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Technical Briefs

Examination of Initialization and Geometric Details on the Results of CFD Simulations of Diesel Engines

[+] Author and Article Information
Michael J. Bergin, Sage Kokjohn, Rolf D. Reitz

Engine Research Center, University of Wisconsin, Madison, WI 53706

Ettore Musu1

Engine Research Center, University of Wisconsin, Madison, WI 53706

1

Visiting scholar at the University of Pisa, Pisa, Italy.

J. Eng. Gas Turbines Power 133(4), 044501 (Nov 18, 2010) (4 pages) doi:10.1115/1.4001941 History: Received June 04, 2009; Revised January 07, 2010; Published November 18, 2010; Online November 18, 2010

Computational fluid dynamic simulations using the AVL FIRE and KIVA 3V codes were performed to examine commonly accepted techniques and assumptions used when simulating direct injection diesel engines. Simulations of a steady-state impulse swirl meter validated the commonly used practice of evaluating the swirl ratio of diesel engines by integrating the valve flow and torque history over discrete valve lift values. The results indicate the simulations capture the complex interactions occurring in the ports, cylinder, and honeycomb cell impulse swirl meter. Geometric details of engines due to valve recesses in the cylinder head and piston cannot be reproduced axisymmetrically. The commonly adopted axisymmetric assumption for an engine with a centrally located injector was tested by comparing the swirl and emissions history for a noncombusting and a double injection low temperature combustion case with varying geometric fidelity. Consideration of the detailed engine geometry including valve recesses in the piston altered the swirl history such that the peak swirl ratio at TDC decreased by approximately 10% compared with the simplified no-recess geometry. An analog to the detailed geometry of the full 3D geometry was included in the axisymmetric geometry by including a groove in the cylinder head of the mesh. The corresponding emissions predictions of the combusting cases showed greater sensitivity to the altered swirl history as the air-fuel ratio was decreased.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Engine geometry showing honeycomb impulse torque meter (left), engine cylinder (middle), and helical (near right) and tangential (far right) ports

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Figure 2

Swirl history with various geometries for swirl=2.2

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Figure 3

Sector mesh with groove place in cylinder head surface

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Figure 4

Pressure and heat release for IMEP 10.5 bar case with 3D geometry

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Figure 5

CO emissions for sector mesh and 3D cases at 10.5 bar IMEP

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