Performance and Emission Analysis of Rubber Seed Methyl Ester and

Article pubs.acs.org/EF

Performance and Emission Analysis of Rubber Seed Methyl Ester and Antioxidant in a Multicylinder Diesel Engine Ibrahim Khalil Adam,†,‡ A. Rashid A. Aziz,† M. R. Heikal,†,§ and Suzana Yusup*,∥ †

Centre for Automotive Research and Electric Mobility, Mechanical Engineering Department, Universiti Teknologi PETRONAS, 32610, Seri Iskandar, Perak, Malaysia ‡ Mechanical Engineering Department, Blue Nile University, 143, Er Roseires, Ad Damazin, Sudan § Environment and Technology Department, University of Brighton Cockcroft Building, Lewes Road, Brighton BN2 4GJ, United Kingdom ∥ Center of Biofuel and Biochemical Research, Biomass Processing Laboratory, Chemical Engineering Department, Universiti Teknologi PETRONAS, 32610, Seri Iskandar, Perak, Malaysia ABSTRACT: In this study, the potential of using a nonedible biodiesel source (rubber seed oil) was explored. Rubber seed oil (RSO) is a promising nonedible source for producing a sustainable biodiesel in Malaysia. However, due to the lower oxidation stability of the produced biodiesel, which is the result of its higher unsaturation content (78.73%), an oxidation inhibitor is required. This paper examines the effect of antioxidants addition to rubber seed biodiesel (RB) on the combustion, engine performance, and emissions. Four antioxidants, namely, N,N′-diphenyl-1,4-phenylenediamine (DPPD), 2-tert-butylbenzene-1,4diol (TBHQ), N-phenyl-1,4-phenylenediamine (NPPD), and 2(3)-tert-butyl-4-methoxyphenol (BHA), were added at concentrations of 1000 and 2000 ppm to 20% RB (RB20). The results showed that TBHQ had the greatest ability to increase the stability of RB20 followed by BHA, DPPD, and NPPD, respectively, without a significant effect on physical properties. The experiments were conducted in a 55 kW multicylinder diesel engine at full load conditions. The results showed that RB20 produced a lower brake power (BP) of 3.07%, higher brake specific fuel consumption (BSFC) of 3.68%, and higher maximum in-cylinder pressure of 6.7% compared to neat diesel. Antioxidants addition reduced the NO, heat release rate (HRR), and maximum in cylinder pressure by an average of 0.85− 4.12%, 5.78−14.74%, and 1.77−3.97%, respectively, compared to RB20. All antioxidant fuels showed a similar start of combustion (−12 °CA BTDC), but for diesel and RB20 the values were −10 and −13 °CA BTDC, respectively. However, carbon monoxide (CO) and hydrocarbon (HC) emissions increased by 10.17− 15.25% and 13.35−19.68%, respectively, compared to RB20. It can be concluded that the RB20 blend treated with antioxidants can be used in diesel engines without any further modifications. antioxidants.5 Antioxidants are classified as free radical terminators, oxygen scavengers, and metal ion chelators.6 The effectiveness of an antioxidant is determined by a parameter called the stabilization factor and is calculated by F = IPx/IP0, where IP0 is the induction period without antioxidant and IPx is the induction period with the antioxidant.7 The increasing induction period with antioxidant is because the antioxidant scavenges the reactive radicals (peroxyl radicals, ROO•) and forms phenoxyl radicals (R-O•), which have poor reactivity and limit oxidative reaction.8 Many researchers have used different antioxidant additions to increase biodiesel stability and investigated their effects on engine combustion.9 Varatharajan and Cheralathan10 evaluated DPPD and NPPD antioxidant additions to soybean biodiesel in a single cylinder diesel engine. Compared to NPPD, DPPD showed the highest NOx reduction of 9.35% and 28.36% for B20 and B100 blends, respectively. In another study, Varatharajan et al.11 tested the DPPD, NPPD, and ethylenediamine (EDA) effect on 20% and 100% jatropha biodiesel using a single cylinder diesel engine. They claimed that a 1500 ppm (0.15m) concentration was the optimum

1. INTRODUCTION Energy demand has increased significantly because of industrialization, population growth, and change in lifestyle. Environmentally, it is believed that 98% of the carbon emissions in the atmosphere are due to fossil fuel burning.1 The major emissions are carbon dioxide, nitrogen oxides, carbon monoxide, sulfur dioxide, particulate matter, soot, and unburned hydrocarbons. These emissions are responsible for a number of health problems.2 Energy needs and environmental concern are important factors driving the need for the search for renewable and sustainable fuel sources.3 Biodiesel is a carbon fuel, is renewable, has a higher cetane number, is nonflammable, and is thought to be an alternative replacement for fossil diesel fuels. However, the properties of biodiesel fuels vary depending on the feedstocks and their basic components such as chain length, position of the double bond, and expansion number.4 Despite the advantages of biodiesel, there is still a question about the trade-off between biodiesel’s tendency to oxidize and cold flow properties. Biodiesels with higher saturation components have higher oxidation stability and cetane number compared to those of unsaturated components. Biodiesel autoxidation increases when it is in contact with the air, heat, metal, and light, because of the double bond molecule in the free fatty acid. The practical solution to increase biodiesels stability is to treat them with © XXXX American Chemical Society

Received: November 12, 2016 Revised: February 13, 2017 Published: March 6, 2017 A

DOI: 10.1021/acs.energyfuels.6b02994 Energy Fuels XXXX, XXX, XXX−XXX

stability, engine performance and emissions

1 cylinder, 4S, rated power 4.4 kW, NOx reduction for PPDA, BHT, α-tocopherol acetate, and 8 injection pressure 200 bar, injection L-ascorbic acid; antioxidants were 43.55%, 32.73%, 17.84%, timing of 23° BTDC (before top dead 14.51%, and 5.86%, respectively, at concentration of 0.025%-m center), and compression ratio 17.5:1 compared to neat biodiesel; BSFC was higher with BHT, α-tocopherol acetate, and L-ascorbic acid whereas for PPDA and EDA were lower than neat biodiesel; however, CO and HC are increased significantly

engine type

results compared to base diesel fuel remarks

B

the properties of CB20 met the ASTM specifications; BHA showed better stability than BHT; no combustion study has been performed the performance was reduced with and without antioxidant additive; no combustion study has been observed

