A turbulent entrainment model for the turbulent combustion process in spark-ignition engines is described. The model uses the basic quantities of turbulent flow; i.e. the integral length scale, micro length scale, and turbulent intensity. The characteristic reaction time for a large eddy τ is calculated using the characteristic reaction time τc for the microscale, λ/S ℓ, where S ℓ is the laminar flame speed and propagation of ignition sites within a coherent turbulent structure. τ is related to the flame kernel development time and shows similar trends to the ignition delay time. The combustion model is demonstrated by calculations showing the typical trend behavior of combustion duration with equivalence ratio, exhaust gas recirculation, spark timing and engine speed.