Comparison of Compression Ignition Engine Noise Metrics in Low-Temperature Combustion Regimes

Many combustion researchers use peak pressure rise rate or ringing intensity to indicate combustion noise in lieu of microphone data or using a combustion noise meter that simulates the attenuation characteristics of the engine structure. In this paper, peak pressure rise rate and ringing intensity are compared to combustion noise using a fully documented algorithm similar to the ones used by combustion noise meters. Data from multiple engines operating under several low-temperature combustion strategies were analyzed. The results suggest that neither peak pressure rise rate nor ringing intensity provides a direct correlation to engine noise over a wide range of operating conditions. Moreover, the estimation of both metrics is often accompanied by the filtering of the pressure data, which changes the absolute value of the results. Thus, all ringing intensity and peak pressure rise rate data should be provided with the filter characteristics to allow an independent assessment of the noise potential. The major difference between ringing intensity and peak pressure rise rate on the one hand and noise on the other appears to be in the speed scaling relationship.