4 cylinder, 4S, WC, IDI turbocharged, biodiesel blends shows0.8−3.69% lower BP, 6.79− 9.72% higher 23 max power 55 kW at 4200 rpm, and BSFC, 6.16−11.32% higher NO, 12- 48% lower HC, and compression ratio21:1 9.75−53.06% lower CO; with the addition of antioxidant BP was 4.07−8.24% lower, 5.99−12.46% higher BSFC, 3.503−16.54% lower NO, 3.03−10.20% higher HC, and 1.43−3.99% higher EGT compared to biodiesel blends without antioxidants

viscosity, density, flash point, and stability are increased with antioxidants; BHA shows better stability than BHT; no combustion study has been performed

BHA, BHT, and concentration 4 cylinder, 4S, WC, IDI, turbocharged, BSFC, BTE, CO, HC, and smoke were lower by 6.59%, 0.68%, 22 of 2000 ppm fuel injection pressure 157 bar, max 24.32%, 40.47%, and 32.43%, respectively, but NOx was 10.68% power 55 kW at 4200 rpm, and higher compared to diesel fuel; with the antioxidants CB20 compression ratio 21:1 shows 0.28−0.57% lower BTE, 1.46−1.77% lower BSFC, 3.84−7.78% lower NOx, 7.84−9.09% higher CO, and 24.37−30.67% higher HC compared neat CB20 blend

JB, difference blends (JB5, JB10, DPPD, concentration of 1500 ppm JB15, and JB20), varied speeds (1000− 4000 rpm), and full load)

coconut oil biodiesel, CB20, speeds (1000− 4500 rpm), and full load

palm biodiesel (PB), blend BHA, BHT, and concentration 4 cylinder, 4S, WC, IDI turbocharged (B20), various speeds (1000− of 1000 ppm diesel engine, max power 42 kW at 4000 rpm), and 100% load 4000 rpm, and compression ratio 18.5:1

BHA, BHT, TBHQ, and concentration 2000 ppm

B20 blend shows 0.68−1.02% lower BP, 4.03−4.71% higher BSFC, 21 2.23− 2.55% lower BTE (brake thermal efficiency), 16.9−25.5% higher NOx, and 29.87−36.79% lower CO compared to diesel fuel; however, BHA and BHT addition produce 9.8−12.6% lower NOx, 8.6−12.3% higher CO, and 9.1−12.0% higher HC compared to neat B20 blend

antioxidant reduces the calorific value and increases viscosity, density, flash point, and oxidation stability

stability order was TBHQ > BHT > BHA; CIB20 produces 1.42% 20 lower BP, 4.9% higher BSFC, 5.5% higher NOx, 39.14% lower CO, and 26.5% lower HC compared to diesel fuel; CIB20 blended antioxidants produce 0.42−0.83% lower BP, 0.5−1.5% higher BSFC, 1.6−3.6% lower NOx, and 9.9−21.6% lower HC compared to CIB20

calophyllum inophyllum biodiesel (CIB), CIB20, speeds (1000− 4500 rpm) and 100% load

2.5 L, 4 cylinder, 4S, IDI, WC, max power 55 kW at 4000 rpm, and compression ratio21:1

oxidation stability, density, viscosity, and flash point increased with antioxidant addition; BHT showed better stability; no combustion study been performed

TBHQ, BHA, BHT, propyl SB and edible frying oil gallate (PrG), and biodiesel blends, speed of α-tocopherol; concentrations 1500 rpm, difference loads of 100, 300, 500, 1000, and (0, 25, 50, 75, 90 and 100%) 2000 ppm

coconut biodiesel (CB) and JB BHA, BHT, at concentration of 4 cylinder, 4S, WC, turbocharged IDI, the stability of CB20 BHA and CB20 BHT were 96.13 and 94.47 h, 19 2000 ppm max power 55 kW at 4000 rpm, and whereas for JB20 BHA and JB20 BHT were 39.33 and 68.47 h, blends, various speeds compression ratio21:1 respectively; BP of CB and JB were 0.95% and 2.97% lower (1000−4500 rpm) and full compared to diesel fuel; with the additized fuels, BP was 0.5−0.6 load % lower compared to neat CB and JB; BSFC was 0.78−0.79% and 0.55−0.67% lower and CO was 22.3−35.8% and 17.5−37.7 % lower, respectively, for BHA and BHT compared to diesel fuel; BHA and BHT produced an average NO reduction of 3.9−4.8% and 2.6−5%, respectively, for JB20 and CB20

TBHQ shows the best oxidation stability; antioxidants have few effects on exhaust emissions of diesel engine using biodiesel

NOx reduction effectiveness order was PPDA > EDA > α-tocopherol acetate > BHT > L-ascorbic acid

TBHQ and PrG antioxidants were recommended to be used; no significant change in emissions with antioxidant addition

refs.

the efficiency of antioxidants was in order of TBHQ > PrG > BHA 18 4 cylinder, 4S, WC, IDI, HD D4BB > BHT > α-tocopherol; BSFC was lower with the additized fuel diesel engine, max torque and power 166 N m at 2200 rpm, 60 kW at 4000 than nonadditized; HC and smoke were lower compared to diesel fuel rpm, and compression ratio 22:1

the stability effectiveness order was TBHQ > PrG > BHA > BHT 17 soybean oil biodiesel (SB); BHT, propyl gallate (PrG), HD D4BB diesel engine, IDI, > α-tocopherol; biodiesel combustion pressure was higher than engine loads of 0, 25, 50, 75, α tocopherol, TBHQ, BHA, 4 cylinder, 4S, WC, max torque and 90 and 100% and concentrations of 100, power 166 N m at 2200 rpm, 60 kW that of diesel but no significant pressure difference between biodiesel with and without antioxidants; BSFC with the addition 300, 500, 1000, and 2000 ppm at 4000 rpm, and compression ratio of antioxidant was higher compared to diesel fuel 22:1

antioxidants

P-phenylenediamine (PPDA), BHT, α-tocopherol acetate, ethylenediamine (EDA) and, L-ascorbic acid; concentrations of 0.005, 0.015, 0.025, 0.035, and 0.05%-m

fuel and test condition

jatropha biodiesel (JB), 1500 rpm and various loads

Table 1. Description of Engine Performance and Emissions Using Various Antioxidants

