A Comprehensive Experimental Investigation of Combustion and Heat Release Characteristics of a...

Fuel 89 (2010) 2802–2814

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Fuel

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A comprehensive experimental investigation of combustion and heat releasecharacteristics of a biodiesel (hazelnut kernel oil methyl ester) fueled directinjection compression ignition engine

M. Gumus *

Automotive Division, Department of Mechanical Education, Marmara University, Ziverbey 34722, Istanbul, Turkey

a r t i c l e i n f o a b s t r a c t

Article history:Received 20 November 2009Received in revised form 26 January 2010Accepted 27 January 2010Available online 6 February 2010

Keywords:BiodieselHazelnut kernel oil methyl esterDiesel engineCombustionHeat release

0016-2361/$ - see front matter � 2010 Elsevier Ltd. Adoi:10.1016/j.fuel.2010.01.035

* Tel.: +90 216 3365770x321; fax: +90 216 337898E-mail address: [email protected]

In the present study, hazelnut (Corylus avellana L.) kernel oil was transesterified with methanol usingpotassium hydroxide as catalyst to obtain biodiesel and a comprehensive experimental investigation ofcombustion (cylinder gas pressure, rate of pressure rise, ignition delay) and heat release (rate of heatrelease, cumulative heat release, combustion duration and center of heat release) parameters of a directinjection compression ignition engine running with biodiesel and its blends with diesel fuel was carriedout. Experiment parameters included the percentage of biodiesel in the blend, engine load, injection tim-ing, injection pressure, and compression ratio. Results showed that hazelnut kernel oil methyl ester andits blends with diesel fuel can be used in the engine without any modification and undesirable combus-tion and heat release characteristics were not observed. The modifications such as increasing of injectiontiming, compression ratio, and injection pressure provided significant improvement in combustion andheat release characteristics.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

A number of studies have shown that biodiesel obtained fromvegetable oils hold promise as alternative fuels for diesel engines[1–4]. Numerous vegetable oil esters called biodiesel have beentried as alternative to diesel fuel. A lot of researchers have reportedthat with the use of biodiesel as a fuel in diesel engines, a diminu-tion in harmful exhaust emissions as well as equivalent engine per-formance with diesel fuel were achieved [5–13]. Several studieshave found that biodiesel seems to emit far less of the most regu-lated pollutants than standard diesel fuel. Decreasing of carbondioxide (CO2) by using biodiesel contributes to reduce greenhouseeffect. In other sense, diminishing of carbon monoxide (CO), hydro-carbons (HC), nitrogen oxides (NOx) and smoke density improveair quality [1,14,15]. Similar results were also reported in theearlier study on hazelnut kernel oil methyl ester (HOME) used ina direct injection (DI) compression ignition (CI) engine by the pres-ent author [16]. Previous research has shown that biodiesel hascomparable performance to diesel fuel with significant reductionin emissions of CO, HC, and smoke but slightly increased in NOxemissions and brake specific fuel consumption.

Combustion and heat release (HR) characteristics of biodieselmust be known in order to achieve the reduction of engine emis-

ll rights reserved.

7.

sions and fuel consumption while keeping other engine perfor-mance parameters at an acceptable level. The differences inphysical properties between diesel and biodiesel fuels affect thecombustion and HR characteristics [2,17–21]. A lot of studies re-lated to combustion and HR characteristics of biodiesel have beenreported in the literature. Test parameters of these studies includethe percentage of biodiesel in the blend, engine speed, engine load(EL), injection timing (IT), injection pressure (IP) and engine com-pression ratio (CR). Biodiesel and its blends also show a slight dropin the engine power with decreased peak cylinder gas pressure(CGP) and reduced ignition delay (ID) when compared to diesel fuel.The premixed combustion phase of biodiesel and its blends takeplace earlier with diesel fuel because of shorter ignition delay. Themaximum rate of pressure rise (ROPR) and the maximum rate ofheat release (ROHR) of biodiesel are generally lower than that of die-sel. Biodiesel also shows higher diffusion combustion compared tostandard diesel operation. Moreover, when the test engine is fueledwith biodiesel and its blends, the brake specific fuel consumptionincreases slightly relative to diesel fuel due to different physicalproperties, combustion and HR characteristics of biodiesel [22–31].

Engine simulation and modeling of various processes have beenused alongside experimental techniques to achieve understanding,analysis and control of the biodiesel spray combustion processes.Such simulations and models are also used for biodiesel in orderto reduce the number of the costly development tests. The CIengine simulation models can be classified into three categories;

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Nomenclature

ATDC after top dead centerBMEP brake mean effective pressuresBSFC brake specific fuel consumptionBTDC before top dead centerBTE brake thermal efficiencyCA crank angleCD combustion durationCFPP cold Filter Plug PointCGP cylinder gas pressureCHR cumulative heat releaseCI compression ignitionCO carbon monoxideCO2 carbon dioxideCOHR center of heat releaseCR compression ratio

DI direct injectionEL engine loadLHV lower heating valueHC hydrocarbonHOME Hazelnut kernel oil methyl esterHR heat releaseID ignition delayIP injection pressureIT injection timingNOx nitrogen oxidesrpm revolution per minuteROPR rate of pressure riseROHR rate of heat releaseSD standard deviationTDC top dead center

M. Gumus / Fuel 89 (2010) 2802–2814 2803

zero dimensional single-zone models (thermodynamics model),quasi-dimensional multi-zone models and multi-dimensionalmodels [32–35].

