MODELING COMMON RAIL FUEL INJECTION SYSTEM IN DIESEL ENGINES

In the present work, a mathematical model is developed to simulate and predict the performance of electronically controlled fuel injection system for diesel engines at different operating conditions. The fuel system employs common rail techniques which characterized by symmetrical fuel injection for all engine cylinders and injection pressure beyond 1 k bar. The resultant spray configuration and the availability of multiple injections each cycle leads to achieve significant improvement in combustion efficiency and emissions. The mathematical model introduced in the present work includes the simulation of control signals from electronic control unit "ECU". The model considered the injection timing and firing order when dealing with multiple injectors. Besides, the model includes mathematical simulation of electromagnet power solenoid valves, kinematics of pump plungers due to cam rotation, dynamics of valves and needles motion and finally the flow of fuel through the entire system elements taking into consideration the compressibility effect. The results of the present model are compared with experimental and the available mathematical models to validate the present model. Comparison shows fair agreement. The model shows the great importance of solenoid response in injection timing. The model is proven to be a good tool for exploring the capability of electronically controlled common rail injection system to perform different injection strategies as well as its ability to run with different fuel types. The model can serve also as sub-model in sophisticated CFD codes to simulate realistic combustion process in Diesel engines.