Energy & Fuels Article


Article

refs. stability, engine performance and emissions

TBHQ produced better stability among the additized fuels; lower NO, peak cylinder pressure, and HRR; no significant effect of antioxidant additions on SOC have been observed the stability order was TBHQ > BHA > DPPD > NPPD; RB20 this study blend shows 2.91% lower BP, 3.68% higher BSFC, 27.39% lower CO, 36. 85% lower HC, and 5.67% higher NO compared to neat diesel; RB20 added antioxidants produced 0.92−2.56% lower BSFC, 10.17−15.25% higher CO, 13.35−19.68% higher HC, 0.87−4.29% lower NO, 1.77−3.97% lower peak cylinder pressure, and 5.78−14.74 lower HRR compared to RB20 4 cylinder, 4S, WC, IDI, 4D68, max power 55 kW at 4500 rpm, and compression ratio 22.4:1

engine type antioxidants fuel and test condition

Table 2. List of Equipment’s Used and Their Standard Methods parameter acid value (mg KOH/g oil) iodine value (mg/I2/g oil) density (kg/cm3)

DPPD, NPPD, BHA, TBHQ, and concentrations of 1000 and 2000 ppm

results compared to base diesel fuel

Table 1. continued

concentration based on the lower emissions criteria. NOx was reduced by 43.55%, but HC and CO increased compared to the baseline biodiesel. Il̇ eri and Koçar9b investigated the effect of BHA, BHT (butylated hydroxytoluene), TBHQ, and EHN (2-ethylhexyl nitrate) antioxidant additions to 20% canola biodiesel (B20) fuel. No significant differences in density and viscosity were observed with antioxidant additives. BSFC and NOx decreased by 4.09−10.19% and 1.21−4.63%, respectively, compared to B20. The effectiveness order for NOx reduction was EHN > BHT > BHA > TBHQ. CO emission of B20 decreased by 11.05%, whereas with antioxidant it increased by 1.72−20.47%. Hess et al.12 investigated the effect of BHA and BHT antioxidant additions to 20% soybean biodiesel. They found that NOx was reduced with the addition of the antioxidant. Rashedul et al.13 investigated the use of calophyllum inophyllum oil biodiesel treated with 6-di-tert-butyl-4-methylphenol and 4-methyl-6-tert-butylphenol antioxidant. The results indicated that the addition of antioxidants increased the density, viscosity, flash point, and oxidation stability but decreased the calorific value. BSFC, NOx, and peak cylinder pressure of biodiesel blends (CIB30) were higher compared to diesel fuel. The detailed literature of antioxidants used and their effect on combustion and emissions is shown in Table 1. The rubber tree is part of the Euphorbiaceae family originated from South America. It grows in tropical or subtropical climates with a minimum rainfall of 1200 mm/year and a temperature of 28 °C. In Malaysia, there are 1 229 940 ha of rubber plantations according to the association of Natural Rubber Producing Countries (NRPC), and the projected annual production is estimated to be 1.2 million metric tons per year.14 Statistically, about 46% of the total world rubber plantations belong to Malaysia. They are distributed in Peninsular, Sarawak, Sabah, Negeri Sembilan, Melaka, and north Johor. This very huge amount of unutilized rubber seeds can be used for biodiesel production and overcome the food versus fuel issue. It is reported that one tree yields 1.3 kg twice a year, and the kernel has an average oil of 40−60 wt % that can be used for biodiesel synthesis.15

viscosity (mm2/s) calorific value (J/g) oxidation stability (h) cetane number flash point (°C) cold filter plugging point (°C) cloud point and pour point (°C) surface tension (Nm) CHNS analyzer (wt %)

rubber seed biodiesel, RB20, various speeds (1500−3500 rpm), and 100% load

remarks

Energy & Fuels

fatty acid composition triglycerides and glycerine, mono, di (wt %) C

standard method

equipment

AOCS-Cd 3d-63 AOCS-Cd 1d-92 ASTM 5002 and ASTM D4502 DIN53015 and DIN12058 DIN51900 and ASTM D4868 AOCS-Cd 12b-92 and EN14112 ASTM D 613 ASTM D 93 ASTM D 6371

titration titration AMA 4500M, Anton Paar Lovis 2000M, Anton Paar C5000 IKA Werke, Germany 873 Rancimat, Metrohm Shatox Octane meter CLA 5, Petrotest FPP 5 Gs, ISLby PAC

ASTM D 2500 and ASTM D 97 pendant drop method

CPP 5G′s

AOCS- Ce 1−62 ASTM D6584

rame hart model 260 series II, CHNS/O 2400, PerkinElmer gas chromatographer GC-FID, Shimadzu 2010


Article

Energy & Fuels

antioxidants on the engine performance, combustion characteristics and emissions of a multicylinder diesel engine were also investigated, and the results were compared with diesel and baseline biodiesel.

Table 3. Crude Rubber Seed Oil (RSO) Properties property acid value (mg KOH/g) iodine value (mg/I2/g oil) free fatty acid (%) density (kg/m3) at 20 °C viscosity (mm2/s) at 40 °C calorific value (J/g) sulfur (wt %) nitrogen (wt %) glycerides (wt %) monoglycrides diglycerides triglycerides fatty acid composition myristic acid (wt %) (C14:0) stearic acid (C18:0) palmitic acid (C16:0) linoleic acid (C18:2) oleic acid (C18:1) linolenic acid (C18:3)

mean ± std. dev.(n = 5) 60 ± 0.16 129.8 ± 0.816 21.63 ± 0.02 917.8 ± 0.029 49.2 ± 0.25 37.922 ± 0.012 0.266 ± 0.002 0.358 ± 0.0014 6.42 ± 0.163 8.8 ± 0.125 58.01 ± 0.078 n.d.

2. MATERIALS AND METHODS 2.1. Materials. Commercially acquired crude rubber seed oil and neat diesel fuel were used in this study. The equipment used and the property analysis of rubber seed oil is presented in Tables 2 and 3, while Table 4 shows the properties of antioxidants used. 2.2. Biodiesel Production. A hydrodynamic cavitation reactor with 50 L capacity was used for the biodiesel production. The system consisted of a double jacketed glass, double diaphragm pump, and air compressor with a maximum power of 4 kW to operate the double diaphragm pump as the main device to dissipate the energy in the hydrodynamic cavitation reactor. The previously optimized plate geometry with a 1 mm diameter, 21 holes, 16.5 mm2 total flow area, and 65.98 mm perimeter was used.24 The main line value and bypass line were used to regulate the inlet pressure at 2 bar. The reaction temperature and its desired level were achieved by circulating liquid glycerin through the jacket surrounding the reactor. A total of 30 kg of rubber seed oil per run was pretreated using a sulfuric acid catalyst of 8 wt %, methanol to oil ratio of 6:1, reaction temperature of 55 °C, and time of 30 min.25 The reactant mixture was settled down gravitationally for 4 h. The catalyst was discharged, and the product was washed with deionized warm water. After esterification, the product was transferred to the transesterification process at optimized conditions with a catalyst concentration of 1 wt %, alcohol to oil ratio of 6:1, reaction temperature of 55 °C, and time of 30 min used.26 After the specified time, the reaction was stopped, and the product was left to settle down under gravity. After 4 h, two layers of liquid, methyl ester and glycerol, were formed. The catalyst and byproduct were discharged. The methyl ester was washed with deionized warm water to remove impurities, whereas the methanol and remaining water were removed using the rotary vacuum evaporator. To ensure the product was water free, 10 g of anhydrous sodium sulfate was added and shaken for 1 min, and the product was filtered using a 541 Whatman filter paper. Finally, the produced biodiesel was stored for the properties study and engine testing. 2.3. Experimental Setup. The experiments were carried out on a Mitsubishi (model 4D68) multicylinder diesel engine. A schematic diagram of the engine test rig is shown in Figure 1. An eddy current dynamometer, model SE 150, was used. The detailed specifications of the engine and the dynamometer are listed in Table 5. The engine and the dynamometer were controlled using an engine control unit (ECU)