Since Turkey is the main hazelnut producing country, hazelnutkernel oil can be used as an alternative to diesel fuel especially bythe farmers around Black Sea region which is main productionarea. But there is not a comprehensive investigation on combustionand HR characteristics of HOME in DI-CI engines. In the previousstudy, an experimental investigation was carried out to examinethe performance and emissions of a DI diesel engine running withHOME and its blends with diesel fuel. Results showed that HOMEand its blends with diesel fuel are generally comparable to dieselfuel and small modifications such as increasing IT, CR and IP pro-vide significant improvement in performance and emissions [16].The objectives of this experimental study were to investigate com-bustion characteristics and HR behaviors of biodiesel and its blendswith diesel fuel. Test parameters included the percentage of bio-diesel in the blend, EL, IT, IP, and CR.

2. HOME production and its characterization

The basic composition of hazelnut kernel oil is triglyceride,which is the ester of three fatty acids and one glycerol. Composi-tion of different Turkish hazelnuts growing in the Eastern BlackSea Region of Turkey is given in previous study. Hazelnut has highenergy (27.17–28.46 MJ/kg) and contains 61.66% oil, 20.59% pro-tein, and 10% carbohydrates as mean values [16].

HOME has been produced as a biodiesel by transesterificationmethod. Transesterification of hazelnut kernel oil was includedheating of oil until 65 �C, addition of KOH (1% of oil by weight)and methyl alcohol 1/5 volumetric ratio of hazelnut kernel oil, stir-

Table 1The properties of biodiesel and diesel fuel.

Property Units EN 14124 limits

Density kg m�3, 15 �C 860–900Kinematic viscosity mm2 s�1, 40 �C 3.5–5.0Lower heating value MJ kg�1

Cetane numbera 51 minFlash point �C 120 minCFPP �C �15–0Ash content % mass 0.02 maxWater % volume

a Calculated from cetane index (distillation temperature, ASTM D 976).

ring of mixture, separation of glycerol, washing with distilledwater and heating for removal of water. The reaction time withstirring continued for 1 h at constant temperature. After glycerolseparation, the methyl ester was washed twice with a 1:1 volumeof distilled water for 1 h. The ordinary diesel fuel was obtainedfrom the Turkish Petroleum Refineries Corporation. The propertiesof fuels were determined at the laboratories of The Scientific andTechnological Research Council of Turkey-Marmara Research Cen-ter. The properties of diesel fuel and biodiesel are given in Table 1.

The kinematic viscosity values biodiesel and the diesel fuelsused in the experiments were measured at 40 �C. Transesterifica-tion of hazelnut kernel oil provided a significant reduction in vis-cosity. The variation of biodiesel viscosity is very close to that ofdiesel fuel. It was further reduced with increase in diesel fuelamount in the blend. A similar reduction in specific gravity wasalso observed. However, calorific value of biodiesel was found tobe 37.23 MJ/kg, which is less than calorific value of diesel fuel(43.15 MJ/kg). As the percentage of diesel fuel in the blends in-creased, the calorific value increased. The flash points of biodieselwere found to be greater than 120 �C, which represents a safety forstorage and handling. In this study, legend BX represents a blendincluding X% biodiesel i.e. B5 indicates a blend including 5% biodie-sel and the legend B100 represents pure biodiesel.

3. Experimental set-up and procedure

The combustion and HR characteristics of biodiesel and itsblends with diesel fuel were investigated as compared with dieselfuel. The CI engine used in the study was a Lombardini 6 LD 400 DI,single cylinder, four-stroke, naturally aspirated, air-cooled engine.The combustion chamber of the CI engine is characterized by a re-

ASTM D 6751 limits Biodiesel[16] Diesel[46]

884.3 8301.9–6.0 5.4 2.4

37.23 43.1541 min 55 50130 min 182.5 59

�14 �100.02 max 0.008 0.0010.05 max 0.0028 0.0002

Table 2Main characteristics of the engine used during the testing procedure [47].

Trademark and model Lombardini 6 LD 400

Number of the cylinder SingleBore 86 mmStroke 68 mmSwept volume 395 cm3

Compression ratio 18:1Maximum engine power 8 kW at 3600 rpmMaximum engine moment 21 Nm at 2200 rpmBMEP 0.64 MPa at 20 NmInjector opening pressure 20 MPaCone angle of spray 160�Number of nozzle hole 4Fuel injection timing 20 �CA BTDC

2804 M. Gumus / Fuel 89 (2010) 2802–2814

entrant toroidal bowl piston with a protuberance in the bottomof the chamber. Details of the engine specification are given inTable 2. A Cussons-P8160 type single cylinder test bed equippedwith an instrument cabinet, fitted with a strain gauge load sensor,electrical tachometer and switches for load remote control wasused in experiments. The engine was loaded by an electrical dyna-mometer rated at 10 kW and 380 V. An inductive pickup speedsensor was used to measure the engine speed. Air consumptionwas measured using a sharp edged orifice plate and an inclinedmanometer. Different digital thermocouples monitored the tem-peratures of intake air, engine oil, and exhaust. Fuel consumptionwas determined by using calibrated burette with an accuracy of0.1% and a stopwatch with an accuracy of 0.5% s.

