Construction and Validation of a Five-Component Fuel Simplification

Subscriber access provided by Kaohsiung Medical University

Combustion

The construction and validation of a five-component fuel simplification mechanism for HCCI engine Weidong Xiong, Zhaolei Zheng, and Tao Peng Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02215 • Publication Date (Web): 14 Nov 2018 Downloaded from http://pubs.acs.org on November 14, 2018

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 34

0.1

0.1

0.625% C2H5OH, 7.50% O2

1.25% C2H5OH, 7.50% O2 0.01

91.25% Argon (φ=0.5) and 3.3 bar.

Ignition delay time(s)

0.01

1E-3

1E-4

Experiment Simulation

1E-5

91.875% Argon (φ=0.25), and 2.0bar.

1E-3

1E-4

Experiment Simulation 1E-5

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

6.8

7.0

7.2

7.4

10000K/T

7.6

7.8

10000K/T

Fig. 1 C2H5OH ignition delay time validation with the experiment[29]

0.001 0.000 -0.001 -0.002 -0.003

3

6.8

(mole/cm .sec)

1E-6 6.6

The reaction rate of C2H5OH


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

-0.004 -0.005 -0.006

R139 R140 R143 R144 R145 R149 R150 R151 R153 R155

-0.007 -0.008 -14

-12

-10

-8

-6

Crank Angle/°CA

Fig. 2 The main fuel consumption rate diagram

Fig. 3 The reaction path of C2H5OH

ACS Paragon Plus Environment

-4

8.0

8.2

8.4

8.6

Energy & Fuels

R159

Elementary reaction

R158 R155 R35

550K 425K

R34 R27 R23 R21 R5 R2 -2

-1

0

1

2

3

4

Temperature sensitivity coefficient Fig. 4 Temperature sensitivity analysis of different initial temperatures

0.01

0.04

R21 R22 R23 R26 R27 R33 R155 R156 R183 R184

0.03

-0.03

-0.04 -9

-8

-7

-6

.sec)

3

-0.02

0.02

(mole/m

3

The reaction rate of H2O2

R29 R30 R31 R32 R35 R122 R152 R153 R181 R205

-0.01

(mole/m .sec)

The reaction rate of CH4

0.00

0.01 0.00 -0.01 -0.02 -0.03 -0.04

-5

-9

-8

-7

-6

-5

Crank Angle/°CA

Crank Angle/°CA

(a) CH4

(b) H2O2

Fig. 5 The reaction rate analysis of CH4 and H2O2

0.1

0.1

0.625%C2H5OH, 7.50% O2 91.25% Argon (φ= 0.25), and 2 bar.

0.01


0.01


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 34

1E-3

1E-4

Experiment Simulation （Detailed） Simulation（Simplified）

1E-5

0.625% C2H5OH, 7.50% O2 91.875% Argon (φ=0.5), and 3.4 bar.

1E-3

1E-4

Experiment Simulation （Detailed） Simulation（Simplified）

1E-5

1E-6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

6.8

7.0

7.2

7.4

7.6

10000/T(K)

10000K/T

(a) P = 2 bar

(b) P = 3.4 bar


7.8

8.0

8.2

8.4

Page 3 of 34

Fig. 6 Comparison of the fuel ignition delay time between simulation and experiment[28]

2000 80

In-cylinder temperature/K

In-cylinder pressure/bar

1800 60

40

20

Simplified mechanism Detailed mechanism

0

1600 1400 1200 1000 800


600 400

-50

-40

-30

-20

-10

0

10

20

30

40

50

-50

-40

-30

-20

Crank Angle/°CA

-10

0

10

20

30

40

50

Crank Angle/°CA

(a) Condition 1 2400

160 140



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

120 100 80 60 40


20

2200 2000 1800 1600 1400 1200


1000 800 600

0 400

-40

-20

0

20

40

-50

-40

Crank Angle/°CA

-30

-20

-10

0

10

Crank Angle/°CA

(b) Condition 2 Fig. 7 Comparison of internal pressure and internal temperature of cylinder


20

30

40

50

Energy & Fuels

0.1

0.01

iso-Octane/Toluene/n-Heptane/Diisobutylene/ Ethanol - air [30% / 25% / 22% / 13% / 10%] φ = 1.0 P=10bar

Ignition delay time（s）


0.1

1E-3

1E-4

Experiment This paper Andrae’ detailed Andrae’s simplified

1E-5

0.01


1E-3

1E-4

Experiment This paper Andrae’s detailed Andrae’s simplified

1E-5

1E-6

1E-6 0.80

0.85

0.90

0.95

0.80

1.00

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1000K/T

1000K/T

（a）

（b）

Fig. 8 Comparison of fuel C ignition delay time between mechanism and experiment [33] 0.1

0.1

0.01


Toluene / iso-Octane / n-Heptane / Diisobutylene - air [45% / 25% / 20% / 10% ] φ = 1.0 P=10bar

1E-3

Experiment This paper Andrae's detailed Andrae's simplified

1E-4

1E-5 0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1.02


0.01

1E-3


1E-4

1E-5 0.85

1.04

0.90

0.95

1.00

1.05

1000K/T

1000K/T

(a)

(b)

1.10

1.15

0.1



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 34

0.01


1E-3

1E-4


1E-5

1E-6 0.90

0.95

1.00

1.05

1.10

1.15

1.20

1000K/T

(c) Fig. 9 Comparison of fuel B ignition delay time between mechanism and experiment [31]


1.20

1.25

Page 5 of 34

0.1

Ethanol / iso-Octane / n-Heptane / Toluene - air [40% / 37.8% / 10.2% / 12%] φ = 1.0

0.01

1E-3

Experiment(P=10bar) This paper(P=10bar) Experiment(P=30bar) This paper(P=30bar) Experiment(P=50bar) This paper(P=50bar)

1E-4

1E-5

n-Heptane / iso-Octane / Ethanol - air [18% / 62% / 20%] φ = 1.0

0.01

Ignition delay time（S)


0.1

1E-3


1E-4

1E-5

1E-6

1E-6 0.8

0.9

1.0

1.1

1.2

0.8

1.3

0.9

1.0

1.1

1.2

1.3

1000K/T

1000K/T

（a）

（b）

Fig. 10 Comparison of ignition delay time between mechanism and experiment [31][32]

50


70



40

80


30

20

10

OP1 experiment Simulation 0

60 50 40 30 20

OP2 experiment Simulation

10 0

-70

-60

-50

-40

-30

-20

-10

0

10

20

-70

-60

-50

-40

Crank Angle/°CA

-30

-20

-10

0

10

20

30

Crank Angle/°CA

Fig. 11 Comparison of fuel A ignition delay time between mechanism and experiment[27] 50

70

Toluene / iso-Octane / n-Heptane / Diisobutylene - air [45% / 25% / 20% / 10% ] φ=0.25

60


40


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

30

20

10


0 -70

50

Toluene / iso-Octane / n-Heptane / Diisobutylene - air [45% / 25% / 20% / 10% ] φ = 0.25

40 30 20


10 0

-60

-50

-40

-30

-20

-10

0

10

20

-70

-60

-50

-40

-30

-20

-10

0

Crank Angle/°CA

Crank Angle/°CA

Fig. 12 Comparison of fuel B ignition delay time between mechanism and experiment[27]