7.8 ± 0.60 9.5 ± 0.081 40.6 ± 0.124 25.7 ± 0.24 15.01 ± 0.123

A few studies in the literature have used antioxidants in biodiesel−diesel blends.8,16 However, no information is available on the rubber seed methyl ester stability using antioxidants. Additionally, most of the papers used antioxidant concentrations up to 1000 ppm, but there are a few related to a high concentration of 2000 ppm. To date, the reported literature is on engine performance and emissions, while only three papers13,16b,17 have reported on combustion characteristics of a diesel engine using biodiesel treated antioxidants. Rubber seed oil has very low oxidation stability because of its high content of unsaturated fatty acid (78.73%), making it sensitive to oxidative degradation during storage, and it needs antioxidant treatment. Therefore, in this study, rubber seed methyl ester was produced in a hydrodynamic cavitation reactor using a two-step (acid esterification and transesterification) process. The effect of antioxidants, DPPD, NPPD, BHA, and TBHQ, on the fuel properties of rubber seed biodiesel were studied and compared with EN 14214 and ASTM standards. The influence of four Table 4. Antioxidants Properties

D


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Energy & Fuels

Figure 1. Schematic diagram of engine testing.

Table 5. Engine and Dynamometer Specifications parameter

Table 7. Accuracies and Uncertainties of the Measured Parameters

value/comment

parameters

engine type

four cylinder in-line diesel engine, IDI, 4D68 displacement volume 1998 cm3 bore × stroke 82.7 × 93 mm compression ratio 22.4:1 combustion type swirl chamber engine cooling water cooling pressurized circulation dynamometer specifications dynamometer type SE 150 model maximum torque, power and speed 500 N m, 150 kW and 8000 rpm (standard) torque and speed calibration ±0.25 N m and ±1 accuracy minimum flow and supply pressure 107 L/min and 1 kg/cm3 maximum outlet water 60 °C temperature weight 560 kg maximum voltage and current 250 V AC and 5 A pulse pick up inductive load cell strain gaugefull bridge energising coil voltage 90 V input resistance 375 ohms sensitivity and excitation 2.7 MV/V and 10 V DC overall size (length × width × 632 × 470 × 689 mm height)

torque BSFC speed CO HC NO pressure crank angle encoder

measurement limit 500 N m 8000 rpm 10 vol % 9999 ppm 5000 ppm 250 bar 20 000 rpm

accuracy

uncertainty

±0.25 N m ±0.05 l/min ±1 rpm ±0.001 vol % ±1 ppm ±1 ppm ±0.5 bar ±0.2 rpm

±0.86 ±0.97 ±1.4 ±1.38 ±2.49 ±1.72 ±0.82 ±0.2

of torque, engine oil and cooling water inlet and outlet temperatures, and fuel mass flow. To measure the exhaust gas emissions (CO, HC, NO, and CO2), a BOSCH (model BEA 460) exhaust gas analyzer was used. Detailed specifications of the exhaust gas analyzer are presented in Table 6. The test fuels were neat diesel and RB20 with and without antioxidant addition. To determine the effects of antioxidants, 1000 and 2000 ppm of DPPD, NPPD, BHA, and TBHQ were added to RB20 (RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ) and stirred mechanically for 30 min at 2500 rpm before being used for engine testing. The cylinder pressure measurement was performed using a Kistler Piezoelectric pressure transducer type 6061B1, angle encoder type 2613B1, signal conditioner type 2613B2, and line terminator type 2613B4. The pressure sensor was installed in the first cylinder of the engine and was cooled using water. The electric charge generated by the pressure transducer was amplified and converted to voltage, while the crank angle encoder was used to determine the angular position for every pressure reading and to establish top dead center. The amplified signal was fed into a DEWETRON hardware data acquisition combustion analysis system to acquire and store the pressure data at each crank angle. 2.4. Uncertainty Analysis. The error analysis in the experiments is needed to know the repeatability and reproductively of the results. The experiment was repeated three times, and the variations of performance, combustion characteristics, and exhaust emissions were

equipped with sensors, logging, and a data acquisition device. The experiments started with the engine warming up for about 30 min using diesel fuel before the biodiesel fuels were tested. Likewise, the engine was flushed with fossil diesel after every fuel change and run for 45 min to ensure full exhaustion of the pervious sample. To carry out the performance and emission testing, the engine was run fully loaded at various speeds in the range 1500−3500 rpm with a 500 rpm interval. The experiments were repeated three times to ensure stable readings

Table 6. Detail Specifications of the Exhaust Gas Analyzer equipment

method

measurement

upper limit

accuracy

BOSCH exhaust gas analyzer

nondispersive infrared flame ionization detector nondispersive infrared electro-chemical transmitter

CO HC CO2 NO

10.00 vol % 9999 ppm 18.00 vol % 5000 ppm

±0.001 vol % ±1 ppm ±0.01 vol % ±1 ppm

E


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Energy & Fuels Table 8. Thermophysical Properties of Rubber Seed Biodiesel and the Blends property acid value (mg KOH/g oil) density (g/m3) at 20 °C viscosity at 40 °C (mm2/s) calorific value (MJ/kg) cetane number oxidation stability (h)

1000 ppm 2000 ppm

flash point (°C) cloud point (°C) pour point (°C) cold filter plugging point (°C) surface tension (Nm) PerkinElmer, CHNS, 2400 carbon (wt %) hydrogen (wt %) nitrogen (wt %) sulfur (wt %) oxygen (wt %)

