The mathematical model of the compression, combustion, and expansion phases of the Renault IFP variable compression ratio research engine reported here is an attempt to combine as many as possible of the basic characteristics of engine combustion. Finite rates of flame propagation and heat release are computed on the basis of Semenov's theory. To allow for the effects of turbulence, Semenov's estimate of laminar burning velocity is multiplied by a term derived from flame speed measurements in the engine. Dissociation of the burned gases is compensated by chemical equilibrium and heat transfer data due to Annand.The computer model makes possible a parametric study of the effects of variables such as mixture composition, spark timing, compression ratio, engine speed, exhaust residuals and injected water as a means of controlling certain obnoxious emissions resulting from use of propane, isooctane, and benzene fuels. Experimental data corroborate the accuracy of the model.