A one-dimensional model for. the spark ignition Wankel engine combustion is presented, The model is based on the use of a turbulent diffusivity for heat and mass transfer by which the motion of the finite-thickness, unsteady turbulent flame is calculated. A one-step second order reaction rate equation is used and wall heat transfer losses are included. The instantaneous chamber pressure and the local and instantaneous gas temperature, density, and velocity are calculated. Results are presented for a typical engine design. Initial results of two parametric studies are also reported, but their generalization is not undertaken, at this point, due to the complexity of the process.