10

20

Energy & Fuels

40

n-Heptane / iso-Octane / Toluene - air [17% / 63% / 20%] φ = 0.25

100



50

30

20

10

experiment Simulation OP1

0 -70

-60

-50

-40

-30

-20

-10

0

10

80


60

40

experiment Simulation

OP2

20

20

-60

-40

Crank Angle/°CA

-20

0

20

Crank Angle/°CA

Fig. 13 Comparison of fuel E ignition delay time between mechanism and experiment[27] 120

40


30

20

experiment Simulation OP1

10

-60

-40

-20

0

20


50


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 34

100


80

60

40


OP2

20

-70

-60

-50

Crank Angle/°CA

-40

-30

-20

-10

0

Crank Angle/°CA

Fig. 14 Comparison of fuel F ignition delay time between mechanism and experiment[27]

Table 1 Main engine technical parameters

Index

Numerical value

The cylinder diameter (mm)

115

Stroke (mm)

80

Clearance volume (cm3)

49.36

Compression ratio

17.5

Speed (rpm)

1000

Temperature (K)

425

Pressure (atm)

1.0

Inlet valve opening/ °CA BTDC

13.5

Inlet valve closing/ °CA ABDC

38.5

Table 2 Results of temperature sensitivity analysis

Number

Reaction

Number


Reaction

10

20

Page 7 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

R2

O + OH = O2 + H

R5

H + O2(+N2) = HO2(+N2)

R21

HO2 + HO2 = H2O2 + O2

R23

OH + OH(+M) = H2O2(+M)

R27

H2O2 + OH = H2O + HO2

R34

CH3 + HO2 = CH3O + OH

R35

CH3 + HO2 = CH4 + O2

R155

C2H5OH + HO2 = CH3CHOH + H2O2

R158

CH3CH2O + M = CH3HCO + H + M

R159

CH3CH2O + M = CH3 + CH2O + M

Table 3 Operation condition of HCCI engine

Condition

Equivalence ratio

Initial pressure (MPa)

Initial temperature (K)

Speed (rpm)

1

0.25

0.2

550

1000

2

0.25

0.1

425

1000

Table 4 The reactions related to ethanol in the paper of Andrae[27]

C2H5OH + OH = CH3CHOH + H2O C2H5OH + OH = CH3CH2O + H2O C2H5OH + HO2 = CH3CHOH + H2O2 JC8H16 => IC4H8 + CH2CHCH2 + CH3 C2H3 + O2 = CH2HCO + O C2H4 + OH = C2H3 + H2O CH3 + HO2 = CH3O + OH OC8H15O + O2 => C2H3 + 2CH2O + H2CCCH2 + CH3 + HO2 CH3 + HO2 = CH3O + OH

Table 5 The coefficient table for small molecule reactions

The reaction rate K = A𝑇 𝑏 𝐸/𝑅𝑇

A: The former factor, b: The temperature index, E: Activation energy

Reaction

𝐴𝑎

𝑛𝑎

𝐸𝑎

Ref

C2H4 + OH => C2H3 + H2O

8.02E+13

0

5955

[30]

C2H4 + H(+M) = C2H5(+M)

1.10E+12

0.5

1822

[30]

C2H3 + O2 = CH2CHO + O

2.50E+15

−0.8

3135

[30]

C2H2 + O = HCCO + H

1.40E+07

2

1900

[28]

C2H2 + O = CH2 + CO

6.10E+06

2

1900

[30]

HCCO + O2 => HCO + CO + O

9.78E+11

0

850

[28]

HCCO + O2 => HCO + CO2

6.52E+11

0

850

[28]

CH3CO(+M) = CH3 + CO(+M)

2.80E+13

0

17100

[30]


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 34

CH2CO + OH = HCCO + H2O

1.00E+07

2

3000

[28]


8.00E+12

0

0

[30]

CH3 + O = CH2O + H

8.40E+13

0

0

[30]

CH2 + O2 = CO + H2O

2.20E+22

−3.3

2867

[30]

CO + OH = CO2 + H

3.09E+11

0

733.81

[30]

CH3OH + OH = CH3O + H2O

1.00E+06

2.1

497

[28]

Table 6 Volume fraction of fuel components

Surrogate mixture

n-heptane

Toluene

Iso-octane

Ethanol

A

18%

62%

20%

B

20%

45%

25%

C

22%

25%

30%

10%

D

10.2%

12%

37.8%

40%

Eiisobutylene (DIB)

Ref. [31]

10%

[31]

13%

[33] [32]

Table 7 Comparison of three types of five-component mechanism

Name

Components

Reaction

Type

Ref

Andrae

1121

4961

Detail

[26]

Andrae

143

672

Simplification

[27]

This paper

124

244

Simplification

Table 8 The volume fraction of each component of the fuel

Surrogate mixture

n-heptane

Toluene

Iso-octane

Ethanol

62%

20%

Diisobutylene (DIB)

Ref

A

18%

B

20%

45%

25%

E

17%

20%

63%

[34]

F

17%

14%

69%

[34]

[31] 10%

[31]

Table 9 HCCI engine operating condition

Condition

Equivalence ratio



Speed (rpm)

1

0.25

0.1

523

1000

2

0.25

0.2

353

1000


Page 9 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

The construction and validation of a five-component fuel simplification mechanism for HCCI engine Weidong Xiong1, Zhaolei Zheng1*, Tao Peng1 (1, Key Laboratory of Low-grade Energy Utilization Technologies and Systems, Ministry of Education, Chongqing University, Chongqing 400044, China)

Abstract The detailed chemical kinetics of ethanol was reduced by means of path analysis and sensitivity

analysis. The important components and reaction pathways of ethanol combustion were sorted out, and

a reduced chemical kinetics model of ethanol containing 37 components and 78 reactions was developed.

Based on the reduced mechanism of the gasoline surrogate (iso-octane, n-heptane, toluene, and

diisobutylene (DIB)), the reduced mechanism of ethanol was then coupled. A reduced chemical kinetic

model of a five-component (iso-octane, n-heptane, toluene, diisobutylene (DIB), ethanol) fuel containing

124 components and 244 reactions and suitable for homogeneous charge compression ignition (HCCI)

combustion was finally obtained. Simulation results of the five-component reduced mechanism are

compared with the ignition delay of four different components of gasoline surrogate under a shock tube.

These results well matched the experimental value. At the same time, the simulation results of the model

well matched the experimental results of combustion under HCCI engine condition, showing that the

model was suitable for the HCCI combustion simulation of gasoline.

Key Words: Chemical kinetics model; Gasoline surrogate; Homogeneous charge compression ignition

(HCCI); Five-component fuel


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 Introduction

The rapid economic development has been accompanied by the rapid growth of car ownership. Consequently,

oil consumption increases every year, resulting in serious pollution caused by automobile exhausts. To solve the

problem of fuel shortage, control the automobile-exhaust pollution, and meet relevant emission regulations,

researchers need to start with the combustion technology of internal combustion engines. Some popular combustion methods are described below.[1][2]

Premixed charge compression ignition (PCCI)[3][4] belongs to the scope of the low-temperature premixed combustion and avoids the high incidence of NOx and soot. Low-temperature combustion[5] (LTC) uses a lot of exhaust gas recirculation (EGR) to reduce the oxygen content and temperature in the cylinder. Reactivity controlled compression ignition (RCCI)[6][7] can reduce the emission of NOx and soot and solve the uncontrollable problem of low-temperature premixed combustion. Homogeneous charge compression ignition (HCCI)[8][9]

combines the characteristics of ignition and combustion of both diesel and gasoline engines. It improves the

thermal efficiency of the engine combustion and can reduce the pollutant emission.

