Modelling and injection rate estimation of common-rail injections for direct-injection diesel engines

Diesel engines have evolved in order to meet stringent emission standards and to satisfy consumer demand for better fuel efficiency and increased power. The common-rail injection system was introduced in order to satisfy stringent emission standards, low fuel consumption, and low noise in recent years. The performance of a fuel injection system is strongly influenced by the injector characteristics. In this study, non-linear mathematical models are proposed for solenoid-operated and piezo-actuated injectors for control applications. Based on these models, the injection rate, which is one of the most important factors for the injection characteristics, is estimated using a sliding-mode observer. The simulation results and the experimental data show that the proposed sliding-mode observers can effectively estimate the injection timing and the injection rate for both types of common-rail injector.