柴油机燃烧噪声的传递特性

为研究柴油机燃烧噪声的传递特性,测量了发动机工作和倒拖时的气缸压力,并在不同转速下从4个不同方向上对一台单缸柴油机进行了1/3倍频程噪声频谱分析,分离出燃烧噪声压力级,计算其传递函数.基于柴油机燃烧示功图进行快速傅立叶变换得到气缸压力级频谱,同时计算两种不同工况下的柴油机衰减曲线.结果表明,与倒拖工况相比,4个方向上燃烧工况的噪声级相对增加率均大于4.5%.各个方向上的最大噪声级均出现在中高频范围.随着频率增加4个方向上的传递函数也缓慢增加,两种转速下的衰减曲线走向基本相同.

Transfer characteristics of combustion noise in diesel engines

To investigate the transfer characteristics of combustion noise in a diesel engine,the one-third octave band spectrum was analyzed under the same operating conditions for four different directions with the help of combustion and motoring tests.The pressure level of combustion noise was separated and the transfer functions were calculated.FFT was used to get the frequency spectrum of cylinder pressure level on the basis of combustion indicator diagram in a diesel engine.At the same time,the attenuation curves of structure were calculated in two different operating conditions.The results showed that the relative increasing rate in the noise level of operating condition was over 4.5 percent in contrast with that of motoring condition in four different directions.The maximum noise levels in different directions all occur in the medium and high frequency range.The transfer functions also increase with the rise of frequency in four different directions.The trend of attenuation curves are almost the same.