HCCI has its own advantages over the other combustion methods, and HCCI combustion is only associated

with the chemical reaction kinetics of itself. Thus, to realize the wide application of HCCI in the market, the

chemical kinetics of fuel needs to be studied. In this study, the research object is to study the chemical kinetic

model and combustion rate of the gasoline fuel.

Gasoline is a complex hydrocarbon mixture consisting of hundreds of fuels, mostly C5 to C12 aliphatic

hydrocarbons and naphthenic hydrocarbon and a certain amount of aromatic hydrocarbons. Gasoline has a high

octane value; thus, gasoline has been the main fuel of the internal combustion engine for a long time. Gasoline is

made from petroleum refining; thus, if the origin of the oil is different or its refining process is different, the


Page 10 of 34

Page 11 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

gasoline component will be different. This makes it impossible to model the chemical dynamics directly in the

study of gasoline. Although the study of fuel combustion often adopts the method of numerical simulation, the

computer capacity remains limited. The gasoline-combustion number is very wide making modern computers

unable to simulate the gasoline combustion.

Hence, the study needs to select limited number of components to be mixed according to the actual physical

and chemical properties of gasoline. To enable studies on the combustion characteristics of gasoline in an engine

by numerical simulation, the mixture is used to replace the actual gas fuel.

1.1 Research on gasoline surrogate mixtures

1.1.1 One component of iso-octane

In the development process of chemical kinetics model of gasoline surrogate, iso-octane first appeared in the

field of study because of its high octane value and simple composition. In the combustion simulation of gasoline HCCI, iso-octane is the simplest and most common kind of gasoline surrogate fuel. Jia et al.[10] built an iso-octane

skeleton mechanism of oxidation which includes 40 kinds of components and 69 reactions, and it can be able to

accurately calculate the combustion rate and hydrocarbons, CO and NOx emissions. Although iso-octane has a

good advantage in the study of gasoline HCCI simulation, because of the different octane values of gasoline due to

its composition, iso-octane cannot express well the gasoline spontaneous combustion characteristics. In the process

of HCCI, the gasoline spontaneous combustion characteristics is one of the most important factors; therefore, the

scholars begun to study primary reference fuel (PRF) that contains iso-octane and n-heptane.

1.1.2 Primary reference fuel (PRF)

Primary reference fuel (PRF) can match the gasoline octane value according to the different proportion of


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

iso-octane and n-heptane and is widely used in the study of chemical kinetics of gasoline substitution mixtures.

The chemical kinetics model for PRF still needs a lot of research at home and abroad. As early as 1998, Curran et al.[11] proposed a mechanism of PRF chemical reaction involving 990 components and 4060 reactions. In addition,

according to HCCI combustion and considering the combustion emission performance, the simplification mechanism named Ra[12] includes 41 kinds of components and 130 reactions can predict well the ignition delay

time and the relative error of pressure variation in simulation cylinder is small. Although the PRF can match

different octane values of gasoline, it does not show the difference between octane number (RON) and motor

octane number (MON) sensitivity. The fuel sensitivity of gasoline is a very important property of gasoline,

indicating the adaptability and sensitivity to the operating condition. That is, the relative sensitivity of gasoline fuel

to the explosion after the engine operating condition is strengthened, such as increase of intake temperature, increase

of ignition advance angle, increase of intake flow. Therefore, in the study of gasoline HCCI combustion simulation,

the gasoline surrogate fuels which include more components need to be adopted.

1.1.3 Toluene reference fuel[13-15] (TRF)

Pitz et al.[16] found that adding toluene to the primary reference fuel named toluene reference fuel (TRF),

which contains iso-octane, n-heptane, and toluene, is closer to the gasoline in the physical and chemical properties

than primary reference fuel (PRF) as the gasoline surrogate. In addition, it is more suitable for gasoline HCCI combustion simulation than basic fuel PRF. Chaos et al.[17] proposed a mechanism of TPF fuel chemical kinetics

with 469 kinds of components and 1221 reactions. The simulation results of the reaction mechanism are well

verified in the shock-tube test and can predict the ignition delay time more accurately.

Machrafi et al.[18] used actual gasoline, PRF fuels (volume fraction ratio of iso-octane is 95% and for

n-heptane is 5%), and TRF fuels (volume fraction ratio of iso-octane, n-heptane, and toluene is 59, 11, and 30%,


Page 12 of 34

Page 13 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

respectively) in the HCCI engine combustion and compared the three kinds of fuel combustion characteristic. In

contrast, the combustion of actual gasoline and TRF fuel between cool flame and the main heating stage also

released fewer calories, shows the three stages of the ignition characteristics of the fuel combustion, but PRF fuel

did not appear this phenomenon. It also shows that TRF fuel is more suitable for gasoline HCCI combustion

simulation than PRF fuel, which can better reproduce the ignition characteristics of gasoline fuel.

The actual content of olefin in gasoline is only less than that of alkanes and aromatic hydrocarbons. The

content of olefin in gasoline is also different in different countries due to different refining methods. The study

shows that the cross-reactions between olefins and toluene can affect the ignition delay time of TRF fuel. For

example, the cross reaction between toluene and dehydrogenation products of olefins, C6H5CH3 + JC8H15-A = C6H5CH2 + JC8H16, C6H5CH3 + JC8H15-B = C6H5CH2 + JC8H16. Olefins have great significance for further development of the three-component surrogate fuel research for iso-octane, n-heptane, and toluene. Not only that,

olefins are important part of the actual gasoline; thus, in the study of the chemical dynamics model of gasoline

substitution mixtures, the study needs to consider the olefins.

1.1.4 Toluene reference fuel (TRF)/diisobutylene (DIB)[19-21]

Ranzi et al.[22] put forward the theory that the choice of the gasoline surrogate components needs to follow

principle and similarity principle; the study of adding diisobutylene (DIB) to TRF fuel to HCCI for combustion has

become a hot research topic in the internal combustion engine in recent years.

Liang[23] studied the chemical kinetics of diisobutylene (DIB). On this basis, Liang added DIB to TRF fuel to

form a four-component surrogate mixture and proposed a TRF/DIB chemical kinetics mechanism. The mechanism

was small, including 103 kinds of components and 199 reactions. In addition, the simulation results of the

mechanism are satisfactory in the test of the shock tube and HCCI engine, which also shows that the mechanism is


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

suitable for the combustion simulation of gasoline HCCI.

1.1.5 Ethanol and its application in gasoline fuel substitution mixtures

With the increase of energy and environmental problems, ethanol has been valued by the academic

community for its better combustion emission performance. Many scholars had suggested that the addition of

ethanol to gasoline combustion cannot only reduce the emission of pollutants but also further improve the

compression ratio of internal combustion engines, thus improving the thermal efficiency of internal combustion engines. For example, Alireza Rahbari[24] studied the performance of HCCI engines using ethanol fuel. The study

showed that using ethanol fuel can improve the thermal efficiency of HCCI engines. Thus, for gasoline HCCI

combustion simulation study can add ethanol to TRF/DIB and constitute multicomponent gasoline surrogate fuels

and it is also in line with the tendency of gasoline surrogate mixture toward the multicomponent.

Zheng et al.[25] constructed a simplified mechanism of toluene oxide. Based on iso-octane, n-heptane, and

ethanol, a chemical dynamic model about adding ethanol to TRF was constructed containing 75 kinds of

components and 305 reactions. The experimental results showed that the four-component chemical dynamic model

can simulate gasoline combustion well under certain conditions.

