Sound quality improvement for a four-cylinder diesel engine by the block structure optimization

Abstract High sound quality and low radiated noise are two dominant demands for the vibro-acoustic performance of internal combustion engines. Such engines with high acoustic quality will greatly improve the acoustic environment both inside and outside of the passenger compartment of an automobile. In this paper, this performance of the block of a four-cylinder diesel engine was simulated and bench-tested. Then the vibro-acoustic problems were diagnosed and optimized. The finite element analysis method was adopted to numerically analyze the natural modes of the block. The finite-element model of the block was verified by the experimental modal analysis utilizing the single-input and multiple-output technology. The results indicate that the modal frequency errors from the simulation and experiment are permissible in respect of engineering and the accuracy of the finite-element model highly matching the real one is validated. Then, the flexible multi-body dynamics model of the diesel engine was constructed and excited by the boundary conditions comprised of in-cylinder gas pressures, cylinder liner-piston contact induced lateral forces and valve system motion induced impact forces. The simulated vibration velocity levels from the block surface were obtained under the rated condition (75 kW/3600 rpm) and well verified by the bench test. Boundary element analysis method was employed to acquire the radiated acoustic pressures from the block surface in the frequency range of interest. Optimized schemes are implemented to the block surface in order to reduce the radiated noise and enhance the sound quality of the diesel engine. Finally, the optimal block was cast. And the bench-test results indicate that the sound quality of the new-block engine is substantially improved. The research achievements validate the feasibility and reliability of the optimal design for the block.