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JSAE 20077106

SAE 2007-01-2038

Effect of Ethanol on the HCCI Combustion

Kohtaro Hashimoto

Honda R & D Co., Ltd.

Copyright 2007 Society of Automotive Engineers of Japan, Inc. and Copyright 2007 SAE International

ABSTRACT

Bio-ethanol is one of the most promising alternativefuels for vehicles. It is important for the spread of bio-ethanol to investigate its ignition quality and itsoptimum combustion procedure. It is particularlyimportant for the application of bio-ethanol to a

homogeneous-charge compression ignition (HCCI)engine to investigate the HCCI combustioncharacteristics of ethanol. In this study, the inhibitingeffects of ethanol on the HCCI combustion of heptanewere investigated by using a rapid compressionmachine (RCM) under various conditions. The resultsindicate that ethanol effectively retarded the hotignition period of HCCI combustion due to its effectiveretardation of the cool flame period. The hot ignitionpeak period for 30 wt% ethanol/70 wt% heptane wasmore delayed than that of PRF having an octane

number of 60 under the =0.4 condition. In addition,

the hot ignition peak period for 50 wt% ethanol/50wt% heptane was more delayed than that of PRFhaving an octane number of 80. Furthermore, theeffects of diethyl ether, which can be produced fromethanol, on HCCI combustion were investigated byusing RCM. Diethyl ether had significantly highignition quality, suggesting that HCCI combustioncontrol with ethanol and diethyl ether would beeffective.

INTRODUCTION

A sustainable energy system such as that provided

by bio-fuel should be established to satisfy the COP3requirements and to confer energy security. Bio-ethanol is one of the most promising bio-fuels forvehicles because it can be easily produced from suchbiomass as sugar, starch and cellulose, and becauseit is suitable for a spark-ignition (SI) engine due to itshigh octane number and fairly low boiling point.

The research and development of SI engines forethanol fuel have been presented, and flexible fuelvehicles which can use both ethanol and gasoline,pure or mixed in any proportions, have beencommercialized in Brazil and the United States.

Nakata et al. have presented a study of an ethanol-fueled SI engine having high torque and thermalefficiency [1].

It is important for the further application of bio-ethanol to utilize such characteristics as its lowignition quality for a new combustion method likehomogeneous charge compression ignition (HCCI)[2]. As the most important issue of HCCI engine is itsdifficulty to control the ignition, it is necessary for theapplication of bio-ethanol to an HCCI engine to

investigate the HCCI characteristics of ethanol undervarious conditions. Also, diethyl ether, which is easilyproduced from ethanol by using an acid catalyst, hashigh ignition quality, and HCCI control can beachieved by using ethanol and diethyl ether producedonboard. Thus, it is important for HCCI control withethanol and diethyl ether to investigate the ignitionquality of a diethyl ether/ethanol mixture. On the otherhand, few studies on the effect of ethanol and diethylether on HCCI combustion have been presented [3].

The objective of this study is to obtain basicinformation about the effect of ethanol on HCCI

combustion in order to be able to control HCCIcombustion by using ethanol. The inhibiting effects ofethanol on the HCCI combustion of heptane wereinvestigated in this study by using a rapidcompression machine (RCM). The effect of diethylether on the HCCI combustion of ethanol was alsoinvestigated for HCCI combustion control usingdiethyl ether and ethanol.

EXPERIMENTS

EXPERIMENTAL APPARATUS

The HCCI combustion experiments were conductedwith a rapid compression machine as shown in Figure1. This machine was designed according to thedescription presented by Murase et al [4]. It consistsof a driving air reservoir, a cam-driving piston, a cam,a compression piston, a compression cylinder, and acombustion chamber head. Compressed air isintroduced into the driving air reservoir. The cam-driving piston is pushed by this air when a signal fromthe control panel opens six solenoid valves. The camis mounted on a linear roller rail and connected to thedriving piston with a push rod. The compression

piston is pushed upwards by the rod following thecam which reproduces the compression stroke of areciprocating engine. Cooling water is introduced intothe pancake-shaped cylinder head compression

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cylinder block to keep the wall temperature constant.The stroke of the compression piston is 80 mm andthe compression ratio can be varied. The combustionchamber is a cylinder of 80 mm in diameter andvolume of 402 cm

3.