Andrae[26], based on the detailed chemical kinetics of alternative fuel of three-component gasoline, such as

iso-octane, n-heptane, and toluene, built a detailed chemical kinetic model of petrol-fuel surrogates for five

components which contains n-heptane, iso-octane, toluene, diisobutylene (DIB), and ethanol; the model also

contains 1121 kinds of components and 4961 responses. By conducting the ignition delay test of the shock tube,

Andrae found that the experimental results have certain errors with the prediction results of the model and that the

model is very sensitive to the changes of the working conditions. To further develop the chemical kinetics of the five-component gasoline alternative fuels, Andrae et al.[27] developed a chemical kinetics simplified model that


Page 14 of 34

Page 15 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

contains 142 kinds of components and 142 reactions of the five components (iso-octane, n-heptane, toluene,

ethanol, diisobutylene (DIB)) based on the detailed chemical kinetic model. However, compared with the

experimental results, some errors still exist, and in some cases, the error is still large.

To develop the chemical kinetics of gasoline-surrogated fuel for five components, this article makes the error

between the simplified models and experiment becoming smaller. The surrogate fuels are more close to the actual

gasoline fuel and at the same time scales of calculation are more appropriate, in this study. First, a simplified

model of ethanol chemical kinetics consisting of 37 components and 78 reactions is constructed, which provides

the basis for the construction of the simplified mechanism of the five components (iso-octane, n-heptane, toluene,

diisobutylene (DIB), ethanol). Then, this study develops a suitable five-component simplified model of chemical

kinetics for HCCI combustion. The validation mechanism of the shock tube and HCCI engine is proved.

2 Computational model

2.1 Calculation software

This study uses Chemkin-Pro software as a simulation software to calculate the fuel combustion process. The

software was developed in 1980 by the Sandia Laboratory in the United States. With the development of

combustion research and computer, the software has undergone several updates and upgrades, and its functions

became more powerful. Today, Chemkin software is widely used to simulate the combustion process of fuel

because of its powerful functions, high computing power, and friendly interface.

2.2 The validation of the detailed mechanism of ethanol

In this study, the detailed mechanism of C2H5OH chemical reaction kinetics was constructed by Marinov[28], which contains 57 components and 383 reactions. Fig. 1 shows the ignition delay time verification for the detailed


Energy & Fuels

mechanism with the experiment.[29] In the two conditions, equivalent ratio is 0.5 and pressure is 3.3 bar in the first

and equivalent ratio is 0.25 and pressure is 2.0 bar in the second. The ignition delay ethanol experiment of

simulation value and experiment value present a good alignment, which shows the effectiveness of the detailed

mechanism. 0.1

0.1

0.625% C2H5OH, 7.50% O2

1.25% C2H5OH, 7.50% O2 0.01

91.25% Argon (φ=0.5) and 3.3 bar.

Ig n itio n d e la y tim e (s )

0.01

Ignition delay tim e(s)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 34

1E-3

1E-4

Experiment Simulation

1E-5

91.875% Argon (φ=0.25), and 2.0bar.

1E-3

1E-4

Experiment Simulation 1E-5

1E-6 6.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

6.8

7.0

7.2

7.4

10000K/T

7.6

7.8

8.0

8.2

8.4

8.6

10000K/T

Fig. 1 C2H5OH ignition delay time validation with the experiment[29]

3 The construction and validation of the simplification mechanism

3.1 The construction of the ethanol simplification mechanism

3.1.1 Analysis of the reaction path of C2H5OH

For the HCCI engine combustion process of ethanol, this study needs the detailed mechanism of ethanol on

the reaction path for analysis to obtain the detailed mechanism of ethanol in the important primitive reaction and

the reaction path and thus simplify the detailed mechanism of ethanol.

The data of engine parameters simulated by Chemkin-Pro software are shown in Table 1.

Table 1 Main engine technical parameters

Index

Numerical value

The cylinder diameter (mm)

115

Stroke (mm)

80

Clearance volume (cm3)

49.36


Page 17 of 34

Compression ratio

17.5

Speed (rpm)

1000

Temperature (K)

425

Pressure (atm)

1.0

Inlet valve opening/ °CA BTDC

13.5

Inlet valve closing/ °CA ABDC

38.5

Fig. 2 shows the chemical reaction of ethanol fuel in the air with equivalent ratio of 0.25. Ethanol is mainly

consumed by its own decomposition reaction R139 and dehydrogenation reaction (R143, R144, R145); besides,

ethanol is mainly generated by the reaction R140. Among them, R143, R144, and R145 are dominant in the whole

combustion process.

R139 C2H5OH(+M) = CH3 + CH2OH(+M)

R140 C2H5 + OH(+M) = C2H5OH(+M)

R143 C2H5OH + OH = C2H4OH + H2O

R144 C2H5OH + OH = CH3CHOH + H2O

R145 C2H5OH + OH = CH3CH2O + H2O

0.001 0.000 -0.001 -0.002

(mole/cm .sec)

-0.003

3

The reaction rate of C2H5OH

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

-0.004 -0.005 -0.006

R139 R140 R143 R144 R145 R149 R150 R151 R153 R155

-0.007 -0.008 -14

-12

-10

-8

-6

-4

Crank Angle/°CA

Fig. 2 The main fuel consumption rate diagram According to dehydrogenation reaction path analysis and direct decomposition reaction path analysis, an

important flow chart of ethanol is obtained, as shown in Fig. 3.


Energy & Fuels

Fig. 3 The reaction path of C2H5OH

3.1.2 Temperature sensitivity analysis

It is important to consider the effect of temperature on the combustion of ethanol; therefore, this study needs

to analyze the temperature sensitivity of the ethanol’s detailed model in the engine condition of different initial

temperatures and to determine the important reaction that is sensitive to the temperature.

Then, the temperature sensitive reaction is checked with the reaction path of the preceding text, and the

unrepeatable reaction is added to the simplified reaction path. The engine operating conditions are shown in Table

1. The initial temperature sensitivity analysis was set at 425 and 550 K.

Fig. 4 shows the reaction of temperature sensitivity in the detailed mechanism of ethanol at different initial

temperatures. Table 2 shows these primitive reactions.

R159 R158

Elementary reaction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 34

R155 R35

550K 425K

R34 R27 R23 R21 R5 R2 -2

-1

0

1

2

3

4

Temperature sensitivity coefficient


Page 19 of 34

Fig. 4 Temperature sensitivity analysis of different initial temperatures Table 2 Results of temperature sensitivity analysis

Number

Reaction

Number

Reaction

R2

O + OH = O2 + H

R5

H + O2(+N2) = HO2(+N2)

R21

HO2 + HO2 = H2O2 + O2

R23

OH + OH(+M) = H2O2(+M)

R27

H2O2 + OH = H2O + HO2

R34


R35

CH3 + HO2 = CH4 + O2

R155

C2H5OH + HO2 = CH3CHOH + H2O2

R158

CH3CH2O + M = CH3HCO + H + M

R159

CH3CH2O + M = CH3 + CH2O + M

Reaction paths of R35 and R155 were not present in the reaction path constructed in the previous article, and

the mechanism of ethanol simplification should be added. The reaction path of product CH3CHOH is analyzed in simplified mechanism. The consumption path of the product of R35 and the product of R155 is shown in Fig. 5 (a)

and Fig. 5 (b). The main consumption reaction of CH4 was R31 and R32, and the main consumption reaction of H2O2 was R23 and R27. The simplified mechanism was included.

