A Study on Generation Mechanisms of Combustion Induced Noise in Diesel Engine

点击翻译按钮获取中文摘要

In diesel engine structure, there are three main excitation sources whichare strongly related with the combustion impact, that is, (1) gas excitation caused by rapid rise of cylinder pressure, (2) shocks caused by striking the elements at bearings or gears, (3) impulsive excitations caused by piston-slaps. The multi-coherence analysis between impulsive responses caused by these three excitations and the engine noise was examined to clarify each contribution to the total engine noise. In this analysis, the residual spectrum method was employed remove the influences of other excitations.It was clarified through these analyzes that (1) had a large coherence with the low and middle frequency components, beside (2) and (3) had a distinguished corelation with the high frequency component of the engine noise. These methods were applied to a small sized engine, and it was clarified that the predominant cause of the acceleration noise of engine was pistonslaps.The influence of lubricating oil film in bearings to combustion induced noise was investigated considering the temperature and feed of oil, the pressure of oil film, and the displacement of crank shaft. From these experiments, it became clear that the contribution of lubricating oil in bearings to the combustion induced noise of engine was atmost 2dB in over-all value.Vibration intensity measurement was proposed as a means for the identification of impact sources in an engine structure. The destributions of the dircetion of intensity vectors were shown on each outer wall of a diesel engine. Through these measurements, the transmission paths of combustion impact were clarified.