The development of analytic models of diesel engine flow, combustion and subprocesses is described. The models are intended for use as design tools by industry for the prediction of engine performance and emissions to help reduce engine development time and costs. Part of the research program includes performing engine experiments to provide validation data for the models. The experiments are performed on a single-cylinder version of the Caterpillar 3406 engine that is equipped with state-of-the-art high pressure electronic fuel injection and emissions instrumentation. In-cylinder gas velocity and gas temperature measurements have also been made to characterize the flows in the engine.The KIVA code is being used for the computations, with improved submodels for liquid breakup, drop distortion and drag, spray/wall impingement with rebounding, sliding and breaking-up drops, wall heat transfer with unsteadiness and compressibility, multistep kinetics ignition and laminar-turbulent characteristic time combustion models, Zeldovich NOx formation, and soot formation with Nagle Strickland-Constable oxidation. The code also allows computations of the intake flow process in the realistic engine geometry with the two moving intake valves.Significant progress has been achieved in modeling diesel combustion and emissions using the improved submodels. Comparisons with measured engine cylinder pressure, and soot and NOx emission data show that the model results are in good agreement with the experiments. This indicates that computer models are now available to provide direction for engine design.Other experimental results have been obtained recently that show that significant reductions in soot and NOx emissions are possible using split injections. The KIVA model is currently being used to gain insight into the reasons for this improved engine performance.