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A simple model for cyclic variations in a spark-ignition engine

C.S. Dawa, C.E.A. Finneyb, J.B. Green, Jr.a, M.B. Kennela, J.F. Thomasa, F.T. Connollyc

aEngineering Technology Division
Oak Ridge National Laboratory
Oak Ridge TN 37831-8088

bCollege of Engineering
University of Tennessee
Knoxville TN 37996-2200

cFord Motor Company
Dearborn MI 48121-2053

We propose a simple, physically oriented model that explains important characteristics of cyclic combustion variations in spark-ignited engines. A key model feature is the interaction between stochastic, small-scale fluctuations in engine parameters and nonlinear deterministic coupling between successive engine cycles. Prior-cycle effects are produced by residual cylinder gas which alters volume-average in-cylinder equivalence ratio and subsequent combustion efficiency. The model's simplicity allows rapid simulation of thousands of engine cycles, permitting in-depth statistical studies of cyclic variation patterns. Additional mechanisms for stochastic and prior-cycle effects can be added to evaluate their impact on overall engine performance. We find good agreement with our experimental data.

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Daw CS, Finney CEA, Green JB Jr, Kennel MB, Thomas JF, Connolly FT (1996). A simple model for cyclic variations in a spark-ignition engine. SAE Paper No. 962086.
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