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Research Papers: Internal Combustion Engines

Knocking Suppression by Stratified Stoichiometric Mixture With Two-Zone Homogeneity in a DISI Engine

[+] Author and Article Information
Shi-jin Shuai

State Key Laboratory of Automotive
Safety and Energy,
Tsinghua University,
Beijing 100084, China

Contributed by the IC Engine Division for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 21, 2010; final manuscript received May 5, 2011; published online November 26, 2012. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(1), 012803 (Nov 26, 2012) (9 pages) Paper No: GTP-10-1107; doi: 10.1115/1.4005113 History: Received April 21, 2010; Revised May 05, 2011

Knocking is the main obstacle of increasing the compression ratio in order to improve the thermal efficiency of gasoline engines. This paper proposes a concept of a stratified stoichiometric mixture (SSM) with two-zone homogeneity (TZH) for suppressing knocking and validated the concept by means of a numerical simulation and an experimental study in a DISI engine. The results show that the SSM can effectively suppress knocking and the knocking intensity decreases when the zone around the spark plug is richer and the end-gas zone is leaner. The less rich zone (fuel/air equivalent ratio of ϕ ≤ 1.2) of the SSM can speed up the initial burning velocity in order to avoid a thermal efficiency decrease, while the over rich zone (ϕ > 1.2) would decrease the combustion velocity when knocking was suppressed. The SSM leads to higher CO and lower HC and NOx emissions, which can be effectively after-treated using a three-way catalyst. The SSM can also reduce the decrease of power output compared to the method of retarding spark timing for suppressing knocking and has better fuel economy and fewer emissions than the method of enriching the mixture. The TZH can effectively alleviate combustion deterioration and soot formation due to the stratified mixture combustion. As a result, the SSM with TZH suppresses knocking, thus simultaneously lowering fuel consumption and emissions.

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Figures

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Fig. 1

Schematic diagram of the SSM with TZH

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Fig. 2

Schematic of the engine test system

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Fig. 3

Cylinder pressure and knocking wave

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Fig. 4

Computational mesh

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Fig. 5

Calibration of the numerical model

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Fig. 6

Simulation results of the heat release rate with different equivalent ratios

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Fig. 7

Simulation and experiment results of the knocking intensity with different equivalent ratios

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Fig. 8

HSM and the SSM at spark timing

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Fig. 9

Heat release rates of the HSM and the SSM

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Fig. 10

Knocking intensity of the HSM and the SSM

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Fig. 11

Simulation results of the heat release rate and knocking intensity with different stratified ratios

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Fig. 12

Mixture formation by single-stage and two-stage injection in the DISI engine

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Fig. 13

Experimental results of the HSM and the SSM

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Fig. 14

Emissions of the HSM and the SSM

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Fig. 15

Knocking intensity and the IMEP of the three methods

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Fig. 16

Emissions of the enriching mixture method

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Fig. 17

Equivalence ratio and vaporization fraction with different SOI2 and gb2/gb

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Fig. 18

Comparison of the combustion characteristics using homogeneous and stratified mixtures

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Fig. 19

Combustion efficiencies of the one-stage injection and the two-stage injection

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Fig. 20

Soot emissions with the homogeneous and stratified mixtures

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