the blends were kept in bottles and stored at ambient temperature for a month. The blends 7 of 20 were visually observed, and no sign of separation occurred during the test period. The blends also remained as one-phase clear and transparent liquid. Thus, the blends were considered highly stable and suitable 3. Results Energies 2018, 11,for x long-term storage and transportation. Figure 5 shows the appearance of blended 7 of 20 fuels after being stored for one month. 3.1. Gravitational Gravitational Stability Stability Test Test 3.1. Energies 2018, 11, 3146

All the the blends blends were were kept kept in in bottles and stored stored at for a The blends blends All bottles and at ambient ambient temperature temperature for a month. month. The were visually observed, and no sign of separation occurred during the test period. The blends also were visually observed, and no sign of separation occurred during the test period. The blends also remained as one-phase clear and transparent liquid. Thus, the blends were considered highly stable remained as one-phase clear and transparent liquid. Thus, the blends were considered highly stable and suitable transportation. Figure 5 shows the appearance of blended fuels and suitable for forlong-term long-termstorage storageand and transportation. Figure 5 shows the appearance of blended after being stored for one month. fuels after being stored for one month.

Figure 5. Appearance of hybrid biofuel after a month. (a) MCO25RPO75; (b) MCO50RPO50; (c) MCO75RPO25.

3.2. Chemical Constituent of Melaleuca Cajuputi oil Figure 6 presents the chromatogram of Melaleuca Cajuputi oil (MCO). Meanwhile, Table 2 lists the relative content of the main composition from MCO expressed as the percentage from the total area Figure obtained from the gas chromatography mass spectrometry (GC-MS)(b)analysis. Overall, 5. Appearance ofofhybrid a amonth. (a) (a) MCO25RPO75; MCO50RPO50; (c)there Appearance hybridbiofuel biofuelafter after month. MCO25RPO75; (b) MCO50RPO50; wereMCO75RPO25. 35MCO75RPO25. compounds (96.6% of the total oil) identified. Hydrocarbon is the major group at 64.8% and (c) oxygenated product at 34.6%. Under oxygenated products, seven alcohols were identified to 3.2. Chemical Chemical Constituent Constituent of of Melaleuca Melaleuca Cajuputi Cajuputi Oil 3.2. represent 6.8% of the total oil. The presence ofoil alcohol is important for its antibacterial properties [37], and to enhance the volatility of the oil. The high compound of hydrocarbons (HC) and the presence Figure 6 presents the chromatogram of Melaleuca Cajuputi oil (MCO). (MCO). Meanwhile, Meanwhile, Table lists Figure 6 presents the chromatogram of Melaleuca Cajuputi oil Table 22 lists of alcohols are possibly the reasons for the high calorific value (CV) of MCO compared to that of the relative relative content content of of the the main main composition composition from from MCO MCO expressed expressed as as the the percentage percentage from from the the total total the dieselobtained fuel. Thefrom highthe compound of HC also indicated that MCO is a(GC-MS) potentialanalysis. source ofOverall, biofuel [38]. area obtained gas mass Overall, there area from the gas chromatography chromatography mass spectrometry spectrometry (GC-MS) analysis. there Individually, the main components of MCO are 1,8-cineole (27.7%), alpha-pinene (26.1%), were 35 compounds (96.6% of the total oil) identified. Hydrocarbon is the major group at 64.8% and were 35 compounds (96.6% of the total oil) identified. Hydrocarbon is the major group at 64.8% and tetratetracontane (25.9%). TheUnder cyclic ether 1,8-cineole, has seven high stability and low chemical oxygenated product atat 34.6%. oxygenated products, alcohols were identified to reactivity represent oxygenated product 34.6%. Under oxygenated products, seven alcohols were identified to which make it resistant to polymerization, oxidation, and thermal decomposition [22]. It is reported 6.8% of the total oil. The presence of alcohol is important for its antibacterial properties [37], and represent 6.8% of the total oil. The presence of alcohol is important for its antibacterial properties [37], that theenhance blend oiloil. (which is rich in 1,8-cineole) either with (HC) gasoline or has to enhance the of volatility of the TheThe high compound of hydrocarbons andand thebiodiesel presence of and to theeucalyptus volatility of the oil. high compound of hydrocarbons (HC) the presence enhanced the performance and exhaust emissions of the engine [21,22,39]. Thus, sole or blended alcohols are possibly the reasons for the high calorific value (CV) of MCO compared to that of diesel of alcohols are possibly the reasons for the high calorific value (CV) of MCO compared to that of MCOThe with other fuels is expected to provide reliable engine andsource exhaust fuel. high of HC of also indicated that MCO aperformance potential source of biofuel [38]. [38]. diesel fuel. Thecompound high compound HC also indicated that is MCO is a potential of emissions. biofuel Individually, the main components of MCO are 1,8-cineole (27.7%), alpha-pinene (26.1%), and tetratetracontane (25.9%). The cyclic ether 1,8-cineole, has high stability and low chemical reactivity which make it resistant to polymerization, oxidation, and thermal decomposition [22]. It is reported that the blend of eucalyptus oil (which is rich in 1,8-cineole) either with gasoline or biodiesel has enhanced the performance and exhaust emissions of the engine [21,22,39]. Thus, sole or blended MCO with other fuels is expected to provide reliable engine performance and exhaust emissions.

Figure 6. Chromatogram of of Melaleuca Melaleuca Cajuputi Figure 6. Chromatogram Cajuputi oil. oil.

Figure 6. Chromatogram of Melaleuca Cajuputi oil.

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Table 2. List of compounds identified by gas chromatography mass spectrometry (GC-MS) analysis. No.

