A numerical study of the turbulent combustion in a direct-injection stratified charge engine is presented. The focus of the present paper is incorporating detailed reaction schemes as well as coupling the turbulent flow characteristics to chemical reactions. In the present application most of the combustion occurs in diffusion dames, and the combustion takes place in the flamelet regime for turbulent combustion. The present model extends the flamelet model for turbulent diffusion flames to conditions of internal engine combustion. The computations are performed using the KIVA-II code that is modified to include the present combustion model. Results are presented for three different engine load conditions. For comparison, there are numerical integrations with simplified chemistry as well as measurements of both the pressure history and the chemical composition of the exhaust gas. The discrepancies between measurements and calculations with the simplified model are greatly improved, for instance, from about 56% to about 19% for the modified flamelet model for the mass of CO for the full-load case.