Experimental study on the role of ethanol on performance emission trade-off and tribological characteristics of a CI engine

Renewable Energy 86 (2016) 972e984

Contents lists available at ScienceDirect

Renewable Energy journal homepage: www.elsevier.com/locate/renene

Experimental study on the role of ethanol on performance emission trade-off and tribological characteristics of a CI engine Udayan Majumder a, *, Prasun Chakraborti a, Rahul Banerjee a, Bishop Debbarma b a b

Department of Mechanical Engineering, NIT Agartala, Tripura, 799055, India Department of Production Engineering, NIT Agartala, Tripura, 799055, India

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 January 2015 Received in revised form 20 August 2015 Accepted 3 September 2015 Available online 21 September 2015

An experimental study of engine combustion, performance and emission characteristics using diesel eethanol blends along with investigation of tribological effects of ethanol on engine oil was done in present work using 1-butanol as emulsifier. Thorough observations of dieseleethanol miscibility resulted that 25% v/v ethanol is miscible with diesel using only 3% v/v emulsifier. Tribological effects of ethanol on engine oil were investigated by analyzing the engine oil samples through FT-IR (Fourier Transform Infrared Spectroscopy). Overall experimentation re-evaluated the potential of ethanol in reduction of NOx, Soot and in-cylinder temperature with slight penalty for HC, CO and BSEC prominently at low load. All fuels produced more NO but lesser NO2 at higher load satisfying Zeldovich mechanism. A comparative trade-off analysis was done in between NHC, Soot and BSEC to reflect the performance and emission characteristics at a time. Trade-off study revealed D78E20B02 (78% diesel 20% ethanol 2% butanol) as optimal blend among all fuels used in present work. FT-IR analysis depicted negligible variation in the compounds in engine oil samples for the specified operational period. Statistical analysis showed larger Coefficient of variation for D78E20B02 blend due to higher absorbance of a particular compound. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Diesel-ethanol blends Trade-off study FT-IR Tribological characteristics

1. Introduction Rapid increasing rate of population, modernization and stringent emission standards have compelled researchers since many years to find out a source of alternative energy due to depletion of fossil fuels day by day which was first enormously understood by global fuel crisis on 1970s. Consequently number of alternative fuel sources in liquid as well as gaseous form is developed, but unfortunately very few sources can be treated as complete substitute of fossil fuels. Since 1975, study regarding scope of ethanol (ethyl alcohol) as a complementary of conventional fuels is still going on and incorporated successfully in SI engines in Brazil [1] followed by USA [2]. Literature survey yields that, ethanol with its inherent properties such as renewability, higher octane number, oxygen

Abbreviations: FT-IR, Fourier transform infrared spectroscopy; BSEC, Brake specific energy consumption; hbth, Brake thermal efficiency; CO, Carbon monoxide; HC, Hydrocarbon; NOx, Nitrogen oxides; NO, Nitric oxide; NO2, Nitrogen dioxide; COV, Co-efficient of variation; BMEP, Brake mean effective pressure; BTDC, Before top dead centre; ATDC, After top dead centre; BBDC, Before bottom dead centre; ABDC, After bottom dead centre; CA, Crank angle. * Corresponding author. E-mail address: [email protected] (U. Majumder). http://dx.doi.org/10.1016/j.renene.2015.09.007 0960-1481/© 2015 Elsevier Ltd. All rights reserved.

content and higher latent heat of vaporization has already been established as a commendable auxiliary for diesel fuel with reduction in emissions like Soot, NOx, CO, HC with a penalty for SFC, hbth etc. But ethanol is also associated with number of limitations like miscibility with diesel, lower heat content, lower cetane number, corrosiveness etc. when it is to be used in CI engine. Lower cetane number may cause cyclic irregularity and D.C. Rakopoulos et al. [3] concluded that at least for the low contents (up to 15%) of ethanol in diesel fuel has no influence on the cyclic pressure variations thus ensuring no degradation in performance or emission characteristics. Effects of ethanol on engine oil are also not discussed by any researcher according to the author's knowledge. These in turn increases the scope of further investigation to reduce the limitations of ethanol on CI engine. The development of alternative fuel sources has drawn the vivid attention in various countries, with particular emphasis on the biofuels that possess the added advantage of being renewable fuels that can be replenished through the growth of plants or production of livestock, showing an ad-hoc advantage in reducing the emitted carbon dioxide [4]. D.C. Rakopoulos et al. [5] carried out a comparative evaluation of five different bio-fuels concerning combustion, performance and emissions in a ‘Hydra’ CI engine with

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

a conclusion that it is a very convenient and welcome fact that all bio-fuels/diesel fuel blends performed very well performance and emissions wise without any change of the engine operating conditions, e.g. by optimization to some parameter [5]. It was aimed in present study to enlighten the effects of ethanol on combustion, performance and emission parameters using minimum additive along with tribological effects of ethanol on engine oil. Concentration of ethanol was consistently increased from 2% to 25% in used dieseleethanol blends to emphasize the effects of ethanol chronologically. Participation of NO and NO2 in total NOx was also studied in context of Zeldovich mechanism. A comprehensive trade-off analysis was done in between NHC, Soot and BSEC which offers a scope to investigate the best possible fuel combination at different load conditions, which will simultaneously reduce NOx and smoke opacity at optimum fuel consumption. 1.1. Butanol in present study Generally when ethanol is mixed with diesel due to strong hydrophobic properties of ethanol it separates from diesel in two layers which is influenced by ethanol concentration, atmospheric temperature and moisture content. When the ambient temperature decreases, the Brownian motion of molecules is weakened and the surface tension of the liquid increases, which results in an increase in the pressure on the interfacial film. Once the interfacial film breaks, the ethanol molecules will break through it and congregate, then the ethanol liquid is formed and the phase separation of ethanolediesel blends happens [6]. So, additives are used as either emulsifier to maintain the stability of dieseleethanol blends with higher concentration of ethanol in wide range of temperature variation, or cetane improver to increase the cetane number of the blends. Among lots of additives 1-butanol commonly known as normal butanol was selected as an emulsifier in present work. Butanol [CH3(CH2)3OH] has a 4-carbon structure and is a more complex alcohol (higher-chain) than ethanol as the carbon atoms can either form a straight chain or a branched structure, thus resulting in different properties [7]. It was aimed in present study to use minimum concentration of 1-butanol as an emulsifier to highlight the effects of ethanol on various parameters.