Compression Piston

Compression

Cylinder

Roller RailPush Rod

Cam Driving Piston

Driving Cylinder

Compression

Rod

Driving Air Reservoir

Cam

Pressure Transducer

Combustion Chamber

Solenoid Valves

Figure 1 Rapid Compression Machine

FUELS

Different mixtures of ethanol and heptane wereprepared to investigate the effect of ethanol on HCCIcombustion by RCM experiments. Mixtures of diethylether and ethanol were also prepared to investigatethe effect of diethyl ether on auto-ignition under HCCIcombustion conditions. The primary reference fuel(PRF, a mixture of heptane and iso-octane) havingvarious octane numbers was also used under eachexperimental condition, and toluene/heptane mixtureswere used to compare the inhibiting effects becausetoluene is the typical high-octane component ingasoline.

EXPERIMENTAL PROCEDURE

The experimental conditions to investigate the effectof ethanol on HCCI combustion are shown in Table 1.The RCM combustion chamber was evacuated byusing a vacuum pump before the fuel mixture wasinjected by a syringe. Five minutes after this fuelinjection, heated air was introduced to thecombustion chamber to set the pressure to the

atmospheric level. Another 5 minutes later, theair/fuel mixture was compressed. The pressure in thecombustion chamber was measured by a pressuretransducer located at the center of the cylinder headand recorded on a PC. Figure 2 (a) shows pressure-time profiles of the heptane/air mixture (0.3 equivalent

ratio; ) and compressed air. The difference in

pressure between the fuel/air mixture compressionand air-only compression is considered to representthe pressure rise by oxidative heat release (dashed

line). Figure 2 (b) shows the temporal differentialprofiles of the pressure rise for heptane, in which thecool flame peak and hot ignition peak can be clearlyseen. The differential profiles of the pressure rise foreach fuel enable the time of the maximum pressurerise ratio at the cool flame (cool flame peak period),cool flame pressure rise (integral of the temporaldifferential profiles during a cool flame), and the timeof the maximum pressure rise ratio (hot ignition peakperiod) during hot ignition to be obtained.

RESULTS AND DISCUSSION

EFFECT OF ETHANOL ON HOMOGENEOUS-

CHARGE COMPRESSION IGNITION

The APPENDIX shows the experimental resultsfrom HCCI combustion of the ethanol-mixed fuelunder all the experimental conditions used in thisstudy. The standard deviation of cool flame peakperiod or hot flame peak period of heptanecombustion from day to day was less than 0.5ms.

The analysis was initially focused on the result

obtained for a compression ratio of 13.9, =0.4, and

initial temperature of 40. Figure 3 shows the effect

of adding ethanol to heptane on the hot ignition peakperiod for HCCI combustion with the RCM. Theresults are compared with those for PRF and showthat ethanol retarded the hot ignition of HCCIcombustion. The hot ignition peak period for the 20wt% ethanol fuel was same as that for PRF having an

0

1

2

3

4

5

6

40 45 50 55 60

Time (ms)

Pressure(MPa)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Pressure(MPa)

Air

heptane =0.3

Difference

(a)

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

40 45 50 55 60

Time (ms)

dp/dt(MPa/ms)

(b)

Figure 2 (a) The pressure time profiles of the heptane / air

mixture (:0.3) , and difference in pressure (dashed line)

(b) Temporal differential profiles of the pressure rise of

heptane combustion C.R.: 13.9, Initial Temperature: 40

Table 1 Experimental Condition of RCM Experiments

Compression Ratio (C.R.) 12.1, 13.9, 16.1

Initial Temperature40, 50 (C.R.:12.1)30 (C.R.:16.1)

Equivalent Ratio () 0.3, 0.4

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octane number (O.N.) of 40. The hot ignition peakperiod for the 50 wt% ethanol fuel was more delayedthan that for PRF having an octane number of 80.Figure 4 shows the effect of adding ethanol to

heptane on the cool flame peak period for HCCIcombustion with the RCM. It can be seen that ethanoleffectively retarded the cool flame of HCCIcombustion. The cool flame peak period for the 30wt% ethanol fuel was almost same as that for PRFhaving an octane number of 90. Figure 5 shows theeffect of adding ethanol to heptane on the cool flamepressure rise for HCCI combustion with the RCM.Although this figure indicates that ethanol reducedthe cool flame heat release of HCCI combustion, theeffect was not particularly strong in comparison withits cool flame retarding effect. The cool flame heatrelease for the 50 wt% ethanol fuel was almost the

same as that for PRF having an octane number of 70.The author's study on the HCCI combustion ofvarious hydrocarbons using the same RCM suggeststhat hot ignition peak period was affected by both thecool flame period and cool flame heat release [5]. Itcan thus be said that ethanol effectively inhibitedHCCI combustion not only by reducing the cool flameheat release but also by retarding the cool flameperiod.