Compound

Chemical Class

Molecular Formula

Composition (%)

1

α-Pinene

C10 H16

26.12

2

1,8-Cineole

C10 H18 O

27.66

3 4 5 6 7

γ-Terpinene Terpinolene Undecane Trans-decalin, 2-methylTrans-9-methyldecalin 1-Isopropenyl-4-methyl-1,2cyclohexanediol Naphthalene, decahydro-2,3-dimethyl-

hydrocarbon oxygenated product (ether) hydrocarbon hydrocarbon hydrocarbon hydrocarbon hydrocarbon oxygenated product (alcohol)

C10 H16 C10 H16 C11 H24 C11 H20 C11 H20

1.23 0.38 0.15 0.31 0.40

C10 H18 O2

0.53

hydrocarbon

C12 H22

0.35

C10 H20 O

2.49

C10 H18 O

0.87

C10 H16 O

0.36

C12 H24 C14 H30 C13 H28 C16 H34 C13 H28 C13 H28

0.37 0.24 0.11 0.13 0.11 0.08

C12 H20 O2

0.10

C15 H24 C15 H24 C15 H24 C15 H24 C15 H24 C15 H24 C15 H24 C15 H24

0.02 0.44 0.24 0.07 0.20 0.17 0.03 0.03

C15 H24 O

0.03

C15 H26 O

0.17

C15 H26 O

0.06

C21 H44 O3 S C17 H36

0.16 1.50

C17 H36 O

2.32

C35 H70 C44 H90

6.33 25.85

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

oxygenated product (alcohol) oxygenated α-Terpineol product (alcohol) oxygenated Verbenol product (alcohol) Cyclohexane, (4-methylpentyl)hydrocarbon 6-Methyltridecane hydrocarbon Undecane, 2,3-dimethylhydrocarbon Dodecane, 2-methyl-6-propylhydrocarbon Undecane, 2,9-dimethylhydrocarbon Tridecane hydrocarbon oxygenated α-Terpinyl acetate product (acetate) Ylangene hydrocarbon β-Caryophyllene hydrocarbon α-Caryophyllene hydrocarbon Longifolene-(v4) hydrocarbon β-Selinene hydrocarbon α-Selinene hydrocarbon α-Bergamotene hydrocarbons δ-Cadinene hydrocarbon oxygenated Caryophyllene oxide product oxygenated Viridiflorol product (alcohol) oxygenated β-Eudesmol product (alcohol) Sulfurous acid, butyl heptadecyl ester others Tetradecane, 2,6,10-trimethylhydrocarbon Oxygenated 1-Hexadecanol, 2-methylproduct (alcohol) 17-Pentatriacontene hydrocarbon Tetratetracontane hydrocarbon Class compositions Hydrocarbons Oxygenated products Others Total composition 1-Menthol

64.8 34.6 0.2 99.6

Individually, the main components of MCO are 1,8-cineole (27.7%), alpha-pinene (26.1%), and tetratetracontane (25.9%). The cyclic ether 1,8-cineole, has high stability and low chemical reactivity which make it resistant to polymerization, oxidation, and thermal decomposition [22]. It is reported that the blend of eucalyptus oil (which is rich in 1,8-cineole) either with gasoline or biodiesel has enhanced the performance and exhaust emissions of the engine [21,22,39]. Thus, sole or blended MCO with other fuels is expected to provide reliable engine performance and exhaust emissions.

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3.3. Basic Physicochemical Properties of RPO-MCO Blends The properties of biofuel are important to ensure the suitability of the oil before being introduced to the engine. The basic properties of MCO, RPO, and their blends are presented in Table 3. The kinematic viscosity of MCO was 2.2 mm2 /s, which is comparable to diesel fuel, yet significantly lower compared to those of vegetable oils. Mostly, vegetable oils either edible or non-edible have viscosity in the range of 25–40 mm2 /s. The low viscosity suggests that MCO will offer a good flow property, especially during cold weather. MCO density was determined at 869 kg/m3 which was within the range of diesel. Viscosity and density are the well-known factors that have significant effects on fuel atomization and injection spray characteristics. MCO, having low viscosity and density, is expected to provide a decent quality of spray characteristics and enhance fuel atomization for a better air fuel mixture. Notably, the amount of energy (CV) obtained from MCO is comparable to that of diesel fuel. High CV is important to provide good engine thermal efficiency and reduce fuel consumption. The flash point of MCO was 50 ◦ C, which is mostly similar to diesel fuel. Its low flash point value indicated that MCO is a volatile oil, which is important for fuel atomization. However, water content and acid value of the oil were high compared to the ASTM 6751 standard. The high moisture and acid content could lead to corrosion of certain parts of the engine and fuel system. On the other hand, the kinematic viscosity of RPO was significantly higher compared to the maximum limit of ASTM D6751/EN 14214. The high viscosity of RPO comes from triglycerides that contain three fatty acids and one glycerol. The fatty acid composition of RPO is presented Table 4. The major compositions identified were oleic and palmitic acid at 49% and 32.6%, respectively. Specifically, high content of oleic acid contributes to a good oxidative stability [40]. However, high content of oleic acid contributes to high density of RPO [41]. The high viscosity and density are the main reasons that limit its potential as engine fuel. High viscosity and density will increase the fuel impingement with cylinder wall and piston due to longer fuel spray penetration. Impingement would lead to the formation of carbon deposit and higher unburnt hydrocarbon emissions. Notably, the strategy to blend high viscosity RPO with low viscosity MCO successfully reduced the viscosity and density of hybrid biofuel. The higher the fraction of MCO, the lower the viscosity and density of the blends observed. The blend of RPO25MCO75 was found to have viscosity and density levels within the ASTM/EN standards. In addition, the calorific value of the blend was also close to diesel, which is important to provide good combustion efficiency. It was observed that all the blends exhibited lower flash points, similar to the diesel range. The flash point value describes the tendency of the fuel to initiate flash and start the flame. The higher the MCO fraction in the blends, the lower the flash point values obtained. The blends also obtained lower boiling points which could enhance the atomization and evaporation of the fuel. Table 3. Physicochemical properties of neat and blends of refined palm oil-Melaleuca Cajuputi oil (RPO-MCO). Property Kinematic viscosity at 40 ◦ C (mm2 /s) Density (kg/m3 ) Calorific value (MJ/kg) Flash point (◦ C) Boiling point (◦ C) Water content (vol. %) Acid value (mg KOH/g)