The diesel engine was fully equipped for measurements of com-bustion parameters. The CGP time history was measured by a Kis-tler Model 6052B air-cooled piezo-quartz pressure sensor whichwas mounted on the cylinder head. The cylinder signals were thenpassed onto matching Kistler Model 5644A charge amplifier. A Kis-tler Model 4067 A2000 piezo-resistive pressure sensor with chargeamplifier was mounted on the fuel line for measuring fuel linepressure. Crankshaft position was obtained using a crankshaft an-gle sensor to determine CGP as a function of crank angle (CA). ALeCroy Model LT374 digital oscilloscope having four channels,500 MHz bandwidth and 4 GS/s maximum sample rate was usedto convert analog signals to digital form and to collect the neces-sary data as well as to store the data in a personal computer forcombustion and HR analysis. The sound pressure level of the CIengine was also measured by PULSE multi analyzer system withBürüel&Kj �ær Model 4189 free-field microphone and Bürüel&Kj �ærModel 2669 microphone preamplifiers at a position of one meterfrom the engine surface in four directions.

Before each experiment, the engine was regulated according tothe catalogue values. All data were collected after the engine stabi-lized. The engine was sufficiently warmed up for each test. The en-gine was allowed to run for a few minutes until it reached steady-state conditions, around 85–90 �C and the data were collected sub-sequently. After measurements, the engine was allowed to cool.The test procedure is repeated three times and the values givenin this study are the average of these three results. Test parametersincluded the percentage of biodiesel in the blend (0% pure dieselfuel, 5%, 20%, 50%, and 100% proportions by volume), EL (10 and20 Nm), IT (5 �CA advanced, original, and 5 �CA retarded), IP (20and 24 MPa), and CR (18 and 20). The original working parametersof the test engine are 20 �CA before top dead center (BTDC) IT,20 MPa IP, and 18 CR. Thickness of the advance shim, located inthe connection place between the engine and fuel pump, was chan-ged to adjust IT. The IP was increased by using different washer.The increasing of washer thickness increased spring stress so theIP increased properly. The increasing of CR was achieved by placinglower thickness spacers between the cylinder and the cylinder

head thus decreasing the clearance volume thereby increasingthe CR. All tests were conducted at a constant engine speed of2200 rpm, obtained maximum torque.

4. Calculation of heat release

The comprehensive investigation of combustion characteristicsand the analysis of HR were performed based on the CGP data. Thesignals of CGP sensors were acquired for every 0.264 �CA and theacquisition process covered 100 cycles. The averaged CGP data of100 cycles was used for calculation of the combustion parametersand analysis of HR. HR analysis can yield valuable informationabout the effect of engine design changes, fuel injection system,fuel type and engine operating conditions on the combustion pro-cess and engine performance [36].

In this study, the CGP data were used to evaluate the ROHRwhich is a simplified thermodynamic model. The ROHR was calcu-lated by a first law analysis of the average CGP. It is assumed thatthe cylinder content is a homogeneous mixture of air and combus-tion products and is at uniform temperature and pressure at anymoment during the combustion process. The ROHR at each CAwas determined by the following formula:

Q ¼ cc� 1

ðPdVÞ þ 1c� 1

ðVdPÞ þ Q w

where Q is the ROHR (J), c is the ratio of specific heats which is cal-culated according to an empirical equation [37], P is the CGP (Pa), Vis the instantaneous volume of the cylinder (m3) and Qw is heattransfer rate (J) from the wall calculated based on the Hohenbergcorrelation [38] and the wall temperature was assumed to be723 K. For this calculation the contents of the cylinder were also as-sumed to behave as an ideal gas (air) with the specific heat beingdependent on temperature [39] and blow-by through the pistonrings was neglected.

The ID was defined as CA interval from the maximum pressureof fuel line to the maximum ROPR. The combustion duration (CD)was calculated as CA interval from the maximum ROPR to the max-imum cumulative heat release (CHR). The center of heat release(COHR) is calculated as CA by using the expression given below:

/c ¼R /e

/s

dQd/ /d/

R /e/s

dQd/ d/

5. Results and discussion

5.1. Combustion characteristics

The combustion characteristics were determined via the inves-tigation of variation in CGP with respect to CA. Figs. 1 and 2 showthe changes in CGP with respect to CA for different fuels, ITs, IPsand CRs at 10 and 20 Nm ELs. Fig. 3 shows rate of ROPR with re-spect to CA different fuels and ITs at 20 Nm EL. Peak CGP, ROPRand ID were determined by analysis of CGP. Combustion parame-ters such as peak CGP, maximum ROPR, start of combustion, IDare shown in Table 3.

5.1.1. Cylinder gas pressure (CGP)Figs. 1 and 2 show CGP versus CA for different fuels, ITs, IPs, CRs,

and ELs. As observed in figures, the peak CGP was higher for dieselfuel at all tests. This result can be related to the differences in theHR pattern shown in Figs. 4 and 5. The peak CGP mainly dependson the combustion rate in initial stages, which is influenced bythe fuel taking part in uncontrolled HR phase [40]. High viscosityand low volatility of the biodiesel lead to poor atomization and

3

4

5

6

7

Cyl

inde

r P

ress

ure

(MP

a)

Injection timing = 20 oCA BTDC Injection pressure = 20 MPa

Compression ratio = 18 Load = 10 Nm

B0

B5

B20

B50

B100

-20 -10 0 10 20 30 402

3

4

5

6

7

8

9

Crank Angle (deg)

Cyl

inde

r P

ress

ure

(MP

a)

Injection timing = 20 oCA BTDCInjection pressure = 20 MPa


B0

B5

B20B50

B100

(a)

(b)

2

Fig. 1. CGP versus CA for different fuels at 10 Nm (a) and 20 Nm (b) load.