973

Table 1. Fuel properties can also be found out using following equations as [8]-

Qcal ¼

ðxd  rd  Qd Þ þ ðxeth  reth  Qeth Þ þ ðxbut  rbut  Qbut Þ ðxd  rd Þ þ ðxeth  reth Þ þ ðxbut  rbut Þ

(1)

wcal ¼

ðxd  rd  wd Þ þ ðxeth  reth  weth Þ þ ðxbut  rbut  wbut Þ ðxd  rd Þ þ ðxeth  reth Þ þ ðxbut  rbut Þ

(2)

Where, Qcal, wcal ¼ Calculated calorific value and kinematic viscosity of a blend. xd, rd, Qd, wd ¼ Volume, density, calorific value and kinematic viscosity of diesel. xeth, reth, Qeth, weth ¼ Volume, density, calorific value and kinematic viscosity of ethanol. xbut, rbut, Qbut, wbut ¼ Volume, density, calorific value and kinematic viscosity of 1-butanol.

2.2. Stability period of various blends To find out the minimum concentration of additive required to mix up to 25% of ethanol with diesel, sample blends were prepared as shown in Fig. 1. These sample blends were kept in complete observation for 30 days during which atmospheric temperature varied between 10  C and 25  C. From this observations exact timing of separation of various blends were recorded. Fig. 2 represents the sample blends after 30 days. For a particular concentration of ethanol the blends which were stable up to 30 days with minimum additives are only shown in Fig. 2 eliminating the other blends with higher concentration of additive. Designation of blends consists of each of the initial letters of its constituents followed by its volume percentage e.g. D72E25B03 stands for 72% diesel, 25% ethanol, 3% 1-butanol and so on. Observations for blends used as fuel in present study are tabulated in Table 2. 3. Pre-data accumulation stage 3.1. Methodology adopted

2. Preparatory phase of fuels 2.1. Properties of fuels Diesel used in present study is high speed diesel (HSD) and ethanol is 99.9% pure ethanol. Ethanol and butanol were collected from chemical feedstock. Properties of fuels are tabulated in

Experimentation of present work was divided into two parts as 1st phase of experiment which consists of collection of combustion, performance and emission data and 2nd phase of experiment which consists of collection of lubricating oil samples for FT-IR. Brief methodology and apparatus used to conduct overall experiment is as below-

Table 1 Properties of fuels. Fuels

Diesel (HSD) Ethanol Butanol D98E02B0 D94E05B01 D89E10B01 D83E15B02 D78E20B02 D72E25B03

Properties Density (kg/m3)

Kinematic viscosity (cSt)

Lower calorific value (MJ/kg)

Cetane number

Enthalpy of vaporization (kJ/kg)

Oxygen content

844 789.4 810 842 840 838 835 832 839

2.6 1.2 2.46 2.6 2.5 2.5 2.4 2.3 2.3

42.6 26.8 33.3 42.2 41.7 41.0 40.1 39.3 38.4

53 8 25 e e e e e e

250 [9] 825 [9] 550 [9] e e e e e e

0 [9] 34.73 [9] 21.59 [9] e e e e e e

974

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

Fig. 1. Sample blends just after immediate preparation.

Fig. 2. Sample blends after 30 days.

3.1.1. Methodology for 1st phase of experimentation From prepared sample blends as described in Section 2.2, based on minimum additive concentration and stability of 7 days D98E02B0, D94E05B01, D89E10B01, D83E15B02, D78E20B02, D72E25B03 blends were chosen to be used as fuel along with neat diesel. Using these seven fuels performance, combustion and emission data were collected at five different load points as 10% (BMEP 0.54 bar), 25% (BMEP 1.34 bar), 50% (BMEP 2.68 bar), 75% (BMEP 4.01 bar) and full load (BMEP 5.35 bar) in the mentioned diesel engine test rig in Section 3.2. The set of data obtained using neat diesel was set as reference data. During experiments the engine was kept running for 5 min after changing each load. Entire fuel line was cleaned properly to eliminate any contamination before each and every experiment.

present study. Four engine oil samples were collected by running the engine 8 h continuously at full load with four different fuels from the seven fuels used in 1st phase of experimentation. After collecting the engine oil the crankcase was drained out and cleaned properly and filled with unused engine oil each time. Four fuels were chosen as-

3.1.2. Methodology for 2nd phase of experimentation After completion of 1st phase of experiment, 2nd phase was done which consisted of collection of engine oil samples for FT-IR to conduct tribological analysis. Servo 20W40 engine oil was used in

3.2. Apparatus used

a. Blend having maximum amount of ethanol i.e. 25% ethanolD72E25B03. b. Blend having minimum amount of ethanol i.e. 2% of ethanolD98E02B0. c. Optimum blend obtained based on trade-off analysisD78E20B02. d. Neat diesel

The experiment was conducted on an existing single cylinder naturally aspirated four stroke CI engine as shown in Fig. 3(1)

Table 2 Observed stability period of blends used as fuel. Blend samples D98E02B0 D94E05B01 D89E10B01 D83E15B02 D78E20B02 D72E25B03

After immediate preparation

Separation time

Clear Clear Clear Clear Clear Clear

Beyond 30 days Beyond 30 days After 16 days After 14 days After 8 days After 7 days

Condition after 30 days Crystal clear mixture Crystal clear mixture Separated in two layers. Separated in two layers. Separated in two layers. Separated in two layers.

After After After After

shaking shaking shaking shaking

cloudiness cloudiness cloudiness cloudiness

occurs. occurs. occurs. occurs.

