Experimental measurements from a converted indirect injection diesel Kubota D905 engine fueled with a simulated biomass derived gas are compared with simulation results using a multizone homogeneous charge compression ignition (HCCI) engine model. Two different fuel blends were tested and each consisted of varying amounts of CH4, CO2, N-2, H-2, and CO to mimic the gaseous constituents of producer gas. The multizone model was originally developed as a 32 bit serial application for use with primary reference fuels (PRFs). However, for the purpose of this study, the model has been parallelized using Message Passing Interface (MPI) for Fortran and is executed in a 64 bit environment to further reduce computational time. Once calibration was complete, the numerical model showed good pressure trace matching with the experimental data across both fuel mixture compositions and various equivalence ratios. Correspondingly, heat release rate (HRR) curves showed good matching as well. Calibration settings from one engine operating point for a given fuel mixture were readily transferable to other operating points and the second fuel mixture. However, there were some discrepancies in predicting pressure traces when operating the model near the misfire limit of the engine due to cyclic variability, which exceeds the limitations of the model. (C) 2011 Elsevier Ltd. All rights reserved.