M. Gumus / Fuel 89 (2010) 2802–2814 2805

mixture preparation with air during the ID period. The peak CGP ofbiodiesel and its blends were lower due to the deterioration duringthe preparation process of air–fuel mixture as a result of high fuelviscosity [27]. Table 3 shows the peak CGP values and points inwhich the peak CGPs were observed in terms of CA after top deadcenter (ATDC) for different fuels, ITs, IPs, CRs, and ELs.

Fig. 1 shows the CGP in terms of CA for different fuels at 10and 20 Nm ELs. As seen in the figures, peak CGP slightly decreaseswith the addition of biodiesel content in the blend. While the peakCGPs of 10 Nm EL were occurred between 6.61 and 7.05 MPa, thepeak CGPs in 20 Nm EL were occurred between 7.54 and7.96 MPa for all test fuels. The peak CGPs occurred within the rangeof 2.87–5.884 �CA ATDC for all test fuels. With the addition ofbiodiesel content in the blend, the peak CGP slightly goes awayfrom top dead center (TDC) due to poor atomization, mixturepreparation and combustion process. When comparing CGPs’traces of 10 and 20 Nm ELs, it is seen that the peak CGP increasedwith increasing EL. Experimental results showed that fuelconsumption per unit time increased with increasing EL, thisbehavior provided an increase in peak CGP for 20 Nm. Locationsof peak CGP got closer to TDC at 20 Nm EL because the starting fuelinjection occurred earlier than that of 10 Nm and ID also decreasedwith 20 Nm EL.

Modifications such as increasing of IT, IP, CR increase peak CGPbecause these modifications improve combustion rate in theuncontrolled combustion phase of all test fuels. In all tests, thepeak CGP was 8.95 MPa (at 1.80 �CA ATDC) occurring at‘B0EL20CR20’ condition while the minimum peak CGP was6.10 MPa (at 7.82 �CA ATDC) occurring at ‘B100EL10IT15’ condi-tion. Increasing of CR was the most effective factor on the increasein CGP. Increasing CR enhances density of air charge in cylinder.The more density provides the higher angles of spray cone and thisresult in increase in the amount of air entrainment into the fuelspray. The more air in the fuel spray contributes completion ofcombustion and increases the CGP [16].

5.1.2. Rate of pressure rise (ROPR)The maximum ROPR and position of the maximum ROPR in

terms of CA ATDC at different ITs, IPs, CRs, and ELs for biodiesel,diesel and their blends are shown in Table 3. Biodiesel and itsblends showed lower ROPRs as compared to diesel fuel due to low-er ID and premixed combustible mixture would make less fuel tobe burned in the premixed burning phase. The reasons for the lesspremixed combustible mixture are higher viscosity and lower vol-atility of biodiesel as compared to those of diesel fuel. Because ofthis, the CGP and ROPR decreased [25,41]. The ROPR increased with

Injection pressure = 20 MPaCompression ratio = 18

Load = 20 Nm

Cyl

inde

r P

ress

ure

(MP

a)

B0, 15 oCA BTDC

B0, 20 oCA BTDC

B0, 25 oCA BTDC

B100, 15 oCA BTDC

B100, 20 oCA BTDC

B100, 25 oCA BTDC

Injection timing = 20 oCA BTDC Compression ratio= 18

Load = 20 Nm

Cyl

inde

r P

ress

ure

(MP

a)

B0, Pinj = 20 MPa

B20, Pinj = 20 MPa

B20, Pinj = 24 MPaB100, Pinj = 20 MPa

B100, Pinj = 24 MPa

-10 0 10 20 30 40

2

3

4

5

6

7

8

9

3

4

5

6

7

8

9

-202

3

4

5

6

7

8

9


Load = 20 Nm

Crank Angle (deg)

Cyl

inde

r P

ress

ure

(MP

a)

B0, C.R.= 18

B20, C.R.= 18

B20, C.R.= 20B100, C.R.= 18

B100, C.R.= 20

(a)

(b)

(c)

2

Fig. 2. CGP versus CA for different IT (a), IP (b), CR (c) at 20 Nm load.

2806 M. Gumus / Fuel 89 (2010) 2802–2814

the rise in EL for all test fuels due to increase in the quantity of fuelinjected in the cylinder per CA. The increasing of IT, IP, and CR alsoincreased ROPR because these modifications improved combustionrate and increased burned fuel in the uncontrolled combustion

phase of all test fuels. Advanced IT has effects on the ROPR. Fig. 3shows ROPR versus CA for B0 and B100 at different ITs. It may benoticed from the figure that the advanced IT increased the maxi-mum ROPR for diesel and biodiesel. Advanced IT drops air pressure

-20 -10 0 10 20 30 40-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Injection pressure = 20 MPa Compression ratio = 18

Load = 20 Nm

Crank Angle (deg)

Rat

e of

Pre

ssur

e R

ise

(MP

a/de

g)B0, 15 o CA BTDC

B0, 20 o CA BTDC

B0, 25 o CA BTDC

B100, 15 o CA BTDC

B100, 20 o CA BTDC

B100, 25 o CA BTDC

Fig. 3. ROPR versus CA for B0 and B100 at different IT and 20 Nm load.