ASTM D6751

EN 14214

Diesel

RPO25 MCO75

RPO50 MCO50

RPO75 MCO25

RPO32 MCO68

RPO

MCO

1.9–6.0

3.5–5.0

3.4

4.6

9.6

19.0

5.45

42

2.2

880

860–900

835

878.2

887.1

895.98

880.20

905.5

871.4

-

35

44.8

42.3

41.5

40.8

42.1

40.3

43.2

100–170 Max. 0.05 Max. 0.5

>120 -

50–55 150–343

51–52 134

53–55 141

65–67 189

52–53 135

210–215 >250

50–51 121

-

-

0.31

0.33

0.43

0.32

0.56

0.28

Max. 0.5

-

0.55

0.69

0.89

0.60

7.28

5.52

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Table 4. Fatty acid composition of RPO. Fatty Acid

Mol. Formula

Composition (%)

Lauric Myristic Palmitic Stearic Oleic Linoleic

C12 H24 O2 C14 H284 O2 C16 H32 O2 C18 H36 O2 C18 H34 O2 C18 H32 O2

2.4 1.2 32.6 2.9 49 11.9

Even though the blend of RPO25MCO75 successfully achieved the viscosity and density within the ASTM D6751/EN 14214 standards, the present work targeted to obtain the blend that has the highest RPO percentage but still obtain viscosity and density levels within the allowable limits. Thus, further optimization analysis was carried out to select the optimum blend ratio. 3.4. Optimization of Hybrid Biofuel To predict and select the optimum blend ratio, the regression analysis method was employed. This method developed the mathematical model of correlation between the blends’ fraction and their effect on the viscosity and the density. Figure 7 shows the correlation between the MCO fraction and viscosity obtained from the experimental data. From the regression analysis, the following mathematical equation was proposed: v = 41.135e−0.029x

(1)

where v is kinematic viscosity (mm2 /s) and x is volume fraction of MCO in the blend. The exponential regression obtained high R2 value of 0.9996 which shows a good fit of regression trend line with the measured data. Meanwhile, the correlation between MCO fraction and density is shown in Figure 8. From the tabulated data, linear regression with R2 of 0.9967 is the best fit to describe the correlation of MCO fraction and density of the blends. The mathematical equation of the correlation is given by: ρ = −0.3439x + 904.83

(2)

where ρ is density (kg/m3 ) and x is volume fraction of MCO in the blend. The optimization was performed based on the mathematical equations obtained from the regression analysis. The goal of the optimization was set to maximize the fraction of RPO in the blend and the desirable viscosity and density within the ASTM D6751/EN 14214 requirements. From the evaluation of Equations (1) and (2), the optimum blend ratio of RPO32MCO68 was suggested. The predicted kinematic viscosity and density obtained are 5.7 mm2 /s and 881.44 kg/m3 , respectively. To evaluate the accuracy of the predicted values obtained, the measured data were compared to the calculated data. The comparison and the discrepancy between measured and calculated data were tabulated in Table 5. Notably, the discrepancy is less than 5% which indicates that the mathematical models obtained were reliable to predict the viscosity and density of the RPO-MCO blends. Therefore, the blend ratio of RPO32MCO68 was selected to further analyze its performance and emissions on a diesel engine.

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Figure 7. Correlation between MCO fraction and viscosity. Figure 7. 7. Correlation Correlation between between MCO MCO fraction fraction and and viscosity. viscosity. Figure

Figure 8. Correlation between MCO fraction and density. Figure 8. Correlation between MCO fraction and density. Table 5. Comparison between measured andMCO calculated data of density. viscosity and density. Figure 8. Correlation between fraction and

Table 5. Comparison between measured and calculated data of viscosity 3and density. 2

Kinematic Viscosity (mm /s) Density (kg/m ) Discrepancy Discrepancy Table Blend (vol. %) 5. Comparison between measured and calculated data of viscosity and density. (%) (%) Measured Calculated Measured Calculated

Kinematic Viscosity 3) Density (kg/m Discrepancy Discrepancy Kinematic 4.60 (mm2Viscosity 2.2 878.20 879.04 0.10 3) /s) 4.70 Density (kg/m Discrepancy Discrepancy (%) (%) 9.60 (mm2/s) 9.70 1.0 887.10 887.64 0.10 Measured Calculated Measured Calculated (%) (%) RPO75MCO25 19.0 19.90 4.7 895.98 896.23 0.03 Measured Calculated Measured Calculated RPO32MCO68 5.45 5.70 4.6 880.20 881.44 0.14 RPO25MCO75 4.60 4.70 2.2 878.20 879.04 0.10 RPO25MCO75 4.60 4.70 2.2 878.20 879.04 0.10 RPO50MCO50 9.60 9.70 1.0 887.10 887.64 0.10 RPO50MCO50 9.60 9.70 1.0 887.10 887.64 0.10 3.5. Combustion Analysis RPO75MCO25 19.0 19.90 4.7 895.98 896.23 0.03 RPO75MCO25 19.0 19.90 4.7 895.98 896.23 0.03 RPO32MCO68 5.45 5.70 4.6 880.20 881.44 0.14 The comparison of in-cylinder pressure between optimized hybrid biofuel (RPO32MCO68) RPO32MCO68 5.45 5.70 4.6 880.20 881.44 0.14 and baseline diesel fuel at various engine speeds is presented in Figure 9. The pressure curves plotted were 3.5. Combustion Analysis the average of 100 consecutive combustion cycles. It can be observed that an engine running on hybrid 3.5. Combustion Analysis biofuel a slightly lower peak pressure at low and medium engine speeds. However, at high engine Thehad comparison of in-cylinder pressure between optimized hybrid biofuel (RPO32MCO68) and Thethe comparison in-cylinder pressure optimized hybrid biofuel (RPO32MCO68) and baseline diesel fuel atofvarious engine speedsbetween ishybrid presented in and Figure 9. The pressure speeds, peak pressure differences between biofuel diesel became larger.curves At theplotted engine baseline diesel fuel at various engine speeds is presented in Figure 9. The pressure curves plotted speedthe of average 2000 rpm, peak cylinder pressure of the RPO32MCO68 blend occurred earlier running than diesel were of 100 consecutive combustion cycles. It can be observed that an engine on were the average of 100 consecutive combustion cycles. It can be observed that an engine running on ◦ hybrid biofuelthe had a slightly lower peakofpressure atwas lowfound and medium engine However, at fuel. Notably, peak cylinder pressure the blend to be 80.0 bar atspeeds. 367.4 after top dead hybrid biofuel had a slightly lower peak pressure at low and medium engine speeds. However, at high engine speeds, the peak pressure differences between hybrid biofuel and diesel became larger. high engine speeds, the peak pressure differences between hybrid biofuel and diesel became larger. RPO25MCO75 Blend (vol. %) RPO50MCO50 Blend (vol. %)

