Impact of Oxygenated Additives on Diesel Engine Performance with Jatropha Biodiesel Blend

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Effect of n-butanol and diethyl ether as oxygenated additives

on combustion–emission-performance characteristics of a multiple cylinder diesel engine fuelled with diesel–jatropha biodiesel blend

S. Imtenan

^⇑

, H.H. Masjuki

^⇑

, M. Varman, I.M. Rizwanul Fattah

^⇑

, H. Sajjad, M.I. Arbab

Centre for Energy Sciences, Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

a r t i c l e i n f o

Article history:

Received 1 November 2014 Accepted 18 January 2015

Keywords:

Diesel–biodiesel blend n-Butanol

Diethyl ether Combustion

Engine performance-emission

a b s t r a c t

Jatropha biodiesel is considered as one of the most prospective renewable energy sources of Malaysia in recent years. Hence, an investigation was conducted for the improvement of jatropha biodiesel–diesel blend with the addition of 5–10%n-butanol and diethyl ether by vol. which are commonly known as oxygenated cold starting additive. Engine tests were conducted at variable speed, ranging from 1000 rpm to 3000 rpm at constant 80 N m torque on a 4-cylinder turbocharged indirect injection diesel engine. Engine performance parameters like brake specific fuel consumption, brake specific energy consumption, brake thermal efficiency and engine emissions like carbon monoxide, unburned hydrocarbons, nitrogen oxide and smoke opacity were measured. Performance and exhaust emissions variation of the modified blends from the baseline fuel (jatropha biodiesel–diesel blend) were compared for the assessment of the improvement quantitatively. In-cylinder pressure diagram of all the test fuels were acquired and the heat release rate analysis was conducted at different operating conditions to explore the features of combustion mechanism and correlate them with the performance and emission characteristics to acquire better understanding of the scenario. However, in a nut-shell, the investigation reveals the potential of n-butanol and diethyl ether to be used as the additive of jatropha biodiesel–diesel blend in the context of combustion, performance and emission characteristics.

1. Introduction

Biodiesel refers to the fatty acid methyl esters which are derived from lipid substances from oils, fats, waste greases, recy- cled oils, etc. To produce biodiesel, vegetable oils of edible origin were treated as one of the potential feedstocks once. Due to food vs. fuel controversy of usage of edible oil for fuel production, other sources e.g. non-edible oils of plant origin with high free fatty acid (FFA) content, etc. are now being used for biodiesel production.

Malaysia is one of the leading palm oil producers in the world [1]. In addition, it also facilitates the use of palm oil as fossil diesel replacement. The government of Malaysia has recently mandated the use of 5% palm biodiesel with diesel nationwide for all diesel vehicle [2]. However, because of the edible nature of the palm oil, recently jatropha has drawn immense attention of both private

and government sectors in Malaysia.Jatropha curcasis non-edible in nature, physicochemical properties of its biodiesel are quite similar to the palm biodiesel and most interestingly, it has been reported as one of the best contestants of cheap biodiesel source in future[3]. Hence, Malaysian government started a project con- cerning jatropha cultivation and economic viability study of jatropha biodiesel production [4]. It has been reported that, Forest Research Institute of Malaysia (FRIM) has completed a 6000 J. curcastree plantation project and the agency has conﬁrmed that it is ready to proceed to commercial scale[5]. Therefore, being a prospective non-edible renewable energy source with satisfactory physicochemical properties, jatropha biodiesel deserves profound investigation regarding its viability in the diesel engines.

Many experiments were done with neat jatropha biodiesel or its blends with diesel to study their effects on engine performance and emission characteristics. Huang et al.[6]studied with jatropha biodiesel and reported 3.6% higher brake thermal efficiency (BTE) compared to diesel at higher loads in expense of higher brake specific fuel consumption (BSFC). Sundaresan et al.[7]also found from their study that the engine efficiency and BSFC for jatropha were inferior to that of diesel fuel. However, pre-heating and blending

⇑Corresponding authors. Tel.: +60 146985294; fax: +60 3 79675245 (S. Imtenan).

Tel.: +60 3 79675245; fax: +60 3 79675245 (H.H. Masjuki). Tel.: +60 3 79674448;

fax: +60 3 79675245 (I.M. Rizwanul Fattah).

E-mail addresses:[email protected](S. Imtenan),[email protected].

my(H.H. Masjuki),[email protected](I.M. Rizwanul Fattah).

Contents lists available atScienceDirect

Energy Conversion and Management

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with diesel have been reported conducive for engine performance characteristics[8]. Manieniyan and Sivaprakasam[9]reported sig- niﬁcant improvement of performance while they tried 20% blend of jatropha biodiesel which was also supported by the work of Sahoo et al.[10]. Therefore, blending with petroleum diesel as a single biodiesel[11] or as an optimized multiple biodiesel blend [12]

have already been studied by several researchers.

The problems associated to biodiesel is its high viscosity and auto ignition temperature (AIT) compared to that of diesel. To min- imize these drawbacks as well as to increase the fuel bound oxygen (to facilitate combustion) and to keep lubricity at reasonable levels, oxygenated additives such asn-butanol and diethyl ether (DEE) are usually added in a small portion[13].n-butanol has emerged as a potential oxygenated additive to improve the fuel properties of both diesel and biodiesels recently.n-butanol, also better known as 1-butanol, is produced from alcoholic fermentation of biomass feedstocks [14]. Hence, it is a renewable additive with a straight-chain structure with the OH group at the terminal carbon.

n-butanol is a strong competitor of ethanol and has less hydrophilic tendency, higher cetane number, higher miscibility with diesel and biodiesels and higher caloriﬁc value[15]. Yao et al.[16]investigated the inﬂuence of n-butanol-diesel blend on the performance and emissions of a heavy-duty diesel engine with multi-injection and various EGR (exhaust gas recirculation) ratios. They reported that, the soot and CO emissions can be improved by the addition of n-butanol without a severe impact on the BSFC. Altun et al.[17]

studied the effect ofn-butanol on cottonseed biodiesel–diesel blend and reported that, emissions of NOx, HC and CO reduced in expense of higher BSFC. Lebedevas et al.[18]experimented with butyl esters of rapeseed oil-diesel blend with the addition of 15–25%n-butanol and reported improvement on emission characteristics and overall efficiency factor. In their study, Mehta et al.[19]studied the effect of varying percentage ofn-butanol with jatropha biodiesel–diesel blend and reported significant reduction in CO and NO emission in expense of lower engine performance. However, they did not analyse their data with sufficient insight on combustion phenomena at each condition. Thus, the disadvantage of higher viscosity of biodiesel and the lower cetane number ofn-butanol than biodiesel can be offsetted with the addition ofn-butanol as additive.

