Mathematical model of diesel fuel injection equipment incorporating non-linear fuel injection

Abstract

Stringent legislation on vehicle noise and pollutant emissions has created increasingly severe demands on the fuel injection equipment fitted to automotive diesel engines. In particular, the use of high pressure across smaller nozzle holes to reduce particulate emissions has increased the effects of non-linear compression of the fuel in the passages and volumes in the systems. The mathematical model to simulate high pressure injection system needs to incorporate this high-pressure non-linear behaviour. Condensation, which is continuous across the fuel phase boundary, has been introduced to replace the pressure. This non-linearity in compression has been incorporated into the wave equations by using a non-linear equation of state where the bulk modulus is assumed to change linearly with pressure. The calculation methods for wave disturbances and losses have been investigated and improved methods are presented. The model has been validated with a rotary pump—pipe—nozzle system, but it can be equally applied to other designs such as unit injector and common rail systems. Even though the linear model prediction is in accord with experimental results, the nonlinear model predictions of injection timing and peak line pressure are significantly better.