Effects of Palm–Coconut Biodiesel Blends on the ... - ACS Publications

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Effects of Palm−Coconut Biodiesel Blends on the Performance and Emission of a Single-Cylinder Diesel Engine M. Habibullah,* I. M. Rizwanul Fattah,* H. H. Masjuki,* and M. A. Kalam Centre for Energy Sciences, Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia S Supporting Information *

ABSTRACT: This study aims to investigate the effects of palm or coconut biodiesel blend and their combination on the performance and emissions of a single-cylinder diesel engine. A 20% v/v blend of palm biodiesel (PB20) or coconut biodiesel (CB20) and varying percentage mixtures of these two feedstocks (PB15CB5, PB10CB10, and PB5CB15) were used in the experiments. Biodiesel was produced using one-step transesterification. Physicochemical analysis showed that both palm and coconut biodiesel met the specifications of ASTM D6751. A 10 kW, horizontal, one-cylinder, four-stroke direct injection diesel engine was used to carry out tests under full load conditions at varying speeds from 1400 to 2400 rpm with an interval of 200 rpm. Burning of CB20 reduced break power by 1.72% and increased brake-specific fuel consumption (BSFC) and NOx emission by 4.07% and 4.49%, respectively. Conversely, burning of PB20 negligibly reduced brake power and increased NOx emission by only 1.79%. Meanwhile, combined palm−coconut biodiesel at a constant final blend reduced NOx emission by 0.54% to 1.85% and slightly improved brake power and BSFC. Thus, the advantages of the high cetane number of coconut and the high ignition quality of palm biodiesel were aggregated in the combined blends.

1. INTRODUCTION Biodiesel is a prospective alternative to diesel fuel because it is produced from renewable biological sources, such as vegetable oil and animal fats.1,2 In addition, biodiesel contains a high oxygen content (approximately 11 wt %), which accounts for its lower soot, hydrocarbon (HC), and carbon monoxide (CO) emissions than petroleum fuels.3,4 The use of biodiesel can reduce global warming and greenhouse effect through the following mechanism: the important greenhouse gas carbon dioxide produced by the combustion of biodiesel fuel is reabsorbed into the earth by plants, which then yield lipids, the raw material for biodiesel production.5 The future energy supply scenario includes 385 million hectares of biomass energy plantations worldwide in 2050, with the major portion established in developing countries.6 This statistics pushes the progressive implementation of biodiesel, and the increasing trend of renewable energy consumption supports this phenomenon. The use of vegetable oil as engine fuel is limited by its high viscosity and low volatility, which cause poor cold-start performance, misfire, and ignition delay.7 Transesterified vegetable oil blended up to 20% with diesel can be easily used in the existing diesel engine without any engine modification.8,9 Thus, the present study adopted a 20% biodiesel−diesel blend. Among the biodiesel plant families, palm is the most popular and extensively cultivated. Palm can be cultivated in tropical areas such as Malaysia and Indonesia, where the weather is humid and hot.10 Palm biodiesel is more saturated than other popular feedstocks, such as soybean and rapeseed; hence, this biodiesel contains high saturation percentage, which corresponds to high cetane number (CN). CN is a commonly used parameter of diesel fuel quality that is related to ignition delay time and combustion quality. The high CN of palm biodiesel © XXXX American Chemical Society

ensures good cold-start performance and minimizes white smoke performance.11 Moreover, palm tree cultivation requires low fertile land and minimal manpower. Malaysia produces approximately 19.4 million tons palm oil annually, which currently accounts for 44% of world exports.12 The oil content of coconut ranges from 63% to 65%, which is much higher than that of other biodiesel feedstocks.13 Given its high saturation content, coconut biodiesel has lower density and viscosity, higher lubricity, higher CN, lower iodine value, and higher oxygen content than other feedstocks.14 High CN and oxygen contents promote complete combustion and reduce CO, HC, and PM emissions; hence, engines fueled by coconut biodiesel run smoothly with longer maintenance intervals than those fueled by other biodiesels.15,16 The low density and viscosity of coconut biodiesel also minimize the carbon deposits formed in the fuel injectors and combustion chambers during long operations.17 Moreover, the high lubricity of coconut biodiesel facilitates smooth fuel flow through fuel lines, injector nozzles, and ports, thereby reducing friction losses and increasing engine efficiency. Coconut biodiesel also ensures good cold-start performance. In the present study, the advantages of the high ignition quality of palm and high oxygen content of coconut were aggregated by combining the two biodiesels (5% to 15%) blended with diesel. Then, the effects of 20% palm biodiesel (PB20) or coconut biodiesel (CB20) blend, their combination, and pure diesel on the performance and emissions of a singlecylinder diesel engine were compared. Recent studies have investigated the production, properties, performance, and emission of engines fueled by palm/coconut Received: April 3, 2014 Revised: January 12, 2015