Diethyl ether is another biomass based oxygenated additive produced from ethanol, which is produced itself from biomass [20]. It is a colorless liquid with high volatility and ﬂammability.

It has got very high cetane number, reasonable energy density and low AIT with high oxygen content. It has high miscibility with both diesel and biodiesel. Consequently, it is very much suitable to be used in diesel engine either with diesel or biodiesels[21]. Many researchers have studied diesel-DEE blend to improve the performance and emission characteristics. Blending with neat biodiesel or biodiesel–diesel blend has also been tried by the researchers.

Babu et al.[22]evaluated the effect of DEE on mahuva methyl ester and reported that, CO and smoke emission decreased more than 50% after addition of DEE. Sivalaksmi and Balusamy[23] added 5–15% DEE on neat neem biodiesel and reported improvement of BSFC and BTE. Qi et al.[24]studied effect of 5% DEE addition with soybean biodiesel–diesel blend. They observed signiﬁcantly lower CO emission with better BSFC with the addition of DEE into the diesel–biodiesel blend. Thus, it can be concluded that, addition of DEE results in improved performance and emission characteristics of diesel engines.

Jatropha biodiesel has the potential to be used as partial replacement of diesel in Malaysia after palm oil. Therefore, an attempt was taken previously by the authors for the improvement with the addition ofn-butanol and DEE[4]. On that investigation it was observed that addition of 5%n-butanol and DEE improved the brake power (3.5%), brake thermal efﬁciency (3.4%) and also reduced the emissions of NOx(9%), CO (20%) and smoke opacity

(22%) of the modified blends than J20 blend on average with an unmodified single cylinder diesel engine. Apart from that, there is an absence of comparative study in the literature on the effects of higher percentages ofn-butanol and DEE as additives on jatropha biodiesel–diesel blends on multiple cylinder engines. There- fore, in the present investigation the authors have attempted to increase the percentage ofn-butanol and DEE in the quest of study- ing the effects in a four cylinder, water cooled turbocharged diesel engine. In addition, combustion analysis has been incorporated at different operating conditions to get in-depth understanding of the combustion mechanisms and their correlation with the performance and emission characteristics. Cost analysis of all the modified blends have also been incorporated into this study to provide an economic comparison of different tested fuels.

2. Materials and method

2.1. Feedstock and additive

FRIM (Forest Research Institute Malaysia) supplied the jatropha biodiesel.n-butanol and DEE were purchased from Nacalai Tesque, Inc., Kyoto, Japan; certiﬁed as 99.5% pure. Petroleum diesel was supplied from the local market supplier.

2.2. Fatty acid composition (FAC)

In this investigation Shidmadzu, GC-2010A series gas chro- matograph was used to explore the FAC of jatropha biodiesel.

Tables 1 and 2 show the GC operating conditions and the FAC results of the biodiesel. Jatropha biodiesel contains 24.3% satu- rated, 42.6% mono-unsaturated and 33.1% poly-unsaturated methyl esters. Higher portion of saturation indicates higher oxidation stability and CN (cetane number). On the contrary it also indicates lower iodine value and CFPP according to the literature review[25].

2.3. Test fuels

The preparation of the test fuels and characterization of the properties were carried out at the Engine Tribology Laboratory, Department of Mechanical Engineering, University of Malaya. A total of six test fuels were selected for this investigation. The test fuels were (a) 100% petroleum diesel, (b) 20% Jatropha biodiesel + 80% diesel (J20), (c) 15% Jatropha biodiesel + 5% n- butanol + 80% diesel (J15B5), (d) 10% Jatropha biodiesel + 10%

n-butanol + 80% diesel (J10B10), (e) 15% Jatropha biodiesel + 5%

DEE + 80% diesel (J15D5), (f) 10% Jatropha biodiesel + 10%

DEE + 80% diesel (J10D10). The proportions mentioned here were all volume based. Diesel and biodiesel blending was completed

Table 1

GC operating condition for determination of fatty acid composition.

Item Speciﬁcation

Column 0.32 mm⁄30 m, 0.25lm

Injection volume 1lm

Carrier gas Helium, 83 kPa

Injector Split/splitless 1177, full EFC control

Temperature 250°C

Split ﬂow 100 mL/min

Column 2 ﬂow Helium at 1 ml/min constant ﬂow

Oven 210°C isothermal

Column temperature 60°C for 2 min 10°C/min to 200°C 5°C/min to 240°C Hold 240°C for 7 min

Detector 250°C, FID, full EFC control

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by a blending machine at 4000 rpm for 15–20 min. Asn-butanol and DEE are volatile in nature, after addition of n-butanol and DEE, the blends were taken into a closed container and shaked with a shaker machine for about 30 min.

2.4. Equipment for fuel property test

Table 3shows the list of the equipment used to measure the physicochemical properties of the base fuels (diesel and biodiesels) and fuel blends. The following equations were used to calculate the saponiﬁcation number (SN), iodine value (IV) and cetane number (CN) of the biodiesel[25].

SN¼X 560Ai MWi

ð1Þ

IV¼X 254DAi MWi

ð2Þ

CN¼46:3þ 5458 SN

ð0:225IVÞ ð3Þ

Here, A_i= percentage of each component, D = number of double bonds, MWi= mass of each component. Molecular weight of each component is given inTable 2.

