Control-oriented model-based ignition timing prediction for high-degrees-of-freedom spark ignition engines

Abstract

The pressure to improve automotive fuel economy and emissions has driven the introduction of more complex spark ignition engines. As the number of control actuators increases, traditional ignition timing calibration and control methods become restrictive, creating a need for new feedforward approaches to manage transient operation. This research was conducted to determine whether a control-oriented turbulent flame entrainment model could be developed to predict the ignition timing of an engine with a large number of control actuators. A physics-based approach is used to capture the influence of additional control actuators on the complex interactions affecting the ignition timing. Each actuator is characterized by its influence on the fundamental combustion parameters, such as the residual gas fraction and the turbulence intensity. Experimental results are used to generate semiempirical input and combustion models that are capable of running in real time within an engine controller. The model is used to predict the combustion duration, from the spark to 50% mass fraction burned, at every crank angle position within a reasonable ignition timing window for each engine operating point. With minimal engine mapping, the model was capable of predicting the spark timing to within several degrees of ideal values, demonstrating the feasibility of this approach for use in high-degrees-of-freedom spark ignition engines.