A

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Energy & Fuels oil biodiesel blended with diesel.18−20 Research shows that biodiesel from a particular feedstock and its blends show low brake power (BP), reduced CO and unburned HC emissions, and high brake-specific fuel consumption (BSFC) and nitrogen oxide emissions.21,22 In addition, Liaquat et al.22 investigated the effects of PB20 and diesel fuel on injector nozzle deposits and lubricating oil; they found that PB20 results in greater carbon deposits on and around the injector tip and higher wear metal concentrations than diesel. Ozawa et al.23 reported that combustion chamber wall temperature quickly increases and that the ignition timing is advanced with increasing blend percentage. They also concluded that coconut oil methyl ester possesses excellent compression ignition characteristics during cold-start. Apart from high NOx emission, low oxidation stability and poor cold flow properties are also considered major technical problems.24,25 According to Knothe,25,26 an approach to solve these problems is to modify fatty acid composition (FAC). Considering this approach, several researchers have studied the binary mixture of biodiesels. Sanjid et al.27 evaluated the production, physicochemical properties, engine performance, and exhaust emission characteristics of palm, jatropha, and palm− jatropha biodiesel (PBJB5 and PBJB10) in an unmodified diesel engine. Compared with diesel fuel, PBJB5 and PBJB10 showed 7.55% and 19.82% higher BSFC, slightly lower BP, 9.53% and 20.49% lower CO emission, and 3.69% and 7.81% lower HC emission, respectively. Arbab et al.28 attempted to optimize the fuel properties of palm−coconut biodiesel using MATLAB optimization tool. Other researchers have studied the effect of biodiesel feedstocks and their chemical structure on physicochemical properties and engine emissions.29−31 The present study aims to assess the feasibility of using coconut−palm biodiesel blend as a partial replacement to diesel fuel. The coconut−palm biodiesel blend improved engine performance matrices (BSFC and BP) when compared with CB20 and reduced engine emissions (HC and CO) when compared with PB20. A 20% blend comprising each biodiesel (5% to 15%) and diesel was used and compared with PB20, CB20, and petroleum diesel alone in terms of effects on engine performance and emission.

Table 1. GC Operating Conditions property

specifications

carrier gas linear velocity flow rate detector temperature column head pressure column dimension injector column oven temperature ramp

helium 24.4 cm/s 1.10 mL/min (column flow) 260.0 °C 56.9 kPa BPX 70, 30.0 m × 0.25 μm × 0.32 mm ID 240.0 °C 140.0 °C (hold for 2 min) 8 °C/min 165.0 °C 8 °C/min 192.0 °C 8 °C/min 220.0 °C (hold for 5 min)

Value (IV), Saponification Number (SN), and Cetane Number (CN) were calculated using the following equations32

SN =

IV =

⎛ 560*A i ⎞ ⎟ ⎝ MWi ⎠

(1)

⎛ 254*D*A i ⎞ ⎟ ⎝ MWi ⎠

(2)

∑⎜ ∑⎜

⎛ ⎞ ⎛ 5458 ⎞ ⎟ − (0.225*IV)⎟ CN = ⎜46.3 + ⎜ ⎝ SN ⎠ ⎝ ⎠

(3)