2.5. Fuel properties

Tables 4 and 5show the physicochemical properties of the base fuels and the blends respectively. Each property was tested several times and then mean value was taken.

Kinematic viscosity of the biodiesels depends on the fatty acid proﬁle[28].Table 4shows that, kinematic viscosity of the jatropha biodiesel satisﬁes the ASTM-D6751 and EN 14214 standards.

Though jatropha biodiesel is meeting the standard, still it is 15%

higher than the diesel fuel. FromTable 5it can be seen that, addition ofn-butanol and DEE reduced the value of kinematic viscosi- ties of the modiﬁed blends at best 26%. All the blends meet the ASTM D7467 standard of viscosity. Lower kinematic viscosity is supposed to assist the modiﬁed blends to get better atomization during the injection than the J20 blend.

Density of the jatropha biodiesel was 3.4% higher than diesel fuel. However, blending with diesel (J20) reduced the density to some extent. Compared to J20,n-butanol and DEE blends showed further reduction. Up to 4.4% reduced density was observed for the modiﬁed blends than J20. Increasing portion ofn-butanol and DEE reduced the density accordingly which made the values much similar to diesel fuel.

The calorific value of jatropha biodiesel was lower than diesel as expected. On top of that, calorific values ofn-butanol and DEE were even lower than the biodiesel. Consequently, all the blends J20, J15B5, J10B10, J15D5 and J10D10 showed lower calorific values than diesel, yet the values were only 2.95% lower on average than diesel.

Flash point of the jatropha biodiesel was very much higher than diesel fuel, which is positive in terms of transportation and han- dling. Flash points ofn-butanol and DEE were very low, therefore modified blends showed quite lower flash points than J20. How- ever, generally a flash point higher than 66°C is considered as safe [29]and on top all the modified blends satisfy the ASTM D7467 standard for flash point. Therefore, in this study it can be said that all the fuels were safe to handle.

The cloud point and pour point values are of limited concern in tropical and hot countries of Asia, but it has much greater impor- tance in countries where the weather is cold. It can be seen from Table 4that cloud point and pour point of jatropha biodiesel was quite higher than the diesel. However, as then-butanol and DEE Table 2

Fatty acid composition of biodiesels.

FAME Structure Molecular weight Formula JBD (wt.%)

Methyl laurate 12:00 214.34 CH3(CH2)10COOCH3 0

Methyl myristate 14:00 242.4 CH3(CH2)12COOCH3 0.1

Methyl palmitate 16:00 270.45 CH3(CH2)14COOCH3 17.7

Methyl palmitoleate 16:01 268.43 CH3(CH2)5CH@CH(CH2)7COOCH3 0.8

Methyl stearate 18:00 298.5 CH3(CH2)16CO2CH3 6.4

Methyl oleate 18:01 296.49 CH3(CH2)7CH@CH(CH2)7COOCH3 41.8

Methyl linoleate 18:02 294.47 CH3(CH2)3(CH2CH@CH)2(CH2)7COOCH3 32.9

Methyl linolenate 18:03 292.46 CH3(CH2CH@CH)3(CH2)7COOCH3 0.2

Methyl archidate 20:00 326.56 CH3(CH2)18COOCH3 0.1

Methyl eicosenoate 20:01 324.54 CH3(CH2)16CH@CHCOOCH3 0

Methyl behenate 22:00 354.61 CH3(CH2)20COOCH3 0

Methyl lignocerate 24:00 382.66 CH3(CH2)22COOCH3 0

Saturation 24.3

Mono-unsaturation 42.6

Poly-unsaturation 33.1

Unsaturation 75.7

Table 3

Equipment of fuel property test.

Property Equipment Manufacturer Standard

method

ASTM D6751 limit

Accuracy

Kinematic viscosity at 40°C SVM 3000-automatic Anton Paar, UK D7042 1.9–6.0 ±0.35%

Density at 40°C SVM 3000-automatic Anton Paar, UK D7042 n.s. 0.0005 g/cm3

Flash point Pensky–Martens ﬂash point-automatic NPM 440 Normalab, France D93 130 min ±0.1°C

Oxidation stability 873 Rancimat-automatic Metrohm, Switzerland EN 14112 3 h ±0.01 h

Higher heating value C2000 basic calorimeter-automatic IKA, UK D240 n.s. ±0.1% of reading

Cloud point Cloud and Pour point tester-automatic NTE 450 Normalab, France D2500 Report ±0.1°C

Pour point Cloud and Pour point tester-automatic NTE 450 Normalab, France D97 ±0.1°C

CFPP Cold ﬁlter plugging point-automatic NTL 450 Normalab, France D6371 n.s.

Acid value G-20 Rondolino automated titration system Mettler Toledo, Switzerland D664 0.5 max ±0.001 mg KOH/g

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are well accepted as the cold starting additives, it is not necessary to measure the cloud point and pour point of the modiﬁed blends [30].

2.6. Experimental setup

This investigation was performed using an inline four-cylinder, water-cooled, turbocharged diesel engine without any catalytic converter. Schematic diagram of the test setup is given inFig. 1.

Engine speciﬁcations are listed inTable 6. An eddy current dynamometer, which can be operated at a maximum power of 250 kW was coupled to the engine. Measurement of HC, NO and CO emissions were conducted by Bosch BEA-350 exhaust gas ana- lyzer. Smoke opacity was measured by Bosch RTM 430 smoke opacimeter. The method for measuring the HC and CO emissions

was Non-dispersive infrared and the method for NO was electro- chemical. Smoke opacity was measured by photodiode receiver method.

Engine performance and emission tests were carried out varying the engine speed ranging from 1000 to 3000 rpm at constant 80 N m torque. For data acquisition, REO-DEC data control system was used, which was monitored with the help of REO-DCA software. Measured engine performance parameters of this investigation were BSFC (brake specific fuel consumption), BSEC (brake specific energy consumption) and BTE (brake thermal efficiency).

2.7. Combustion characteristics analysis

The test system was equipped with necessary sensors for combustion analysis. In-cylinder pressure was measured by using a Table 4

Property of the base fuels.