0.01

0.04

R21 R22 R23 R26 R27 R33 R155 R156 R183 R184

0.03

T h e re a c tio n ra te o f H 2 O 2 ( m o le /m 3 .s e c )

0.00

T h e re a c tio n ra te o f C H 4 (m o le /m 3 .s e c )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

R29 R30 R31 R32 R35 R122 R152 R153 R181 R205

-0.01

-0.02

-0.03

-0.04 -9

-8

-7

-6

-5

0.02 0.01 0.00 -0.01 -0.02 -0.03 -0.04 -9

Crank Angle/° CA

(a) CH4

-8

-7

-6

-5

Crank Angle/° CA (b) H2O2

Fig. 5 The reaction rate analysis of CH4 and H2O2 By simplifying the mechanism of ethanol chemical kinetics, a simplified mechanism of ethanol which

contains 37 kinds of components and 78 reactions was obtained, and the simplified mechanism of ethanol is

presented in the Appendix.

3.1.3 Ignition delay time validation


Energy & Fuels

In Fig. 6, the condition of the temperature range is at 1080 k–1660 k, the pressure at 2 and 3.4 bar, the

stoichiometric ratio at 0.25, 0.625% C2H5OH, 7.5% O2, and 91.875% Ar. The simulation results of ethanol detailed model and the simplified mechanism of ethanol were constructed by shock wave tube experiment and a comparison with the experimental value of Dunphy et al.[29] had been made. For Fig. 6 (a), the pressure is 2 bar,

and for Fig. 6 (b), the pressure is 3.4 bar, and the other conditions are as mentioned above. 0.1

0.1

0.625%C2H5OH, 7.50% O2 91.25% Argon (φ= 0.25), and 2 bar.

0.01


0.01


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 34

1E-3

1E-4

Experiment Simulation （ Detailed） Simulation（ Simplified）

1E-5

0.625% C2H5OH, 7.50% O2 91.875% Argon (φ=0.5), and 3.4 bar.

1E-3

1E-4

Experiment Simulation （ Detailed） Simulation（ Simplified）

1E-5

1E-6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

10000/T(K)

10000K/T

(a) P = 2 bar

(b) P = 3.4 bar

Fig. 6 Comparison of the fuel ignition delay time between simulation and experiment[28] Fig. 6 (a) and Fig. 6 (b) show the detailed chemical kinetics mechanism of ethanol constructed by Marinov[28]

and the ethanol simplified mechanism of this chapter. The simulated results of the shock wave tube are

approximately the same as the experimental values. In addition, the ethanol simplification mechanism is in good

agreement with the experimental values in all working conditions.

3.1.4 HCCI engine validation

The verification of chemical mechanism needs to satisfy not only the verification of ignition delay time but

also the change of the state of HCCI engine cylinder. Its validation is done by simplified mechanism compared with the detailed mechanism constructed by Marinov[28] of engine parameters. The engine parameters are the same

as in Table 1, and two working conditions are selected for verification, as shown in Table 3.


Page 21 of 34

Table 3 Operation condition of HCCI engine

Condition

Equivalence ratio



Speed (rpm)

1

0.25

0.2

550

1000

2

0.25

0.1

425

1000

2000 80



1800 60

40

20


0

1600 1400 1200 1000 800


600 400

-50

-40

-30

-20

-10

0

10

20

30

40

50

-50

-40

-30

-20

Crank Angle/°CA

-10

0

10

20

30

40

50

Crank Angle/°CA

(a) Condition 1 2400

160

2200

140



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

120 100 80 60 40


20

2000 1800 1600 1400 1200


1000 800 600

0

400 -40

-20

0

20

40

-50

-40

-30

Crank Angle/°CA

-20

-10

0

10

20

30

40

50

Crank Angle/°CA

(b) Condition 2 Fig. 7 Comparison of internal pressure and internal temperature of cylinder From Fig. 7 in both working conditions, the cylinder internal simulation of ethanol simplification mechanism

is more consistent with the cylinder internal simulation of ethanol. From the point of ignition time point, ignition

delay time of the mechanism of ethanol simplified ignition was later than the detailed mechanism of ethanol, the

main reason is that the step removed some reactions which can promote ethanol oxidation reaction, making

ignition time slightly delay. However, considering the factors of model scale, the simplification mechanism is


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

acceptable.

3.2 The construction and validation of the five-component fuel simplification mechanism

3.2.1 The construction of the five-component fuel simplification mechanism

In this chapter, the simplified mechanism of five-component fuel is based on the simplified mechanism of TRF/DIB[23], adding the simplified mechanism of ethanol as mentioned earlier, and then, the coefficients of the

two mechanisms superimposed on the reaction were selected. In addition, the study needs to take into account the

intersecting reactions and sensitive chemical reactions of the newly added ethanol and TRF/DIB. According to the sensitive analysis of the addition of ethanol to the basic fuels constructed by Andrae et al.[27], these more sensitive

responses were taken from the detailed mechanism of the Andare’s five-component mechanisms for sensitive

analysis of the addition of ethanol to basic fuels.

For these reactions, we add those that are related to ethanol to the five-component simplified mechanism. In addition, according to previous research,[28][30] the simplified mechanism of the newly added ethanol and the simplified mechanism of TRF/DIB[23] were screened and then added to the five-component simplification

mechanism of the initial construction. The other reactions are filtered and then added to the five-component

simplification mechanism. In addition, the results and sources of the coefficient selection of the two mechanisms

superposition reaction are shown in Table 4.

Table 4 The reactions related to ethanol in the paper of Andrae[27]

C2H5OH + OH = CH3CHOH + H2O C2H5OH + OH = CH3CH2O + H2O C2H5OH + HO2 = CH3CHOH + H2O2 JC8H16 => IC4H8 + CH2CHCH2 + CH3 C2H3 + O2 = CH2HCO + O C2H4 + OH = C2H3 + H2O CH3 + HO2 = CH3O + OH OC8H15O + O2 => C2H3 + 2CH2O + H2CCCH2 + CH3 + HO2


Page 22 of 34

Page 23 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

CH3 + HO2 = CH3O + OH Table 5 The coefficient table for small molecule reactions

The reaction rate K = Aܶ ௕ ‫ܧ‬/ܴܶ

A: The former factor, b: The temperature index, E: Activation energy

‫ܣ‬௔

Reaction

݊௔

‫ܧ‬௔

Ref

C2H4 + OH => C2H3 + H2O

8.02E+13

0

5955

[30]

C2H4 + H(+M) = C2H5(+M)

1.10E+12

0.5

1822

[30]

C2H3 + O2 = CH2CHO + O

2.50E+15

−0.8

3135

[30]

C2H2 + O = HCCO + H

1.40E+07

2

1900

[28]

C2H2 + O = CH2 + CO

6.10E+06

2

1900

[30]

HCCO + O2 => HCO + CO + O

9.78E+11

0

850

[28]

HCCO + O2 => HCO + CO2

6.52E+11

0

850

[28]

CH3CO(+M) = CH3 + CO(+M)

2.80E+13

0

17100

[30]

CH2CO + OH = HCCO + H2O

1.00E+07

2

3000

[28]


8.00E+12

0

0

[30]

CH3 + O = CH2O + H

8.40E+13

0

0

[30]

CH2 + O2 = CO + H2O

2.20E+22

−3.3

2867

[30]

CO + OH = CO2 + H

3.09E+11

0

733.81

[30]

CH3OH + OH = CH3O + H2O

1.00E+06

2.1

497

[28]

This section finally formed a five-component (iso-octane, n-heptane, toluene, diisobutylene (DIB), ethanol)

fuel chemical kinetics mechanism of the simplified model that contains 124 components and 124 reactions; the

details are shown in the Appendix.

