SAE International Advanced Mathematical Modeling of Electronic Unit-Injector Systems for Heavy Duty Diesel Engine Application 2008-01-1195

A rather complete mathematical model to simulate HD-diesel- engine EUI-system dynamics was developed and applied as a complementary tool of experimentation, for supporting design and performance optimization. The thermo-fluid dynamics of the hydraulic components, including plunger cavity, internal injector pipes and nozzle, was modeled with the solenoid-circuit electromagnetics and the mechanics of rocker arm and follower subsystem. Onedimensional flow equations in conservation form were used to simulate wave propagation phenomena through the injector high-pressure drilled passages. To calculate the temperature variations due to the compressibility of the liquid fuel, the energy equation was used in addition to mass conservation and momentum balance equations. Furthermore, in order to determine the value of the electromagnetic force acting on the spill-valve, the application of a practical procedure was made using easily available experimental current and voltage data. An advanced mechanical model of the rocker arm and follower subsystem was developed, taking the mechanical drive deformability into account. It was capable of accurately simulating the effects of the pressure wave dynamics on the plunger kinematics as well as on the Hertzian contact forces at the plunger-follower and cam-rocker- arm interfaces. The numerical code was validated at different working conditions through the comparison of predicted results and experimental data in terms of pressure in the plunger cavity, injected flow-rate, needle- and spill-valve lift time-histories. The developed EUI model was then applied for better understanding the cause and effect relationships in the analysis of system transients. Furthermore, a parametric study was carried out to assess the effects of important geometrical and mechanical system parameters on EUI operation. Finally, design keys were provided to improve the trade off between the hydraulic injector performance, the engine-out emission levels as well as the mechanical noise reduction.