With the aim of simulating homogeneous charge compression ignition (HCCI) combustion the three-dimensional computational fluid dynamics (CFD) model AIM2Z is presented. AIM2Z allows for the fact that a mixture is not necessarily homogeneous at the subgrid-scale level. In each cell this model distinguishes a zone where fuel and air are not yet mixed from a zone where turbulence yields a mixture that is assumed to first order to be homogeneous. It is only in the latter zone that chemical kinetics-in the form of reduced schemes to limit CPU time in. three-dimensional CFD applications - are applied. After the description of the model formulation, we evaluate a simple kinetic scheme for autoignition of n-heptane and iso-octane mixtures. Then basic implementation tests on sample diesel engine configurations are presented: a homogeneous case and a stratified case with liquid injection are simulated with AIM2Z and the simple scheme. They demonstrate the feasibility of AIM2Z and its a priori satisfactory behavior in an engine environment.