3.2.2 Ignition delay time validation

First, this study adopts the ignition delay data of four gasoline surrogate mixtures to verify the effectiveness

of the five-component simplification mechanism. The composition and its proportion are shown in Table 6. The

fuels were tested under the initial pressure of 10, 30, and 50 bar except the fuel C. The experimental data were measured at the temperature range of 690–1200 K by Fikri et al.[31][32]. The ignition delay time verification of fuel C was under the initial pressure of 10 and 30 bar, and its experimental data were measured by Cancino et al.[33] in

the temperature range of 720–1220 K. For fuel B and fuel C, this study also includes the simulation results of the


Energy & Fuels

five-component detailed mechanism of Andare[26] construction and the five-component simplified mechanism[27].

Table 7 shows the details of these three mechanisms.

Table 6 Volume fraction of fuel components

Surrogate mixture

n-heptane

Toluene

Iso-octane

Ethanol

A

18%

62%

20%

B

20%

45%

25%

C

22%

25%

30%

10%

D

10.2%

12%

37.8%

40%

Eiisobutylene (DIB)

Ref.

[31] 10%

[31]

13%

[33] [32]

Table 7 Comparison of three types of five-component mechanism

Name

Components

Reaction

Type

Ref

Andrae

1121

4961

Detail

[26]

Andrae

143

672

Simplification

[27]

This paper

124

244


1E-3

1E-4

Experiment This paper Andrae’ detailed Andrae’s simplified

1E-5

0.01

Ignition delay time （ s）

0.01

Simplification 0.1

0.1

Ignition delay time （ s）

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 34


1E-3

1E-4

Experiment This paper Andrae’s detailed Andrae’s simplified

1E-5

1E-6

1E-6 0.80

0.85

0.90

0.95

1.00

0.80

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

1.25

1000K/T

1000K/T

（a）

（b）

Fig. 8 Comparison of fuel C ignition delay time between mechanism and experiment[33] The comparison of ignition delay data for the simplified mechanism and five-component to replace gasoline

mixture C was shown in Fig 8. When the equivalent ratio is 1, the initial temperature of the shock-tube ignition

delay experiment ranges from 720 to 1220 K, and the initial pressure was 10 and 30 bar. This study compared the five-component simplification mechanism, the five-component detailed mechanism[26] of Andrae, the five-component simplified mechanism[27] of Andrae, and the experimental data obtained by Cancino et al.[33]. The


Page 25 of 34

initial pressure of Fig 8 (a) is 10 bar, and the initial pressure of Fig 8 (b) is 30 bar. The tendency of ignition delay

time with temperature for the five-component simplification mechanism in this study, the five-component detailed mechanism[26] of Andrae and his simplified mechanism[27] can fit well with the pressure of 10 bar and 30 bar. The

simulation data of the five-component simplification mechanism constructed in this study are more closely related to the experimental data than the five-component detailed mechanism[26] and the simplified mechanism[27]

constructed by Andrae. When the initial pressure was 30 bar and the temperature varies from 720 K to 1000 K, the

relative error of the simulation value of the simplified mechanism in this study is small.

Comparing Fig. 8 (a) and Fig. 8 (b), the relationship between the shock-tube ignition delay times with

temperature change can be more accurately reflected in the condition of initial pressure of 30 bar than the initial

pressure of 10 bar in the simplified mechanism of this study. That means that compared with the low pressure (10

bar), the simplified mechanism of this study is more accurate in predicting the ignition delay time when the pressure is high (30 bar). In addition, the five-component simplified mechanism completed by Andrae et al.[27]

matches well with the experiment data when the initial pressure is 10 and 30 bar based on Fig. 8. Therefore, in the

process of constructing the five-component simplification mechanism, to refer to the sensitivity analysis of the mechanism is feasible.[27] 0.1


0.01

1E-3


1E-4

1E-5 0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1.02

1.04


0.1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

0.01


1E-3


1E-4

1E-5 0.85

0.90

0.95

1.00

1.05

1000K/T

1000K/T

(a)

(b)


1.10

1.15

1.20

1.25

Energy & Fuels

0.1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 34

0.01


1E-3

1E-4


1E-5

1E-6 0.90

0.95

1.00

1.05

1.10

1.15

1.20

1000K/T

(c) Fig. 9 Comparison of fuel B ignition delay time between mechanism and experiment[31] Fig. 9 shows the comparison of the ignition delay data between the mechanism and four-component gasoline substitution mixture.[31] The equivalent ratio is 1, the shock-tube ignition delay time experimental initial

temperature ranges from 690 K to 1200 K, and the initial pressure in Fig. 9 (a) is 10 bar, 30 bar for Fig 9 (b) and 50

bar for Fig 9 (c).

Fig. 9 shows the comparison between the results of the three mechanisms in the initial pressure of 10, 30, and 50 bar and the experimental results obtained by Fikri et al.[31] In general, the simulation value of the

five-component simplification mechanism constructed in this study is closer to the experimental data than the five-component detailed mechanism[26] proposed by Andrae and the five-component simplified mechanism.[27]

Especially in the case of middle pressure and high pressure, such as 30 and 50 bar, the mechanism of this study predicts the ignition delay time more accurately than the detailed mechanism[26] and simplified mechanism[27]

proposed by Andrae, and the relative error of the mechanism and the experimental data is smaller.

Fig. 10 (a) shows the comparison of the ignition delay data between the mechanism in this study and

four-component gasoline mixture D. The equivalent ratio is 1, initial shock-tube ignition delay experiment

temperature ranges from 690 K to 1200 K, and the initial pressure is 10, 30, and 50 bar. Comparing the combustion

simulation results of the five-component simplified mechanism and the experimental data obtained by Cancino et al.[32], we show that the simulation results of the TRF/ethanol four-component fuel are more consistent with the


Page 27 of 34

corresponding experimental values under high pressure (50 bar).

Fig. 10 (b) shows the comparison of the ignition delay data between the mechanism in this study and

four-component gasoline mixture A. When the equivalent ratio is 1, the initial temperature ranges from 690 K to

1200 K, and the initial pressure is 10 bar, 30 bar and 50 bar, Making a comparison between the combustion simulation results of the five-component simplified mechanism and the experimental data obtained by Fikri et al.[31]

Obviously, the relative error in the prediction of the ignition delay between the low pressure (10 bar) and the

experimental value is relatively large, especially in the low temperature part. Under medium pressure (30 bar), the

relative error in the prediction of the ignition delay between the low pressure (10 bar) and the experimental value is

large. However, under the high pressure (50 bar), the simulation results of this mechanism matches well with the

experimental value, and the error in the low temperature part is relatively small. Therefore, the mechanism of this

study has to be further modified in the low temperature. 0.1

0.1

Ethanol / iso-Octane / n-Heptane / Toluene - air [40% / 37.8% / 10.2% / 12%] φ = 1.0

0.01

Ignition delay time（ S)

0.01

Ignition delay time（ s）

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

1E-3


1E-4

1E-5

1E-6 0.8


1E-3


1E-4

1E-5

1E-6

0.9

1.0

1.1

1.2

1.3

0.8

0.9

1.0

1.1

1.2

1.3

1000K/T

1000K/T

（a）

（b）

Fig. 10 Comparison of ignition delay time between mechanism and experiment[31][32] In summary, compared to the five-component detailed[26] mechanism and five-component simplified mechanism[27] constructed by Andrae, the mechanism of this study has two advantages. On the one hand, the

mechanism of this study is more accurate than the detailed mechanism and simplified mechanism made by Andrae

in predicting the ignition delay times, on the other hand, this mechanism is smaller than the previous two in size


Energy & Fuels

and it can greatly shorten the computation time, especially when the mechanism and three dimensional calculation

software are coupling calculated.