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At the engine speed of 2000 rpm, peak cylinder pressure of the RPO32MCO68 blend occurred earlier than diesel fuel. Notably, the peak cylinder pressure of the blend was found to be 80.0 bar at 367.4° after dead center thepressure peak cylinder pressure obtained forfuel baseline diesel was◦ centertop (ATDC), while (ATDC), the peak while cylinder obtained for baseline diesel was 82.4 bar fuel at 369.5 82.4 barThe at 369.5° ATDC. The pressure difference about 2.9% as compared to diesel Atfound 2500 ATDC. pressure difference was about 2.9% aswas compared to diesel fuel. At 2500 rpm, fuel. it was ◦ rpm, it was found that the peak pressure for baseline diesel was 76.0 bar at 369.6° ATDC, meanwhile, that the peak pressure for baseline diesel was 76.0 bar at 369.6 ATDC, meanwhile, the RPO32MCO68 ◦ ATDC. the RPO32MCO68 biofuel blend obtained pressure of 73.1 bar atThe 368.1° ATDC. Thepressure drop in peak biofuel blend obtained peak pressure of peak 73.1 bar at 368.1 drop in peak was pressure wasAs about 3.8%. As the engine speed increased to 3000 the pressure peak cylinder pressure for about 3.8%. the engine speed increased to 3000 rpm, the peak rpm, cylinder for baseline diesel ◦ ◦ baseline diesel was 71.6 bar at 371° ATDC and 69.7 bar at 369.5° for the RPO32MCO68 biofuel blend. was 71.6 bar at 371 ATDC and 69.7 bar at 369.5 for the RPO32MCO68 biofuel blend. The pressure The pressure reduction was about Upon further of engine speed to 3500 peak reduction was about 2.7%. Upon2.7%. further increase ofincrease engine speed to 3500 rpm, the rpm, peak the cylinder ◦ cylinder pressure for baseline diesel was recorded at 69.1 bar at 370.3° ATDC, while the peak cylinder pressure for baseline diesel was recorded at 69.1 bar at 370.3 ATDC, while the peak cylinder pressure pressure for the RPO32MCO68 wasatrecorded at 371.6 61.7 ◦bar at 371.6° ATDC. The in for the RPO32MCO68 blend wasblend recorded 61.7 bar at ATDC. The difference in difference pressure was pressure was At about 10.7%.ofAt all ranges of testing,pressure the in-cylinder of hybrid biofuel about 10.7%. all ranges testing, the in-cylinder of hybridpressure biofuel (RPO32MCO68) is (RPO32MCO68) is slightly lower as compared to baseline diesel fuel. This is probably due to lower slightly lower as compared to baseline diesel fuel. This is probably due to lower calorific value of calorific value of hybrid biofuel which leads to lower heat release duringprocess. the combustion process. In hybrid biofuel which leads to lower heat release during the combustion In addition, hybrid addition, hybrid biofuel has aviscosity slightly higher viscosity and density compared to diesel fuel, and has biofuel has a slightly higher and density compared to diesel fuel, and has contributed to contributed to poor fuel atomization and low combustion efficiency, which reduces the in-cylinder poor fuel atomization and low combustion efficiency, which reduces the in-cylinder peak pressure. peak pressure. Generally, forpeak bothcylinder fuels, the peak cylinder decreases the engine speed Generally, for both fuels, the pressure decreasespressure as the engine speedasincreases. From the increases. From the analysis, it was found that the RPO32MCO68 blend has shown remarkable peak analysis, it was found that the RPO32MCO68 blend has shown remarkable peak cylinder pressure cylinder pressure close to the baseline Taking into that this blend only close to the baseline diesel. Taking intodiesel. consideration thatconsideration this blend involved only twoinvolved neat biofuels, two neat biofuels, theare results are quite impressive. the results obtained quiteobtained impressive.

(a)

(b) Figure 9. Cont.

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(c)

(d) Figure 9. Cylinder Cylinder pressure pressure versus versus crank crank angle angle degree degree for for tested testedfuels fuelsat at(a) (a) 2000 2000 rpm; rpm; (b) (b) 2500 2500 rpm; rpm; Figure (c) 3000 rpm, and (d) 3500 rpm.