RB

RB20

0.36 0.878 3.82 39.3 51.9 8.2

0.053 0.849 3.31 43.201 50.1 53.52

152 3.4 −1.3 0 29.88 75.38 11.78 0.07 0.00 12.62

86.32 −11.8 −22.62

RB20 DPPD

⎛ SError ⎞ ⎜ ⎟ × 100 ⎝ X̅ ⎠

σ n

RB20 TBHQ

0.052 0.854 3.31 43.18

0.052 0.855 3.32 43.19

57.82 65.96 87.6 −11.81 −22.71

55.76 60.52 87.6 −11.81 −22.71

73.09 78.53 87.6 −11.81 −22.71

78.65 84.23 87.6 −11.81 −22.71

Diesel 0.003 0.825 3.064 44.28 47 103.6 72.4 −17 −32 27.08 86.62 13.21 0.01 0.16 0.0

3.2. Performance Analysis. The effect of antioxidant additives on BP, BSFC, NO, HC, CO, and combustion characteristics of rubber seed methyl ester in a diesel engine were evaluated at full load conditions. The results of the tested antioxidant mixtures were compared with those of neat diesel and untreated RB20. 3.2.1. Brake Power (BP). The effect of rubber seed biodiesel blends with and without antioxidants on BP at different engine speeds is shown in Figure 2. The PB obtained from the tested

(1)

where SError is the standard error and X̅ is the mean of the collected data. The standard error is calculated using eq 2.

SError =

RB20 BHA

0.052 0.854 3.33 43.19

27.51 83.36 12.61 0.018 0.13 3.15

used to calculate the uncertainty using percent relative standard error (RES), as in eq 1.27

RSE (%) =

RB20 NPPD

0.052 0.857 3.32 43.19

(2)

where σ is the standard deviation and n is the repeatable readings of performance, combustion characteristics, and emissions parameters. Accuracies and uncertainties of the measured parameters are given in Table 7.

3. RESULTS AND DISCUSSION 3.1. Analysis of Biodiesel Fuel Properties. The commercialization of any biodiesel fuel requires it to meet a set of specifications which are defined in ASTM D 6751 and EN 14214 standards. The important properties of the tested fuels are shown in Table 8. The density, viscosity, and acid value of RB were 0.878 g/cm3 at 20 °C, 3.82 mm2/s at 40 °C, and 0.32 mg KOH/g, whereas for diesel fuel they were 0.825 g/cm3, 3.064 mm2/s at 40 °C, and 0.003 mg KOH/g oil. The acid value, viscosity, and density of the RB complied with both standards. The density and viscosity of RB were 6.03 and 19.89% higher compared to diesel fuel, respectively. The cetane number was found to be 52, which is within the limits of both standards. The oxidation stability (OS) is one of the critical parameters affecting the use of biodiesel fuels. The OS stability of RB was 8.2 h and satisfied the minimum requirement of EN 14214 and ASTM standards. The carbon to hydrogen ratio (C/H) of RB was found to be 6.399 compared to that of diesel fuel, which is 6.557. The addition of DPPD, NPPD, BHA, and TBHQ to RB20 at concentrations of 1000 ppm showed stability periods of 57.82, 55.76, 73.09, and 78.65 h, respectively, whereas for 2000 ppm concentration, these values were 65.96, 60.52, 78.53, and 84.23 h, respectively. Thus, for long-term storage, a 2000 ppm concentration is recommended. The stabilization factors of DPPD, NPPD, BHA, and TBHQ at 2000 ppm concentration were 1.23, 1.13, 1.47, and 1.58, respectively. Thus, antioxidants form a stable radical intermediate.

Figure 2. Variation of the BP with respect to engine speed.

fuels ranged from 21.23 to 46.52 kW at a speed range of 1500− 3500 rpm. The maximum BP values obtained for diesel, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ were 46.52, 43.59, 43.65, 43.87, 43.59, and 44.69 kW, respectively, at 3500 rpm. On average, over the speed range, the PB for diesel, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ were 37.70, 36.54, 36.77, 36.93, 36.73, and 37.45 kW, respectively. Among the antioxidant blends, RB20 BHA shows the lowest BP because of the lower energy content (Table 7). More so, the evidence of a lower viscosity and density resulted in a loss of power due to higher leakages in the fuel pump compared to DPPD, NPPD, and TBHQ blends.28 Compared to diesel fuel, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ produced lower brake powers (about 3.07%, 2.47%, 2.05%, 2.58%, and 0.67%) due to the combined effect of F


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Energy & Fuels their lower calorific value and higher density and viscosity.20,29 Similar results were elucidated by Palash et al.,30 who reported a 0.82−3.68% reduction in BP using coconut biodiesel blends. The addition of DPPD, NPPD, BHA, and TBHQ showed a higher PB of 0.62%, 1.07%, 0.52%, and 2.49%, respectively, compared to RB20. The increased BP with antioxidants was due to the higher density and viscosity (see Table 7), resulting in more fuel mass being injected into the engine for the same fuel volume.20,21,31 The higher the viscosity of the fuel, the lower the leakage in the fuel pump.32 Thus, the higher mass flow rate compensated for the lower energy content of biodiesel fuel and antioxidant.33 Additionally, the cetane number might have enhanced the combustion9b and hence produced better power outputs with antioxidant addition compared to RB20. 3.2.2. Brake Specific Fuel Consumption (BSFC). The variation of BSFC of the tested fuels as a function of engine speed is depicted in Figure 3. The BSFC depends on the relationship

Fattah et al.20 claimed 0.5%, 1.3%, and 1.5% reductions of BSFC with CIB20 with BAH, BHT, and TBHQ antioxidants, respectively. 3.3. Combustion Analysis. Combustion refers to the fuel oxidation accompanied by heat release. The fuel reaction rate depends on the concentration of free radicals that must be obtained before initiation and propagation of reactions. The cylinder pressure, averaged over 400 consecutive cycles, as a function of crank angle (CA) at 2000 rpm for the tested fuels is

Figure 4. Variation of cylinder pressure at 2000 rpm at full load.