where Ai is the percentage of each component, D is the number of double bonds, and MWi is the mass of each component.12 The molecular mass of each component is given in Table 3. The units for IV and SN are g I2/100 g and mg KOH/g. CN is a dimensionless parameter. The IV, SN, and CN for palm biodiesel are 196.41, 57.97, and 61.05, and those of coconut biodiesel are 246.89, 13.25, and 65.43, respectively. 2.3. Fourier-Transform Infrared (FTIR) Spectral Analysis. FTIR spectral analysis of palm and coconut biodiesel was carried out using a Perkin−Elmer Spectrum 400 FTIR analyzer equipped with a MIR detector in the range of 4000 cm−1 to 600 cm−1. The equipment was coupled with a standard KBr beam splitter and a DTGS detector. GladiATR from Pike Technologies was used for data collection. Spectra were recorded using four scans and 4 cm−1 resolution. Before background scanning, the crystal was cleaned using acetone−toluene−methanol solvents. Then, 0.4 mL of the sample was added for data collection. The band assignments are shown in Table 5. Two strong bands at wavenumbers of 1166.02 cm−1/ 1169.84 cm−1 (ester C−O) and 1742.51 cm−1/1741.60 cm−1 (ester CO) are characteristic of FAME biodiesel. The nonexistence of the O−H bond stretching in the range of 3640 cm−1 to 3200 cm−1 confirms the absence of residual water in the biodiesel samples. The absence of an alcohol functional group (O−H bond) is confirmed with the absence of a broad frequency band in the range of 3500 cm−1 to 3200 cm−1 or a strong, sharp frequency band in the range of 3640 cm−1 to 3610 cm−1.31 Figures 1(a) and 1(b) illustrate the absence of alcohol functionality in the two biodiesels. The single sharp ester peak at 1740 cm−1 indicates the absence of another band adjacent to this ester band and confirms the absence of carboxylic acids. 2.4. Engine Tests. The experiment was conducted using a naturally aspirated single-cylinder diesel engine in the Heat Engine Laboratory of the Mechanical Engineering Department, University of Malaya. The details of the engine are described in Table 6. Figure 2 shows a schematic of the engine test setup.

2. METHODOLOGY 2.1. Biodiesel Production and FAC. Biodiesel was produced from both palm and coconut biodiesel using traditional transesterification with methanol (25% v/v of oil) and KOH (1% w/w of oil). Gas chromatography (GC, Agilent 6890 model, USA) was performed to determine the FACs of palm and coconut biodiesel. Table 1 shows the operating conditions of GC, and Table 2 shows the comparative FACs of palm and coconut biodiesel. The uncertainty of FAC measurement was ±0.2%. Palm biodiesel contained 44.1% saturated and 55.9% unsaturated fatty acids, whereas coconut biodiesel contained 87.6% saturated and 12.4% unsaturated fatty acids. 2.2. Physicochemical Property Analysis. The producing palm and coconut biodiesel were blended with diesel using a homogenizer during 5 min at 3000 rpm. The properties of all samples were measured in the Tribology Engine Laboratory and Energy Laboratory, Department of Mechanical Engineering, University of Malaya. Table 3 shows the synopsis of equipment and methods used to determine fuel properties, and Table 4 shows some important physicochemical properties. The Iodine B

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Energy & Fuels Table 2. FAC Results of Palm and Coconut Biodiesel FAME name

structure

molecular weight

formula

PBD (wt %)

CBD (wt %)

methyl hexanoate methyl octanoate methyl decanoate methyl laurate methyl myristate methyl palmitate methyl palmitoleate methyl stearate methyl oleate methyl linoleate methyl linolenate methyl arachidate methyl eicosenoate methyl behenate methyl lignocerate saturated monounsaturated polyunsaturated total

6:00 8:00 10:00 12:00 14:00 16:00 16:01 18:00 18:01 18:02 18:03 20:00 20:01 22:00 24:00

130.18 158.24 186.29 214.34 242.4 270.45 268.43 298.5 296.49 294.47 292.46 326.56 324.54 354.61 382.66

CH3(CH2)4COOCH3 CH3(CH2)6COOCH3 CH3(CH2)8COOCH3 CH3(CH2)10CO2CH3 CH3(CH2)12COOCH3 CH3(CH2)14CO2CH3 CH3(CH2)5CHCH(CH2)7COOCH3 CH3(CH2)16CO2CH3 CH3(CH2)7CHCH(CH2)7CO2CH3 CH3(CH2)3(CH2CHCH)2(CH2)7CO2CH3 CH3(CH2CHCH)3(CH2)7COOCH3 CH3(CH2)18COOCH3 CH3(CH2)16CHCHCOOCH3 CH3(CH2)20COOCH3 CH3(CH2)22COOCH3