3.6. Performance Performance Analysis Analysis 3.6. 3.6.1. Engine Torque 3.6.1. Engine Torque Figure 10 shows the engine torque variation as a function of the engine speed for the Figure 10 shows the engine torque variation as a function of the engine speed for the RPO32MCO68 hybrid biofuel blend and baseline diesel fuel. The torque values for both fuels decreased RPO32MCO68 hybrid biofuel blend and baseline diesel fuel. The torque values for both fuels with the increase in the engine speed. The maximum torque was at 2000 rpm and then gradually decreased with the increase in the engine speed. The maximum torque was at 2000 rpm and then decreased as the engine speed increased afterwards. The range of test for the RPO32MCO68 blend gradually decreased as the engine speed increased afterwards. The range of test for the demonstrated a comparable engine torque to that of diesel fuel except for at 3500 rpm. At maximum RPO32MCO68 blend demonstrated a comparable engine torque to that of diesel fuel except for at engine speed, torque for RPO32MCO68 was found to be 21.4% lower compared to baseline diesel 3500 rpm. At maximum engine speed, torque for RPO32MCO68 was found to be 21.4% lower fuel. Lower torque at maximum speed is associated with the low peak pressure obtained during compared to baseline diesel fuel. Lower torque at maximum speed is associated with the low peak the combustion process. This can be related to the fact that the RPO32MCO68 blend has lower CV pressure obtained during the combustion process. This can be related to the fact that the compared to the baseline diesel. In addition, the RPO32MCO68 blend also had slightly higher viscosity RPO32MCO68 blend has lower CV compared to the baseline diesel. In addition, the RPO32MCO68 which affected fuel atomization, thus leading to low combustion efficiency and in-cylinder peak blend also had slightly higher viscosity which affected fuel atomization, thus leading to low pressure [42]. combustion efficiency and in-cylinder peak pressure [42].

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Figure Figure10. 10. Comparison Comparisonof ofengine enginetorque torqueas as aa function function of of engine engine speeds. speeds. Figure 10. Comparison of engine torque as a function of engine speeds.

3.6.2. Engine EngineBrake BrakePower Power 3.6.2. 3.6.2. Engine Brake Power The engine engine brake power is is presented in in Figure 11. The power as as aa function functionof ofengine enginespeed speedfor forallalltested testedfuels fuels presented Figure engine brake power as abrake function ofpower engine speed forthe allRPO32MCO68 tested fuels is presented inslightly Figure At the whole range of speed, the power produced from biofuel biofuel was 11. AtThe the whole range of speed, the brake produced from the RPO32MCO68 was 11. At compared the whole range of baseline speed, brake power produced from the RPO32MCO68 biofuel was lower to baseline dieselthe fuel. The brake power reductions were 3.42%, 4.2%,4.2%, 2.62%, and slightly lower compared to diesel fuel. The brake power reductions were 3.42%, 2.62%, slightly compared toand baseline diesel fuel. The brake powerthe reductions were 3.42%, 4.2%, 2.62%, 20.6% atlower 2000, 2500, 3000, 3500 rpm, respectively. Notably, largest brake power reduction for and 20.6% at 2000, 2500, 3000, and 3500 rpm, respectively. Notably, the largest brake power reduction and 20.6% at 2000, 2500, 3000, and 3500 rpm, Notably, the largest brake power reduction thethe RPO32MCO68 blend waswas recorded at the maximum engine speed. TheThe possible explanation for for RPO32MCO68 blend recorded atrespectively. the maximum engine speed. possible explanation for the RPO32MCO68 blend was recorded at torque the maximum engine speed. Thelower possible explanation thisthis result is related with thethe lower engine torque as as discussed earlier. Despite brake power at for result is related with lower engine discussed earlier. Despite lower brake power for this result is related with theRPO32MCO68 lower engine torque as discussed earlier. Despite lower brake power 3500 rpm, interestingly, the the RPO32MCO68 blend recorded a comparable brake power compared to the at 3500 rpm, interestingly, blend recorded a comparable brake power compared at 3500 rpm, interestingly, the RPO32MCO68 blend recorded a comparable brake power compared baseline fuel at lower engine speed. to the baseline fuel at lower engine speed. to the baseline fuel at lower engine speed.

Figure 11. Comparison of engine power as a function of engine speeds. Figure 11. Comparison of engine power as a function of engine speeds. Figure Comparison of engine power as a function of engine speeds. 3.6.3. Brake Specific Fuel11. Consumption

3.6.2. Brake Specific Fuel Consumption 12 compares the experimental data of brake specific fuel consumption (BSFC) for 3.6.2.Figure Brake Specific Fuel Consumption Figure 12 compares the experimental of brake specific fuel consumption (BSFC) for RPO32MCO68 and baseline diesel fuel. BSFC data is an important parameter to compare the fuel efficiency Figure 12and compares the experimental data of brake parameter specific fuel consumption (BSFC) for RPO32MCO68 baseline diesel fuel. BSFC is an important to compare the fuel efficiency of different tested fuels. It is apparent that the RPO32MCO68 blend recorded a slightly higher BSFC RPO32MCO68 andfuels. baseline diesel fuel.that BSFC isRPO32MCO68 an important parameter to compare the fuel efficiency of different tested It is apparent the blend recorded a slightly higher BSFC than diesel fuel at the entire range of engine speeds. The BSFC increments were 3.3%, 6.6%, 7.5%, and of different tested fuels. It isrange apparent that the RPO32MCO68 blend recorded a3.3%, slightly higher BSFC than fuel at the entire engine speeds. The BSFC increments 6.6%, 6.5%diesel at 2000, 2500, 3000, and 3500ofrpm, respectively. Comparing the twowere results, it can be7.5%, seen and that than diesel fuel at the entire range of engine speeds. The BSFC increments were 3.3%, 6.6%, 7.5%, and 6.5% at 2000, 2500, 3000, and 3500 rpm, respectively. Comparing the two results, it can be seen there was no significant increase in RPO32MCO68 BSFC as compared to baseline diesel fuel wherethat the 6.5% at 2000, 2500, 3000, and 3500 rpm, respectively. Comparing the two results, it can be seen that there was no significant increase in RPO32MCO68 BSFC as compared to baseline diesel fuel where maximum increment was only 7.5%. Higher BSFC obtained by the RPO32MCO68 blend was mainly there was no significant increase in 7.5%. RPO32MCO68 BSFCobtained as compared to RPO32MCO68 baseline diesel blend fuel where the increment wasfuel only Higher BSFC was duemaximum to lower CV where more was required to combust in orderbytothe retain the same engine speed. the maximum increment was more only 7.5%. Higher BSFC byorder the RPO32MCO68 blend was mainly due to lower CV where fuel was required to obtained combust in to retain the same engine mainly due to lower CV where more fuel was required to combust in order to retain the same engine speed. speed.

