Vibration and noise prediction of internal combustion engine based on cascade modeling of components

Abstract

In most machinery noise and vibration problems, a model of the machine as a cascade of subsystems excited by the noise (vibration) source(s) may be used in predicting the effect of any modification in the source(s) or vibration transmission paths. In this study, an acoustic-dynamic model of an internal combustion engine is developed. The excitation sources considered were combustion forces and piston slap. For combustion forces, two transmission paths from each cylinder to the engine block were considered; a path through the piston, crank shaft and bearings [R. DeJong, 1976] and another path through the cylinder head. The piston slap was assumed to be transferred to the block through the cylinder wall and upper deck of the cylinder block [T. Oguchi, 1979]. The combustion forces of each cylinder were determined from the engine design and its operating conditions. The piston slap excitation was estimated on the basis of the shape and size of the piston and cylinder and assumed to occur after the combustion. The block vibration and the radiated sound power spectrum of a four cylinder in-line diesel engine were predicted and measured under different operating conditions. The predicted and measured results agreed well above 400 Hz.