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

Fig. 3. Diesel engine test rig 1: Engine 2: Control panel 3: AVL 415S Smoke Meter.

conforming to the Indian Standards IS: 11170-1985. The engine was coupled with an eddy current dynamometer. Detail specification of engine and dynamometer is mentioned in Table 3. The instrumentation was interfaced to a computer through centralized DAQ platform synchronized with a crank angle encoder onto GUI based post processing software. The DAQ was programmed to acquire incylinder and fuel injection pressure data at 1 crank intervals and present the data smoothened over 200 consecutive cycles to compensate for cyclic variations. For measuring cylinder pressure very precise and robust pressure sensor of piezoelectric type (make Kistler) was used with an inline charge amplifier. The specific fuel consumption was carried out in fuel burette for a time interval of 60 s. To measure soot AVL Smoke Meter 415s was used as shown in Fig. 3(3) and Testo-350 Emission Analyzer was used to measure exhaust gases as shown in Fig. 4(a). The emission parameters were averaged over 6 consecutive test results. For FT-IR analysis of engine oil samples Nicolet-iS10 FT-IR device was used as shown in Fig. 4(b).

975

Fig. 4. a) Testo350 Emission Analyzer b) Nicolet iS10 FT-IR Device.

performance parameters are calculated on the basis of individual accuracies of the components declared by their respective manufacturers [10]. The combined uncertainty analysis for the performance parameters has been carried out on the basis of the root mean square method [11] where the total uncertainty U of a quantity Q has been estimated, depending on the independent variables x1, x2,.,xn [i.e., Q ¼ f (x1,x2,.,xn)] having individual errors Dx1, Dx2,.,Dxn is given by Eq. (3)

ffi vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi u( 2  2 2 )  u vU vU vU DU ¼ t Dx þ Dx þ…þ Dxn vx1 1 vx2 2 vxn

(3)

The accuracy level of Testo-350 gas analyzer and AVL 415s Smoke meter is given in Table A1 in Appendix-A. Total uncertainty was computed as per Eq. (3) and tabulated in Table 4. Individual uncertainties of other instruments are listed in Table A2 in Appendix-A. 5. Results and discussions

4. Uncertainty analysis

5.1. Average rate of heat release (J/deg)

Uncertainty analysis has been carried out to identify the errors arising in various parameters during experimentation to ensure the repeatability of the experiment. The accuracy of the

Table 3 Instrument specifications. Diesel engine Engine Kirloskar-AV1. Engine type Vertical CI engine Type of injection Direct injection Bore size 80 mm Stroke length 110 mm Swept volume 553 cc Cooling Water Compression ratio 16.5:1 HP 5 HP Dynamometer Make Type Load measurement method Maximum load Cooling

Rated speed Injection pressure No. of nozzle holes Nozzle hole dia. Injection timing Inlet valve opens Inlet valve closes Exhaust valve opens Exhaust valve closes Power mag Eddy current Strain Gauge 10 kg Direct

1500 rpm 200 bar 3 0.288 mm 23 BTDC 4.5 BTDC 35.5 ABDC 35.5 BBDC 4.5 ATDC

Rate of heat release depicts instantaneous release of heat at different crank angles. D.C. Rakopoulos et al. [13] discussed advanced models, which calculate the instantaneous composition at each time step incorporating gross HRR with heat transfer relations and temperature calculations. Heat release can be found out by Refs. [14,15]

  dQn cv dV dp PV dm dV dme þV  þP þ he ¼ P d4 d4 m dt d4 d4 R d4

(4)

Equation of state is 

(5)

PV ¼ mRT

Where, Qn ¼ net heat release, 4 ¼ crank angle, he ¼ specific enthalpy of the cylinder content, cv and R ¼ specific heat at constant volume and specific gas constant respectively, P ¼ pressure, V ¼ volume. Fig. 5 represents average rate of heat release vs. crank angle diagram for each fuel at different loading conditions. Graphical analysis depicts that-heat release rate increased consistently for each fuel with increasing load as expected. At low load premixed combustion and diffusion combustion are obvious, but at high loads prolonged diffusion combustion prevails and premixed combustion

976

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

Table 4 Total percentage of uncertainty of performance parameters. Performance parameter

Measured variables

Instrument involved in measurement

% Uncertainty of measuring instrument [12]

BP BSEC

Load, RPM SFC, BP

Load sensor, Load indicator, Speed measuring unit. Fuel measuring unit, Fuel flow transmitter, BP

0.2, 0.1, 1.0. 0.065, 1.5, 1.02

25 20 15 10 5 0 -5 -10 -25 -20 -15 -10

-5

0

5

10

15

20

25

30

35

40

45

Avg. rate of heat release (J/degree)

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

30

50

65

50% LOAD

60

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

55 50 45 40 35 30 25 20 15 10 5 0 -5 -10 -25 -20 -15 -10

-5

0

5

10

15

20

25

30

35

40

45

Avg. rate of heat release (J/degree)

Crank angle (degree)

pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð0:22 þ 0:12 þ 12 Þ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ð0:0652 þ 1:52 þ 12 Þ

50

25% LOAD

40

30 25 20 15 10 5 0 -5 -10 -25 -20 -15 -10 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 0 -5 -10 -25 -20 -15 -10

-5

0

5

FULL LOAD

90

15

20

25

30

75% LOAD

-5

0

5

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

80 70 60 50 40 30 20 10 0 -10 -25 -20 -15 -10

10

-5

0

5

10

15

20

25

30

35

35

40

45

50

Crank angle (degree)

10

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

15

20

25

30

Crank angle (degree)

100

1.02. 1.81

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

35

Crank angle (degree) Avg. rate of heat release (J/degree)

Avg. rate of heat release (J/degree) Avg. rate of heat release (J/degree)

10% LOAD

Total % uncertainty

lesser heat release rate up to 50% load. Beyond 25% load each blend had maximum rate of heat release except D72E25B03 which had beyond 50% load. Particularly at full load an increasing trend in heat release with increasing concentration of ethanol can be found. Higher latent heat of vaporization of ethanol played major role to reduce the heat release up to 25% load for dieseleethanol blends. But at higher load as amount of fuel injected was more, the higher

tends to disappear. The same trend for premixed and diffusion combustion was obtained by D.C. Rakopoulos et al. [7]. Fig. 6 depicts that-crank angle at which maximum heat release occurred is higher for dieseleethanol blends than neat diesel and maximum for D72E25B03. Lower cetane number of ethanol caused this ignition delay. Maximum rate of heat release was lesser for each dieseleethanol blend up to 25% load except D72E25B03 which had

35

Calculation

40

Crank angle (degree) Fig. 5. Average rate of heat release vs. crank angle.