Table 3Combustion characteristics of the fuels for different engine conditions.

10 Nm 20 Nm

B0 B5 B20 B50 B100 B0 B5 B20 B50 B100

OriginalInjection timing

(20 �CA BTDC)Compression ratio (18)Injection pressure(20 MPa)

Maximum CGP (MPa) 7.05 7.02 6.97 6.82 6.61 7.96 7.94 7.90 7.71 7.54Maximum CGP (�CA ATDC) 4.52 4.85 5.18 4.97 5.84 3.20 2.87 3.76 3.86 4.52Maximum ROPR (MPa/deg) 0.39 0.39 0.38 0.37 0.37 0.50 0.49 0.49 0.46 0.46Start of combustion (�CA BTDC) 5.97 6.11 6.63 6.44 7.29 9.27 9.60 9.93 10.07 10.92Ignition delay (�CA) 14.03 13.90 13.37 13.57 12.71 10.73 10.40 10.07 9.94 9.08

Injection timing(15 �CA BTDC)




Compression ratio(20)


Injection pressure(24 MPa)


M. Gumus / Fuel 89 (2010) 2802–2814 2807

and temperature at the point of injection and results in longer IDand thereby more premixed combustible mixture are generated.Higher ROPR means a greater proportion of the injected fuel beingburnt in the premixed combustion phase [29]. It can be noticedfrom Table 3 that the maximum ROPR increased with increasingIP from 20 to 24 MPa for biodiesel and blends with diesel fuel at10 and 20 Nm ELs. This is due to the finer spray formation resultingin better combustion [3]. The increasing of CR was also the mosteffective factor on the ROPR like CGP due to similar reasons men-tioned above.

In all tests, the maximum ROPR was 0.71 MPa/deg occurring at9.60 �CA BTDC for ‘B0EL20CR20’ condition. The minimum ROPRwas 0.29 MPa/deg occurring at 3.47 �CA BTDC for ‘B100EL10IT15’condition. The position of the maximum ROPR can be consideredas the position in which combustion starts. The start of combustionin terms of CA BTDC for all test fuels at different conditions was gi-ven in Table 3. Combustion starts earlier for biodiesel and blendswith diesel fuel (Fig. 1a and b) due to advanced IT (because of ahigher bulk modulus and higher density of biodiesel) and shorterID.

-5

0

5

10

15

20

25

30



Rat

e of

Hea

t R

elea

se (

kJ/d

eg)

B0

B5

B20B50

B100

-20 -10 0 10 20 30 40-5

0

5

10

15

20

25

30

35



Crank Angle (deg)

Rat

e of

Hea

t R

elea

se (

kJ/d

eg)

B0

B5

B20B50

B100

(a)

(b)

Fig. 4. ROHR versus CA for different fuels at 10 Nm (a) and 20 Nm (b) load.

2808 M. Gumus / Fuel 89 (2010) 2802–2814

5.1.3. Ignition delay (ID)ID is an important parameter in combustion phenomenon. Bio-

diesel and its blends showed shorter IDs as compared to diesel fueldue to higher cetane number of biodiesel. High cetane numbermakes autoignition easily and gives short ID. A lot of parameterssuch as fuel type, fuel quality, air–fuel ratio, engine speed, qualityof fuel atomization, intake air temperature and pressure influencethe ID. The fuel type is an important parameter affecting the ID[26].

When biodiesel is used as alternative fuel, the earlier fuel ITshave been occurred in engines with mechanical injection systems.These earlier ITs obtained with biodiesel have been attributed todifferences in the physical properties between biodiesel and dieselfuels. A critical difference between the diesel fuel and biodiesel fuelproperties is the compressibility (bulk modulus). The compressibil-ity of biodiesel and its blends is lower than that of diesel fuel.When biodiesel is injected, the liquid fuel pressure rise producedby the pump is faster as a consequence of its lower compressibility,and also the pressure waves can propagate quicker toward theinjectors (higher sound velocity). The difference in this physicalproperty has provided that the IT of biodiesel and its blends iseffectively advanced relative to that of diesel fuel [20,42,43].Another physical property having effect on the IT is density. The

biodiesel has a slightly higher density, which affects the fuelcompression process in the volumetric injection pump. The higherdensity of biodiesel causes advance in the IT. Also, this case causesa different quantity of fuel to be injected per stroke for the samevolume of crank angle. In addition, its higher viscosity reducespump leakages leading to an increase in the injection line pressure,to faster evolution of pressure, and thus to advanced IT. Further-more, lower vapor content in a high pressure injection systemcould also be the reason for the advanced IT. By decreasing the va-por volume, the injection delay decreases which results in ad-vanced IT [18,40,44,45].

Table 3 shows IDs of the test fuels for different ITs, IPs, CRs, andELs. The ID decreased with increase in EL for all test fuels. In spiteof slightly higher viscosity and lower volatility of the biodiesel, theignition delay seems to be lower than that with diesel fuel. B100showed shorter ID as compared to diesel fuel due to higher cetanenumbers of biodiesel. Increasing of the cetane number with an in-creased biodiesel addition in blends with diesel fuel is responsiblefor the decrease in the ID. While advanced IT increased ID, retardedIT, increasing of IP and CR decreased ID. Effects of these parameterson the ID increased with addition of biodiesel content in the blend.The minimum and maximum IDs were obtained at ‘B100EL20IT15’and ‘B0EL10IT25’ conditions, respectively.