Figure 6 shows the hot ignition peak period forheptane, 30 wt% toluene/70 wt% heptane, and 30wt% ethanol/70 wt% heptane. The retarding effect of

heptane on the ethanol hot ignition peak period wasgreater than that of toluene, which is known toeffectively inhibit the HCCI combustion [6]. Thus, itcan be said that ethanol is suitable for inhibition ofHCCI combustion.

Next, effects of experimental conditions on the HCCIcombustion of ethanol-mixed fuel were investigated.Figure 7 shows the effect of compression ratio (C.R)and ethanol concentration on the hot ignition peak

period under initial temperature of 40 and =0.4.

Lower compression ratio produced more delayed hotignition period. Under compression ratio of 13.9 and16.1, the hot ignition peak period for the 50 wt%ethanol fuel was more delayed than that for PRFhaving an octane number of 80. Furthermore, the hotignition peak period for the 50 wt% ethanol fuel wasmore delayed than that for PRF having an octane

number of 90 under compression ratio of 12.1. Thus,ethanol effectively retarded the hot ignition peakperiod under each compression ratio.

Figure 8 show the effect of initial temperature andethanol concentration on the hot ignition peak period

under compression ratio of 16.1 and =0.4. Lower

initial temperature produced more delayed hotignition period. Under each initial temperature, the hotignition peak period for the 50 wt% ethanol fuel wasbetween that for PRF having an octane number of 80

and that for octane number 90.

Figure 9 shows the effect of equivalent ratio () and

ethanol concentration on the hot ignition peak periodunder a compression ratio of 13.9 and initial

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 10 20 30 40 50

Ethanol Concentrationwt%

CoolFlame

Press

ure

RiseMPa

PRF 20 O.N.

PRF 40 O.N.

PRF 60 O.N.

PRF 70 O.N.

Figure 5 Effect of Adding Ethanol to Heptane on the Cool

Flame Pressure RIse for HCCI Combustion with the RCM

C.R. :13.9,:0.4, Initial Temperature: 40

46

47

48

49

50

51

52

53

54

55

0 10 20 30 40 50

Ethanol Concentration wt%

CoolFlamePeriodms

PRF 40 O.N.

PRF 70 O.N.

PRF 90 O.N.

Figure 4 Effect of Adding Ethanol to Heptane on the Cool

Flame Peak Period for HCCI Combustion with the RCM


46

47

48

49

50

51

52

Heptane Toluene 30wt% Ethanol 30wt%

HotIgnition

Period(ms)

Figure 6 Hot Ignition Peak Period for Heptane, 30 wt%

Toluene/70wt% Heptane, and 30 wt% Ethanol/70 wt% Heptane

C.R.: 13.9,:0.4, Initial Temperature: 40

46

48

50

52

54

56

58

60

0 10 20 30 40 50

Ethanol Concentration (wt%)

HotIgnitionPeriod(ms)

PRF 40 O.N.

PRF 60 O.N.

PRF 80 O.N

Figure 3 Effect of Adding Ethanol to Heptane on the Hot

Ignition Peak Period for HCCI Combustion with the RCM


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temperature of 40.The hot ignition peak period forthe 50 wt% ethanol fuel was not as delayed as thatfor PRF having an octane number of 80 for=0.3. On

the other hand, the hot ignition peak period for the 50wt% ethanol fuel was more delayed than that for PRF

having an octane number of 80 for =0.4.

