Diesel Injection-System Simulation: Added Value of the Energy Conservation Equation 2011-01-0389
The detailed 1D model of a solenoid injector for high pressure Diesel-injection systems has been developed using the LMS Imagine.Lab AMESim platform.
The paper presents the simulation results focusing on the most important physical events occurring in automotive Diesel injection equipments typically working in unsteady-flow conditions. Inertial effects of hydraulic lines (external connecting pipe, injector return lines and internal piping) are important, especially for studying the hydraulic coupling between pilot and main injections in case of small separation angles. The pilot injection induces important wave propagations inside the injector that can affect the total injected mass during the subsequent injection event - the main injection - especially when the timing is quite reduced.
Highly predictive mathematical models are available within the AMESim hydraulic library for the description of waves' effects; they internally solve the mass and the momentum conservation equations through a Lax-Wendroff numerical scheme taking into account frequency dependent friction. They are consequently called CFD 1D line models.
The detailed description of the injector geometry (nozzle, control plunger and control valve), of the solenoid actuation, and of the resistive-capacitive-inertial effects of both hydraulics and mechanics makes the model a reliable design tool for the optimization of the injection rate shape and of the EMI map curves (injection quantity vs. solenoid excitation time for different pressure levels).
The final step in simulation is to introduce the energy conservation equation and consequently to consider the temperature time-evolution due to heat exchanges, enthalpy flow rates and pressure variations. The fluid properties are then evaluated as functions of both temperature and pressure by an advanced mathematical model taking into account aeration and cavitation.
The paper will compare a model where only mass and momentum conservation equations are considered assuming an adiabatic transformation against a model where the energy conservation equation is further added.