A single zone thermodynamic model, coupled to a kinetic mechanism, is developed and is capable of predicting the ignition timing of Primary Reference Fuels ( PRFs) in a Homogeneous Charge Compression Ignition ( HCCI) engine. A new combination of kinetic mechanisms is used, which includes 120 reactions and 58 species for both ignition and high temperature reactions. The model is validated using a step by step methodology. The validation compares ignition delays predicted by the model with published measurements from a rapid compression machine, shock tube as well as the cylinder pressure histories taken from two different experimental HCCI engines for various operating conditions. The model is able to qualitatively predict the effect of different parameters such as gas temperature, gas pressure, equivalence ratio and octane number on the HCCI ignition delay.