45

50

35

40

45

50

20.0

BASE DIESEL D98 E02 B00 D94 E05 B01 D89 E10 B01 D83 E15 B02 D78 E20 B02 D72 E25 B03

a

17.5 15.0 12.5 10.0 7.5 5.0 2.5 0.0 -2.5

0

10

20

30

40

50

60

70

80

90

100

BASE DIESEL D98 E02 B00 D94 E05 B01 D89 E10 B01 D83 E15 B02 D78 E20 B02 D72 E25 B03

90

Avg max rate of heat release (J/deg)

CA at Avg max rate of heat release (deg CA)

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

80 70

977

b

60 50 40 30 20 0

Load (% of full load)

10

20

30

40

50

60

70

80

90

100

Load (% of full load)

Fig. 6. a) Crank angle at average maximum heat release vs. load b) Average maximum rate of heat release vs. load.

oxygen content of ethanol predominated over lower latent heat of vaporization resulting higher heat release. The oxygen atoms in ethanol require higher thermal energy to dissociate which is available at higher load only. Lu Xingcai et al. [2] got similar result but V. Gnanamoorthi et al. [16] got different result.

Moreover, the lower heating value of ethanol also played an important role to keep in-cylinder temperature low for the blends. B.Q. He et al. [18], E.A. Ajav et al. [19] also found similar effect of ethanol on cylinder temperature. 5.4. Brake specific energy consumption (BSEC)

5.2. Average cylinder pressure (bar) Fig. 7 represents average cylinder pressure vs. crank angle diagram at all loads. Graphical analysis depicts that-with increasing load pressure raised consistently as expected and the CA for maximum cylinder pressure shifted towards TDC. It can be seen that-dieseleethanol blends had maximum pressure more away from TDC, which was due to lower cetane number and higher auto ignition temperature of ethanol. Due to lower flash point and auto ignition temperature of diesel, it burned first raising the temperature inside the cylinder. When the temperature was sufficient enough to ignite ethanol, it started burning resulting in further increase in temperature and pressure. Up to 25% load D72E25B03 had lower pressure peak due to burning of diesel only which implies incomplete combustion caused by higher concentration of ethanol. But with further increase in load as the cylinder temperature rose, the ethanol started burning and exhibited similar trend for cylinder pressure like other blends. Fig. 8 yields that up to 25% load neat diesel had maximum cylinder pressure. At full load D83E15B02 had maximum pressure of 4.07% higher than neat diesel. Overall lesser pressure developed by dieseleethanol blends at low loads was due to higher ignition delay of dieseleethanol blends which caused the blends to burn after the piston started moving towards BDC. Thus, developed pressure was nullified by the pressure depression caused by downward piston movement. But at higher loads as average rate of heat release was more for blends as the oxygenated ethanol boosted combustion and pressure developed also increased for blends. A. Paul et al. [17] also obtained the similar trend for cylinder pressure. 5.3. Average maximum in-cylinder temperature Fig. 9 represents average maximum in-cylinder temperature vs. load variation for each fuel which yields that- D72E25B03 had lowest temperature of 11.85% lower than neat diesel at 25% load. Overall trend of all blends depicts that the blends had lower incylinder temperature than neat diesel except D83E15B02 up to 50% load and D98E02B0 at 50% load. Lower temperature of blends was due to higher latent heat of vaporization of ethanol.

BSEC indicates the energy contained by fuel to be consumed per unit power output. The BSEC (kJ/kW-hr) is to be calculated by Ref. [17]

BSEC ¼

ðmd  LHVd Þ þ ðmeth  LHVeth Þ þ ðmbut  LHVbut Þ BP

(6)

Where, md, meth, mbut ¼ mass flow rate of diesel, ethanol, butanol respectively. LHVd, LHVeth, LHVbut ¼ lower heating value of diesel, ethanol, 1-butanol respectively. Fig. 10 represents BSEC variations with load and depicts decreasing BSEC trend with increasing load. Among all blends D72E25B03 had highest BSEC of 34.85% higher than neat diesel at 25% load. This was due to lower heating value and density of ethanol which caused higher energy consumption to produce the same power output. Overall trend of BSEC shows negligible variation at higher load i.e. beyond 25% load in between blends and neat diesel. The trend has similarity with S. Gomasta et al. [20] but not matched with A. Paul et al. [17]. 5.5. Carbon monoxide (CO) CO generates in an engine when there is not enough oxygen to oxidize the carbon atoms into CO2 and signifies incomplete combustion. Fig. 11 represents CO emission with load where it can be found that-up to 50% load almost all blends had higher CO emissions than neat diesel except D98E02B0 and D89E10B01. Average trend shows that with increasing concentration of ethanol CO emission also increased up to 50% load except the above mentioned blends. Among all blends D72E25B03 had highest CO emissions of 355% higher than neat diesel at 50% load. But, at 75% and full load almost all blends had lesser CO emissions except D94E05B01, D83E15B02 and D78E20B02. At low loads higher latent heat of vaporization of ethanol caused a temperature reduction inside the cylinder, which prevented oxidation of CO. So, the more was amount of ethanol the more was CO emission at low loads as reflected significantly by D72E25B03. But at higher loads, higher in-cylinder temperature provides sufficient energy to break oxygenecarbon bond of ethanol

U. Majumder et al. / Renewable Energy 86 (2016) 972e984 55

45 40 35 30 25 20 15

70

25% LOAD

55 50 45 40

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

35 30 25 20 15

10 -30 -25 -20 -15 -10 -5

0

5

10 -30 -25 -20 -15 -10 -5

10 15 20 25 30 35 40 45 50

Crank Angle (degree)

