Research On Combustion Noise And Sound Quality Performance Optimization Of Diesel Engine Based On Injection Strategy

With the rapid development of the automobile industry,vehicle noise performance has been paid more and more attention by people,and it has become one of the important indicators reflecting the comprehensive competitiveness of its products.The evaluation index of noise is gradually covered by traditional acoustic parameters to psychoacoustic parameters.Combustion noise plays a dominant role in diesel engine at idling and low speed and small-load conditions,which has an important influence on the whole engine noise,especially on the sound quality.Therefore,this paper researches the combustion noise and sound quality of low-speed and small-load conditions of the vehicle diesel engine based on fuel injection strategy,and then improves the noise performance of the whole engine by optimizing multiple fuel injection parameters.Firstly,a synchronous test and analysis platform for the combustion process and noise performance of the test engine is built.The psychoacoustic evaluation indexes of the diesel engine are clarified,then the calculation and analysis methods of combustion noise are given.At the same time,the cylinder pressure of the combustion process is decomposed into three parts,the influencing factors of the cylinder pressure level spectrum are analyzed,and the critical filtering frequency of the high-frequency oscillation of the pressure is established.A sound quality evaluation method based on segmented combustion pressure oscillation is proposed.Secondly,the influence of fuel injection parameters on combustion noise and sound quality is studied,and the correlation between sound quality parameters and combustion process is analyzed and summarized.The results show that the combustion noise generally shows a monotonous change trend by changing main injection timing and common rail pressure.With the increase of pilot injection interval and quantity,it shows a trend of decreasing first and then increasing.The noise of the whole engine is obviously affected by the combustion noise,which is roughly the same as the change law.In terms of sound quality,except for the fluctuation,the other sound quality parameters have different effects on the changes of the fuel injection strategy.The influence of the main injection timing and the common rail pressure is slightly larger than the pilot injection interval and quantity.Correlation analysis shows that the loudness has a high correlation with the main injection combustion process under different load conditions,which reduces the pressure oscillation of the main injection combustion process can effectively reduce the loudness.The sharpness is obviously affected by the pilot injection combustion process under the 10% load condition.By reducing the pressure oscillation of the pilot injection combustion process,the high-frequency noise can be effectively suppressed to reduce the sharpness.Under the condition of 50% load,the influence of pressure oscillation and high-frequency noise of the main injection combustion process on the sharpness are more obvious.Roughness has a high correlation coefficient with the whole combustion process under various load conditions.By optimizing the pressure oscillation energy of the whole combustion process,the roughness can be reduced to some extent.The correlation between roughness and each combustion process is slightly lower than other sound quality parameters.Finally,the combustion noise and sound quality performance of diesel engine at idling and low speed and small-load conditions(1000-2000r/min,10% and 50% load conditions)were optimized.In the optimization process,the psychoacoustic annoyance(PA)is used to comprehensively evaluate the sound quality performance of the diesel engine.After optimization,the noise performance of the diesel engine is improved under the premise that the NOx and soot emissions are equal to or slightly lower than the original engine.Under the idling condition,the sound pressure level is reduced by 0.8dB(A),and the PA is reduced by 6.1% compared with the original engine.At the speed of 1000-2000r/min,the sound pressure level is reduced by 1.0dB(A)and 0.7dB(A)respectively,and the PA is reduced by 7.2% and 6.5% respectively compared with the original engine under load conditions of 10% and 50%.