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TECHNICAL PAPERS: Internal Combustion Engines

Experimental Validation of an Improved Squish Velocity Model for Bowl-in-Piston Combustion Chambers

[+] Author and Article Information
P. Lappas1

Department of Mechanical Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canadalappas@mech.ubc.ca

R. L. Evans

Department of Mechanical Engineering, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada

1

Corresponding author.

J. Eng. Gas Turbines Power 128(2), 403-413 (Jul 16, 2005) (11 pages) doi:10.1115/1.2130730 History: Received February 24, 2004; Revised July 16, 2005

A simple two-zone mass transfer model was used to predict the mean squish velocity history at the rim of a conventional bowl-in-piston combustion chamber. The chamber’s geometry produces gas flow that converges radially inwards (“squish”) as TDC (top dead center) is approached. The squish flow generates turbulence, which can be used to enhance the combustion rate. When compared with PIV (particle image velocimetry) measurements, the peak squish velocity at the bowl rim was 12% less than the value predicted by the simple mass transfer model. After a thorough examination, the assumption of uniform density in the simple model was strongly suspected to be the cause of this discrepancy. Improvements were made to the simple model to account for density variations that are caused by nonuniform heat transfer in the combustion chamber. The revised model yielded velocities that were in close agreement with PIV measurements.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Simple example of squish flow in bowl-in-piston combustion chamber

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Figure 2

The two control volumes (zones) assigned inside the combustion chamber. Mass conservation on these zones can yield the average squish velocity through area As

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Figure 3

The particle seeding system. The conical flask doubles as a cyclone separator

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Figure 4

PIV measurement plane (plane A) for the bowl-in-piston combustion chamber. Dimensions are in millimeters. The polar coordinate system in any plane parallel to the cylinder head is also described

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Figure 5

Illustration of PIV system

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Figure 6

Raw PIV image pair captured for bowl-in-piston chamber at 25 deg BTDC. The rightmost photograph was taken 170μs after the left one. Displacements of particle groups in the left image are determined by spatial cross correlation analysis with the right image

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Figure 7

The simulated displacement history for three differently sized particles following fluctuating squish flow inside the bowl-in-piston chamber. The motion of the air that the particles are responding to is also shown. The particles have a density of 1000kg∕m3. The motion of the 2 micron particle coincides with that of the air.

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Figure 8

Mean PIV velocity maps in combustion chamber. Units for X and Y axes are mm.

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Figure 9

Summary of PIV measurements in plane A for the bowl-in-piston chamber. The evolution of the mean radial squish velocity is shown for a set of radial positions.

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Figure 10

Temporal evolution of the mean squish velocity for the bowl-in-piston chamber. Results from the ideal two-zone mass transfer model and from PIV results are shown for comparison. Crank speed is 800rev∕min.

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Figure 11

The radial distribution (in plane A) of the 90% confidence interval for the mean radial velocity (⟨Vr⟩) in the bowl-in-piston chamber. The distribution is shown for two different crank angles.

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Figure 12

Classification of possible causes for discrepancies in squish velocity between PIV results and mathematical model

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Figure 13

Effect of heat transfer correction on predicted squish velocity history

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