60 55 50 45

35 30 25 20 15 10 -30 -25 -20 -15 -10 -5

0

5

10 15 20 25 30 35 40 45 50

10 15 20 25 30 35 40 45 50

70 65 60 55 50

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

45 40 35 30 25 20 15 10 -30 -25 -20 -15 -10 -5

Crank angle (degree)

0

5

10 15 20 25 30 35 40 45 50

Crank angle (degree)

85

Avg. cylinder pressure (bar)

5

75% LOAD

75

40

0

Crank angle (degree)

80

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

50% LOAD

65

Avg. cylinder pressure (bar)

Avg. cylinder pressure (bar)

50

Avg. cylinder pressure (bar)

60

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

10% LOAD

Avg. cylinder pressure (bar)

978

FULL LOAD

80 75 70 65 60 55

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

50 45 40 35 30 25 20 15 10 -30 -25 -20 -15 -10 -5

0

5

10 15 20 25 30 35 40 45 50

Crank angle (degree) Fig. 7. Average cylinder pressure vs. crank angle.

which oxidized CO into CO2 and reduced CO emission. J. Huang et al. [1], L. Zhu et al. [21] also got similar trend for CO. 5.6. Hydrocarbons (CxHy) Hydrocarbons are organic emissions as a consequence of incomplete combustion of hydrocarbon fuel [22]. With a fuel rich mixture there is not enough oxygen to react with all the carbon, resulting in high levels of hydrocarbon and CO in the exhaust products [23]. Fig. 12 represents HC emission of all fuels with load variation. It is evident from graphical analysis that-almost all blends had higher HC emissions than neat diesel at all loads. Especially at low loads HC emission by the blends augmented tremendously. But, at higher loads higher cylinder temperature enhanced oxidation of unburned fuels and HC emission reduced.

Among all blends D72E25B03 had highest HC emission of 254% higher than neat diesel at 10% load. Lowest HC emission was for neat diesel at full load. The trend of HC emission by the dieseleethanol blends shows that with increasing concentration of ethanol the HC emission increased almost at all loads. Blending of ethanol causes a reduction in in-cylinder temperature due to the higher latent heat of evaporation of ethanol, which causes a slower evaporation and locally lower equivalence ratio. The extension of the ignition delay is also one of the reasons for the increase in HC emission by ethanol blending [24]. But a few authors consider the lower cetane number of alcohol blends that promotes quenching effect, to be the main parameter that favors the increase of HC emissions [9]. The result is consistent with Jilin L. et al. [6], Octavio A. et al. [9] but inconsistent with S. Gomasta et al. [20].

U. Majumder et al. / Renewable Energy 86 (2016) 972e984 80

70 65

15 14 13 12

60 55 50

11 10 9 8 7 6 5 4

45

3 2

40 35

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

16

CO (g/kW-hr)

Avg maximum cyl. press. (bar)

17

BASE DIESEL D98 E02 B00 D94 E05 B01 D89 E10 B01 D83 E15 B02 D78 E20 B02 D72 E25 B03

75

979

1 0

0

10

20

30

40

50

60

70

80

Load (% of full load)

90

100

0

10

20

30

40

50

60

70

80

90

100

110

Load (% of full load) Fig. 11. Carbon monoxide vs. load.

Fig. 8. Avg. max. cylinder press. vs. load.

5.7. Nitrogen oxides (NOx) 1700 1600

Avg. max cyl. temperature (C)

Nitric oxide (NO) and Nitrogen dioxide (NO2) are collectively termed as NOx. NOx production is strongly dependent on temperature (primary dependence), local concentration of oxygen and duration of combustion; other notable factors are injection timing and fuel properties [25]. Four major routes of NOx formation have been identified in combustion processes: Thermal NOx (Zeldovich Mechanism), Prompt NOx (Fenimore), N2O route, and Fuel Bound Nitrogen (FBN) [26]. The thermal NOx accounts for more than 99% of the NOx formation in conventional diesel engines. The elementary reactions for formation of NO and NO2 [1,27,28] are as below-

BASE DIESEL D98 E02 B00 D94 E05 B01 D89 E10 B01 D83 E15 B02 D78 E20 B02 D72 E25 B03

1500 1400 1300 1200 1100

O þ N2 4NO þ N N þ O2 4NO þ O N þ OH4NO þ H

1000 900

0

10

20

30

40

50

60

70

80

90

100

110

Load (% of full load)

NO in turn can further react to form NO2 by various means, including [23].

NO þ H2 O4NO2 þ H2

Fig. 9. Avg. max. cylinder temp. vs. load.

NO þ O2 4NO2 þ O

BASE DIESEL D98 E02 B00 D94 E05 B01 D89 E10 B01 D83 E15 B02 D78 E20 B02 D72 E25 B03

60 55

BSEC (MJ/kW-hr)

50 45 40 35 30 25 20 15

2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6

10

0.4

5

0.2

0

0

10

20

30

40

50

60

70

80

Load (% of full load) Fig. 10. BSEC vs. load.

90

100

110

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

2.2

CxHy (g/kW-hr)

65

0.0

0

10

20

30

40

50

60

70

80

Load (% of full load) Fig. 12. Hydrocarbon vs. load.

90

100

110

980

U. Majumder et al. / Renewable Energy 86 (2016) 972e984 12

10 9 8

NOx (g/kW-hr)

every fuel produced lesser amount of NO and higher NO2 at low load (up to 25% load) but higher amount of NO and lesser NO2 at higher loads (beyond 25% load). NO formation increased tremendously beyond 50% load suppressing NO2 formation. This was because-when the cylinder temperature rose to near about 1600  C the molecular Nitrogen (N2) and Oxygen (O2) dissociates into their atomic state and react to form NO which is according to Zeldovich mechanism.