Property Unit Diesel JBD n-butanol^c Diethyl ether^c ASTM D6751^a EN 14214^b

Kinematic viscosity at 40°C mm²/s 3.46 4.27 3.00 0.22 1.9–6.0 3.5–5.0

Density at 40°C kg/m³ 833 861 812 712 n.s. n.s.

Lower heating value MJ/kg 44.66 39.83 34.33 33.89 n.s. n.s.

Oxidation stability h 59.10 3.11 – 3 (min) 6 (min)

Flash point °C 69.5 202.5 35 40 130 (min) 120 (min)

Cloud point °C 8 3 report n.s.

Pour point °C 7 2 89 – n.s. n.s.

CFPP °C 8 8 n.s. n.s.

Acid value Mg KOH/g – 0.18 – 0.5 (max) 0.5 (max)

Saponiﬁcation number (SN) 192.6 – n.s. n.s.

Iodine value (IV) G I2/100 g 93.8 – n.s. 120

Cetane number (CN) 48 53.5 25 125 47 (min) 51 (min)

n.s. = not speciﬁed.

a Data obtained from[26].

b Data obtained from[27].

c Provided by the supplier, measured at 20°C.

Table 5

Property of the fuel blends.

Property Diesel J20 J15B5 J10B10 J15D5 J10D10 ASTM D7467

Kinematic viscosity at 40°C 3.46 3.60 3.29 3.24 3.22 3.15 1.9–4.1

Density at 40°C 833 837 834 831 830 823 n.s.

Lower heating value

MJ/kg 44.66 43.69 43.40 43.15 43.39 43.10 n.s.

Flash point°C 69.5 96.5 87.5 79.5 83.5 71.5 52 (min)

Fig. 1.Schematic diagram of the engine test bed.

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Kistler 6058A type pressure sensor. It was installed in the swirl chamber through the glow plug port. Kistler 2614B4 type charge ampliﬁer was used to amplify the charge signal outputs from the pressure sensor. A high precision incremental encoder (2614A type) was used to acquire the top dead center (TDC) position and crank angle signal for every engine rotation. Simultaneous sam- plings of the cylinder pressure and encoder signals were performed by a computer with Dewe-30-8-CA data acquisition card. One hun- dred consecutive combustion cycles of pressure data were collected and averaged to eliminate cycle-to-cycle variation in each test. To reduce noise effects, Savitzky–Golay smoothing ﬁltering was applied to the sampled cylinder pressure data. Other combustion parameters, such as heat release rate and start of combustion (SOC) were computed by using Matlab^ÒR2009a software.

Heat release rate (HRR) analysis is the most effective way to gather information for the combustion mechanism in diesel engines. This method simplifies the identification of start of combustion (SOC) timing and differences in combustion rates from the HRR versus crank angle diagram[31]. Hence, HRR analysis is a significant parameter in understanding the combustion mechanism. Average in-cylinder pressure data of 100 consecutive cycles with a 0.1 crank angle (CA) resolution were used to calculate HRR. Analysis was derived from the first law of thermodynamics, as shown in Eq.(4), without taking into account heat loss through cylinder walls. Here, main combustion chamber and pre- combustion chamber were considered to be combined into a single zone thermodynamic model. It is expected that, in between the two chambers, there is no passage throttling losses. Fuel vaporization and mixing, temperature gradients, non-equilibrium conditions and pressure waves can be ignored[32].

dQ

dh¼V^dP_dhþ

c

P^dV_dh

c

1 ð4Þ

where^dQ_dh¼rate of heat release (J/°CA),V= instantaneous cylinder volume (m³),h¼crank angle (°CA),P= instantaneous cylinder pressure (Pa),

c

¼ speciﬁc heat ratio which is considered constant at 1.35[33]. The input values are the pressure data and cylinder volume (with respect to crank angle). TheVand^dV_dhterms are shown in the following equations:

V¼VcþAr 1cos

p

h 180

þ1 k 1

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1k²sin²

p

h

180

( s )

" #

ð5Þ dV dh¼

p

A

180

r sin

p

h 180

þ k²sin² ₁₈₀^p^h 2

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1k²sin² ₁₈₀^p^h q

8>

<

>:

9>

=

>; ð6Þ Here,k¼_r^landA=^p^D₄², wherel= connecting rod length,r= crank radius = 0.5stroke,D= cylinder bore, andV_c= clearance volume.

2.8. Accuracies and uncertainties

Uncertainty in the measurements may happen due to experimental conditions, equipment calibration, instrument selection and inaccuracies. Therefore, it is much needed to analyze the uncertainty of the measured values. Uncertainty of this experiment was analyzed through a study of the instruments’ precision and accuracy (given inTable 7) along with the repeatability of the tests using the similar method by Fattah et al.[34]. Experiments were performed several times, and data were collected at least three times. Average values were used for graph plotting.

3. Results and discussions

3.1. Combustion characteristics 3.1.1. Analysis of in-cylinder pressure

The parameters used to compare the combustion characteristics in this investigation were cylinder gas pressure, start of combustion (SOC) and heat release rate (HRR). With focus on the ‘hot’ part around TDC (top dead center), cylinder pressure against crank angle diagram for jatropha biodiesel blend and its modified blends withn-butanol are illustrated inFig. 2at 1000, 2000 and 3000 rpm keeping the toque constant at 80 N m. It can be seen from the figure that, there were no significant differences on the maximum in- cylinder pressures among the fuels. Such result actually replicates that, conversion of fuel energy into mechanical energy was as effi- cient for the modified blends as for the diesel fuel[32].

However, for J20 and its modiﬁed blends with additives, maximum in-cylinder pressure occurred after top dead center (ATDC) within the range of 8–10.5°CA. It can be seen fromFig. 2that, as the speed increased, in-cylinder pressure increased accordingly.