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Figure 12. Comparison of brake specific fuel consumption (BSFC) as a function of engine speeds. Figure 12. Comparison of brake specific fuel consumption (BSFC) as a function of engine speeds. Figure 12. Comparison of brake specific fuel consumption (BSFC) as a function of engine speeds.

3.7. Emissions 3.7. Emissions Analysis Analysis 3.7. Emissions Analysis 3.7.1. NOxxEmission Emission

3.7.1.Figure NOx Emission variation of of NO NOxx emission 13 shows the variation emission for the RPO32MCO68 blend in comparison to diesel fuel. High NOx mainly to temperature. baseline High NOx formation formation was mainly related to the the high high combustion combustion temperature. Figure 13 shows the variation of NOxwas emission forrelated the RPO32MCO68 blend in comparison to graph shows that both fuels exhibited a similar trend where the NO X was low at low engine The graph shows that both fuels exhibited a similar trend where the NO was low at low engine speed, X baseline diesel fuel. High NOx formation was mainly related to the high combustion temperature. speed, significantly increased at medium speed, and gradually decreased toward high engine speed. significantly increased atboth medium speed, and decreased toward high engine The graph shows that fuels exhibited agradually similar trend where the NO X was lowspeed. at lowNotably, engine Notably, at the entire range ofatRPO32MCO68 test, the RPO32MCO68 blend produced NO X as compared to at the entire range of test, the blend produced lower NOlower to baseline X as compared speed, significantly increased medium speed, and gradually decreased toward high engine speed. baseline diesel fuel. The NO X reductions were 3.9%, 3.5%, 7.7%, and 17.3% at 2000, 2500, 3000, and diesel fuel. The NO reductions were 3.9%, 3.5%, 7.7%, and 17.3% at 2000, 2500, 3000, and 3500 rpm X range of test, the RPO32MCO68 blend produced lower NOX as compared to Notably, at the entire 3500 rpmdiesel respectively. reduction was possibly because ofand lower heat released during the respectively. This possibly because lower heat released during the combustion baseline fuel.reduction The This NOX was reductions were 3.9%, of 3.5%, 7.7%, 17.3% at 2000, 2500, 3000, and combustion process due toFurthermore, low CV [43]. Furthermore, slightly viscosity of the during blend process duerespectively. to low CV [43]. slightly high viscosity of high the blend also contributed to also low 3500 rpm This reduction was possibly because of lower heat released the contributed to low combustion temperature in comparison to baseline diesel. combustion temperature in comparison to baseline diesel. combustion process due to low CV [43]. Furthermore, slightly high viscosity of the blend also contributed to low combustion temperature in comparison to baseline diesel.

Figure 13. Comparison of nitrogen oxide emission as a function of engine speeds. Figure 13. Comparison of nitrogen oxide emission as a function of engine speeds.

3.7.2. CO Emission Figure 13. Comparison of nitrogen oxide emission as a function of engine speeds. 3.7.2. CO Emission The CO emission as a function of engine speed for tested fuel is presented in Figure 14. 3.7.2.emission CO CO Emission The emission a function engine speed for tested fuel iswith presented in Figure 14.CO CO CO is mainly as formed whenofthere is lack of oxygen to react the carbon to form 2. emission is mainly formed when there is lack of oxygen to react with the carbon to form CO 2. As can As can be seen in Figure 14, at all range of engine speeds, the CO emission of the RPO32MCO68 blend The CO emission as a function of engine speed for tested fuel is presented in Figure 14. CO be seen surpassed inis Figure 14, at allwhen range of fuel. engine speeds, theto emission the RPO32MCO68 blend slightly baseline diesel COof was high atCO low speed andof progressively as emission mainlythe formed there is lack oxygen react with the carbon to formdecreased CO 2. As can slightly surpassed the baseline diesel fuel. CO was high at low speed and progressively decreased as the engine speed increased. Relatively high CO at low engine speed was mainly due to the engine be seen in Figure 14, at all range of engine speeds, the CO emission of the RPO32MCO68 blend the engine increased. Relatively high at high low speed wasprogressively mainly due to theto engine operating atspeed rich air-fuel mixture, where more fuel wasengine but and there was less oxygen react. slightly surpassed the baseline diesel fuel. COCO was atinjected low speed decreased as operating rich air-fuel mixture, where more wasengine injected butmixture there was oxygen toengine react. Moreover, incomplete combustion due to non-homogenized air-fuel alsoless led to the formation the engineat speed increased. Relatively high COfuel at low speed was mainly due to the Moreover, incomplete combustion to non-homogenized air-fuel alsoless led oxygen to the formation operating at rich air-fuel mixture, due where more fuel was injected butmixture there was to react. Moreover, incomplete combustion due to non-homogenized air-fuel mixture also led to the formation

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of CO [43]. As the engine speed increased, more oxygen was introduced into the combustion of CO CO[43]. [43]. the engine speed increased, more was into the combustion chamber, which allowed the engine to operate lean oxygen mixture, thusintroduced reducing CO emission. AsAsthe engine speed increased, moreat oxygen was introduced into the combustion chamber, chamber, whichthe allowed engine to at leanthus mixture, thusCO reducing CO emission. which allowed enginethe to operate atoperate lean mixture, reducing emission.