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

11

7 6 5

5.8. Soot

4 3

Along with NOx, particulate matters (PM) are also one of the major issues of diesel engine emissions. Diesel particulates consist of combustion generated carbonaceous material (soot) on which some organic (arisen mainly from unburned fuel and lubricating oil) or inorganic compounds have been absorbed [25]. Fig. 15 represents variation of soot with load for each fuel which depicts that-with increasing load soot emission also increased for each fuel. Overall trend shows that-soot emission of almost each blend at each load was lesser than neat diesel except D83E15B02 and D78E20B02 at 10% load and D98E02B0 at 50% load. This reduced soot emission of dieseleethanol blends was due to its higher oxygen content which oxidized the unburned carbon atom prohibiting the formation of soot. At lower load due to lesser fuel air ratio formation of soot was usually less. But at higher load as fuel air ratio increased, soot formation also increased. Furthermore, blended fuels have characteristics that promotes mixture formation, which can be expected to reduce the amount of soot even more, such as a low cetane number, low viscosity, low surface tension, and a low boiling point [9]. R. Michikawauchi et al. [30], M. Lapuerta et al. [31], B. Q. He et al. [18] also got similar trend.

2 1 0 -1

0

10

20

30

40

50

60

70

80

90

100

110

Load (% of full load) Fig. 13. Nitrogen oxides vs. load.

The rate constants for the thermal mechanism are slow, and NO formation (and decomposition) is significant only when there is a high enough temperature (say, above 1800 K) and sufficient time [29]. Fig. 13 represents variation of NOx with load from which it is evident that- NOx emission increased with increasing load for each fuel. Almost all blends had lesser NOx emission than neat diesel at all loads except D94E05B01. D94E05B01 produced highest NOx at full load and D72E25B03 produced lowest NOx at 10% load. Overall trend shows that- NOx emitted by blends was lesser than neat diesel. This was due to higher latent heat of vaporization and lower heating value of ethanol which restricts cylinder temperature to lower value suppressing the NOx formation. Generally, cooling effect of ethanol fuel due to higher latent heat of vaporization is more dominant than the combustion promotion by the oxygen content in the ethanol fuel at the low engine load condition [18]. But, at higher load due to higher combustion rate the cylinder temperature also raised promoting NOx formation. This result has similarity with A. Paul et al. [17] but not matched with S. Gomasta et al. [20]. Fig. 14 represents NO and NO2 variation with load in total NOx for each fuel. From graphical analysis it is evident that-neat diesel produced 42% NO and 58% NO2 at 10% load where as 96% NO and 4% NO2 at full load, D94E05B01 produced 26% NO and 74% NO2 at 10% load whereas 94% and 6% NO2 at full load out of total amount of NOx. Likewise, overall analysis for all fuels implies that-each and

NHC (NOx þ HC), Soot and BSEC trade-off study emphasizes the characteristics of each fuel to get a comprehensive idea with respect to emission and performance at a time. Fig. 16 represents trade-off graph between NHC, Soot and BSEC for each fuel. The graph is drawn at particularly 50%, 75% and full load only, which is the region of higher emissions and fuel consumption. In the graph the fuels were designated by the load as prefix followed by the letter ‘B’ stands for ‘fuel’ followed by concentration of ethanol on that fuel e.g. 75B10 means the fuel which contains 10% ethanol at 75% load and so on. From Fig. 16 it can be seen that at 50% load all fuels had higher 150

Diesel D98 E2 D94 E5 B1 D89 E10 B1 D83 E15 B2 D78 E20 B2 D72 E25 B3

1350 1200 1050 900

b

a 125

100

NO2 (ppm)

1500

NO (ppm)

5.9. Trade-off study of soot, NHC and BSEC

750 600 450

75

50

300 25

150 0 0

10

20

30

40

50

60

70

80

Load (% of full load)

90

100

110

0

0

10

20

30

40

50

60

70

80

Load (% of full load)

Fig. 14. a) Variation of NO with load; b) Variation of NO2 with load.

90

100

110

U. Majumder et al. / Renewable Energy 86 (2016) 972e984 1.50

indecision on the choice of selection of calibrated control variables as yielded by optimization study, a strategy has been undertaken by formulating an adaptive penalty or merit function to meet the objectives. In present study following merit function was used [32]-

DIESEL D98 E02 B00 D94 E05 B01 D89 E10 B01 D83 E15 B02 D78 E20 B02 D72 E25 B03

1.25

1.00

(

0.75

Soot

981

AMF ¼ f 0.50

NHCexp NHCT

a      d ) SOOTexp b COexp c BSFCEQ ; exp ; ; ; SOOTT COT BSFCEQ ; T (7)

0.25

0.00 0

10

20

30

40

50

60

70

80

Load (% of full load)

90

100

110

Fig. 15. Soot vs. load.

BSEC but lower NHC and Soot except B5, which had slightly lower BSEC but very high NHC. At 75% load almost all fuels had more or less same BSEC along with variation in emission levels especially for B5, which had higher NHC. At full load BSEC reduced for each fuel than any other load with wide variation in emissions. At full load B0 (neat diesel) had highest Soot emission among all fuels at all loads with relatively lower BSEC. At full load B5 had lowest BSEC among all fuels at all loads with penalty for maximum NHC. So, it depicts that at 50% load addition of ethanol had minimum emissions with higher BSEC. Neat diesel had relatively lower BSEC than the blends with penalty for Soot and NHC emissions. 5.10. Study of trade-off merits- adaptive merit function In order to facilitate the reduction of computational cost and

Where, NHCexp ¼ Combination of NOx and HC obtained during experiment. NHCT ¼ Standard amount of combined NOx and HC as per the EPA standard. SOOTexp ¼ Soot values obtained by experiment. SOOTT ¼ Standard soot value as per EPA standard. BSFCEQ, exp ¼ Obtained BSFCEQ during experimentation. BSFCEQ, T ¼ Target value of BSFCEQ as rated by the engine. A, b, c, d ¼ Arbitrary constants e.g. 1, 2, 3, 4. It is evident from the expression of AMF that all desired objectives have been encapsulated in it such as emission as well as performance characteristics. Thus, the concept of AMF brings forth a distinct index of comparison of fuel performance. Determining AMF values for each fuel at each load, it was found that different blends had maximum AMF values at different loads. But, D78E20B02 blend had maximum values at 75% and full load indicating minimum emission at these loads. As D78E20B02 had minimum emission at maximum loading ranges indicated by maximum AMF values, it is considered as the optimum blend among all blends used as fuel in present study.