0 0 0 0.3 1 38.1 0.2 4.1 44.2 11 0.3 0.4 0.2 0.1 0.1 44.1 44.6 11.3 100

0.3 6.5 6 42.1 17.4 11.3 0.2 3.8 9.2 3 0 0.2 0 0 0 87.6 9.4 3 100

Table 3. List of Equipment Used for Testing Physicochemical Properties property

standard method

equipment

manufacturer

model

accuracy

density at 40 °C kinematic viscosity at 40 and 100 °C higher heating value (HHV) flash point oxidation stability cloud point

ASTM D445 ASTM D445

Stabinger viscometer Stabinger viscometer

Anton Paar Anton Paar

SVM 3000 SVM 3000

±0.1 mm2/s ±0.1 mm2/s

ASTM D240 ASTM D93 EN ISO 14112 ASTM D2500

IKA, UK Normalab, France Metrohm, Switzerland Normalab, France

C2000 NPM440 873 Rancimat NTE 450

±0.1% of reading ±0.1 °C ±0.01 h ±0.1 °C

pour point

ASTM D97

Normalab, France

NTE 450

±0.1 °C

acid value

ASTM D 664

basic calorimeter−automatic Pensky-martens flash point tester Rancimat 873 metrohm cloud and pour point tester-automatic NTE 450 cloud and pour point tester-automatic NTE 450 automated titration system

Mettler Toledo, Switzerland

G-20 Rondolino

±0.001 mg KOH/g

Table 4. Physicochemical Properties of Tested Fuels properties density at 40 °C kinematic viscosity at 40 °C kinematic viscosity at 100 °C viscosity index flash point higher heating value acid value oxidation stability cloud point pour point

unit kg/m3 cSt cSt °C MJ/kg mg KOH/g H °C °C

diesel

PB100

CB100

PB20

CB20

PB10CB10

PB15CB5

PB5CB15

829.6 3.0738 1.3438 132 68.5 45.238

870.2 4.6175 1.7641 197.8 182.5 39.910 0.42 2.88 13 15

858.2 4.0927 1.5856 183.4 106.5 38.284 0.38 4.12 −4 −3

837.7 3.3825 1.4279 150.5 73.5 44.469 0.23 7.61 10 12

835.3 3.2775 1.3920 137.8 70.5 43.762 0.21 9.33 7 −16

836.9 3.3305 1.4101 146.4 70.5 44.010 0.29 8.30 7 −8

837.2 3.3564 1.4190 147.4 71.5 44.391 0.30 7.98 7 −6

835.9 3.3041 1.4011 140.2 69.5 43.858 0.28 8.65 7 −10

35 7 8

by a gas analyzer (AVL DiCom4000). Details of the analyzer are shown in Table 7. The engine was run with diesel until a steady operating condition was achieved. Then, the fuel was changed to biodiesel blend. After running the engine for 5 min, data acquisition was started to ensure the removal of residual diesel in the fuel line. This procedure was followed for each blend. Table 8 shows the test fuel samples for this study. After each test, the engine was again run with diesel to drain the blend out of the fuel line. The engine was operated between 1400 and 2400 rpm with an interval of 200 rpm at 100% load condition. Statistical analysis

The test engine was directly coupled with a SAJ SE-20 eddy current dynamometer. The torque was measured using a strain gauge load cell with a measurement accuracy of ±0.25 N m. Fuel flow was measured using a Kobold ZOD positivedisplacement type flow meter. Engine oil, cooling water, exhaust gas, and inlet air temperatures were measured using a K-type thermocouple. Data collection was performed using the DASTEP8 data acquisition system with a rate of 10 samples per second. The engine fuel system was modified by adding separate tanks with two-way valves, which allowed the rapid switching of fuels. CO, HC, and NOx emissions were measured C

