Computations were performed Co evaluate and, if necessary, improve a combustion submodel and to assess the current ability of the multidimensional code to model combustion, wall heat transfer and nitric oxide emissions in the homogeneous-charge spark-ignition engine. As opposed to a conventional one-step global combustion rate expression, a modified form gave a better match with measurements. This modified expression required case-to-case tuning when the volumetric efficiency or fuel-air equivalence ratio changed. However, the pre-exponential factor required for such tuning correlated with residual fraction and equivalence ratio. Computed wall heat-transfer and emission results compared well with measurements.