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Research Papers: Gas Turbines: Cycle Innovations

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
e-mail: 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
e-mail: hanzhiyu@yahoo.com

1Present address: State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body, College of Mechanical and Vehicle Engineering, Hunan University, Changsha, 410082, Hunan, China.

Contributed by the Cycle Innovations Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received June 17, 2017; final manuscript received December 16, 2017; published online March 14, 2018. Assoc. Editor: Timothy J. Jacobs.

J. Eng. Gas Turbines Power 140(5), 051704 (Mar 14, 2018) (10 pages) Paper No: GTP-17-1219; doi: 10.1115/1.4039106 History: Received June 17, 2017; Revised December 16, 2017

In the present study, multidimensional computational fluid dynamics (CFD) 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. First, 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 5500 rpm, full load condition mixture composition throughout the cylinder is flammable, and for 2000 rpm, 2 bar 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 2000 rpm, full load condition, by 4.85% compared to the baseline, which is in line with experimental observation.

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Figures

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Fig. 1

Computational domain at bottom dead center (BDC)

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Fig. 2

Evolution of tumble ratio and swirl ratio in the cylinder

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Fig. 3

Evolution of overall equivalence ratio in the cylinder

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Fig. 4

Evolution of trapped gas mass in the cylinder

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Fig. 5

Evolution of turbulence kinetic energy in the cylinder

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Fig. 6

Evolution of average pressure in the cylinder

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Fig. 7

Comparison of cylinder pressure and heat release rate between the experimental data and simulated results

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Fig. 8

Fuel mass fraction distributions in a cut plane for the three operating conditions during the intake stroke

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Fig. 9

Fuel mass fraction distributions in a cut plane for the three operating conditions during the compression stroke

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Fig. 10

Equivalence ratio distribution at spark timing

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Fig. 11

Schematic injection profiles for the three injection strategies

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Fig. 12

Comparison of in-cylinder swirl ratio for different intake valve open schemes

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Fig. 13

Comparison of in-cylinder tumble ratio in the x-direction for different intake valve schemes

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Fig. 14

Comparison of in-cylinder tumble ratio in the y-direction for different intake valve schemes

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Fig. 15

Mixture inhomogeneity at spark timing for different intake valve schemes

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Fig. 16

Equivalence ratio distribution at spark timing for the nonsynchronous intake valve open scheme

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Fig. 17

Trapped gas mass for different intake valve schemes

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Fig. 18

Experimental torque for different intake valve schemes

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