A Study on the Decay Process in the Time-Frequency-Dependent Combustion-Noise-Generation Model for Diesel Engines

Abstract

<div class="section abstract"><div class="htmlview paragraph">We experimentally investigated the process of decay of engine noise from a single-cylinder diesel engine considering the time-frequency-dependent combustion-noise-generation model. In this model, the vibration energy of each frequency component is assumed to accumulate in the engine structure excited by the combustion impact during the combustion period in a cycle and decay over time, and the combustion noise is assumed to radiate from the engine surface. We used wavelet transform analysis as a time-frequency analysis of the sound pressure to obtain the decay rate, <i>c</i>, of the engine noise power. In order to investigate the dependence of the decay rate, <i>c</i>, on the sound-source location, we placed eight microphones in different positions near the engine. In order to investigate the dependence of the decay rate on the maximum in-cylinder pressure rise, we conducted experiments under three different operating conditions. The shape of the temporal variation of the engine-noise power depended on the sound-source location while the value of the engine noise power depended on the maximum in-cylinder pressure rise. Based on the time-frequency-dependent combustion-noise-generation model, we obtained the engine-noise decay rate, <i>c</i>, as the absolute value of the time differentials of the natural logarithm of the combustion noise power by line approximation. The results show that the decay rate, <i>c</i>, depends on the sound source location while it is almost independent of the maximum in-cylinder pressure rise.</div></div>