Figure Figure 14. 14. Comparison Comparison of of carbon carbon monoxide monoxide emission emission as as aa function function of of engine engine speeds. speeds. Figure 14. Comparison of carbon monoxide emission as a function of engine speeds.

3.7.3. HC HC Emission Emission 3.7.3. 3.7.3. HC Emission HC emission emission is is the the product product of of incomplete incomplete combustion combustion due due to to fuel fuel properties, properties, fuel fuel spray spray HC characteristics, and engine operating conditions. Figure 15 shows the HC emission variation HC emission the product of conditions. incompleteFigure combustion duethe to HC fuelemission properties, fuel spray characteristics, and isengine operating 15 shows variation as as a a function engine speed RPO32MCO68 hybrid biofuel blend baseline diesel fuel. characteristics, and engine operating conditions. Figure 15 shows the HC emission variation function of of thethe engine speed forfor thethe RPO32MCO68 hybrid biofuel blend andand baseline diesel fuel.as Ata At the entire range of engine speeds, HC emission ofthe theRPO32MCO68 RPO32MCO68 blend washigher higher compared function of the engine speed for the RPO32MCO68 biofuel blendblend and baseline diesel fuel. At the entire range of engine speeds, thethe HC emission ofhybrid was compared to the baseline diesel fuel. The emission was higher at 2000 rpm but gradually decreased as engine thethe entire rangediesel of engine the HCwas emission RPO32MCO68 blend was higher compared to baseline fuel.speeds, The emission higherofatthe 2000 rpm but gradually decreased as engine speed increased. possible explanation for these results may be to high viscosity and poor to the increased. baseline diesel fuel. The emission for was higher at 2000 rpm butdue gradually decreased as engine speed AApossible explanation these results may be due to high viscosity and poor fuel fuel atomization of blended fuel. Poor atomization formed non-uniform air-fuelmixture, mixture, thus speed increased. A possible for these results may abeanon-uniform due to high viscosity and poorthus fuel atomization of blended fuel.explanation Poor fuelfuel atomization formed air-fuel causing some someofof ofblended thefuel fuelbeing beingPoor unable combust.Another Another possible explanation is the occurrence atomization fuel. fuel atomization formed a non-uniform air-fuel mixture, thus causing the unable totocombust. possible explanation is the occurrence of of fuel impingement with the cylinder and piston due to explanation excessive [6]. causing some of the fuel being unable towall combust. Another is thepenetration occurrence of fuel impingement with the cylinder wall and piston headhead duepossible to excessive spray spray penetration [6]. High High viscosity and density caused large droplets and longer spray penetration compared to baseline fuel impingement with the cylinder wall and piston head duepenetration to excessivecompared spray penetration [6].diesel High viscosity and density caused large droplets and longer spray to baseline diesel Indensity addition, blended fuel contains lower cetane than diesel fuel, causing longer viscosity and caused droplets longer spraynumbers penetration compared tolonger baseline diesel fuel. Infuel. addition, blended fuellarge contains lowerand cetane numbers than diesel fuel, causing ignition ignition delay and acombustion shorter combustion period, thusnumbers leading toHC higher HC emission being produced. fuel. In addition, blended fuel contains cetane diesel fuel, causing longer ignition delay and a shorter period,lower thus leading to higherthan emission being produced. delay and a shorter combustion period, thus leading to higher HC emission being produced.

Figure 15. Comparison of unburned hydrocarbon emission as a function of engine speeds. Figure 15. Comparison of unburned hydrocarbon emission as a function of engine speeds. 3.7.4. Smoke Emission Figure 15. Comparison of unburned hydrocarbon emission as a function of engine speeds.

3.7.4. Smoke Emission The variation in smoke opacity over the engine speed is shown in Figure 16. Overall, the 3.7.4. Smoke Emission The variation in exhibited smoke opacity over the engineasspeed is shown Figurediesel 16. Overall, the RPO32MCO68 blend lower smoke opacity compared to the in baseline fuel. It was The that variation inexhibited smoke opacity over the engine speed is shown in Figure 16. engine Overall, the RPO32MCO68 blend lower smoke as compared to the baseline fuel. Itspeed was observed the smoke opacity was highest atopacity 2000 rpm and gradually decreased asdiesel the RPO32MCO68 blend exhibited lower opacity asrpm compared to the smoke baseline diesel fuel. Itdiesel was observed the smoke opacity was smoke highest at 2000 and gradually decreased asto the increased.that At 2000 rpm, the RPO32MCO68 biofuel blend showed similar opacity theengine observed that theAtsmoke opacity was highest at biofuel 2000 rpm andshowed gradually decreased as the engine speed increased. 2000 rpm, the RPO32MCO68 blend similar smoke opacity to the speed increased. At 2000 rpm, the RPO32MCO68 biofuel blend showed similar smoke opacity to the

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diesel fuel. However, the smoke opacity reduced by 10.4%, and 64.5% at 2500, and 3500 fuel. However, the smoke opacity reduced by 10.4%, 29.4%,29.4%, and 64.5% at 2500, 3000,3000, and 3500 rpm, rpm, respectively. was possibly due to the presence oxygenincontent in that the respectively. LowerLower smokesmoke opacityopacity was possibly due to the presence of oxygenofcontent the blend blend that allowed a more homogenous for better combustion efficiency. Another possible allowed a more homogenous mixture formixture better combustion efficiency. Another possible explanation explanation forblended this is that fuel contained less sulfur, whichtoishelp believed to help reduce smoke for this is that fuelblended contained less sulfur, which is believed reduce smoke opacity [44]. opacity [44]. diesel Meanwhile, diesel fuels containing aromatic have hydrocarbon a greater tendency to Meanwhile, fuels containing aromatic hydrocarbon a greaterhave tendency to produce more produce more[45]. smoke (soot) [45]. smoke (soot)

Figure 16. Comparison of smoke opacity as a function of engine speeds. Figure 16. Comparison of smoke opacity as a function of engine speeds.