Up to 2000 rpm, J20 showed higher maximum in-cylinder pressure than diesel. Higher and slight early maximum pressure for the J20 blend can be attributed to the higher cetane number of the jatropha biodiesel compared to diesel[4]. However, at 3000 rpm, maximum pressure for J20 was lower compared to diesel. Poor atomization and air–fuel mixing due to higher density, viscosity of J20 and less available time due to higher speed resulted reduced premixed charge. Consequently peak in-cylinder pressure reduced [23]. With the addition ofn-butanol into the jatropha biodiesel- diesel blend, it was observed that the peak cylinder pressure decreased and occurred a bit late at all the observed engine speeds.

At 3000 rpm, J15B5 and J10B10 produced 86.95 bar and 86.07 bar of maximum in-cylinder pressures respectively at 9.4°ATDC and 9.9°ATDC. Crank angles for the maximum pressures of these two Table 6

Engine testbed equipment speciﬁcation.

Description Speciﬁcation

No. and arrangement of cylinders

4 in-line, longitudinal

Rated power 65 kW at 4200 rpm

Combustion chamber Swirl chamber Total displacement 2477 cc Cylinder borestroke 91.195 mm

Valve mechanism SOHC

Compression ratio 21:1

Lubrication system Pressure feed, full ﬂow ﬁltration Fuel system Distributor type injection pump

Air ﬂow Turbocharged

Fuel injection pressure 157 bar

Dynamometer Froude Hofmann eddy current dynamometer

Max. Power: 250 kW Max. Torque: 1200 N m Max. Speed: 6000 rpm Fuel ﬂow meter Positive displacement ﬂow meter

Table 7

Measurement accuracy and uncertainty.

Measured quantity Upper limit Accuracy Uncertainty (%)

Fuel ﬂow 36 l/h ±0.02 l/h –

Speed 6000 rpm ±2 rpm –

Power 250 kW ±0.02 kW –

Smoke opacity 100% 0.1% ±0.5%

CO 10.00 vol% 0.02 vol% ±0.01 vol%

HC 9999 ppm vol 1 ppm vol ±1 ppm

NO 5000 ppm vol 1 ppm vol ±5 ppm

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blends were almost similar at the other engine speeds. Descending pressures with the increment of the percentage ofn-butanol can be explained by lower caloriﬁc value of then-butanol compared to diesel and biodiesels[35].

Fig. 3 shows the in-cylinder pressure against crank angle diagram for jatropha biodiesel blend and its modiﬁed blends with

DEE at different engine speed. Similar ton-butanol blends, addition of DEE reduced the maximum in-cylinder pressure. At 3000 rpm, Maximum in-cylinder pressures for J15D5 and J10D10 were observed 86.92 and 86.10 bar respectively at 10.1° ATDC and 10.4°ATDC. Slight late and lower maximum in-cylinder pressures for the DEE blends can be explained more clearly by combining it to the HRR analysis of the corresponding fuels.

3.1.2. Analysis of heat release rate

Heat release rate analysis is one of the ﬁnest tools to get in- depth understanding of the combustion phenomena in an engine.

In-cylinder pressure characteristics of the fuels can be explained in a better way conjoining the HRR analysis. In the present study, the engine has a pump-line-nozzle fuel injection system and advanced start of injection (SOI) can take place if the fuel is denser and has higher bulk modulus of compressibility (and vice versa).

Therefore, instead of measuring the ignition delay, in this study combustion scenario is described with the help of SOCs (start of combustion). In this investigation, SOCs were acquired from the HRR against crank angle diagram. Theoretically, as the piston is near the TDC, fuel vaporization causes a negative heat release and with the start of combustion, heat release momentarily becomes positive at a point. This point is called SOC.

Heat release rate of the jatropha biodiesel blend and its modi- ﬁed blends withn-butanol are given in theFig. 2at different speed.

It can be seen in the figure that, at 1000 and 2000 rpm, premixed combustion (area under the first sharp peak in the HRR diagram) of the J20 blend was quite higher than the diesel fuel, which actually led to a little higher maximum pressure for this fuel[23]. How- ever, at 3000 rpm, premixed part of the combustion was lower for J20 than diesel, which reflected slight lower in-cylinder peak pressure discussed earlier. At 3000 rpm, SOC of the J20 was observed at -3.7°ATDC while at 1000 and 2000 rpm SOCs were almost same at -4°ATDC. It actually demonstrates that J20 encountered difficul- ties regarding proper atomization and consequently at higher speed, higher crank angle revolution was needed to make the charge combustible.

With the addition ofn-butanol, it was detected that J15B5 and J10B10 got late SOCs compared to J20 and diesel at all the observed engine speeds. SOC of J15B5 was observed on -3.9°ATDC whereas for J10B10 it was on -3.5°ATDC on average regarding the 1000, 2000 and 3000 rpm. Similarly, fromFig. 3it can be seen that SOCs of J15D5 and J10D10 were at -3.7°ATDC and -3.1°ATDC on average regarding the observed engine speeds respectively. Since,n-butanol has a lower cetane number, SOC occurred late for comparatively higher ignition delay[36]. On the contrary, despite of higher cetane number of DEE, SOCs of DEE blends retarded due to its higher latent heat of evaporation which is supported by the work of Rakopoulos [13]. Such offset of SOCs were translated into comparatively lower maximum in-cylinder pressures both forn-butanol and DEE blends.

Since the SOCs were late, it was more likely that combustion occurred in a lower temperature environment, consequently low- ered the peak pressures. However, it can be seen that, 10% blends of the additives got more retarded SOCs compared to 5% blends of the additives. Since, current investigation was conducted in a turbocharged engine; fuel–air ratio was very low. Therefore, it is evident that, effect of lower temperature during the vaporization of the fuel was not significant enough for the 5% blends ofn-butanol and DEE. However, 10%n-butanol and DEE helped to create significantly lower temperature during the vaporization of the fuel and delayed the SOCs more. However, in the mixing controlled zone (area after the first sharp peak) both of the modified blends exhibited higher HRR than J20, which actually indicates better atomization of fuel due to lower density and viscosity ofn-butanol and DEE[13].

