In this investigation, an in-house zero-dimensional code has been developed, which simulate the intake, compression, combustion, expansion and exhaust strokes of a homogeneous charge compression ignition (HCCI) engine fueled with compressed natural gas (CNG). Values of the instantaneous overall heat flux from the cylinder gas to the wall surfaces were calculated through the application of a zero-dimensional k−ε turbulence model. This model uses the k−ε turbulence model to determine characteristic velocity for heat transfer calculation for each process in the four stroke cycle to determine the velocity for use in the Reynolds number. Comparison of the zero-dimensional k−ε turbulence model prediction with experimental data shows good agreement.