-5

0

5

10

15

20

25

30

35

40

45

50

Injection pressure = 20 MPa Compression ratio = 18

Load = 20 Nm

Rat

e of

Hea

t Rel

ease

(kJ

/deg

)B0, 15 oCA BTDC

B0, 20 o CA BTDC

B0, 25 o CA BTDC

B100, 15 o CA BTDC

B100, 20 oCA BTDC

B100, 25 o CA BTDC

-5

0

5

10

15

20

25

30

35

Injection timing = 20 o CA BTDC Compression ratio= 18

Load = 20 Nm

Rat

e of

Hea

t Rel

ease

(kJ

/deg

)

B0, Pinj = 20 MPa

B20, Pinj = 20 MPa


B100, Pinj = 24 MPa

-20 -10 0 10 20 30 40-5

0

5

10

15

20

25

30

35

40

45

50

Injection timing = 20 oCA BTDCInjection pressure = 20 MPa

Load = 20 Nm

Crank Angle (deg)

Rat

e of

Hea

t Rel

ease

(kJ

/deg

)

B0, C.R.= 18

B20, C.R.= 18

B20, C.R.= 20B100, C.R.= 18

B100, C.R.= 20

(c)

(a)

(b)

Fig. 5. ROHR versus CA for different IT (a), IP (b), CR (c) at 20 Nm load.

M. Gumus / Fuel 89 (2010) 2802–2814 2809

5.2. Analysis of heat release

HR calculations are an attempt to learn more about thecombustion process in an engine. Several important

parameters such as ROHR, CHR, COHR, and CD were determinedby analysis of HR. Figs. 4 and 5 demonstrate the ROHR andFigs. 6 and 7 illustrate the CHR for different fuels, ITs, IPs, andCRs at 10 and 20 Nm ELs. HR parameters such as maximum

-50

0

50

100

150

200

250

300

350

400

450

500



Cum

ulat

ive

Hea

t Rel

ease

(kJ

)B0B5B20B50B100

-20 -10 0 10 20 30 40

0

100

200

300

400

500

600



Crank Angle (deg)

Cum

ulat

ive

Hea

t Rel

ease

(kJ

)

B0

B5

B20B50

B100

(a)

(b)

Fig. 6. CHR versus CA for different fuels at 10 Nm (a) and 20 Nm (b) load.

2810 M. Gumus / Fuel 89 (2010) 2802–2814

ROHR, CHR, end of combustion, COHR, and CD are shown inTable 4.

5.2.1. Rate of heat release (ROHR)Figs. 4 and 5 demonstrate the ROHR for different fuels, ITs, IPs,

and CRs at 10 and 20 Nm ELs. Because of the vaporization of thefuel accumulated during ID, at the beginning a negative HR isobserved and after combustion, this behavior becomes positive.After the ID, premixed fuel air mixture burns rapidly, followed bydiffusion combustion, where the burn rate is controlled by fuel–air mixture. It can be observed that combustion starts earlier forbiodiesel blends under all engine operating conditions and itbecomes more prominent with higher biodiesel addition in theblends. The premixed combustion HR is higher for diesel owingto higher volatility and better mixing of diesel with air. Anotherreason may possibly be the longer ID of diesel, which leads to a lar-ger amount of fuel accumulation in the combustion chamber at thetime of the premixed combustion stage, leading to a higher ROHR.

As illustrated in the Fig. 4, ROHR decreased with the increase ofbiodiesel in the blends. From the figures it is clear that the maxi-mum ROHR of biodiesel was lower than that of diesel fuel owingto lower premixed burning of biodiesel. At the time of ignition, fuelair mixture prepared for combustion decreases with addition ofbiodiesel content in the blend due to lower volatility, ID and higher

viscosity. Therefore the premixed HR decreases with the additionof biodiesel content in the blend [27]. Also, the lower calorific valueof biodiesel reduces ROHR. Location of the maximum ROHR as CAfor biodiesel and its blends with diesel fuel is earlier than that ofdiesel fuel. As seen in the comparison in Fig. 4a and b, ROHR in-creased with the rise in the EL due to the increase in the quantityof fuel injected in the cylinder.

With the advanced IT (Fig. 5a), the ID increased because the fuelinjected earlier in the combustion chamber. This leads to greateraccumulation of the fuel during ID period and leads to an increasein the premixed HR. Retarded IT leads to a decrease in ID and loweraccumulation of fuel. This is the reason for the lower premixedburning, HR and poor combustion. The premixed HR and the max-imum ROHR improved when the IP was enhanced owing to betterfuel atomization and more mixture preparation (Fig. 5b). The in-creased in the premixed HR for biodiesel is more than that of thediesel fuel when the IP was increased. With an increase in CR(Fig. 5c) the premixed HR and the maximum ROHR increases dueto the fuel injected in hotter combustion chamber and this leadsto higher combustion rate.

As seen in the Table 4, the maximum ROHR was 48.47 kJ/degoccurring at 9.80 �CA BTDC for ‘B0EL20CR20’ condition. The mini-mum ROHR was 17.23 kJ/deg occurring at 7.62 �CA BTDC for‘B100EL10IT15’ condition.

