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The problem of modeling combustion within internal combustion engines is considered. A method is explained to evaluate the comprehensiveness, detail and predicting capability of a model. It consists of considering the equations for the most comprehensive and detailed model and in making successively more restrictive assumptions, thus getting progressively less detailed models. Particular attention is paid to the reasons for the assumptions, how they influence the accuracy of a model, and what basic information is missing. In so doing, the most detailed of the available models, and their predictive capabilities and limitations, are introduced. They include models for reciprocating and rotary engines, with uniform and stratified charges from dual carburetion and direct fuel injection. Examples of their results are given. One of them has been available since 1971, and another one is currently and fruitfully employed to aid the development of a production engine.

Propagation of turbulent flames in spark-ignition engines is considered from the viewpoint of the different possible regimes of premixed turbulent combustion. Nondimensional parameters defining known combustion regimes are reviewed, and numerical values of these parameters are estimated for both research and production engines. The reaction-sheet regime is inferred to apply at least for some operating conditions, and therefore literature on turbulent flame propagation in the reaction-sheet regime is reviewed. Implications of these results on interpretations of existing experimental observations of combustion in engine cylinders and on modeling of turbulent flame propagation in engines are discussed.