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research-article

Numerical Investigation on Mixture Formation in a Turbocharged Port-Injection Natural Gas Engine using Multiple Cycle Simulation

[+] Author and Article Information
Zhenkuo Wu

State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, College of Mechanical and Vehicle Engineering, Hunan University, Changsha, 410082, Hunan, China
wuzhenkuo@gmail.com

Zhiyu Han

State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, College of Mechanical and Vehicle Engineering, Hunan University, Changsha, 410082, Hunan, China
hanzhiyu@yahoo.com

1Corresponding author.

ASME doi:10.1115/1.4039106 History: Received June 17, 2017; Revised December 16, 2017

Abstract

In the present study, multi-dimensional computational fluid dynamics simulations were carried out to study mixture formation in a turbocharged port-injection natural gas engine. In order to achieve robust simulation results, multiple cycle simulation was employed to remove the inaccuracies of initial conditions setting. Firstly, the minimal number of simulation cycles required to obtain convergent cycle to cycle results was determined. Based on this, the in-cylinder mixture preparation for three typical operating conditions was studied. The effects of fuel injection timing and intake valve open scheme on the mixture formation were evaluated. The results demonstrated that three simulation cycles are needed to achieve convergence of the results for the present study. The analysis of the mixture preparation revealed that only in the initial phase of the intake stroke there is an obvious difference between the three operating conditions. At the spark timing, for 5500rpm, full load condition mixture composition throughout the cylinder is flammable, and for 2000rpm, 2bar, operating condition part of the mixture is lean and nonflammable. The fuel injection timing has an insignificant impact on the mixture flammability at the spark timing. It was observed that the designed nonsynchronous intake valve open scheme has stronger swirl and x-direction tumble motion than the baseline case, leading to better mixture homogeneity and spatial distribution. With an increase in volumetric efficiency, particularly at 2000rpm, full load condition, by 4.85% compared to the baseline, which is in line with experimental observation.

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