Control-oriented premixed charge compression ignition combustion timing model for a diesel engine utilizing flexible intake valve modulation

This paper describes a simple, analytical, control-oriented model for prediction of combustion timing during premixed charge compression ignition combustion with early fuel injection. The model includes direct dependence on in-cylinder temperature, in-cylinder pressure, and the total in-cylinder O-2 mass fraction, including the contribution of recirculated exhaust gas, residual burned gas, and backflow during the valve overlap period. The model is extensively validated against experimental premixed charge compression ignition data from a multi-cylinder diesel engine utilizing high-pressure recirculated exhaust gas, variable geometry turbocharging, and flexible intake valve actuation, which allows control over the engine's effective compression ratio. The results show that across a wide range of input conditions, the model predicts the start of combustion within +/- 2 degrees crank angle of the experimental values for all but three of the 180 data points (98%+ accuracy), with a root mean square error of 0.86 degrees crank angle. The experimental start of combustion ranges from as early as -19.3 degrees crank angle to as late as +0.6 degrees crank angle by heavily exercising the control actuators, specifically the commanded start of injection timing SOIecm, the intake valve closure timing, and the engine's air-handling system (recirculated exhaust gas valve position and variable geometry turbocharger position). Analysis is performed to isolate the effects and control authority of each actuator on the ignition delay and start of combustion timing. During these actuator sweeps, the model captures complex relationships and predicts the start of combustion within +/- 2 degrees crank angle of the experimental values. This premixed charge compression ignition combustion timing model can be coupled with a gas exchange model for control algorithm design and analysis.