Abstract: It is difficult to obtain the accurate data of pure exhaust noise under common lab conditions because of interference of background noise. Two practical and effective methods have been proposed to measure the pure exhaust noise of engine in this paper. The experimental study on pure exhaust noise was carried on under the full-load speed characteristics curve of engine through using an acoustic enclosure designed by this paper. Test results indicate that experimental unit is right. The pure exhaust noise become stronger and the middle to high frequency noise increases with engine speed increasing. The pure exhaust noise of engine is coherent with background noise, and the value of which calculated by the theory of coherent acoustic is corresponded with the experimental data, so it is verified that the two measuring methods for pure exhaust noise of engine in this paper is feasible．

Key words: Engine, Exhaust noise, Noise test, Acoustic enclosure

摘要： 由于在普通实验室条件下纯排气噪声的测量受到背景噪声的干扰，难以获得准确的测试数据，本文提出了两种实用有效的发动机纯排气噪声测量方法，设计了一种圆柱形隔声罩，对发动机外特性曲线上的纯排气噪声进行了试验研究。研究结果表明：本实验装置可行；发动机纯排气噪声强度随转速升高而增大，中高频噪声比例也随之加大；发动机纯排气噪声与背景噪声是相干声波，根据相干声波叠加原理计算出的纯排气噪声与实验值较为吻合，验证了两种测量发动机纯排气噪声方法的可行性。

关键词: 发动机, 排气噪声, 噪声测量, 隔声罩