Furthermore, the hot ignition peak period for the

ethanol 10 or 20 wt% mixtures of =0.4 was more

retarded than that of =0.3. These result suggested

that the ethanol mixture having an equivalent ratio of0.4 more effectively retarded the hot ignition peakperiod than that having an equivalent ratio of 0.3. Asshown in Figure 4, ethanol effectively retarded thecool flame of HCCI combustion. Also, fuel-air mixturehaving higher equivalent ratio in the combustionchamber of RCM reaches lower adiabatic coretemperature when it was compressed due to its lower

specific heat ratio. The cool flame period under=0.4

was more delayed than that under =0.3. The

retardation effect of ethanol on cool flame period was

emphasized under=0.4 due to its lower adiabatic

core temperature. Thus, the ethanol mixture havingan equivalent ratio of 0.4 would more effectivelyretard the hot ignition peak period than that having anequivalent ratio of 0.3 due to its effective retardationof cool flame period.

In order to investigate the reason for the cool flameretardation effect of ethanol, a simple chemical

reaction calculation for HCCI combustion wasperformed. The CHEMKIN 4 package was used,which includes a simple HCCI engine combustionsolution, together with the heptane reaction modelfrom Lawrence Livermore National Laboratory whichincludes 544 chemical species and 2446 chemicalreactions [7]. An HCCI engine calculation at 1500rpm was performed under the adiabatic condition at acompression ratio of 13.4. Fuel calculations wereperformed for both heptane alone and 10 wt%ethanol/90wt% heptane. During the period of coolflame heat release, a sensitivity analysis for heatrelease was performed and the important reactions to

inhibit this heat release were picked up. Figures 10(a) and (b) respectively show the calculated pressureprofile and rate of heat release profile. Figure 10 (a)indicates that the chemical reaction calculationreproduced the effective retardation of hot ignition byethanol under the HCCI conditions applied. Figure10 (b) indicates that ethanol not only reduced theheat release of the cool flame, but also retarded thecool flame. The sensitivity analysis for heat releasesuggested that the important factors inhibiting thisheat release were the reaction which consumes thehydroxy radical by the ethanol molecule to producethe 1-hydroxy-1-ethyl radical,

CH3CH2OH + OH CH3CHOH + H2O

and the subsequent reaction of the 1-hydroxy-1-ethylradical with an oxygen molecule to produceacetaldehyde and the hydroperoxy radical,

CH3CHOH + O2 CH3CHO + HO2

It is important for low-temperature oxidation heatrelease to increase the free radicals such as hydroxyradical. The inhibiting mechanism by above reactions

is plausible because these reactions consume thehydroxy radical to produce fairly inactive hydroperoxyradical. As the specific heat of the fuel-air mixturescontaining ethanol heptane was different, thecompressed gas temperature of the ethanol fuel may



44

46

48

50

52

54

56

58

60

0 10 20 30 40 50

Initial Temperature 30Initial Temperature 40

30PRF 90 O.N.

40PRF 90 O.N.30PRF 80 O.N.

40PRF 80 O.N.

Figure 8 Effects of Initial Temperature and Ethanol

Concentration on the Hot Ignition Peak Period

Compression Ratio:16.1, =0.4



40

45

50

55

60

65

70

75

80

0 10 20 30 40 50

C.R. 12.1

C.R. 13.9

C.R. 16.1 CR12.1PRF 90 O.N.

CR13.9PRF 80 O.N.

CR16.1PRF 80 O.N.

CR16.1PRF 90 O.N.

CR13.9PRF 90 O.N.

Figure 7 Effects of Compression Ratio (C.R) and Ethanol


initial temperature: 40, =0.4



45

50

55

60

65

70

0 10 20 30 40 50

=0.3

=0.4

=0.3PRF 90 O.N.

=0.3PRF 80 O.N.=0.3PRF 70 O.N.

=0.4PRF 90 O.N.

=0.4PRF 80 O.N.

Figure 9 Effects on Equivalent Ratio () and Ethanol


initial temperature: 40, Compression Ratio: 13.9

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have been lower than that of heptane. The differencebetween the fuel mixture temperature of heptanealone and 10 wt% ethanol/90wt% heptane at thecrank angle of -20TDC was only 0.5K, so the effectof specific heat was negligible with this 10 wt%addition of ethanol. Ethanol thus retarded the coolflame heat release by chemical effect rather thanthermal effect.

Sakai et al. have studied the effect of ethanol on

octane number and fuel spray ignition [8]. Theirchemical reaction calculation suggests that oneethanol molecule has less inhibition effect thantoluene. However, molar weight of ethanol is muchlower than that of toluene. Thus, the inhibition effectof ethanol per mass fraction would be higher thanthat of ethanol molar fraction.