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for all palm−coconut blends was higher than that for the CB20 blend at all tested engine speeds. 3.1.2. BSFC. Figure 4 illustrates the variation in BSFC for all tested fuels with respect to engine speed. BSFC is the ratio between fuel consumption and BP; for a given fuel, BSFC is inversely proportional to thermal efficiency. The graph shows that the BSFC for all the tested fuels initially decreased, reached the lowest value at 1800 rpm, and then increased with engine speed. As the speed increased from 1400 to 1800 rpm, the fuel consumption for all the fuels decreased because of the increase in atomization ratio; consequently, the air−fuel equivalence ratio, which influences air and fuel mixing, decreased.42 At 1800 to 2400 rpm, the BSFC increased with decreasing volumetric efficiency and increasing piston−cylinder frictional force. The lowest BSFC values for diesel, CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 were 265.63, 275.91, 274.22, 275.70, 275.03, and 274.88 g/kWh, respectively. In addition, the average BSFC and changes with respect to diesel throughout the speed range are shown in Table 9. These changes due to fuel variation compared with diesel were significant (p < 0.01). The increase in BSFC for the biodiesel blends can be attributed to their lower energy densities (i.e., HHV) and higher densities and viscosities than pure diesel. The test engine had a mechanically controlled pump-line nozzle system; the engine load was controlled by the fuel injection volume. Thus, a larger weight percentage of the biodiesel blends than that of diesel was injected into the combustion chamber for the same volume because of their higher densities. High density and kinematic viscosity influence the atomization ratio by slowing down the rate of fuel−air mixing.42 PB15CB5 showed the lowest BSFC among the biodiesel blends at 2200 rpm because of the better interactions between fuel and air in the presence of a small amount of coconut biodiesel in the blend. Meanwhile, CB20 resulted in the highest BSFC at 1400 rpm because of its lowest BP output. As the content of palm biodiesel in the blend was increased, the BSFC reduced and was found the lowest for PB20 because of its highest HHV and BP output. 3.1.3. BTE. BTE is the ratio of BP output to the energy introduced through the fuel. Figure 5 presents the BTE for all the tested fuels with the engine speed. The BTE increased until 1800 rpm, decreased with engine speed, and reached the lowest value at 2400 rpm for all the tested fuels. This result can be attributed to the fact that the highest BSFC was reached because of the combined effect of poor fuel atomization time and increased piston−cylinder frictional force at this speed.46 The highest BTE values for diesel, CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 were 30.00%, 29.81%, 29.52%, 29.77%, 29.74%, and 29.50%, respectively. Thus, the maximum BTE for the biodiesel blends reduced by 0.50% to 1.52%. These changes due to fuel variation were significant (p < 0.02). BTE changed with the variation in the effective work, BSFC, and calorific value of the biodiesel fuel. Combustion phasing also affects the energy conversion of heat energy to work. Early injection of biodiesel together with high CN leads to the early start of combustion (SOC). Early SOC timing increases pumping work and promotes heat loss in the cycle.45 This phenomenon, together with low calorific value and high density and viscosity, negatively affects engine performance.42,47,48 Among the different fuel blends, PB20 showed the lowest BTE because of its highest HHV. The addition of coconut biodiesel in the blend reduced HHV and increased BTE. 3.2. Emission Analysis. NOx, CO, and HC emissions were studied as engine emission parameters in this study.

Table 5. Characteristic Region of Palm and Coconut Biodiesel Spectra palm biodiesel coconut biodiesel wavenumber wavenumber (cm‑1) (cm‑1)

functional group

722.22

722.00

881.60 1016.69 1117.06 1169.84 1196.21 1245.90 1361.91 1435.79 1457.79

877.85 1015.91 1113.02 1166.02 1196.00 1361.09 1435.93 1457.30

−(CH2)n− (n ≥ 3) >CH2 −C−O −C−O −C−O−C O−CH3 −C−O O−H −C−H (CH3) −C−H (CH2)

1742.51 2853.33

1741.60 2853.50

CO (ester) >CH2

2922.16

2922.75

>CH2

mode of vibration

ref

rocking

33

wagging stretching stretching stretching (sym) stretching stretching bending (in plane) bending (asym) bending (scissoring) stretching methylene sym stretch methylene asym stretch

34 34 34 35 36 34 34 35 37 34 33 33

was carried out by applying two-sided Student’s t test in Microsoft Excel 2013 for independent variables to test for significant differences between samples. Differences between mean values at a level of p = 0.05 (95% confidence level) were considered statistically significant.