shown in Figure 4. It can be seen that the maximum cylinder pressure occurred in a crank angle range of 3−13 °CA ATDC for all tested fuels, with no significant trace of knock observed. The maximum cylinder pressure depends on engine type, fuel properties, air−fuel ratio, and the burned fuel fraction during the premixed combustion phase.42 The maximum cylinder pressure of diesel, RB20, DPPD, NPPD, BHA, and TBHQ was 82.38, 88.29, 84.78, 86.58, 86.35, and 86.72 bar, respectively. Compared to RB20, the addition of antioxidant reduced the maximum cylinder pressure by 3.97, 1.93, 2.19, and 1.77%, respectively, for DPPD, NPPD, BHA, and TBHQ. Compared to diesel fuel, the antioxidant blends show 2.91−5.26% higher maximum cylinder pressure. This is because the antioxidant reduced the concentration of free radicals, which are responsible for uncontrolled combustion. Hence, lower combustion pressure and NO emissions were observed. The heat release rate (HRR) shown in Figure 5 indicates the start of combustion (SOC) and the end of combustion (EOC). SOC is defined as the start of the heat release, whereas the EOC is defined as the crank angle where the heat release achieved 90% of total heat release.43 It was observed that with all antioxidant fuels, the SOC angle was almost similar (−12 °CA BTDC), whereas for diesel and RB20, they were −10 and −13 °CA BTDC, respectively. The reason behind this is the higher cetane number, higher density, bulk modulus, and low volatility of the biodiesel fuel.36b,44 Therefore, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ completed their premixed combustion earlier compared to the diesel fuel (see Figure 5), resulting in lower combustion durations. As the calorific values of blends were lower than that of diesel, the HRR is reduced in the diffusion controlled zone, but at premixed combustion the HRR was higher due to the higher cetane number of biodiesel blends (earlier start of combustion).45 From Figure 5, it can be

Figure 3. Variation of the BSFC with respect to engine speed.

between the density, viscosity, calorific value, and volumetric fuel injection system.34 From the figure, it is clear that the BSFC was lowest at 2000−2500 rpm and then increased as engine speed increased.35 At lower speeds, the decrease of BSFC is due to a better in-atomization ratio because of better physical and chemical conditions of the combustion and lower friction loss at maximum brake torque speed of 2000 rpm,36 whereas at higher speeds the friction losses increase, resulting in an increase in the BSFC.37 The BSFC of the biodiesel fueled engine increased as biodiesel percentage increased, as explained by Lapuerta et al.38 The increase in the BSFC is due to higher density and lower heating value (because of fuel borne oxygen), resulting in more fuel being injected into the combustion chamber compared to neat diesel fuel.39 The average BSFC values for neat diesel, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ were 327.53, 339.86, 336.76, 333.86, 334.59, and 329.20 g/kWh, respectively. Thus, RB20 produced 3.68% higher BSFC compared to neat diesel.40 This finding is concordant with Mofijur et al.,41 who observed a 2.98% increase in BSFC with the use of jatropha methyl ester. However, Fattah et al.22 observed a 6.59% higher BSFC with CB20 compared to the baseline fuel. Thus, it can be concluded that the level of BSFC increase depends on the feedstock. The addition of DPPD, NPPD, BHA, and TBHQ to RB20 reduced the average BSFC by 0.92%, 1.76%, 1.5%, and 3.14%, respectively, compared to RB20, in line with similar trends reported by other researchers.22 Compared to diesel fuel, the antioxidant additives result in a 0.51−2.81% increase in the BSFC. G


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prolonged the combustion duration and reduced the possible formation of rich fuel zones and hence reduced CO emission.50 Compared to diesel fuel, the average CO emission reductions were 27.36%, 13.76%, 18.27%, 14.22%, and 9.83%, respectively, for RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ. Thus, RB20 had the lowest CO emission among the tested fuels because of its high oxygen content and higher cetane number.51 These results are in agreement with results reported by Fattah et al.,20,35 who claimed 29.87% and 21.21% CO reduction with PB20 and PB20 BHA, respectively. Fattah et al.22 also reported a CO reduction of 24.32%, 18.39%, and 17.44% for CB20, CB20 BHT, and CB20 BHA, respectively. The addition of DPPD, NPPD, BHA, and TBHQ increased the average CO emissions by 12.80%, 10.17%, 12.35%, and 15.25%, respectively, compared to RB20. The increase in CO for antioxidant blends is because the antioxidant hinders the progression of CO to CO2.22,30 Moreover, during oxidation, peroxyl radicals and hydrogen peroxide (H2O2) are formed, which are further converted into hydroxyl radicals (OH) by absorbing heat from the combustion, converting CO into CO2. It was found that the addition of antioxidant lowered the concentration of hydrogen peroxide and peroxyl radicals, hence significantly affecting the conversion of CO. To study the conversion of CO to CO2 in detail, engine exhaust temperature (EGT) was measured. It is found that biodiesel samples with or without antioxidants show higher EGT. On average, the EGTs of diesel, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ were 314.72, 367.7, 322.25, 338.09, 346.14, and 355.62 °C, respectively. Compared to diesel fuel, the test samples increased EGT by 2.38−12.95%. With the addition of antioxidant, the EGT was lowered by 12.36, 8.05, 5.89, and 3.28%, respectively, for RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ compared to RB20. 3.4.2. Hydrocarbon Emission (HC). Hydrocarbon emissions in a diesel engine are formed due to leaner mixing of the fuel than the lean combustion limit and undermixing of fuel,52 which leaves the fuel injector nozzle late in the combustion at low velocity.19,42a More so, the HC is formed due to fuel trapping in the crevice volumes of the chamber, low temperature bulk quenching of oxidation reactions, incomplete fuel evaporation, and liquid wall films because of excessive spray impingement. It is affected by parameters such as fuel properties, operating conditions, and spray characteristics.53 Figure 7 illustrates the variation of HC emissions for the tested fuels at different engine speeds. The HC emissions of all tested fuels were reduced significantly compared to diesel fuel. The average

Figure 5. Variation of HRR at 2000 rpm at full load.

seen that the HRR decreased with the addition of antioxidants compared to RB20. The peak HRR values were 53.16, 70.76, 60.33, 62.81, 63.59, and 66.67 J/°CA for diesel, RB20, DPPD, NPPD, BHA, and TBHQ, respectively. The higher HRR with RB20 and treated RB20 showed logical agreement with engine emissions. However, the HRR at the late combustion phase for treated fuels and RB20 were lower compared to the diesel fuel. This is believed to be due to an earlier start of combustion, shorter ignition delay, and oxygen content in biodiesel fuels, resulting in complete combustion of the fuel that was left over in the main combustion and continued to burn in the late combustion.46 3.4. Emissions Analysis. 3.4.1. Carbon Monoxide (CO) Emissions. In diesel engine combustion, CO is formed due to low flame temperature, an insufficient air supply, and rich fuel air ratio,47 which hinder the conversion of CO to CO2.9b Moreover, factors such as injection timing, engine speed, engine load, injection pressure, and fuel types also influence the CO formation.48 The fluctuation of CO emissions at different engine speeds with and without antioxidant is shown in Figure 6.

