Research Papers: Flows in Complex Systems

A Numerical Investigation of Combustion and Mixture Formation in a Compressed Natural Gas DISI Engine With Centrally Mounted Single-Hole Injector

[+] Author and Article Information
B. Yadollahi

PhD Graduate
e-mail: Byadollahi@aut.ac.ir

M. Boroomand

Associate Professor
e-mail: Boromand@aut.ac.ir
Amirkabir University of Technology (Tehran polytechnic),
Tehran, Iran 15875-4413

1Corresponding author. Present address: Department of Aerospace Engineering, Amirkabir University of Technology (Tehran Polytechnic), 424 Hafez Avenue, Tehran, Iran, 15875-4413.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received April 29, 2012; final manuscript received May 12, 2013; published online June 10, 2013. Assoc. Editor: Pavlos P. Vlachos.

J. Fluids Eng 135(9), 091101 (Jun 10, 2013) (9 pages) Paper No: FE-12-1219; doi: 10.1115/1.4024560 History: Received April 29, 2012; Revised May 12, 2013

Direct injection of natural gas into the cylinder of spark ignition (SI) engines has shown a great potential to achieve the best fuel economy and reduced emission levels. Since the technology is rather new, in-cylinder flow phenomena have not been completely investigated. In this study, a numerical model has been developed in AVL FIRE software to perform an investigation of natural gas direct injection into the cylinder of spark ignition internal combustion engines. In this regard, two main parts have been taken into consideration aiming to convert a multipoint port fuel injection (MPFI) gasoline engine to a direct injection natural gas (NG) engine. In the first part of the study, multidimensional simulations of transient injection process, mixing, and flow field have been performed. Using the moving mesh capability, the validated model has been applied to methane injection into the cylinder of a direct injection engine. Five different piston head shapes have been taken into consideration in the investigations. An inwardly opening single-hole injector has been adapted to all cases. The injector location has been set to be centrally mounted. The effects of combustion chamber geometry have been studied on the mixing of air-fuel inside the cylinder via the quantitative and qualitative representation of results. In the second part, an investigation of the combustion process has been performed on the selected geometry. The spark plug location and ignition timing have been studied as two of the most important variables. Simulation of transient injection was found to be a challenging task because of required computational effort and numerical instabilities. Injection results showed that the narrow bowl piston head geometry is the most suited geometry for NG direct injection (DI) application. A near center position has been shown to be the best spark plug location based on the combustion studies. It has been shown that advanced ignitions timings of up to 50 degrees crank angle ( °CA) should be used in order to obtain better combustion performance.

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Fig. 4

Comparison of jet penetration and flow field for second validation case

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Fig. 3

Left the inlet mass flow rate for the first validation case [1], and right: the comparison of jet tip penetration

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Fig. 2

The results of jet penetration for grid independency check

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Fig. 1

A view of mesh in the near field of the injector exit

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Fig. 5

A view of base engine geometry and ports

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Fig. 6

Effect of combustion chamber geometry on jet shape at a planar section through injector axis, all cases at 40 °CA BTDC, RAFR = 2.33

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Fig. 7

Temporal variations of mixture characteristics for different combustion chamber geometries

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Fig. 8

Equivalence ratio contours on a planar section through cylinder axis for large bowl geometry at different crank angles

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Fig. 9

A comparison of results for λ = 1.5 and λ = 2.0; left: flammable and rich mass fractions, and right: flammable and rich fuel mass fractions

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Fig. 10

The proposed spark plug locations on a contour plot of equivalence ratio at ignition timing

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Fig. 11

Temperature contour on a planar section through cylinder axis for different spark plug locations, all cases at 10° BTDC

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Fig. 12

The in-cylinder results for spark location study; left: pressure trace, and right: temperature

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Fig. 13

Combustion results for ignition timing study; left: pressure trace, and right: heat release rate

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Fig. 14

The peak pressure crank angle and value for ignition timing study




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