IMWI is an effective way to control combustion temperature and NOx emission for diesel engines, which is widely used on large marine engines[1]. This method increases the ignition delay and peak heat release rate, whereas in-cylinder temperature and NOx emission drop. The decrease in in-cylinder temperature and NOx emission is the result of various effects of IMWI: dilution effect (decrease of inlet oxygen concentration), thermal effect (high latent heat of vaporization and specific heat capacity of injected water) and chemical effect