Dependence of combustion noise on engine calibration parameters by means of the response surface methodology in passenger car diesel engines

Combustion noise from a passenger car diesel engine has been expressed as a function of the heat release rate peaks of pilot and main combustions as well as of the crankshaft angles at which these peaks occur, using a statistical regression model. Furthermore, the values of these heat release rate peaks and of their angles have been correlated with the main engine calibration parameters by means of second-order polynomial regressions. The values of the coefficients of these polynoms have been found to depend on the engine working condition. As a result, it has been possible to calculate the combustion noise as a function of the main engine calibration parameters at different engine working points, which are representative of low, medium and high load and speed conditions within the NEDC working zone.The effects of the pilot injection quantity and timing, of the main combustion phasing and of the rail pressure level have been analyzed for both late PCCI and conventional combustion modes. The definition of the pilot injection quantity and timing has resulted to be relevant for a reduction in combustion noise at low and medium speeds and loads, while a pilot injection should be removed for an optimized combustion noise engine calibration at high speeds and loads.