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

C.S. Daw, J.B. Green Jr., M.B. Kennel, J.F. Thomas
Oak Ridge National Laboratory
Knoxville TN 37932-6472

C.E.A. Finney
University of Tennessee
Knoxville TN 37996-2210

F.T. Connolly
Ford Motor Company
Dearborn MI 48121-2053

We propose a simple 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.

Daw CS, Green JB Jr, Kennel MB, Thomas JF, Finney CEA, Connolly FT (1996). A simple model for cyclic variations in a spark-ignition engine. Proceedings of the 1996 Technical Meeting of the Central States Section of the Combustion Institute (St. Louis, Missouri USA; 1996 May 05-07): 28-33.
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