Figure 6. Variation of CO with respect to engine speed.

It was observed that biodiesel blends with and without antioxidants produced lower CO emissions compared to neat diesel. The reasons were the higher oxygen element and higher cetane number in the biodiesel fuels, which enhanced the combustion process.42a Higher oxygen content ensured complete combustion by allowing more carbon to burn,49 whereas the higher cetane number (higher flame speed and post flame oxidation)

Figure 7. Variation of HC emission with respect to engine speed. H


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CB20 compared to diesel fuel. Some researchers59b,60 claim that the increase in biodiesel NO is due to the molecular structure and physicochemical properties of this fuel being different from those of diesel. Other factors include an advance of injection timing, large spray droplet size, high adiabatic flame temperature, and reduced radiation from soot particles. This argument was contradicted by Mueller et al.,61 who claimed that the increase in biodiesel NO depends on many mechanisms whose effects may tend to reinforce or cancel one another depending on combustion behavior, fuel characteristics and operating conditions. Fenimore62 reported that the reaction between hydrocarbon free radicals (CH2, CH, C, and C2) and molecular nitrogen is behind the increasing of NO emissions. Similar observations were observed by Garner and Brezinsky.63 The addition of DPPD, NPPD, BHA, and TBHQ antioxidants to RB20 showed an average NO reduction of 0.85−4.12% compared to RB20. This is in agreement with the result reported by Fattah et al.,20 who showed a 1.6−3.6% NOx reduction with BHA, BHT, and TBHQ blended CB20 compared to CB20 without antioxidant. Rashed et al.64 also found 4.74% and 1.46% NOx reduction for CIB20 NPPD and CIB20 DPPD, respectively. However, Palash et al.23 reported a 16.54% NO reduction for JB20. Thus, the NO reduction due to antioxidants depends on the feedstock.12 On the other hand, compared to diesel fuel, the NO emission of antioxidant blends was about 3.46−6.92% higher. The NO emissions reduction with antioxidants is due to the antioxidant capability to suppress the peroxyle radicals (HO2) and lower the combustion temperature by reducing the formation of hydroxyl radicals.10

reduction in HC emissions for RB20 was 36.85% compared to diesel fuel. This is believed to be due to the higher flame speed and post flame oxidation resulting from the high cetane number in the RB20, which insures more complete combustion.8,54 The lower carbon to hydrogen ratio and oxygen element in biodiesel fuels may trigger improved combustion, which in turn reduces the HC emissions.55 A similar result was reported by Fattah et al.,21,22 who observed HC emission reductions of 40.47% and 30.8% for CB20 and PB20, respectively. Moreover, Fattah et al.19 claimed a HC reduction of 40.1% with the use of a JB20 blend. With the addition of DPPD, NPPD, BHA, and TBHQ antioxidants to RB20, the HC emissions were reduced by 27.13%, 20.65%, 20.19%, and 25.44%, respectively, compared to diesel fuel. Compared to the RB20 blend, the addition of antioxidants increased the HC emissions by 13.35−19.68%. Treating biodiesel with antioxidants reduced the formation of hydroxyl radicals (OH; oxidation product of peroxyl radicals and hydrogen peroxide), which are responsible for converting the HC into H2O and C2O.8,10 Similar results were observed by other researchers.21 However, Pinzi et al.56 claimed that higher degrees of unsaturation components are less likely to completely vaporize and burn, hence increasing HC emissions. However, HC emission levels were still lower than those of neat diesel fuel. 3.4.3. Nitric Oxide (NO) Emission. In biodiesel engine combustion, the dominant mechanisms to form NO emission are prompt and thermal mechanisms.8,11 NO is the most deleterious pollutant, which depends on oxygen concentration, cylinder temperature, and residence time. It is a frequent target for engine manufactures and researchers. NO emission as a function of engine speed is presented in Figure 8. Compared to

4. CONCLUSIONS Rubber seed is one of the promising sources of biodiesel in Malaysia, but the produced biodiesel and its blends are susceptible to oxidation and hence require antioxidant treatment. Methyl ester of rubber seed oil was produced. The properties of RB and the blends with diesel met ASTM and EN standards. The TBHQ additive produced good stabilization followed by BHA, DPPD, and NPPD. The brake specific fuel consumption and brake power of a diesel engine fueled with RB20 were 3.68% higher and 3.07% lower, respectively, compared to those with diesel fuel. The addition of DPPD, NPPD, BHA, and TBHQ to RB20 reduced the brake specific fuel consumption by 0.92−3.14% and increased the brake power by 0.62−2.49% compared to RB20. The maximum cylinder pressure and heat release rate occurred within a crank angle range of 3−13 °CA ATDC for all tested fuels. Compared to diesel fuel, the CO and HC emissions of RB20 were 27.36% and 36.85% lower, whereas NO emission, maximum in-cylinder pressure, and heat release rate were 7.32%, 6.69%, and 24.87% higher, respectively. The antioxidant fuel increased CO and HC emissions by 10.17−15.25% and 13.35−19.68% compared to RB20. DPPD, NPPD, BHA, and TBHQ addition to RB20 reduced the NO emissions by 4.12%, 2.67%, 2.11%, and 0.85%, respectively, compared to RB20.

Figure 8. Variation of NO emission with respect to engine speed.

other blends, RB20 produced higher NO emissions because of its higher unsaturated components and earlier fuel burning due to a higher initial rate of combustion.52,57 An increase in the combustion pressure and temperature and NO emissions58 occurs due to the fact that the broken double carbon (CC) in unsaturated components releases more energy compared to saturated components. Also, a higher carbon double bond increases free radical hydrocarbon formation and increases NO formation.38,59 On average, NO emissions of diesel, RB20, RB20 DPPD, RB20 NPPD, RB20 BHA, and RB20 TBHQ were 211.37, 228.08, 218.68, 221.96, 223.27, and 226.14 ppm, respectively. Compared to diesel fuel, the NO emission of RB20 increased by 7.32%. Previous studies from Fattah et al.19,20 showed 5.5−8.02% higher NO emissions for CIB20, JB20, and

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +6053687642. Fax: +6053688204. E-mail: drsuzana_yusuf@ petronas.com.my. ORCID