0

100

200

300

400

500

600 Injection pressure = 20 MPa Compression ratio = 18

Load = 20 Nm

Cum

ulat

ive

Hea

t Rel

ease

(kJ

)

B0, 15 oCA BTDC

B0, 20 oCA BTDC

B0, 25 oCA BTDC

B100, 15 oCA BTDC

B100, 20 oCA BTDC

B100, 25 oCA BTDC

0

100

200

300

400

500

600

Injection timing = 20 oCA BTDC Compression ratio= 18

Load = 20 Nm

Cum

ulat

ive

Hea

t Rel

ease

(kJ

)

B0, Pinj = 20 MPa

B20, Pinj = 20 MPa


B100, Pinj = 24 MPa

-20 -10 0 10 20 30 40

0

100

200

300

400

500

600


Load = 20 Nm

Crank Angle (deg)

Cum

ulat

ive

Hea

t Rel

ease

(kJ

)

B0, C.R.= 18

B20, C.R.= 18

B20, C.R.= 20B100, C.R.= 18

B100, C.R.= 20

(b)

(c)

(a)

Fig. 7. CHR versus CA for different IT (a), IP (b), CR (c) at 20 Nm load.

M. Gumus / Fuel 89 (2010) 2802–2814 2811

5.2.2. Cumulative heat release (CHR)The CHR was calculated and illustrated in Figs. 6 and 7. These

figures show the tendency of earlier HR for biodiesel blends butcombustion for diesel fuel quickly exceeds the CHR for biodiesel

blends although combustion for diesel fuel starts later. Resultsshow that the CHR decreased with the increase of biodieselamount in the fuel blend as shown in Table 4. The main reasonfor the decrease in the CHR is lower heating value (LHV) of

Table 4Heat release characteristics of the fuels for different engine conditions.

10 Nm 20 Nm

B0 B5 B20 B50 B100 B0 B5 B20 B50 B100

OriginalInjection timing(20 �CA BTDC)Compression ratio (18)Injection pressure(20 MPa)

Maximum ROHR (kJ/deg) 22.91 22.80 21.92 20.90 20.19 31.01 30.68 30.21 27.78 28.13Maximum ROHR (�CA BTDC) 5.84 6.24 6.50 6.83 7.23 9.47 9.80 10.13 10.57 10.86Maximum CHR (kJ) 449.59 454.26 455.96 442.69 437.03 531.11 531.26 532.05 525.58 522.34End of combustion (�CA ATDC) 36.66 36.66 36.86 39.96 39.77 40.16 40.18 40.23 40.26 40.29Combustion duration (�CA) 42.64 42.77 43.49 46.40 47.06 49.43 49.83 49.99 50.29 51.22COHR (�CA ATDC) 7.71 8.05 7.83 8.52 8.73 6.12 5.91 5.69 7.00 7.18





Compression ratio(20)


Injection pressure(24 MPa)


Table 5BSFC and BTE of the CI engine.

BSFC (g kWh�1) BTE (%)

10 Nm 20 Nm 10Nm 20 Nm

Original B0 299.89 321.47 27.82 25.95B100 367.68 394.34 26.30 24.52

Injection timing (15 �CA BTDC) B0 296.64 318.48 28.12 26.20B100 372.89 419.96 25.93 23.02

Injection timing (25 �CA BTDC) B0 292.94 318.48 28.48 26.20B100 327.37 368.71 29.54 26.23

Compression ratio (20) B0 290.94 322.47 28.68 25.87B100 339.63 382.51 28.47 25.28

Injection pressure (24 MPa) B0 288.13 320.50 28.96 26.03B100 348.99 370.19 27.71 26.12

2812 M. Gumus / Fuel 89 (2010) 2802–2814

biodiesel as compared to diesel fuel. As seen in the comparisonFig. 6a and b, CHR increased with the rise in the EL from 10 to20 Nm due to the increase in the quantity of fuel injected intothe cylinder. CHR increased with the increase in EL for all test fuels.

Table 4 shows the CHR of the test fuels for different ITs, IPs, andCRs. While the increasing of IT, IP, and CR increased CHR, retardedIT decreased CHR. The maximum CHR was 543.04 kJ occurring at36.66 �CA ATDC for ‘B0EL20CR20’ condition. The minimum CHRwas 432.50 kJ occurring at 37.06 �CA ATDC for ‘B100EL10IT15’condition.

It has been accepted that the position of the maximum CHR is endof combustion. The end of combustion as CA ATDC for all test fuels atdifferent engine operating conditions was given in Table 4. The endof combustion changed within the range of 34.16–41.09 �CA ATDCfor all test fuels. With addition of biodiesel content in the blend,the end of combustion went away from TDC due to poor atomiza-

tion, mixture preparation and combustion process. With the in-crease in EL, end of combustion also went away from TDC.

5.2.3. Combustion duration (CD)CD increased with the increase of biodiesel content in the fuel

blend due to the poor atomization and the slow combustion. Thereason of longer CD obtained with biodiesel and its blends can beexplained as a consequence of higher viscosity, flash point andlower volatility. Because adequately fuel was not evaporated dur-ing the main combustion phase the evaporation of fuel continuedin the end combustion phase. More fuel was required in the caseof biodiesel and its blends because the calorific value of biodieselis lower than that of diesel. These factors lead to a longer CD forbiodiesel blends. The CD also increased with increasing of EL forthe all fuels due to increase in the quantity of fuel injected in thecylinder.

