Fuel injection pump phasing effect on geartrain impact noise of diesel engines

Fuel injection pump phasing is one of the most effective methods to reduce gear impact noise in heavy-duty diesel engines. It is well known that pressurizing fuel in the injection pump requires non-uniform torque, which contributes to the speed fluctuations of the engine during its operation. These fluctuations lead to propagation of high levels of impact noise from the engine. Fuel injection pump phasing is a procedure that adjusts the fuel injection timing of the fuel injection pump relative to the crankshaft. Adjusting the injection timing provides reduction of torque fluctuations and can thus be used to control gear impact noise. In this paper, numerical and experimental studies are carried out on a heavy-duty diesel engine to investigate how fuel injection pump phasing may affect the occurrence of gear train impact noise. In both numerical and experimental studies, different phase angles are analysed to determine the best and the worst phase angles for gear impact noise. The so-called Impact Impulse Method is used in the numerical study to quantify the relative change of gear impact noise level as a function of phase angle. Experimental investigations, including vibration and acoustic measurements, are carried out on a heavy-duty diesel engine in a semi-anechoic engine test chamber. Vibration and acoustic responses, partially caused by gear impacts, are measured and processed at different pump phase angles and critical resonance frequencies are detected. Broadband characteristic of the gear impact noise is observed in Campbell diagrams. Both numerical and experimental results obtained in this investigation show that fuel injection pump phasing can significantly change the gear train impact noise as well as the overall engine noise level.