3. RESULTS AND DISCUSSION 3.1. Performance Analysis. Engine BP output, BSFC, and brake thermal efficiency (BTE) were studied as engine performance parameters. 3.1.1. BP. The influence of biodiesel on engine performance depends on the relationship between the fuel injection system and the fuel properties [e.g., oxygen content, density, viscosity, and higher heating value (HHV) of biodiesel], as well as the effects of these properties on spray formation and combustion.38,39 Figure 3 shows the variation in BP output with engine speed among the different fuel blends. For all the tested fuels, the BP steadily increased with engine speed, except at 2400 rpm; this exception can be attributed to the combined effect of poor fuel atomization time and increased piston− cylinder frictional force at this engine speed.40 The maximum BP outputs obtained at 2200 rpm were 7.34, 7.25, 7.32, 7.28, 7.29, and 7.30 kW for diesel, CB20, PB20, PB5CB15, PB10CB10, and PB15CB5, respectively. Thus, the BP output of all biodiesel blends was 0.3% to 1.2% lower than that of diesel. These changes due to fuel variation compared with diesel were significant (0.01 < p < 0.02). Compared with diesel fuel, biodiesel fuel possesses higher viscosity and density but lower volatility, as evidenced by its higher flash point, which is reciprocally related to fuel volatility; as a result, the fuel in the premixed region displays high injection, uneven combustion, poor atomization, and, ultimately, high global fuel−air equivalence ratio.41−43 This result, together with the approximately 11% lower calorific value of biodiesel fuel than conventional diesel fuel, can be attributed to the lower BP output of biodiesel than diesel. The BP for PB20 showed the highest BP output among all the blends; this result can be ascribed to the fact that low HHV and high viscosity reduce the internal leakage in the pump.44,45 Having the lowest HHV among all the blends, CB20 showed the highest reduction in BP at a low speed. The HHV improved with the addition of palm biodiesel. The BP output D

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Figure 1. FTIR spectrum of (a) coconut biodiesel and (b) palm biodiesel.

3.2.1. NOx Emission. NOx forms during biodiesel combustion through the thermal (Zeldovich), prompt (Fenimore), fuel NOx, N2O, and NNH mechanisms.49,50 The Zeldovich mechanism is the most prevalent one for NOx formation. Researchers suggested that NOx forms promptly through the generation of hydrocarbon radicals via molecular unsaturation.51−53 The formation of NOx through fuel effect is generally negligible because of the low natural nitrogen levels in both

diesel and biodiesel.50 Figure 6 illustrates the NOx emission from the single-cylinder engine for all tested fuels at different speeds. The figure shows that NOx formation increased with engine speed. At high engine speeds, combustion temperature is increased because of the slow cooling rate and poor atomization in the premixed region.49 The highest NOx emissions for diesel, CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 were 703, 739, 715, 734, 728, and 720 ppm, respectively. Thus, the E

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The high oxygen content of biodiesel creates a high in-cylinder temperature under both premixed and diffusion combustion conditions.55,56 Thus, biodiesel blends are expected to combust earlier and form higher NOx than diesel. Among the different biodiesel blends, CB20 showed the highest NOx emission despite having the lowest kinematic viscosity and bulk modulus of elasticity. This result can be attributed to the high amount of fuel-borne oxygen (14.5%) and high CN of CB20 resulting from its high saturation percentage.25,57 A high CN corresponds to a short ignition delay, and a high oxygen content promotes complete combustion. The addition of palm biodiesel in coconut biodiesel decreased CN, which outweighed the effect of kinematic viscosity and decreased NOx emission. Thus, PB20 showed the lowest NOx emission among all biodiesel blends. 3.2.2. CO Emission. In general, CO is produced from partial combustion because of insufficient oxygen to produce CO2.58 It is a product of the imperfect combustion of hydrocarbon fuels and is affected by engine speed, air−fuel ratio, fuel pressure, fuel type, and injection timing.49 Figure 7 shows the variation in CO emissions for the different tested fuels at different engine speeds. The figure shows that CO emission decreased with engine speed. This result can be attributed to high in-cylinder temperature due to the high in-cylinder pressure at the tested speeds.45 The reduction in CO emission can also be attributed to the complete combustion as the flame front approached the crevice volume; in other words, excess air helped the conversion of CO to CO2. At 1400 rpm, the highest CO emissions for diesel, CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 were 7.41, 7.12, 7.37, 7.17, 7.26, and 7.32 vol %, respectively. Thus, the CO emissions for CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 reduced by 3.91%, 0.54%, 3.24%, 2.02%, and 1.21%, respectively. The highest reduction (6.92% to 12.11%) in CO emission for these