Fig. 16. NHC-Soot trade-off with respect to BSEC.

982

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

Fig. 17. a) Collected lubricating oil samples b) FT-IR graph of lubricating oil samples.

5.11. Tribological results and discussions Collected samples of engine oil as shown in Fig. 17(a) were analyzed through FT-IR and the graph obtained is shown in Fig. 17(b). Analyzing the graph, depending on various peaks of respective wave number, the compounds associated with the particular wave numbers was found out as below- [33]. Methyl symmetric CeH stretching can be found near about: 2960 cm1 Methyl asymmetric CeH stretching can be found near about: 2870 cm1 Methylene asymmetric CeH stretching can be found near about: 2930 cm1 Methylene symmetric CeH stretching can be found near about: 2850 cm1 Methylene scissoring can be found near about: 1465 cm1 Methylene symmetrical CeH bending can be found near about: 1380 cm1 Oxime NeO stretching can be found near about: 965e930 cm1 Methylene rocking can be found near about: 720 cm1 From the graph of FT-IR it can be seen that only D78E20B2 had a peak at 2879 cm1 which represents Methyl asymmetric CeH stretching. This particular peak is absent for other fuels, whereas the other fuels had peaks at near 2852 cm1 which represents Methylene symmetric CeH stretching. Along with this the difference in absorbance levels was also found for collected oil samples for a particular compound. Absorbance and statistical variations for different compounds is tabulated on Table 5 which depicts thatmaximum COV is 2 for Methyl asymmetric CeH stretching and minimum of 0.07 for Methylene symmetrical bending. Maximum COV was due to higher absorption of D78E20B02 blend only. Statistical analysis depicts that inclusion of ethanol has some effect on engine oil operated for the experimental time period. But, FT-IR resulted in very negligible variation in compounds present in engine oil sample obtained by using diesel and dieseleethanol blends as fuel.

6. Conclusions Vital findings of present study are summarized as belowa) 25% v/v ethanol was successfully mixed with diesel using only 3% v/v 1-butanol and was stable for 7 days. So, miscibility study reflected the potential of 1-butanol as strong emulsifier. b) Overall trend for rate of heat release and cylinder pressure was lesser for dieseleethanol blends than neat diesel at lower load. But at higher loads blends had higher heat release rate and cylinder pressure than neat diesel. c) Up to 50% load D72E25B03 consumed maximum energy indicated by highest BSEC. Beyond 50% load BSEC was almost same for all fuels. d) Almost all dieseleethanol blends emitted higher HC at all loads which again increased with ethanol concentration and decreased with increasing load. Up to 50% load CO emission was higher for almost all blends especially for D72E25B03 than neat diesel. But at higher load blends had lesser CO emission than neat diesel. Except D94E05B01 all blends had lesser NOx than neat diesel at all loads. All fuels had increasing trend for NO but decreasing trend for NO2 at higher load. All blends emitted lesser Soot than neat diesel at all loads. e) Trade-off study implied D78E20B02 as the optimal blend among all fuels used. f) FT-IR analysis of engine oil revealed no significant difference in the compounds present in engine oil samples. But statistical analysis showed some variation in COV and s due to higher absorption of D78E20B02 for the specified engine operational period. So, for the present experimental study it can be concluded from combustion, performance, emission and tribological aspects thatdieseleethanol blends containing very less amount of additive have potential to be used as a promising alternative fuels for CI engine without any engine modification and harmful effect on engine

U. Majumder et al. / Renewable Energy 86 (2016) 972e984

983

0.0284 0.0272 0.0219 0.0219 0.003 0.13

Methylene rocking

components. Appendix A. Supplementary data

0.0099 0.0799 0.0089 0.0094 0.035 1.30 0.0440 0.0383 0.0436 0.0383 0.003 0.07 0.0769 0.1509 0.0764 0.0650 0.039 0.42 0.1340 0.3712 0.1316 0.1184 0.122 0.64 0.2308 0.6004 0.2345 0.1779 0.195 0.62 0.0000 0.3712 0.0000 0.0000 0.186 2.00 0.1326 0.7669 0.1504 0.0611 0.328 1.18 DIESEL D78E20B02 D98E02B0 D72E25B03 Standard deviation (s) Coefficient of variation

Used fuel

Table 5 Statistical analysis of FT-IR data.