4. Conclusions 4. Conclusions In this work, Melaleuca Cajuputi oil (MCO) was introduced as a new potential biofuel to be In this work, Melaleuca Cajuputi oilformulate (MCO) was introduced a new The potential biofuel be blended with refined palm oil (RPO) to a new hybrid as biofuel. present studytowas blended with refined palmFor oilthe (RPO) to formulate a new hybrid biofuel. Thehybrid present studyblend was performed in three phases. first phase, physicochemical properties of the biofuel performed in three phases.the Forkey the properties first phase,were physicochemical of to thethe hybrid biofuel blend were analyzed. Secondly, optimized inproperties accordance ASTM D6751/EN were Secondly, properties werewas optimized accordance the ASTM D6751/EN 14214analyzed. standards. Finally,the thekey optimized blend furtherinexamined to to study its performance, 14214 standards. optimized blend was further examined to study its the performance, combustion, and Finally, emissionthe characteristics in a single cylinder diesel engine. From results of combustion, emission characteristics indrawn: a single cylinder diesel engine. From the results of this this work, theand following conclusions can be work, the following conclusions can be drawn: 1. It was found that MCO is mainly composed of 64.8% hydrocarbons (HC) and 34.6% oxygenated 1. Itproducts. was foundHigher that MCO is mainlyofcomposed of 64.8% 34.6% oxygenated percentage HC contribute to hydrocarbons high calorific (HC) valueand (CV) of MCO which products. Higher percentage of HC contribute to high calorific value (CV) of MCO which indicated it as a potential source of biofuel. The presence of oxygenated products promote better indicated it asefficiency a potential source biofuel. The presence of oxygenated products promote better combustion and lowerofsmoke opacity. combustion efficiency and lower smoke opacity. 2. The blend of high viscosity RPO with low viscosity MCO successfully reduced the viscosity and 2. The blend high viscosity RPO with low viscosity reduced theand viscosity and density of of hybrid biofuel. The higher the fraction ofMCO MCO,successfully the lower the viscosity density of density of hybrid biofuel. The higher the fraction of MCO, the lower the viscosity and density of the blends. CV was increased with the increase of MCO in the blends. CV was increased with the increase of MCO in the blends. 3. the Theblends. key properties of optimum hybrid biofuel (RPO32MCO68) obtained viscosity, density, and 3. The key properties of optimum hybrid biofuel (RPO32MCO68) obtained viscosity, density, and 2 3 CV of 5.45 mm /s, 880.20 kg/m , and 42.1 MJ/kg respectively. These key properties were in 2/s, 880.20 kg/m3, and 42.1 MJ/kg respectively. These key properties were in CV of 5.45 mm accordance with the ASTM 6751/EN 14214 standards and demonstrated comparable properties accordance with the diesel ASTMfuel. 6751/EN 14214 standards and demonstrated comparable properties to those of baseline to those of baseline diesel fuel. 4. At the entire range of speeds, in-cylinder peak pressure, brake torque, and brake power for the 4. At the entire range of speeds, in-cylinder peak pressure, brake torque, and brake power for the optimum hybrid biofuel blend were slightly lower than those of baseline diesel fuel. The largest optimum hybrid biofuel blend were slightly lower than those of baseline diesel fuel. The largest drop in peak pressure, brake torque, and brake power are 10.7%, 21.4%, and 20.6%, respectively. drop in peak pressure, brake torque, and brake power are 10.7%, 21.4%, and 20.6%, respectively. 5. Notably, NOx emission and smoke opacity were decreased as compared to diesel fuel across the 5. Notably, NOx emission and smoke opacity were decreased as compared to diesel fuel across the speed range. The largest NOx reduction was 17.3% and the smoke opacity reduction was 64.5% speed range. The largest NOx reduction was 17.3% and the smoke opacity reduction was 64.5% at maximum engine speed. Meanwhile, CO emission was found similar in comparison to diesel at maximum engine speed. Meanwhile, CO emission was found similar in comparison to diesel fuel. BSFC and HC emissions were found to be slightly higher than those of baseline diesel fuel. fuel. BSFC and HC emissions were found to be slightly higher than those of baseline diesel fuel. 6. Overall, this study has shown that the RPO32MCO68 hybrid biofuel blend has successfully run a diesel engine with comparable engine performance and exhaust emissions to those of diesel fuel. This suggested that the blend is marked as a potential new source of biofuel.

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Overall, this study has shown that the RPO32MCO68 hybrid biofuel blend has successfully run a diesel engine with comparable engine performance and exhaust emissions to those of diesel fuel. This suggested that the blend is marked as a potential new source of biofuel.

Author Contributions: Conceptualization, S.C.M. and M.Y.I.; Methodology, S.C.M., M.Y.I. and Y.H.T.; Experimentation, S.C.M., M.F.H. and Y.H.T.; Data analysis, S.C.M., Y.H.T. and M.F.H.; Resources, M.Y.I. and M.F.H.; Writing—original draft preparation, S.C.M.; Writing—review and editing, Y.H.T., M.Y.I. and S.C.M. Funding: This research was funded by the Ministry of Higher Education Malaysia and Universiti Sains Malaysia under the fundamental research grant (FRGS) scheme (FRGS/1/2016/TK07/USM/02/2; 203.PMEKANIK.6071356) and BRIDGING research grant scheme (304/PMEKANIK/6316119). Acknowledgments: The authors would like to thank the engine laboratory staff who have provided technical support throughout the experimental work. Conflicts of Interest: The authors declare no conflict of interest.

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