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Research Papers

# Effects of Exhaust Gas Recirculation Constituents on Methyl Decanoate Auto-Ignition: A Kinetic Study

[+] Author and Article Information
Jiabo Zhang

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: zhangjiabo@sjtu.edu.cn

Jiaqi Zhai

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: digakii@sjtu.edu.cn

Dehao Ju

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: d.ju@sjtu.edu.cn

Zhen Huang

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: z-huang@sjtu.edu.cn

Dong Han

Key Laboratory of Power Machinery
and Engineering,
Ministry of Education,
Shanghai Jiao Tong University,
Shanghai 200240, China
e-mail: dong_han@sjtu.edu.cn

1Corresponding author.

Manuscript received September 26, 2017; final manuscript received June 21, 2018; published online August 9, 2018. Assoc. Editor: David L. S. Hung.

J. Eng. Gas Turbines Power 140(12), 121001 (Aug 09, 2018) (13 pages) Paper No: GTP-17-1531; doi: 10.1115/1.4040682 History: Received September 26, 2017; Revised June 21, 2018

## Abstract

Biodiesel engines are found to have improved soot, hydrocarbon (HC), and carbon monoxide (CO) emissions, with modestly increased nitrogen oxides (NOx) emissions. Exhaust gas recirculation (EGR) could be used for the NOx emissions control, especially in the fuel-kinetics-dominated engine combustion concepts. A detailed chemical kinetic model of methyl decanoate (MD), a biodiesel surrogate fuel, was used here to simulate the two-stage auto-ignition process of biodiesel with EGR addition. The effects of EGR constituents, including carbon dioxide (CO2), water vapor (H2O), CO and H2, were identified in a constant-pressure ignition process and in a variable pressure, variable volume process. Firstly, numerical methods were used to isolate the dilution, thermal, and chemical effects of CO2 and H2O at a constant pressure. It was found that in the biodiesel auto-ignition processes, the dilution effects of CO2 and H2O always played the primary role. Their thermal and chemical effects mainly influenced the second-stage ignition, and the chemical effect of H2O was more significant than CO2. The triple effects of CO and H2 were also analyzed at the same temperature and pressure conditions. Additionally, the sensitivity analysis and reaction pathway analysis were conducted to elucidate the chemical effects of CO and H2 on the ignition processes at different temperatures. Finally, based on a variable pressure, variable volume model simulating the engine compression stroke, the effects of CO2, H2O, CO and H2 addition under the engine operational conditions were studied and compared to those under the constant pressure conditions.

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## Figures

Fig. 3

The dilution, thermal and chemical effects of CO2 (the left side) and H2O (the right side) on the temperature histories during the MD auto-ignition at different initial temperatures

Fig. 5

Direct chemical effects of H2O addition on the reaction rates of HO2+OH=H2O+O2 and CH2O+OH=HCO+H2O at all initial temperatures

Fig. 4

Indirect and direct chemical effects of H2O addition on the total ignition delay of MD auto-ignition (FH2O non: without chemical effects, FH2O ind chem: only with indirect chemical effect, Real H2O: all chemical effects)

Fig. 2

Comparison of the measured ignition delay times by Li et al. [27] with the predictions of the Herbinet model for MD/air/EGR mixtures at 20 atm

Fig. 1

Ignition delay times of the MD/air mixture versus initial temperature. (Line: calculation based on the MD mechanism by Herbinet et al. [24]; Dot: experimental measurements by Wang and Oehlschlaeger [25])

Fig. 14

Contribution of H2O/CO2 triple effects to MD auto-ignition under the constant pressure condition (Pinitial = 2 MPa, φbase = 0.5) and the variable volume and pressure condition (Pinitial = 1 atm, engine speed = 1500 rpm, φbase = 0.5)

Fig. 6

Normalized rate constant sensitivity coefficients of chemical reactions H2O participating in as the third body on the total ignition delay of MD auto-ignition

Fig. 7

The effects of H2 and CO addition on the temperature histories of MD auto-ignition at different initial temperatures

Fig. 8

Reaction scheme of MD at the initial temperature of 680K

Fig. 9

Top 20 sensitive reactions of the first-stage ignition with or without H2 and CO addition at T0 = 680 K

Fig. 10

Top 10 sensitive reactions in the second stage ignition with or without H2 and CO addition at T0 = 680 K.

Fig. 11

The mole fraction of MO7D, MP2D, C8H16-1 and C7H14-1 with or without H2 and CO addition at T0 = 1000 K.

Fig. 12

Contributions of the main elementary reactions to the production and consumption of H radical during the MD combustion with or without H2 and CO at T0 = 1000 K

Fig. 13

The dilution, thermal, and chemical effects of CO2/H2O on the temperature and pressure history during MD auto-ignition under a variable volume and pressure condition (Pinitial = 1 atm, engine speed = 1500 rpm, φbase = 0.5)

Fig. 15

The dilution, thermal and chemical effects of H2O and CO2 on HO2 and H2O2 concentration during MD auto-ignition at the initial temperature of 360 K (D: dilution, T: thermal, C: chemical, Pinitial = 1 atm, engine speed = 1500 rpm, φbase = 0.5)

Fig. 16

The dilution, thermal, and chemical effects of H2/CO on the temperature and pressure history during MD auto-ignition under a variable volume and pressure condition (Pinitial = 1 atm, engine speed = 1500 rpm, φbase = 0.5).

## Errata

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