The goal of the present study is development of a simple model of heat liberation in preflame reactions which corresponds satisfactorily in a first approximation to experimental data for the temperature and pressure range occurring in internal combustion engines. This model is based on the experimentally justified assumption that the limiting stage in the chain mechanism of preflame oxidation is a first-order reaction (isomerization or monomolecular decay). In mathematical modeling of the operation of a carbureted internal combustion engine, a program was used consisting of several subroutines for calculation of the combustion process, and the intake, compression, power and exhaust strokes, with library subroutines describing the temperature dependence of heat capacity and enthalpy of the components.