Calculation and Measurement Suggest Significance of Cavitation in Spray Combustion: As fuel injection pressure becomes greater, cavitation in the nozzle hole may take place, and bubbles produced due to cavitation collapse inside the nozzle hole and in the spray. The research question is whether or not cavitation affects combustion significantly enough to change exhaust emissions. To answer this question, researchers at Waseda University and Mitsubishi Heavy Industries reported the results of their numerical study. The calculation results were validated with the measurement results obtained in a turbocharged DI diesel engine, and parametric study was performed to evaluate the effect of fuel injection timing and EGR rate on exhaust emissions. This chapter reports the simulation approaches with various equations employed for the model and the results of the parametric study.