Experimental research on evaluation method of valve train’s contribution to diesel engine front-end noise

On the test bench, single cylinder valve train is taken as the research object, and the sound power of diesel engine front-end is measured by using near-field sound intensity method when each cylinder distribution mechanism is working. The contribution of single cylinder valve train excitation to diesel engine front-end noise is separated by using two experimental methods, and the accuracy of the two experimental methods is studied. The results show that the four valve units calculated by these two experimental methods cause more front-end noise power levels than the reference value. At 600 r/min, the difference is 0.36 dB（A）, and when the speed increases to 1 700 r/min, the difference increases to 2.44 dB（A）. More accurate results can be obtained by the experimental method: the sound power at the front end of the engine when the valve mechanism of a single cylinder is used（4 cases） minus the sound power at the front end of the engine when no valve mechanism is operating. When the excitation force of the gear at the front end decreases, the front-end sound power level decreases roughly in parallel when the single-cylinder valve mechanism is working. When the three-cylinder valve mechanism is working at the same time, the front-end sound power level increases at 800 r/min, and decreases when the speed increases to 1 600 r/min.