EFFECT OF DIETHYL ETHER ONHOMOGENEOUS CHARGE COMPRESSIONIGNITION

Figure 11 shows the hot ignition peak period for thediethyl ether/ethanol mixture using RCM under a

compression ratio of 13.9, =0.4, and initial

temperature of 40. Diethyl ether has significantly

high ignition quality. Figure 11 indicates that the hotignition peak period for the 60 wt% diethyl ether/40wt% ethanol fuel was the same as that for heptanealone having an octane number 0. The hot ignitionpeak period of the 30 wt% diethyl ether/70 wt%ethanol fuel was also more delayed than that of iso-

octane having an octane number of 100. Theseresults suggest that HCCI combustion can beeffectively controlled by using ethanol and diethylether. Also, required ethanol-conversion efficiency ofon-board reformer would not be so severe becausethe hot ignition peak period for the 60wt% diethylether/40wt% ethanol fuel was the same as that forheptane.

Diethyl ether undergoes low-temperature oxidation

under HCCI combustion conditions. Figure 12 showsthe estimated low-temperature oxidation mechanismby analogy of dimethyl ether, which can easilyundergo low-temperature oxidation. Furthermore, asthe secondary hydrogen atom of diethyl ether is moreeasily abstracted than the primary hydrogen atom ofdimethyl ether, diethyl ether is more likely to undergolow-temperature oxidation than dimethyl ether. Oguraet al. have calculated the activation energies of inter-molecular hydrogen abstraction reactions of ether-derived alkyl peroxy radicals [9]. Their result showsthat the activation energy of the secondary hydrogenatom abstraction is 5.4kcal lower than that of primary

atom abstraction. Thus, diethyl ether has significantlyhigh ignition quality.

CONCLUSION

The inhibiting effects of ethanol on the HCCIcombustion of heptane were investigated in this study

by using RCM under various conditions. The resultsshow that ethanol effectively retarded the hot ignitionof HCCI combustion not only due to reducing effecton the cool flame heat release but also due to itsretardation effect on the cool flame period. The hot

4050

60

70

80

90

100

110

120

130

140

0 20 40 60 80 100

Diethyl Ether Concentration (wt%)


Heptane

Iso octane

Figure 11 Hot Ignition Peak Period for the Diethyl Ether/Ethanol

Mixture using RCM.

C.R: 13.9,: 0.4, Initial Temperature: 40

CH3

C

H2

OC

H2

CH3 CH3

C

OC

H2

CH3

HCH

3O

C

H2

CHH

OO

CH3

OC

CH3

H

OOH

HCH

3O CH

3H

OOH

H

O

O

+ O2

+ O2

Chain Branchi

Figure 12 Estimated Low-Temperature Oxidation Mechanism

of Diethyl Ether

(a) Pressure Profile

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

-20 -10 0 10 20

Crank Angle

Pressure(kPa)

Heptane

Ethanol 10wt%

(b) Rate of Heat Release Profile

0

1000

2000

3000

4000

5000

6000

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

CranK Angle

RateofHeatRelease(kJ/s) Heptane

Ethanol 10wt%

Figure 10 Chemical Reaction Calculation Result Heptane and

Ethanol 10wt%/Heptane 90wt% Fuel Combustion under HCCI

Engine Condition; (a) Pressure Profile (b) Rate of HeatRelease Profile

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ignition peak period for the 30 wt% ethanol/70 wt%heptane was more delayed than that for PRF having

an octane number of 60 for =0.4. The hot ignition

peak period for the 50 wt% ethanol/50 wt% heptanewas also more delayed than that for PRF having anoctane number of 80. The investigation of the coolflame inhibition mechanism by a chemical reactionanalysis suggests that the reaction of ethanol with thehydroxy radical and the subsequent reaction toproduce acetaldehyde would suppress the cool flame

heat release.

The effects of diethyl ether, which can be easilyproduced from ethanol, on HCCI combustion werealso investigated by using RCM. Diethyl ether provedto offer significantly high ignition quality, suggestingthat HCCI combustion can be effectively controlled byusing ethanol and diethyl ether.

REFERENCES

1. Nakata, K., Utsumi, S., Ota, A., Kawatake, K.,

Kawai, T., Tsunoda, T., "The Effect on Ethanol ona Spark Ignition Engine", SAE Paper, 2006-01-

3380 (2006).