(a)

(b)

-10 0 10 20 30 40 50 60 70

0 10 20 30 40 50 60 70

-20 -10 0 10 20 30 40

Heat release rate (J/ °CA)

Cylinder pressure (bar)

Crank angle (°CA)

Diesel J20 J15B5 J10B10

-10 0 10 20 30 40 50 60 70 80

0 10 20 30 40 50 60 70 80

-20 -10 0 10 20 30 40

Heat release rate (J/°CA)

Diesel J20 J15B5 J10B10

(c)

-20 0 20 40 60 80 100

0 10 20 30 40 50 60 70 80 90 100

-20 -10 0 10 20 30 40

Diesel J20 J15B5 J10B10

Fig. 2.Cylinder pressure and heat release rate vs crank angle diagram forn-butanol blends at (a) 1000 rpm, (b) 2000 rpm and (c) 3000 rpm.

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3.2. Engine performance characteristics 3.2.1. Brake speciﬁc fuel consumption

As the test running condition was constant torque (80Nm) with variable speed ranging from 1000 rpm to 3000 rpm, to assess the engine performance with different fuel blends, brake speciﬁc fuel consumption (BSFC) was used as a convenient parameter. BSFC

implies the ratio of fuel consumption rate to brake power output.

As demonstrated in theFig. 4, it can be seen that, BSFC of all the fuels decreased as the engine speed was increased from 1000 rpm to 1500 rpm. Increased atomization ratio is responsible for such decrement whereas increment of BSFC after 1500 rpm can be attributed to the decreased volumetric efficiency during the higher speeds. At 1000 rpm it can be seen that, BSFC of diesel fuel was the highest among the blends. As the injection pump of the test engine was distributor type, at low speed, delivered fuel quantity decreased which affected the atomization rate as well as the fuel–air mixing rate. Therefore, modified biodiesel blends performed well than diesel as they were oxygenated, even in rich fuel–air mixture condition. However, J20 and its modified blends with n-butanol showed reasonably higher BSFC than diesel on average. J20 showed on average 5.4% increment of BSFC than diesel. J15B5 and J10B10 showed better BSFC results than J20. They showed on average 2.3% and 3.9% decrement of BSFC than J20.

J15D5 and J10D10 showed even better results than n-butanol blends. They showed 5.5% and 6.8% decrement of BSFC than J20 respectively. Reason behind for the higher BSFCs of the jatropha biodiesel blend and its modified blends than diesel is the lower energy content of the blends than diesel. Per unit mass heating values of the blends were lower, therefore, consumption had to be higher to attain the constant 80 N m torque. However, DEE blends showed lower BSFCs than even diesel at lower speeds which actually indicates better combustion efficiency of the blends due to their high oxygen content, lower viscosity and density comparative ton-butanol[4]. As the viscosity and density of J20 was higher than its modified blends, adhesion of fuel in the cylinder wall due to higher spray penetration might happen for improper atomization. Therefore, these results surely indicate improvement of atomization of the modified blends.

3.2.2. Brake speciﬁc energy consumption

Brake specific energy consumption (BSEC) is a tool for compar- ing the performance of fuels with different heating values. It is the product of the BSFC and heating value of fuel. It measures how much energy is being consumed in one hour to develop a unit power output. Usually, BSEC decreases with an increase in energy consumption efficiency [37]. Fig. 5 illustrates the BSECs of the jatropha biodiesel blend and its modified blends withn-butanol and DEE at different engine speeds at constant 80 N m engine torque. It can be seen that, J20 gave the highest BSEC, which was on average 2.74% higher than diesel. However, modified blends with n-butanol and DEE showed lower BSECs compared to J20 blend.

They showed on average 3.9% and 7% decrement of BSEC than J20 respectively. It can be seen that, increment of the percentage ofn-butanol and DEE both decreased the BSECs. Such decrement can be attributed to their higher combustion efﬁciency due to

(a)

(b)

-10 0 10 20 30 40 50 60 70

0 10 20 30 40 50 60 70

-20 -10 0 10 20 30 40

Diesel J20 J15D5 J10D10

-10 0 10 20 30 40 50 60 70 80

0 10 20 30 40 50 60 70 80

-20 -10 0 10 20 30 40

Diesel J20 J15D5 J10D10

(c)

-20 0 20 40 60 80 100

0 10 20 30 40 50 60 70 80 90 100

-20 -10 0 10 20 30 40

Diesel J20 J15D5 J10D10

Fig. 3.Cylinder pressure and heat release rate vs crank angle diagram for DEE blends at (a) 1000 rpm, (b) 2000 rpm and (c) 3000 rpm.

260 280 300 320 340 360 380

1000 1500 2000 2500 3000

BSFC (g/kW-h)

Speed (RPM)

Diesel J20 J15B5 J10B10 J15D5 J10D10

Fig. 4.BSFC vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

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higher oxygen content and lower density and viscosity which in- turn improved atomization[38].

3.2.3. Brake thermal efﬁciency

Brake thermal efﬁciency (BTE) measures the efﬁciency of the conversion of chemical energy into useful work in an engine.

Dividing the useful work by the heating value of the fuel is the way to calculate BTE.Fig. 6shows the BTEs of the modified blends of jatropha biodiesel withn-butanol and DEE at different speeds with a constant 80 N m torque. It can be seen that, J20 exhibited lowest BTE among the fuels on average (25.4%). On the other hand, modified blends of jatropha biodiesel J15B5 and J10B10, improved BTE than J20 on average 2.8% and 5.3% respectively. Similarly, J15D5 and J10D10 improved the BTE on average 6.6% and 8.8% than J20. Reasons for the improvement of BTEs of the modified blends are totally analogous to the reasons of improving the BSECs.

3.3. Engine emission characteristics 3.3.1. Nitrogen oxide emission

Fig. 7illustrates the NO emission for the test fuels. The mechanisms which mostly take part inside the cylinder for NO formation are thermal (Zeldovich), N2O pathway, prompt (Fenimore), NNH mechanism and the fuel bound nitrogen[34]. NO formation generally depends on oxygen concentration, air surplus coefﬁcient, in- cylinder temperature and residence time[39]. In this investigation, J20 produced 8.2% higher NO emission on average than diesel.

