Combustion Noise Prediction Of Direct Injection Diesel Engine

With the vehicle NVH requirements improving, vehicle noise has become a hot topic of the automotive industry. Because the engine is the noise and vibration sources of vehicle, vibration and noise problems of engine have been paid more and more attention. Direct injection diesel engine combustion noise has been an important research aspect of the internal combustion engine vibration and noise field. The4100QBZL direct injection diesel engine is selected as the research object to predict the combustion noise in this paper, which can be a theoretical reference for combustion noise control. The main contents of this paper are as follows:1) The work process simulation models of4100QBZL diesel engine and diesel engine fueled with M15methanol/diesel fuel are established by GT-POWER software to get the cylinder pressure curves and pressure rise rate curves.2) Then simplify the model appropriately and built the finite element model of engine block using ANSYS software. The engine block free mode and constrained mode analysis are done to understand the engine block structural dynamic characteristics generally. It can be seen from the vibration shape diagram that the vibration of the engine body skirt is big, which is the main vibration resource of radiation noise. In order to reduce the vibration, the wall thickness is increased to improve the rigidity of the body.3) The main bearing force is calculated by using EXCITE-Designer software. The cylinder pressure and the main bearing force are loaded on the engine body model for the engine transient analysis using ANSYS software. The vibration condition of the engine under the cylinder pressure and the main bearing force in one working cycle is studied and compared with the experimental results. The calculated results are in agreement with the experiment.4) Based on the transient analysis, using APDL language to compile program, the vibration displacement data of engines block surface nodes with time are changed to that with frequency, which is as the initial and boundary conditions in SYSNOISE software, the engine block combustion noise is predicted using the boundary element method.Through the different operating conditions and parameters analysis, it is found that the combustion noise is bigger as the engine speed increases and the relationship between injection time and combustion noise is not liner, too early or too late injection will contribute to big combustion noise. Low cetane number of M15fuel mixture contributes to low ignition characteristics, long ignition delay period and high pressure rise rate then finally brings about big combustion noise. The results accord with combustion noise changing rules.