This paper describes the investigation of the mechanisms of engine front noise generation and the corresponding countermeasures employed in the development of a diesel engine. According to the analysis of acoustic signals and vibration signals measurement, an investigation of the noise source identification in a diesel engine is presented, and that the noise level of the diesel is comprehended. With the sound intensity method, the major sources of the exterior radiation noise of the engine front are surveyed. The research provides the reliable basis for the engineering practice to reduce vehicle noise level. Furthermore, the measuring data of the acoustic signals are compared by measuring noise from surface vibration, and the results are valid.

A non-linear dynamic model of one type of high-speed rotor system with gas supporting system is set up. The laws between the capacity force and the parameters of bearing, the static equilibrium position and rotating speed are studied on the basis of above model. Then, the failure rotating speed is given in the working state, and the relation between the minimum failure rotating speed and clearance ofbearing is also studied. At last, the stability and failure condition are discussed in different working conditions.

The torsionaI oscillation characteristics on the bending and torsioh coupled vibration of ro. tary shaft system were investigated using the elasto•-dynamic theery and other mathematic meth-ods, such as difference approach, Fourier transfOrm. and wavelet transform. It iS concluded that　mass eccentricity and other exciting modalities affect the bending and torsion coupled vibration of ro. tary shafts. TorsionaI vibration caused by bending vibration features linearity along with the change　of amplitude of bending vibration. Meanwhile, energy spectrum concentrates on high frequency are-a with the wavelet analysis.

The vibratory and acoustic behaviour of the internal combustion engine is a highly complex one, consisting of many components that are subject to loads that vary greatly in magnitude and which operate at wide range of speed. CAE tools development will lead to a significant reduction in the duration of the development period for engine as well as ensure a dramatic increase in product quality. This paper presents today's state-of-the-art CAE capabilities in the simulation of the dynamic and acoustic behaviour of engine and focuses on the relative merits of modification and full-scale structural/acoustic optimisation of engine, together with the creation of new low-noise designs. Modern CAE tools allow the analysis, assessment and acoustic optimisation of the engine.

The multi-body dynamics model of the X6170ZC diesel is established to analyze vibration and acoustic noise. The high quality finite element and simulation models are developed, and nonlin-ear springs are used to imitate the joints of engine components. The acoustic behavior of the struc-ture is evaluated by the velocity of surface vibration. The noise level is reduced by improving the structure of the engine. The result shows that the surface vibration velocity level is decreased about 3.7 dB (A) at-1 600 Hz after the optimization. Based on the contrast between the two structures, it is concluded that through structure design the combined noise can be reduced, and the virtual de-sign mode of diesel engines is feasible.