Table 6. Engine Specification specification model type fuel system aspiration cylinder bore × stroke displacement continuous rated output maximum rated output dimension engine dry weight fuel injection pressure cooling system lubrication system EGR

descriptions TF 120 M 1-cylinder, horizontal, water-cooled, 4-cycle diesel engine mechanical direct injection natural aspiration 92 mm × 96 mm 638 cc 2400 rpm, 10.5Ps, 7.7 kW 2400 rpm, 12 Ps, 8.8 kW length (695.5 mm) × width (348.5 mm) × height (530 mm) 101.5 kg 200 kg/cm2 radiator cooling system completed enclosed forced lubricating system not present

NOx emissions for CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 were 5.12%, 1.71%, 4.41%, 3.56%, and 2.42% higher than those for diesel fuel. These changes due to fuel variation were significant (0.01 < p < 0.03). The high combustion temperature and presence of fuel-borne oxygen are the major factors influencing the high NOx formation of biodiesel blends.53 The higher NOx of biodiesel blends than diesel can also be attributed to their higher bulk modulus of elasticity and higher CN.54 The higher bulk modulus of biodiesel compared with that of fossil diesel leads to the early opening of the nozzle and advanced injection. This phenomenon also increases global fuel−air equivalence. Compared with diesel, biodiesel possesses shorter ignition delay because of its higher CN.

Figure 2. Schematic diagram of engine test setup. F

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Energy & Fuels Table 7. Details of the Gas Analyzer equipment

measurement

method

measurement range

resolution

AVL DiCom 4000

CO CO2 HC NOx O2

nondispersive infrared nondispersive infrared nondispersive infrared electrochemical detector electrochemical detector

0−10% vol. 0−20% vol. 0−20,000 ppm vol. 0−5000 ppm vol. 0−25% vol.

0.01% vol. 0.1% vol. 1 ppm 1 ppm 0.01% vol.

Table 8. Composition of Fuel Samples

Table 9. BSFC for Different Fuels and Their Variation

no.

fuel name

compositions

blend

1 2 3 4

diesel PB20 CB20 PB15CB5

5

PB10CB10

diesel CB20 PB20 PB5CB15 PB10CB10 PB15CB5

6

PB5CB15

100% fossil diesel 80% fossil diesel + 20% palm oil biodiesel 80% fossil diesel + 20% coconut biodiesel 80% fossil diesel + 5% coconut biodiesel + 15% palm oil biodiesel 80% fossil diesel + 10% coconut biodiesel + 10% palm oil biodiesel 80% fossil diesel + 15% coconut biodiesel + 5% palm oil biodiesel

average BSFC 284.35 295.91 293.57 295.23 294.40 293.94

g/kWh g/kWh g/kWh g/kWh g/kWh g/kWh

increase compared to diesel 4.07% 3.24% 3.83% 3.54% 3.37%

Figure 5. Variation of BTE with engine speed for 100% load condition. Figure 3. Variation of brake power with engine speed for 100% load condition.

Figure 6. Variation of NOx emission for the test fuels with speed at 100% load. Figure 4. Variation of BSFC with engine speed for 100% load condition.

biodiesel fuel than in diesel fuel. CB20 had the lowest CO emission among the tested fuels. This result can be ascribed to the higher oxygen content and higher CN of CB20 than the other biodiesel blends.44,59 A high CN corresponds to a short ignition delay and improves combustion. A high oxygen content of biodiesel also enhances combustion. As reported in a previous

blends was recorded at 2400 rpm. These changes due to fuel variation were significant (p < 0.01). The presence of higher oxygen content in all tested biodiesel blends allowed complete combustion, which ensured that less CO was formed in the G

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ranged between 8.70% and 16.52%. These changes due to fuel variation were significant (p < 0.01). These reductions can be attributed to the higher CN and oxygen contents but less carbon and hydrogen contents of biodiesel fuel than diesel fuel.45,61 These parameters ensure complete combustion, thereby significantly reducing HC. To explain further, biodiesel with a high CN exhibits a short ignition delay and promotes complete combustion. Then, the high oxygen content of the biodiesel enhances combustion. A high oxygen content ensures a high incylinder combustion temperature, which promotes the complete combustion of fuels.60 CB20 had the lowest HC emission among the tested fuels because of its high oxygen content and high CN.44,59 The overall average HC emission for CB20, PB20, PB5CB15, PB10CB10, and PB15CB5 reduced by 7.01%, 3.36%, 6.27%, 5.12%, and 4.18%, respectively, compared with that for diesel. Thus, the addition of palm biodiesel with coconut biodiesel decreased the HC emission reduction potential of coconut biodiesel. Figure 7. Variation of CO emission for the test fuels with speed at 100% load.

