This paper describes a new autoignition submodel for engine modeling codes. This submodel does not require extensive computational resources and is easily portable to various computational environments. It also considers variation of natural gas composition due to propane addition. Computation results show that the knock occurrence crank angle can be predicted within 2degrees CA when the model is coupled to a zero-dimensional engine model, which was also developed for the present work. The results with the model incorporated into a multi-dimensional model (KIVA) are also promising. KIVA was able to predict if the engine was going to knock or not and also gave correct trends in the knock intensity. (C) 2003 Elsevier Science Ltd. All rights reserved.