Manufacturers of heavy-duty diesel engines are facing increasingly stringent, emission standards. These standards have motivated new research efforts towards improving the performance of diesel engines. The objective of the present program is to develop a comprehensive analytical model of the diesel combustion process that can be used to explore the influence of design changes. This will enable industry to predict the effect of these changes on engine performance and emissions. A major benefit of the successful implementation of such models is that engine development time and costs would be reduced through their use. The computer model is based on the three-dimensional KIVA-II code, with state-of-the-art submodels for spray atomization, drop breakup / coalescence, multi-component fuel vaporization, spray/wall interaction, ignition and combustion, wall heat transfer, unburned HC and NOx formation, and soot and radiation. The accuracy of the predictions is assessed by comparison with available experimental data. Improved combustion, wall heat transfer and spray/wall impingement submodels have been implemented in KIVA during the first year activity. In addition, work is in progress on a revised atomization model, since preliminary results show that existing atomization models are inaccurate under conditions of high gas temperature and pressure (e.g., turbocharged conditions). Finally, a methodology is being developed for modeling the intake flow process to provide more realistic initial conditions for engine computations.