MODELLING OF DYNAMIC RESPONSES OF AN AUTOMOTIVE FUEL RAIL SYSTEM, PART I: INJECTOR

Abstract

This paper presents a computer model for simulating dynamic responses of an automotive fuel rail system. Part I of this paper deals with the mathematical modelling of an individual injector. To reduce the complexity of this problem, the injector is discretized into three segments with a filter at the top, a coil spring and needle assembly in the middle, and four orifices at the bottom. The fluid flowing through these segments is coupled and described by a one-dimensional unsteady Bernoulli's equation. Loss factors KFand KOare used to account for the losses of kinetic energy as fluid enters the injector through the filter at the top and discharges through orifices at the bottom respectively. The value of KFis assumed constant and determined experimentally. The value ofKO , however, varies because the fluid kinetic energy changes with the passage cross-sectional area between the needle and the valve seat. In this investigation, KOis correlated to the needle motion, which is governed by a second order ordinary differential equation. The forces exerted on the needle include the magnetic and coil spring forces, which control the opening and closing of the injector. The pressure fluctuations inside the injector caused by the opening and closing of the needle are described by a damped wave equation. The dynamic responses of the injector are then obtained by solving a set of nine equations simultaneously. The calculated pressure fluctuations inside an injector are compared with the measured data under various pulse widths and speeds. Good agreement is obtained in each case.