Higher NO for J20 can be attributed to higher fuel bound oxygen.

Higher oxygen content of biodiesel delivers higher local peak temperature which results in higher NO formation. Another reason which can be mentioned is the higher cetane number of jatropha biodiesel. Due to higher cetane number, combustion advances,

combustion duration reduces and premixed part of the combustion increases where NO is formed mostly[39]. However, 5% blend of n-butanol showed even higher NO emission (5.05%) than J20.

Higher oxygen content of the modiﬁed blend was the most proba- ble cause for such higher emission of NO. Nevertheless, increased portion ofn-butanol (J10B10) reduced NO emission than J20 about 8.83% on average primarily due to higher latent heat of evaporation ofn-butanol[24]. It is evident that, on the case of 5% blend the effect of higher oxygen content was dominant while for 10% blend, amount ofn-butanol was good enough to create lower in-cylinder temperature which has been shown by other researcher for other fuels[17]. For higher latent heat of evaporation, in cylinder temperature and the premixed peak of the combustion was reduced (validated by comparative lower in-cylinder pressures). On top of that, for 10% n-butanol blend, the SOC was quite retarded and combustion occurred on a comparatively lower temperature environment[13]. Consequently, NO emission of J10B10 reduced.

Similarly, J15D5 produced slight increased and J10D10 produced about 12% decreased NO emission than J20. Explanation of the consequence is just analogous to then-butanol case.

3.3.2. Carbon monoxide emission

In two ways CO can be formed: through an overly lean mixture or an overly rich mixture. Flame cannot propagate through mixture in overly lean mixtures, consequently fuel pyrolysis with partial oxidation causes CO. On the contrary, for the overly rich mixture, the fuel cannot mix with sufﬁcient amount of air. Even if they mix, however, they do not have enough time to oxidize[40]. How- ever, generally CO forms at rich air–fuel mixture areas because of unavailability of oxygen to completely oxidize all CO content in the fuel. In Fig. 8, emission of CO for the test fuels at different engine speed has been illustrated. It can be seen that, for all the fuels, up to 2000 rpm emission reduced and afterwards increased.

Initially, increment of speed increased the in-cylinder temperature which favored the CO oxidation, however, later on higher speed than 2000 rpm may be reduced the time available for oxidation mechanism[39]. J20 produced quite a reduced emission compared to diesel all over the speed range. About 27.5% decrement on average was noticed for J20 than diesel. It can be attributed to higher oxygen content of biodiesel which assisted to achieve more complete combustion. Another explanation which can be mentioned here is the lower carbon/hydrogen (C/H) ratio possessed by biodiesel than diesel fuel. It was similarly assisting to produce lower CO emission [34]. However, modified blends reduced the emission even better. J15B5, J10B10, J15D5 and J10D10 reduced the CO emission than J20 about 23%, 30.7%, 11% and 20.6% respectively because of more oxygen content [18]. Therefore, lower density and viscosity of the modified blends increased the atomization efficiency and on top of that higher oxygen content really assisted complete oxidation of the fuels, hence reduced CO emission.

10 11 12 13 14 15 16 17

1000 1500 2000 2500 3000

BSEC (MJ/kW-h)

Speed (RPM)

Fig. 5.BSEC vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

21 22 23 24 25 26 27 28 29 30

1000 1500 2000 2500 3000

BTE (%)

Speed (RPM)

Fig. 6.BTE vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

50 100 150 200 250 300 350 400

1000 1500 2000 2500 3000

NO (PPM)

Speed (RPM)

Fig. 7.NO emission vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

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3.3.3. Hydrocarbon emission

Comparative HC emission from the test fuels at constant 80 N m torque with different engine speeds are shown inFig. 9. There are number of reasons for the HC emission during combustion. Fuel trapping in the crevice volumes of the combustion chamber is one of the major reasons of HC emission. Locally over-lean or over-rich mixture, incomplete fuel evaporation and liquid wall films for excessive spray impingement are also have been mentioned as significant factors[33]. It can be seen from the figure that J20 gave significantly lower HC than diesel fuel all over the engine speed range. It gave about 28% decreased emission than diesel on average. Such decrement can be attributed to the higher oxygen content of biodiesel which influenced the amount of hydrocarbon oxidation. On the contrary, J15B5 and J10B10 showed 28.4% and 48% increment of HC emission than J20 on average while J15D5 and J10D10 showed 32% and 52% increment. HC emission was supposed to be reduced due to even higher oxygen content of n-butanol and DEE. However, slip of fuel out of the cylinder especially at low speed during expansion stroke might be the reason for such higher emission as additives like n-butanol and DEE made fuel evaporation easier [24]. Hence, IDI diesel engine inherently creates a homogeneous charge, consequently, addition of n-butanol and DEE may create lean outer flame zone. This is actually the envelope of the spray boundary where because of over-mixing the fuel is already beyond the flammability limit[4].

Over-mixing is a common scenario during the combustion of the fuels with such additives as the lower density and viscosity cer- tainly affect the mixing process.

3.3.4. Smoke opacity

Smoke opacity indicates the soot content on the exhaust gas which is one of the main components of particulate matter. Hence, this parameter can be associated with fuels propensity to form particulate matter during combustion.Fig. 10illustrates the exhaust

smoke opacity of the test fuels. J20 gave about 6.2% decreased smoke opacity than diesel fuel. It can be attributed to advanced start of combustion of J20 for higher cetane number. Hence, the combustion started early, it allowed more time for the oxidation of soot[41]. Again, soot formation takes place generally at the ini- tial premixed combustion phase when the fuel–air equivalence ratio remains at stoichiometry. Therefore, higher oxygen content of J20 provided oxygen in the fuel rich zones and reduced smoke opacity especially at higher speeds. J15B5 and J10B10 also followed the trend of J20 and they gave on average 17% and 27% lower smoke opacity respectively as they are more oxygenated. Similarly J15D5 and J10D10 reduced smoke opacity about 30% and 38.5% on average than J20. Therefore, it is obvious that such oxygenated blends reduced the probability of rich fuel zone formation and assisted to decrease the soot emission.

