To improve the prediction accuracy of the spark ignition and combustion processes in spark ignition engines, improved ignition and flame propagation models have been developed and implemented in the CFD code. KIVA-3V An equation to calculate the spark ignition kernel growth rate is derived that considers the effects of the spark ignition discharge energy and flow turbulence on the ignition kernel growth. In addition, a flamelet combustion model based on the G equation combustion model was developed and implemented. To test the ignition and combustion models, they were applied to a homogeneous charge pancake-shaped-combustion-chamber engine, in which experimental heat flux data from probes in the engine head and cylinder liner were available. By comparing the flame arrival timings with the simulation predictions. the ignition and combustion models were validated. In addition, the models were also applied to a homogeneous charge propane-fueled SI engine. Good agreement with experimental cylinder pressures and NO data was obtained as a function of ignition timing. engine speed, and EGR levels. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.