3.2.3 HCCI engine validation

The further verification of the five-component simplification mechanism is realized by HCCI engine verification. The engine details are shown in the article[27] and the two operating points are selected for verification.

The specific data is shown in Table 9.

Four gasoline substitution mixture was selected in the experiment, besides the fuel A and B, there were two

gasoline substitution mixture (TRF) added, the details are shown in Table 8.

Table 8 The volume fraction of each component of the fuel

Surrogate mixture

n-heptane

A

18%

B

20%

45%

25%

E

17%

20%

63%

[34]

F

17%

14%

69%

[34]

Toluene

Iso-octane

Ethanol

62%

20%

Diisobutylene (DIB)

Ref [31]

10%

[31]

Table 9 HCCI engine operating condition

Condition

Equivalence ratio



Speed (rpm)

1

0.25

0.1

523

1000

2

0.25

0.2

353

1000

50

40

80


70



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 34

30

20

10

OP1 experiment Simulation 0

60


50 40 30 20


10 0

-70

-60

-50

-40

-30

-20

-10

0

10

20

-70

-60

-50

Crank Angle/°CA

-40

-30

-20

-10

0

10

Crank Angle/°CA

Fig. 11 Comparison of fuel A ignition delay time between mechanism and experiment[27]


20

30

Page 29 of 34

50

60



Toluene / iso-Octane / n-Heptane / Diisobutylene - air [45% / 25% / 20% / 10% ] φ = 0.25

70

Toluene / iso-Octane / n-Heptane / Diisobutylene - air [45% / 25% / 20% / 10% ] φ=0.25

40

30

20

10


0

50 40 30 20


10 0

-70

-60

-50

-40

-30

-20

-10

0

10

-70

20

-60

-50

-40

-30

-20

-10

0

10

20

Crank Angle/°CA

Crank Angle/°CA

Fig. 12 Comparison of fuel B ignition delay time between mechanism and experiment[27] n-Heptane / iso-Octane / Toluene - air [17% / 63% / 20%] φ = 0.25

40

100



50

30

20

10


0 -70

-60

-50

-40

-30

-20

-10

0

10

80


60

40


OP2

20

20

-60

-40

Crank Angle/°CA

-20

0

20

Crank Angle/°CA

Fig. 13 Comparison of fuel E ignition delay time between mechanism and experiment[27] 120

40


30

20


10

-60

-40

-20

0


50


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

20

100


80

60

40


OP2

20

-70

-60

-50

Crank Angle/°CA

-40

-30

-20

-10

0

10

20

Crank Angle/°CA

Fig. 14 Comparison of fuel F ignition delay time between mechanism and experiment[27] As can be seen from the Fig 11, the mechanism in cylinder pressure curve can fit the experimental data well

in cylinder pressure trend of change in OP1 and OP2 condition. The mutation point of the pressure in the cylinder

are almost identical, the same as their fire moment. For OP2 condition, the pressure mutation point in the cylinder

appears when the pressure of the cylinder decreases slightly.

The Fig 12 shows that TRF/DIB in OP1 and OP2 conditions in this study, the mechanism of crankshaft angle

change trend in cylinder pressure with better agreement with the experimental results, and the curve doesn't have a


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

mutation point, it means that there is no obvious fire in this working condition.

It can be seen from Fig 13 and Fig 14 that, the fuel E and F in OP1 and OP2 operating conditions, pressure of

the cylinder of this study is consistent with the experimental results.

Above all, from the results of ignition delay time verification and HCCI engine verification, the

five-component simplification mechanism constructed in this study is reliable, the chemical dynamic

simplification model can effectively simulate the combustion process of HCCI engine.

4 Conclusion

(1) The main consumption paths of HCCI combustion of ethanol are direct decomposition reaction and

dehydrogenation reaction. In the dehydrogenation reaction path of ethanol, ethanol first generates C2H4OH, CH3CHOH and CH3CH2O under the action of OH. The main intermediate products of ethanol dehydrogenation reaction pathway are CH3HCO, CH2HCO, HCOOH, CH3CO, CH2O, etc. In the direct decomposition reaction path of ethanol, ethanol is directly decomposed into CH3, CH2OH and C2H5 by reaction R139 and R140. CH3O, HCCO and CH2 are the main intermediate products in the direct decomposition path of ethanol. Through the ethanol reaction path and temperature sensitivity analysis, a simplified mechanism of ethanol containing 37 components

and 78 reactions was obtained and a flow diagram of the simplified mechanism was constructed. The simplified

mechanism is in good agreement with the experimental value and detailed mechanism in the test of ignition delay

and HCCI engine combustion validation.

(2) Based on the simplified mechanism of four-component fuel (iso-octane, n-heptane, toluene, diisobutylene

(DIB)), combining the mechanism of ethanol simplification, which was constructed in the last chapter, this study

finally constitutes a simplified mechanism of the five-component fuel chemical kinetics that contains 124

components and 244 reactions.


Page 30 of 34

Page 31 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(3) The simulation value of the five-component simplified mechanism is compared with the ignition delay of

the four different components of gasoline in the shock-tube condition, and the results show that the ignition delay

time and the temperature curve of the simulation form can fit well with the results. In summary, compared to the five-component detailed[26] mechanism and five-component simplified mechanism[27] constructed by Andrae, the

mechanism of this study has two advantages. On the one hand, the mechanism of this study is more accurate than

the detailed mechanism and simplified mechanism made by Andrae in predicting the ignition delay times, on the

other hand, this mechanism is smaller than the previous two in size and it can greatly shorten the computation time,

especially when the mechanism and three dimensional calculation software are coupling calculated.

(4) The simulation value of the five-component simplification mechanism is compared with that of the four

groups of gasoline alternative fuel in the cylinder under HCCI condition. The results show that the change trend of

the internal pressure and the crankshaft angle of the simulation can fit the experimental results well. As can be

seen from the Fig 11, the mutation point of the pressure in the cylinder are almost identical, the same as their fire

moment. For OP2 condition, the pressure mutation point in the cylinder appears when the pressure of the cylinder

decreases slightly. As can be seen from the Fig 12, the curve doesn't have a mutation point, it means that there is

no obvious fire in this working condition.

Acknowledgements

This research is supported by the National Natural Science Foundation of China Program (Grant No.51776024).