M. Gumus / Fuel 89 (2010) 2802–2814 2813

In this study, the CD was calculated as CA interval from themaximum ROPR to the maximum CHR. There is a small vague-ness in this method because there is small slope at the end ofCHR curves as seen from Figs. 6 and 7. But it is probably beinguseful to obtain an idea about CD. The variations in CD with re-spect to different ITs, IPs, CRs, and ELs for all test fuels are shownin Table 4. Increasing of IP increased CD for all test fuels. Thehigher IP caused better spray; atomization and mixture with airand this continued diffusion combustion, where the burn rate iscontrolled by fuel–air mixture. Retarded IT decreased CD for alltest fuels. Advanced IT generally increased CD but the CD de-creased with advanced IT for B20, B50 and B100 at 10 Nm EL.Increasing of CR increased CD for all test fuels at 10 Nm EL whileincreasing of CR decreased CD for all test fuels except B50 at20 Nm EL. The maximum CD was obtained 54.98 �CA at‘B100EL20IT25’ condition. The minimum CD was obtained39.27 �CA at ‘B5EL10IT15’ condition.

5.2.4. Center of heat release (COHR)The COHR became closer to TDC with the increase in EL for all

fuels due to the rise in combustion rate. The COHR went away fromTDC with the increase of biodiesel content in fuel blend due to thepoor atomization and the slow combustion. With the advanced IT,the COHR became closer to TDC and the COHR went away fromTDC with retarded IT as expected. With an increase in CR, the COHRwent away from TDC for all test fuels but the COHR became closerto TDC for only diesel fuel at 20 Nm EL. With increasing IP, theCOHR became closer to TDC for all test fuels. The COHR changedwithin the range of 3.12–12.07 �CA ATDC for all test fuels.

During the experimental study, it was also detected that the en-gine noise was qualitatively less than that of diesel fuel when theengine was running with B100. Biodiesel and its blend with dieselfuels had no traces of unacceptable high CGP rises and the CGPsmoothly varied with respect to CA.

5.3. Engine performance

Brake specific fuel consumption (BSFC) and brake thermal effi-ciency (BTE) were given as engine performance in Table 5 for bio-diesel and diesel fuel at different, ITs, IPs, CRs, and ELs. As shown inTable 5, the BSFC of biodiesel is higher than that of diesel fuel for allconditions owing to the lower LHV and higher viscosity of biodie-sel. Therefore, the amount of fuel introduced to the cylinder for adesired energy input has to be greater with the biodiesel. As seenin the Table 5, increasing of IT, CR and IP decreased BSFC for biodie-sel and diesel fuel. The minimum BSFC values were obtained at ad-vanced IT. The BTE decreased as the biodiesel content increased inthe blended fuel for all conditions. As shown in Table 5, increasingof IT, CR and IP increased BTE for all test fuels. The best results interms of BTE were obtained at advanced IT.

6. Conclusion

In this study, a comprehensive experimental investigation ofcombustion and HR of a DI-CI engine running with HOME and itsblends with diesel fuel was carried out. Based on the experimentalstudy; the main results of combustion and HR analysis are summa-rized as follows:

– Analysis of combustion indicated that biodiesel and all fuelblends exhibited similar pressure–time history as diesel fueland no undesirable combustion features such as unacceptablehigh CGP rises were observed.

– Combustion started earlier as the concentration of biodiesel inthe blend is increased due to decreasing of ID. Retarded IT,

increased IP and CR also decreased ID even more. The minimumID was obtained at ‘B100EL20IT15’ condition.

– While increasing of biodiesel concentration in the blenddecreased the peak CGP, increasing of IT, IP and CR increasedthe peak CGP of biodiesel and its blend with diesel fuel. Themaximum peak CGP and minimum peak CGP were obtained at‘B0EL20CR20’ and ‘B100EL10IT15’ conditions, respectively.

– Biodiesel and its blends showed lower ROPRs as compared todiesel fuel. The CR was the most effective factor on the ROPR.The maximum ROPR was obtained at ‘B0EL20CR20’ condition.

– While the increase in the biodiesel mass fraction decreases theROHR, increasing of IT, IP and CR increased the ROHR of biodie-sel and its blend with diesel fuel. The maximum and minimumROPR were obtained at ‘B0EL20CR20’ and ‘B100EL10IT15’ condi-tions, respectively.

– Increasing the biodiesel mass fraction of blends results in adecrease in the CHR and increasing of IT, CR and IP compensatesthe decrease in CHR.

– The CD increased with addition of biodiesel content in the blenddue to the slow combustion of the biodiesel. The CD alsoincreased with increasing of EL for all the fuels. The CD of allfuels was affected by the variation in IT, CR, and IP.

– The COHR went away from TDC with the increase in the biodie-sel mass fraction. With increase in CR, the COHR went awayfrom TDC for biodiesel and blend fuels. With the increase in IP,the COHR became closer to TDC for all test fuels.

– The BSFC for biodiesel are higher than that for diesel fuel whileBTE for biodiesel is lower than that for diesel fuel. This is result-ing of lower LHV of biodiesel. The advanced IT gave the bestresults for BSFC and BTE compared to the other conditions.

Consequently it can be concluded that biodiesel (hazelnut kerneloil methyl ester) and its blends with diesel fuel can be used in theengine without any modification, and undesirable combustion fea-tures such as unacceptable high CGP rises were not observed. Themodifications such as increasing of IT, CR and IP provided signifi-cant improvement in combustion and HR characteristics.

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