2. Yu, H., Xing, L., Zu, L., Li., J., Zhen, H., "Effect of

High-Octane Oxygenated Fuels on n-Heptane-

Fueled HCCI Combustion", Energy & Fuels, 20

1425-1433 (2006).

3. Mack, J. H., Flowers, D. L., Buchholz, B. A.,

Dibble, R. W., "Investigation of HCCI combustion

of diethyl ether and ethanol mixtures using

carbon 14 tracing and numerical simulations",

Proceeding of the Combustion Institute, 30, 2693-

2700 (2005).

4. Murase, E., Ono, S., Hanada, K., "Developmentof a New Compact Rapid Compression Machine

for Engine Combustion Research", Nainenkikan,

31 9-13 (1992).

5. Hashimoto, K., "Evaluation of Homogeneous-

Charge Compression Ignition Characteristics of

Hydrocarbons Using Rapid Compression

Machine", Proceeding of the 44th symposium

(Japanese) on combustion, 86-87 (2006).

6. Tanaka. S., Ayala, F., Keck. J. C., Heywood, J. B.,

"Two-Stage Ignition in HCCI Combustion and

HCCI Control by Fuels and Additives",

Combustion and Flame, 132, 219-239 (2003).

7. Curran, H. J., Gaffuri, P., Pitz, W. J., and

Westbrook, C. K. "A Comprehensive Modeling

Study of n-Heptane Oxidation" Combustion and

Flame, 114, 149-177 (1998).

8. Sakai, Y., Ogura, T., Koshi, K., Arai, M., Kaneko,

T., "A Study on Mechanism of Octane Number

Increase with Oxygenates Blending",

Transactions of Society of Automotive Engineers

of Japan, 37, 3, 103-108 (2006).

9. Ogura, T., Miyoshi, A., Koshi, M., "A Construction

of a Detailed Reaction Mechanism for ETBE

Oxidation", Proceeding of the 44th symposium(Japanese) on combustion, 110-111 (2006).

CONTACT

Kohtaro Hashimoto

Honda R & D

Fundamental Technology Research Center

1-4-1 Chuo, Wako-shi, Saitama, 351-0193 JAPAN

[email protected]

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APPENDIX

Experimental Results from HCCI Combustion of the Ethanol-mixed Fuel under all the RCM ExperimentalConditions

(a) Compression Ratio: 12.1, Initial Temperature: 40

Ethanol Concentration 0.3 0.4 0.3 0.4 0.3 0.4Cool Flame Peak Period (ms) 49.2 49.2 54.2 57.4 64.8 73.4Cool Flame Pressure Rise (MPa) 0.516 0.621 0.360 0.446 0.211 0.244

Hot Ignition Peak Period (ms) 51.6 50.4 59.4 59.6 76.2 79.8

0wt% 30wt% 50wt%

(b) Compression Ratio: 12.1, Initial Temperature: 50

Ethanol Concentration 0.3 0.4 0.3 0.4 0.3 0.4Cool Flame Peak Period (ms) 44.8 44.8 47.8 48.4 53.2 56.6Cool Flame Pressure Rise (MPa) 0.465 0.547 0.333 0.415 0.215 0.258Hot Ignition Peak Period (ms) 47.2 46.0 52.6 50.8 63.6 62.2

0wt% 30wt% 50wt%

(c) Compression Ratio: 13.9, Initial Temperature: 40


Ethanol Concentration 0.3 0.4 0.3 0.4Cool Flame Peak Period (ms) 49.0 49.6 53.2 54.0Cool Flame Pressure Rise (MPa) 0.382 0.475 0.300 0.326Hot Ignition Peak Period (ms) 52.2 51.4 60.6 58.0

30wt% 50wt%

0wt% 10wt% 20wt%

(d) Compression Ratio: 16.1, Initial Temperature: 40

Ethanol Concentration 0.3 0.4 0.3 0.4 0.3 0.4Cool Flame Peak Period (ms) 44.6 44.2 45.2 46.0 47.4 48.6Cool Flame Pressure Rise (MPa) 0.522 0.611 0.380 0.500 0.186 0.258

Hot Ignition Peak Period (ms) 46.4 45.0 47.8 47.4 53.2 52.0

0wt% 30wt% 50wt%

(e) Compression Ratio: 16.1, Initial Temperature: 30


0wt% 30wt% 50wt%

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