References

(1) Kimura, S.; Aoki, O.; Ogawa, H.; Muranaka S.; Enomoto Y. New Combustion Concept for Ultra-Clean and High-Efficiency Small DI Diesel Engines[C]. SAE Paper No. 1999-01-3681． (2) Kimura, S.; Aoki, O.; Kitahara, Y.; Aiyoshizawa, E. Ultra-Clean Combustion


Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Technology Combining a Low-Temperature and Premixed Combustion Concept for Meeting Future Emission Standards[C]. SAE Paper No. 2001-01-0200． (3) Jeon, J.; Bae, C. The effects of hydrogen addition on engine power and emission in DME premixed charge compression ignition engine, Int. J. Hydrogen Energy. 2013, 38 (1), 265-273. (4) Laguitton, O.; Crua, C.; Cowell, T.; Heikal, M. R.; Gold, M. R. The effect of compression ratio on exhaust emissions from a PCCI diesel engine, Energy Convers. Manage.2007, 48 (11), 2918-2924. (5) Jacobs, T. J.; Assanis, D. N. The attainment of premixed compression ignition low-temperature combustion in a compression ignition direct injection engine. Proceedings of the Combustion Institute. 2007 ,(31), 2913-2920. (6) Jia, Z.; Denbratt, I. Experimental Investigation of Natural Gas-Diesel Dual-Fuel RCCI in a Heavy-Duty Engine, SAE Paper. 2015, 2015-01-0838. (7) Benajes, J.; Molina, S.; García, A.; Belarte, E.; Vanvolsem, M. An investigation on RCCI combustion in a heavy duty diesel engine using in-cylinder blending of diesel and gasoline fuels, Appl. Therm. Eng. 2014, 63, 66-76. (8) Yao, M.; Zheng, Z.; Liu, H. Progress and recent trends in homogeneous charge compression ignition (HCCI) engines, Prog. Energy Combust.2009, 35 (5), 398-437. (9) Neshat, E.; Saray, R. K. Development of a new multi zone model for prediction of HCCI (homogenous charge compression ignition) engine combustion, performance and emission characteristics, Energy. 2014, 73 (7), 325-339. (10) Jia, M.; Xie, M. Z. The iso-octane oxide chemical kinetics model suitable for HCCI engine [C] China internal combustion engine society 2005 annual meeting and APC2005 academic joint academic annual meeting. 2005. (11) Curran, H. J.; Pitz, W. J.; Westbrook, C. K.; Callahan, G. V.; Dryer, F. L. Oxidation of automotive primary reference fuels at elevated pressures[J]. Symposium on Combustion. 1999, 27(1), 379-387. (12) Ra, Y.; Reitz, R. D. A reduced chemical kinetic model for IC engine combustion simulations with primary reference fuels[J]. Combustion & Flame. 2008, 155(4), 713-738. ACS Paragon Plus Environment

Page 32 of 34

Page 33 of 34 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Energy & Fuels

(13) Raj, A.; Prada, I. D. C.; Amer, A. A.; Chung, S. H. A reaction mechanism for gasoline surrogate fuels for large polycyclic aromatic hydrocarbons. Combust and Flame. 2012, 159 (2), 500-515. (14) Mehl, M.; Pitz, W. J.; Westbrook, C. K.; Curran, H. J. Kinetic modeling of gasoline surrogate components and mixtures under engine conditions. Proceedings of the Combustion Institute. 2011, 33 (1), 193-200. (15) Andrae, J. C. G.; Brinck, T.; Kalghatgi, G. T. HCCI experiments with toluene reference fuels modeled by a semidetailed chemical kinetic model. Combust and Flame.2008, 155 (4), 696-712. (16) Pitz, W. J.; Cernansky, N. P.; Dryer, F L. Development of an Experimental Database and Chemical Kinetic Models for Surrogate Gasoline Fuels[C]. SAE Paper. 2007, 2007-01- 0175. (17) Chaos, M.; Zhao, Z.; Kazakov, A.; Gokulakrishnan, P.; Angioletti, M. A PRF + toluene surrogate fuel model for simulating gasoline kinetics[J]. 2007, 25-28. (18) Machrafi, H.; Cavadias, S.; Amouroux, J. The development and experimental validation of a reduced ternary kinetic mechanism for the auto-ignition at HCCI conditions, proposing a global reaction path for ternary gasoline surrogates [J]. Fuel Processing Technology. 2009, 90, 247-263. (19) Wang, Y.; Yao, M.; Zheng, Z. A semi-detailed chemical kinetic model of a gasoline surrogatefuel[J]. Fuel. 2013, 113, 347-356. (20) Mittal, G.; Sung, C. J. Homogeneous charge compression ignition of binary fuel blends[J].Combustion and Flame. 2008, 155(3), 431-439. (21) Wang, Y. F. Numerical simulation and experimental study on the mechanism of low temperature combustion of gasoline fuel[D]. Tianjin university. 2014. (22) Ranzi, E,; Frassoldati, A.; Grana, R.; Cuoci, A.; Faravelli, T.; Kelley, A. P.; Law, C. K. Hierarchical and comparative kinetic modeling of laminar flame speeds of hydrocarbon and oxygenated fuels[J]. Progress in Energy and Combustion Science.2012, 38(4), 468-501. (23) Liang, Z. L. Gasoline fuel alternative mixture research in the chemical dynamics model[D]. Chongqing university. 2015. ACS Paragon Plus Environment

Energy & Fuels 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(24) Rahbari, A. Effect of inlet temperature and equivalence ratio on HCCI engine performance fuelled with ethanol:Numerical investigation[J]. Journal of Central South University. 2016, 23(1), 122-129. (25) Zheng, D.; Zhong, B. J. Four components of petrol chemical kinetics model of alternative fuels[J]. Journal of 26 singhua university natural science. 2015(10), 1135-1142. (26) Andrae, J. C. G. Development of a detailed kinetic model for gasoline surrogate fuels[J]. Fuel. 2008, 87(87), 2013-2022. (27) Andrae, J. C. G.; Head, R. A. HCCI experiments with gasoline surrogate fuels modeled by a semidetailed chemical kinetic model [J]. Combustion and Flame. 2008, 156, 842-851. (28) Marinov, N. M. A detailed chemical kinetic model for high temperature ethanol oxidation[J]. International Journal of Chemical Kinetic. 1999, 31(3), 183-220. (29) Dunphy, M. P.; Simmie, J. M. Journal of the Chemical Society, Faraday Transactions. 1991, 87, 1691-1695, 2549-2559. (30).Tan, Y. X. Gasoline substitute mixture component ratio to determine and study in the chemical dynamics model[D]. Chongqing university. 2014. (31) Fikri, M.; Herzler, J.; Starke, R.; Schulz, C.; Roth, P.; Kalghatgi, G. T. Autoignition of gasoline surrogates mixtures at intermediate temperatures and high pressures[J]. Combustion & Flame. 2008, 152(1-2), 276-281. (32) Cancino, L. R.; Fikri, M.; Oliveira, A. A. M.; Schulz, C. Autoignition of gasoline surrogate mixtures at intermediate temperatures and high pressures: Experimental and numerical approaches[J]. Proceedings of the Combustion Institute. 2009, 32(1), 501-508. (33) Cancino, L. R.; Fikri, M.; Oliveira, .A. A. M.; Schulz, C. Ignition delay times of ethanol-containing multi-component gasoline surrogates: Shock-tube experiments and detailed modeling[J]. Fuel. 2011, 90(3), 1238-1244. (34) Gauthier, B. M.; Davidson, D. F.; Hanson, R. K. Shock tube determination of ignition delay times in full-blend and surrogate fuel mixtures. Combust and Flame. 2004, 139, 300-311. ACS Paragon Plus Environment

Page 34 of 34

Construction and Validation of a Five-Component Fuel Simplification

Recommend Documents