HCCI Engine Combustion-Timing Control: Optimizing Gains and Fuel Consumption Via Extremum Seeking

Homogenous-charge-compression-ignition (HCCI) engines have the benefit of high efficiency with low emissions of $\hbox{NO}_{x}$ and particulates. These benefits are due to the autoignition process of the dilute mixture of fuel and air during compression. However, because there is no direct-ignition trigger, control of ignition is inherently more difficult than in standard internal combustion engines. This difficulty necessitates that a feedback controller be used to keep the engine at a desired (efficient) setpoint in the face of disturbances. Because of the nonlinear autoignition process, the sensitivity of ignition changes with the operating point. Thus, gain scheduling is required to cover the entire operating range of the engine. Controller tuning can therefore be a time-intensive process. With the goal of reducing the time to tune the controller, we use extremum seeking (ES) to tune the parameters of various forms of combustion-timing controllers. In addition, in this paper, we demonstrate how ES can be used for the determination of an optimal combustion-timing setpoint on an experimental HCCI engine. The use of ES has the benefit of achieving both optimal setpoint (for maximizing the engine efficiency) and controller-parameter tuning tasks quickly.