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TECHNICAL PAPERS: Internal Combustion Engines

Supersonic Virtual Valve Design for Numerical Simulation of a Large-Bore Natural Gas Engine

[+] Author and Article Information
Gi-Heon Kim

 National Renewable Energy Laboratory, Golden, CO 80401

Allan Kirkpatrick, Charles Mitchell

Department of Mechanical Engineering, Colorado State University, Fort Collins, CO 80523

J. Eng. Gas Turbines Power 129(4), 1065-1071 (Feb 20, 2007) (7 pages) doi:10.1115/1.2747251 History: Received August 16, 2005; Revised February 20, 2007

In many applications of supersonic injection devices, three-dimensional computation that can model a complex supersonic jet has become critical. However, in spite of its increasing necessity, it is computationally costly to capture the details of supersonic structures in intricate three-dimensional geometries with moving boundaries. In large-bore stationary natural gas fueled engine research, one of the most promising mixing enhancement technologies currently used for natural gas engines is high-pressure fuel injection. Consequently, this creates considerable interest in three-dimensional computational simulations that can examine the entire injection and mixing process in engines using high-pressure injection and can determine the impact of injector design on engine performance. However, the cost of three-dimensional engine simulations—including a moving piston and the kinetics of combustion and pollutant production—quickly becomes considerable in terms of simulation time requirements. One limiting factor is the modeling of the small length scales of the poppet valve flow. Such length scales can be three orders of magnitude smaller than cylinder length scales. The objective of this paper is to describe the development of a methodology for the design of a simple geometry supersonic virtual valve that can be substituted in three-dimensional numerical models for the complex shrouded poppet valve injection system actually installed in the engine to be simulated. Downstream flow characteristics of the jets from an actual valve and various virtual valves are compared. Relevant mixing parameters, such as local equivalent ratio and turbulence kinetic energy, are evaluated in full-scale moving piston simulations that include the effect of the jet-piston interaction. A comparison of the results has indicated that it is possible to design a simple converging-diverging fuel nozzle that will produce the same jet and, subsequently, the same large-scale and turbulent-scale mixing patterns in the engine cylinder as a real poppet valve.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematics of an actual valve currently in use for high-pressure natural gas injection on a large-bore engine (a) and schematics of a simple converging-diverging type virtual valve designed for 3D computations (b)

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Figure 2

Design parameters and conditions for virtual valves

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Figure 3

Computational grids used in axisymmetric computations for an actual-valve injection (a) and for a virtual valve injection (b)

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Figure 4

Mach number profile of the jet issuing from conventional poppet valve at 18cm downstream from shroud nozzle exit. Design exit Mach numbers of virtual-1 and virtual-2 are marked on the graph.

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Figure 5

Comparisons of centerline Mach number profiles among the tested valves (a), axial velocity (in m/s) distribution at 18cm downstream jets (b), and axial momentum flux (in bar) at 18cm downstream jets (c)

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Figure 6

Velocity magnitude contours (in m/s) at 0.3ms, 0.6ms, and 0.9ms for comparison of penetration rates of actual valve (a) virtual-1 (b), and virtual-2 (c).

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Figure 7

Grid systems used for in-cylinder mixing simulations with moving piston top: (a) is for the real valve and (b) is for virtual nozzles

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Figure 8

Equivalence ratio contour sequences from 108deg of crank angle before TDC to TDC in intervals of 27deg of crank angle for actual valve injection (a), for virtual-1 (b), and for virtual-2 (c).

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Figure 9

Flammable mixture fraction changes with crank angle (degrees in BTDC)

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Figure 10

Comparison of mass averaged turbulent kinetic energy at nine crank angle degrees before TDC for each tested valve

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Figure 11

Mass distribution with equivalence ratio for the mixture gas (a) and for the fuel gas (b)

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Figure 12

Comparison of spatial distribution of fuel at nine crank angle degrees before TDC by showing the equivalence ratio contours for actual and for virtual-3 valve

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Figure 13

Comparison of spatial distribution of turbulent kinetic energy (TKE) (in m2/s−2) at nine crank angle degrees before TDC by showing TKE contours for actual and for virtual-3 valve

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