4. CONCLUSION Biodiesel is currently a prospective alternative transportation fuel that is recommended to be directly used at 20% of blend with diesel without any engine modifications. To aggregate the advantages of the high ignition quality of palm and the high oxygen content of coconut, this study compared the effects of 20% palm biodiesel or coconut biodiesel blend, their combination (5% to 15%), and pure diesel on the performance and emissions of a single-cylinder diesel engine. Compared with diesel, PB20, CB20, PB5CB15, PB10CB10, and PB15CB5 had lower average engine BP (0.6% to 1.72%) and higher BSFC (3.24% to 4.07%) because of the low HHV and high density and viscosity of the biofuels. The BTEs of the biodiesel fuels were slightly (0.66% to 1.46%) lower than that of diesel fuel. The average NOx emissions were 1.79% to 4.49% higher for all the tested biodiesel blends compared with diesel because of the higher combustion temperature and presence of fuel-borne oxygen in the biodiesel. The CO and HC emissions in biodiesel burning reduced by 3.36% to 7.01% and 13.54 to 23.79% compared with those in diesel burning. In conclusion, the low BP output and high NOx emission from burning of coconut biodiesel blends can be improved by the addition of palm biodiesel. A list of the nomenclature can be found in Table 10.

study, a high oxygen content ensures a high in-cylinder combustion temperature, which promotes the complete combustion of fuels.60 The addition of palm biodiesel in coconut biodiesel increased density and kinematic viscosity, which consequently increased global fuel−air equivalence ratio. Thus, PB20 (i.e., without coconut biodiesel) showed the highest CO emission. 3.2.3. HC Emission. HC emission in the diesel engine was due to the mixture of fuel to leaner than the lean combustion limit during the delay period. During air−fuel interactions, particularly in the fuel-rich region, the oxygen content of biodiesel provides advantageous conditions (post flame oxidation, high flame speed, etc.) that enhance the oxidation of unburned HC.11 Figure 8 shows the variation in HC emission

Table 10. Nomenclature abbreviation ASTM

PB5

5% palm biodiesel with diesel

PB10 PB20

10% biodiesel with diesel 20% biodiesel with diesel

CN

American Society for Testing and Materials brake power brake specific fuel consumption cetane number

PBJB5

CO

carbon monoxide

PBJB10

5% palm and 5% jatropha biodiesel with 90% diesel 10% palm and 10% jatropha biodiesel with 80% diesel

FAC GC HC IV NOx rpm SN

fatty acid composition gas chromatography hydrocarbon iodine value oxides of nitrogen revolution per minute saponification number

BP BSFC

Figure 8. Variation of HC emission for the test fuels with speed at 100% load.

(in ppm) for all the tested fuel blends at various engine speeds. As shown in the figure, HC emission decreased with increasing engine speed. This result can be attributed to the high incylinder temperature due to the high in-cylinder pressure at high speeds.45 The highest HC emission was recorded at 1400 rpm, with HC emission levels of 115, 96, 105, 99, 100, and 103 ppm for diesel, CB20, PB20, PB5CB15, PB10CB10, and PB15CB5, respectively. Thus, reduction at this level for biodiesel blends H

abbreviation

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ASSOCIATED CONTENT

S Supporting Information *

The experimental setup and calculated average performance and emission data of single cylinder diesel engine. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*Phone: 603 79674448. Fax: 603 79675317. E-mail: habib. [email protected]. *Phone: 603 79674448. Fax: 603 79675317. E-mail: rizwanul. [email protected]. *Phone: 603 79674448. Fax: 603 79675317. E-mail: masjuki@ um.edu.my. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors would like to thank the University of Malaya for financial support through a High Impact Research grant titled as follows: Clean Diesel Technology for Military and Civilian Transport Vehicles having Grant number UM.C/HIR/ MOHE/ENG/07.

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