Suzana Yusup: 0000-0001-8396-4320 I


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corrosive character of stabilised biodiesel exposed to carbon and galvanised steels. Fuel 2013, 107, 609−614. (6) Shahidi, F.; Janitha, P.; Wanasundara, P. Phenolic antioxidants. Crit. Rev. Food Sci. Nutr. 1992, 32 (1), 67−103. (7) Loh, S.-K.; Chew, S.-M.; Choo, Y.-M. Oxidative stability and storage behavior of fatty acid methyl esters derived from used palm oil. J. Am. Oil Chem. Soc. 2006, 83 (11), 947−952. (8) Varatharajan, K.; Cheralathan, M.; Velraj, R. Mitigation of NOx emissions from a jatropha biodiesel fuelled DI diesel engine using antioxidant additives. Fuel 2011, 90 (8), 2721−2725. (9) (a) Karavalakis, G.; Stournas, S.; Karonis, D. Evaluation of the oxidation stability of diesel/biodiesel blends. Fuel 2010, 89 (9), 2483− 2489. (b) Il̇ eri, E.; Koçar, G. Effects of antioxidant additives on engine performance and exhaust emissions of a diesel engine fueled with canola oil methyl ester−diesel blend. Energy Convers. Manage. 2013, 76, 145−154. (c) Jain, S.; Sharma, M. Oxidation stability of blends of Jatropha biodiesel with diesel. Fuel 2011, 90 (10), 3014−3020. (10) Varatharajan, K.; Cheralathan, M. Effect of aromatic amine antioxidants on NO x emissions from a soybean biodiesel powered DI diesel engine. Fuel Process. Technol. 2013, 106, 526−532. (11) Varatharajan, K. Effect of Antioxidant Additives on Nox Emissions from a Jatropha Biodiesel Fuelled DI Diesel Engine; SRM University: Kanchipuram, India, 2012. (12) Hess, M. A.; Haas, M. J.; Foglia, T. A.; Marmer, W. N. Effect of antioxidant addition on NOx emissions from biodiesel. Energy Fuels 2005, 19 (4), 1749−1754. (13) Rashedul, H.; Masjuki, H.; Kalam, M.; Teoh, Y.; How, H.; Fattah, I. R. Effect of antioxidant on the oxidation stability and combustion−performance−emission characteristics of a diesel engine fueled with diesel−biodiesel blend. Energy Convers. Manage. 2015, 106, 849−858. (14) (a) Eka, H. D.; Tajul, A. Y.; Wan, N.; W, A. Potential use of Malaysian rubber (Hevea brasiliensis) seed as food, feed and biofue. Int. Food Res. J. 2010, 17, 527−534. (b) Bashar, M. A.; Salimon, J. Physicochemical characteristics of Malaysian rubber (Hevea Brasiliensis) seed oil. Eur. J. Sci. Res. 2009, 31 (3), 437−445. (15) (a) Ashraful, A. M.; Masjuki, H. H.; Kalam, M. A.; Rizwanul Fattah, I. M.; Imtenan, S.; Shahir, S. A.; Mobarak, H. M. Production and comparison of fuel properties, engine performance, and emission characteristics of biodiesel from various non-edible vegetable oils: A review. Energy Convers. Manage. 2014, 80, 202−228. (b) Ramadhas, A. S.; Jayaraj, S.; Muraleedharan, C. Biodiesel production from high FFA rubber seed oil. Fuel 2005, 84, 335−340. (16) (a) Balaji, G.; Cheralathan, M. Study of antioxidant effect on oxidation stability and emissions in a methyl ester of neem oil fuelled DI diesel engine. J. Energy Inst. 2014, 87 (3), 188−195. (b) Kivevele, T. T.; Kristóf, L.; Bereczky, Á .; Mbarawa, M. M. Engine performance, exhaust emissions and combustion characteristics of a CI engine fuelled with croton megalocarpus methyl ester with antioxidant. Fuel 2011, 90 (8), 2782−2789. (17) Ryu, K. The characteristics of performance and exhaust emissions of a diesel engine using a biodiesel with antioxidants. Bioresour. Technol. 2010, 101 (1), S78−S82. (18) Ryu, K. Effect of antioxidants on the oxidative stability and combustion characteristics of biodiesel fuels in an indirect-injection (IDI) diesel engine. J. Mech. Sci. Technol. 2009, 23 (11), 3105−3113. (19) Fattah, I. R.; Masjuki, H.; Kalam, M.; Wakil, M.; Rashedul, H.; Abedin, M. Performance and emission characteristics of a CI engine fueled with Cocos nucifera and Jatropha curcas B20 blends accompanying antioxidants. Ind. Crops Prod. 2014, 57, 132−140. (20) Fattah, I. R.; Masjuki, H.; Kalam, M.; Wakil, M.; Ashraful, A.; Shahir, S. A. Experimental investigation of performance and regulated emissions of a diesel engine with Calophyllum inophyllum biodiesel blends accompanied by oxidation inhibitors. Energy Convers. Manage. 2014, 83, 232−240. (21) Rizwanul Fattah, I. M.; Masjuki, H. H.; Kalam, M. A.; Mofijur, M.; Abedin, M. J. Effect of antioxidant on the performance and emission characteristics of a diesel engine fueled with palm biodiesel blends. Energy Convers. Manage. 2014, 79, 265−272.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank the Universiti Teknologi PETRONAS for the Graduate Assistantship Scheme (GA), Blue Nile University, Ali Elheber Ahmed, Mhadi Abakar, Salaheldin Mohammed, Firman Syah, Ezrann Zharif Zainal, Ahmad Shahrul, Mahfuzrazi B. Misbahulmunir, and Mohammed El Adawy for their support.

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ABBREVIATIONS RSO = rubber seed oil RB = rubber seed biodiesel DPPD = N,N′-diphenyl-1,4-phenylenediamine NPPD = N-phenyl-1,4-phenylenediamine BHA = 2(3)-tert-butyl-4-methoxyphenol TBHQ = 2-tert-butylbenzene-1,4-diol BP = brake power BSFC = brake specific fuel consumption NO = nitric oxide HRR = heat release rate CO = carbon monoxide HC = hydrocarbon EDA = ethylenediamine BHT = butylated hydroxytoluene EHN = 2-ethylhexyl nitrate TDI = turbocharged direct injection engine CIB = calophyllum inophyllum oil biodiesel JB = jatropha biodiesel SB = soybean biodiesel CB = cocos nucifera biodiesel PB = palm biodiesel S = stroke WC = water cooled IDI = indirect injection diesel engine °CA BTDC = before top dead center Std = standard deviation ECU = engine control unit OS = oxidation stability CA = crank angle °CA ATDC = after top dead center SOC = start of combustion EOC = end of combustion

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