Methyl symmetric CeH stretching

Methyl asymmetric CeH stretching

Methylene asymmetric CeH stretching

Methylene symmetric CeH stretching

Methylene scissoring

Methylene symmetrical bending

Oxime NeO stretching

Supplementary data related to this article can be found at http://dx.doi.org/10.1016/j.renene.2015.09.007. References [1] J. Huang, Y. Wang, S. Li, A.P. Roskilly, H. Yu, H. Li, Experimental investigation on the performance and emissions of a diesel engine fuelled with ethanolediesel blends, Appl. Therm. Eng. 29 (11) (2009) 7. [2] L. Xing-cai, Y. Jian-Guang, Z. Wu-Gao, H. Zhen, Effect of cetane number improver on heat release rate and emissions of high speed diesel engine fueled with ethanolediesel blend fuel, Fuel 83 (14) (2004) 8. [3] D.C. Rakopoulos, C.D. Rakopoulos, E.G. Giakoumis, R.G. Papagiannakis, D.C. Kyritsis, Experimental-stochastic investigation of the combustion cyclic variability in HSDI diesel engine using ethanolediesel fuel blends, Fuel 87 (8) (2008) 14. [4] R.C. Brown, T.R. Brown, Biorenewable Resources: Engineering New Products from Agriculture, John Wiley & Sons, 2013. [5] D.C. Rakopoulos, C.D. Rakopoulos, E.G. Giakoumis, R.G. Papagiannakis, D.C. Kyritsis, Influence of properties of various common bio-fuels on the combustion and emission characteristics of high-speed DI (direct injection) diesel engine: vegetable oil, bio-diesel, ethanol, n-butanol, diethyl ether, Energy 73 (2014) 13. [6] J. Lei, L. Shen, Y. Bi, H. Chen, A novel emulsifier for ethanolediesel blends and its effect on performance and emissions of diesel engine, Fuel 93 (2012) 7. [7] D.C. Rakopoulos, C.D. Rakopoulos, R.G. Papagiannakis, D.C. Kyritsis, Combustion heat release analysis of ethanol or n-butanol diesel fuel blends in heavy-duty DI diesel engine, Fuel 90 (5) (2011) 13. [8] Z. Sahin, O. Durgun, Prediction of the effects of ethanol-diesel fuel blends on diesel engine performance characteristics, combustion, exhaust emissions, and cost, Energy & Fuels 23 (3) (2009) 11. [9] O. Armas, R. Garcia-Contreras, A. Ramos, Pollutant emissions from engine starting with ethanol and butanol diesel blends, Fuel Process. Technol. 100 (2012) 10. [10] G.R. Kannan, R. Anand, Experimental investigation on diesel engine with diestrolewater micro emulsions, Energy (2011) 01. [11] C.D. Rakopoulos, A.M. Dimaratos, E.G. Giakoumis, D.C. Rakopoulos, Investigating the emission during acceleration of a turbocharged diesel engine operating with bio-diesel or n-butanol diesel fuel blends, Energy 35 (2010) 12. [12] P.K. Bose, R. Banerjee, An experimental investigation on the role of hydrogen in the emission reduction and performance trade-off studies in an existing diesel engine operating in dual fuel mode under exhaust gas recirculation, J. Energy Resour. Technol. 134 (012601) (2012) 15. [13] D.C. Rakopoulos, Heat release analysis of combustion in heavy-duty turbocharged diesel engine operating on blends of diesel fuel with cottonseed or sunflower oils and their bio-diesel, Fuel 96 (2012) 11. [14] J. Heywood, Internal Combustion Engine Fundamentals, McGraw-Hill, New York, 1988. [15] C. Ferguson, Internal Combustion Engines, Willey, New York, 1986. [16] V. Gnanamoorthi, G. Devaradjane, Effect of dieseleethanol blends on performance, combustion and exhaust emission of a diesel engine, Int. J. Curr. Eng. Technol. 3 (1) (2013) 7. [17] A. Paul, P.K. Bose, R.S. Panua, R. Banerjee, An experimental investigation of performance-emission trade off of a CI engine fueled by dieselecompressed natural gas (CNG) combination and dieseleethanol blends with CNG enrichment, Energy 55 (2013) 16. [18] B.Q. He, S.J. Shuai, J.X. Wang, H. He, The effect of ethanol blended diesel fuels on emissions from a diesel engine, Atmos. Environ. 37 (35) (2003) 7. [19] E.A. Ajav, B. Singh, T.K. Bhattacharya, Experimental study of some performance parameters of a constant speed stationary diesel engine using ethanolediesel blends as fuel, Biomass Bioenergy 17 (4) (1999) 9. [20] S. Gomasta, S.K. Mahla, An experimental investigation of ethanol blended diesel fuel on engine performance and emission of a diesel engine, Int. J. Emerg. Technol. 3 (1) (2012) 6. [21] L. Zhu, C.S. Cheung, W.G. Zhang, Z. Huang, Combustion, performance and emission characteristics of a DI diesel engine fueled with ethanolebiodiesel blends, Fuel 90 (5) (2011) 8. [22] H. Kose, M. Ciniviz, An experimental investigation of effect on diesel engine performance and exhaust emissions of addition at dual fuel mode of hydrogen, Fuel Process. Technol. 114 (2013) 9. [23] V. Ganeshan, Internal Combustion Engines, Tata McGraw Hill, 2007. [24] S.H. Park, J. Cha, H.J. Kim, C.S. Lee, Effect of early injection strategy on spray atomization and emission reduction characteristics in bioethanol blended diesel fueled engine, Energy 39 (1) (2012) 13. [25] E.G. Giakoumis, C.D. Rakopoulos, A.M. Dimaratos, D.C. Rakopoulos, Exhaust emissions with ethanol or n-butanol diesel fuel blends during transient operation: a review, Renew. Sustain. Energy Rev. 17 (2013) 21. [26] Sara McAllister, J.-Y. C, A. Carlos Fernandez-Pello, Fundamentals of

984

[27]

[28] [29] [30]

U. Majumder et al. / Renewable Energy 86 (2016) 972e984 combustion processes, in: F.F. Ling (Ed.), Mechanical Engineering Series, Springer, 2011. C.S. Lee, K.H. Lee, D.S. Kim, Experimental and numerical study on the combustion characteristics of partially premixed charge compression ignition engine with dual fuel, Fuel 82 (5) (2003) 8. M. Skottene, K.E. Rian, A study of NOx formation in hydrogen flames, Int. J. Hydrogen Energy 32 (15) (2007) 14. R.S.J.K. Ball, Automotive Engineering Fundamentals, SAEeInternational, United States of America, 2004. R. Michikawauchi, S. Tanno, Y. Ito, M. Kanda, Combustion improvement of

diesel engine by alcohol addition-investigation of port injection method and blended fuel method, SAE Int. J. Fuels Lubr. 2011-01-0336 4 (1) (2011) 10. [31] M. Lapuerta, O. Armas, J.M. Herreros, Emissions from a dieselebioethanol blend in an automotive diesel engine, Fuel 87 (1) (2008) 7. [32] D.T. Montgomery, R.D. Reitz, Optimization of Heavy-duty Diesel Engine Operating Parameters Using a Response Surface Method, Technical Paper 2000-01-1962, SAE, 2000. [33] B. Stuart, Infrared Spectroscopy: Fundamentals and Applications, John Wiley & Sons, Ltd, 2004.