Diesel injector dynamic modelling and estimation of injection parameters from impact response Part 1: Modelling and analysis of injector impacts

Part 1 of this paper presents the development and validation of a detailed dynamic model for the needle motion of a common hole-type diesel fuel injector as used in a direct injection diesel engine. The injector needle motion is described as a two-mass piece-wise linear vibro-impact system, unlike the conventional modelling techniques which use a single-mass approach. The use of two masses permits analysis of both the needle impact behaviour and of the more general dynamics of the fuel injection process. Model parameters are derived from a combination of measurement and estimation, and the subsequent model is evaluated via direct measurement of the spring seat displacement. The opening and closing needle impact behaviour is shown to exhibit close correlation with key injection parameters, including fuel injection pressure, fuelling rate and timing. The model revealed that the impact of the needle when opening is found to exhibit lower amplitude but more high-frequency components than the impact associated with the closing. The measurement of the injector body vibration response to these impacts is shown to enable non-intrusive estimation of injection parameters, alleviating the problems associated with conventional intrusive needle-lift measurement.