4. Economic analysis of the fuels

InTable 8, per liter cost of all the components of the blends and tested fuels are given. From the average BSFC and per gram cost of the respective fuels, cost for per kW-h was calculated to acquire a comparative idea of economic cost. As the prime purpose of this study was to compare the engine performance-emission and combustion parameters of the sample fuel blends, the cost analysis pre- sented here is only a present market price scenario of the fuel blends. The analysis does not include the required subsidies for production and commercial distribution of the proposed sample fuel blends, which are currently provided for diesel. Thus, in this analysis the cost of modiﬁed fuel blends appears much higher than diesel. Implementation of optimum production technologies of jatropha biodiesel and the additives, analysis of global and local markets and subsidy from the government can surely trigger the commercial application of these alternative fuel blends.

0 0.1 0.2 0.3 0.4 0.5

1000 1500 2000 2500 3000

CO (% VOL)

Speed (RPM)

Fig. 8.CO emission vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

0 2 4 6 8 10 12 14

1000 1500 2000 2500 3000

HC (PPM)

Speed (RPM)

Fig. 9.HC emission vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

40 50 60 70 80 90 100

1000 1500 2000 2500 3000

Smoke opacity(%)

Speed (RPM)

Fig. 10.Smoke opacity vs speed diagram for jatropha biodiesel and its modiﬁed blends at 80 N m torque.

Table 8

Cost analysis of the tested fuels.

Biodiesel blends

Cost USD/L

Cost USD/g

Average BSFC g/kW-h

Cost USD/kW-h

Diesel 0.66 0.000792 309.4 0.24

Jatropha biodiesel 5.71 0.006632 – –

n-Butanol 45.66 0.056232 – –

Diethyl ether 62.7 0.088062 – –

J20 1.67 0.001995 326.2 0.65

J15B5 3.66 0.004388 319.2 1.40

J10B10 5.64 0.006787 313.6 2.12

J15D5 4.51 0.005434 308.2 1.67

J10D10 7.36 0.008943 303.8 2.71

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5. Conclusion

An inclusive investigation was performed to evaluate and compare the combustion, performance and exhaust emissions characteristics of jatropha biodiesel blend (J20) and its modiﬁed blends with different percentages ofn-butanol and DEE which were used to fuel an IDI, high-speed, turbocharged diesel engine. Engine test runs were conducted by using the selected fuels at constant 80 N m torque with variable engine speed ranging from 1000 rpm to 3000 rpm. Exhaust emissions such as total unburned HC, NO, CO and smoke opacity were measured for each test fuel. BSFC, BSEC and BTE were measured and calculated to compare the engine performance characteristics. Combustion characteristics of the test fuels were discussed in terms of in-cylinder pressure diagrams and the HRR analysis at different engine speeds. The in-cylinder pressure diagrams and HRR analysis revealed some signiﬁcant features of combustion mechanisms, which enlightened the performance and emissions characteristics. Thus, the following conclusions are drawn:

Incremental addition ofn-butanol and DEE reduced the density and viscosity of the diesel–biodiesel blend chronologically. In spite of lower calorific value ofn-butanol and DEE, modified blends showed insignificant difference of calorific values than diesel fuel.

J20 produced higher in-cylinder pressure than diesel due to higher cetane number. However, addition of n-butanol and DEE reduced the pressure in consequence of retarded SOC and higher latent heat of evaporation of the additives. Effects of the additives were more prominent on the case of 10% additive blends rather than 5% additive blends. HRR during the premixed part of the combustion was decreased for the additives. How- ever, in the diffusion controlled zone, HRR was better for the modiﬁed blends compared to J20.

J20 showed 5.4% higher BSFC than diesel because of lower caloriﬁc value and inferior atomization quality. However, 10%

n-butanol blend showed 3.9% decreased BSFC than J20 on average which was because of higher combustion efﬁciency due to higher oxygen content, lower density and viscosity ofn-butanol.

Similarly 10% DEE blend showed 6.8% decrement of BSFC than J20 on average. Clearly indicating that DEE performed better thann-butanol. BSEC and BTE values of modiﬁed blends were also promising indicating higher combustion efﬁciency.

J20 produced about 8.2% higher NO than diesel. 5%n-butanol and DEE blends showed slight higher NO emission than J20 due to higher oxygen content. However, 10% blend of both of them reduced NO emission due to comparatively lower temperature environment during combustion. On average 8.8% and 12% lower NO emission was observed for 10%n-butanol and DEE blends respectively.

J20 showed about 27.5% decrement of CO emission than diesel.

J15B5 and J10B10 showed even better results by reducing CO emission by 23% and 30.7% respectively than J20 due to higher oxygen content while J15D5 and J10D10 reduced 11% and 20.6%.

Smoke opacity was also reduced for J20 about 6.2% than diesel.

10%n-butanol and DEE blends reduced the smoke opacity about 27% and 38.5% than J20 on average which is quite better than corresponding 5% blends of the additives. Higher oxygen content ofn-butanol and DEE provided sufﬁcient oxygen even in fuel rich zones for the oxidation of soot. J20 reduced unburned HC emission by 28% than diesel fuel on average. However, due to slip of fuel out of the combustion chamber for the evapora- tive nature of n-butanol and DEE, HC emission increased for the modiﬁed blends.

Therefore, regarding performance and emission characteristics, 10% blends of n-butanol and DEE showed higher improvement than 5% blends. Since, the addition ofn-butanol and DEE into the diesel–biodiesel blend improved the performance and emission characteristics of an engine, its use can be considered as an auspi- cious way to solve intrinsic problems with the use of jatropha biodiesel at aforementioned operating condition.

Acknowledgement

The authors would like to appreciate University of Malaya for ﬁnancial support through High Impact Research grant titled:

‘‘Clean Diesel Technology for Military and Civilian Transport Vehi- cles’’ having grant number UM.C/HIR/MOHE/ENG/07.

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