An integrated numerical model for diesel engine computation has been developed based on the KIVA-II code. Improved submodels include heat transfer, crevice flow, spray, ignition, combustion, soot and NOx emission models. It was found that the details of spray and combustion models have significant influence on the computed results. The current spray model considers the unstable growth of liquid surface wave which induces the liquid breakup. The model computes drop drag coefficient dynamically according to the drop distortion. It also considers the enhanced breakup due to wall impingement. The Shell model is used for ignition modeling. After ignition, both laminar chemistry and turbulent mixing are incorporated in the combustion model to compute the energy release rate. Emission models include a formation-oxidation type soot model and an extended Zeldovich NOx model. This integrated model predicts the cylinder pressure, heat release rate, and soot-NOx trade-off very well.