Correlation of cylinder pressure-based engine noise metrics to measured microphone data

Peak pressure rise rate, ringing intensity, and combustion noise analysis are typically cited measures of the noise generated by combustion in an internal combustion engine. In this publication, peak pressure rise rate, ringing intensity, and the combustion noise calculation results are compared to microphone data over a wide range of engine operating conditions for one gasoline and one diesel engine. Multiple methods for calculation of peak pressure rise rate are explored, including the use of different time steps for gradient calculation, calculation of weighted gradients, application of various digital filters, and ensemble averaging of the pressure signal. The value of peak pressure rise rate was found to vary substantially depending on the data processing method used. Similar sensitivity to the data processing method was observed with ringing intensity. Combustion noise analysis provided the best correlation to microphone noise, especially at lower speeds where engine noise is dominated by combustion noise rather than mechanical noise. No correlation between crank angle based peak pressure rise rate and microphone data was found. The correlation between ringing intensity and microphone noise was very similar to the correlation between time-based peak pressure rise rate and microphone data. The correlation between ringing intensity and microphone noise (and between time-based peak pressure rise rate and microphone noise) was highly dependent on the method used to calculate the peak pressure rise rate. A method and a MATLAB function for calculating combustion noise for simulation data are provided in this study.