Reciprocal Measurement of Transfer Function from Combustion to Engine Vibration

Abstract

A method to identify the vibration transfer function from combustion pressure to engine structural vibration was developed without using complicated apparatus. In the method, which uses Maxwell's reciprocity theorem, a shaker excites structural vibration and the pressure in the combustion chamber is measured. A feasibility study on a simple structure produced transfer functions in the forward and reverse directions that coincided almost perfectly in the relevant frequency range. Transfer functions on a gasoline engine showed reasonable peaks of structural resonances. The method is convenient for identifying peak frequencies of the transfer functions between combustion pressure and engine structural vibration responses.