Coupled vibration of engine structure considering acoustic characteristics of water coolant passage and prediction of liner cavitation (Numerical method and experimental evaluation by model chamber)

Abstract

Liner cavitation induced by piston slap in the diesel engine is caused by the water pressure fluctuation when its negative pressure is reduced to the saturated vapor pressure or less. Cavitation erosion of the cylinder liner is thought to be generated by the impulsive pressure or jet flow impingement following the collapse of cavitation bubble. As the measured results have shown that the water coolant passage of actual engine block has the resonant frequencies, this study presents the numerical method to predict the water pressure fluctuation in the water coolant passage considering vibration of the engine block and rotating shafts induced by engine exciting forces like combustion pressure, piston slap and so on. To examine the validity of this method, rectangular tank model containing the water is used to measure the response of water pressure fluctuation and structural vibration induced by the impulsive force acting on the structure. Measured water pressure response and structural vibration of rectangular tank model agreed well with the analytical results and the validity of the analytical method was confirmed. In this impact vibration experiment, high frequency components of the water pressure were observed just after the water pressure reaches to the saturated vapor pressure or less. These high frequency components seem to show the occurrence of the cavitation. Moreover, it was revealed that water pressure response is affected by the proximity of the natural frequencies of water acoustic field and structural vibration.

Keywords

• water coolant passage
• pressure fluctuation
• cavitation
• acoustic field
• piston slap
• engine vibration
• rotating shafts
• modal analysis