Closed-Loop Control of SI-HCCI Mode Switch Using Fuel Injection Timing

Homogeneous charge compression ignition (HCCI) provides improved efficiency and emissions relative to current engine technologies. One of the barriers to implementing HCCI on production engines is the development of a robust control strategy to transition from traditional spark-ignition (SI) mode to HCCI mode and back. This paper presents such a strategy, based on the control of combustion phasing using fuel injection timing during the mode switch from SI to HCCI. The controller is based on a cycle-by-cycle combustion model developed in previous work. In order to obtain a state estimator for both modes, the model is linearized around operating points corresponding to the steady-states before (SI) and after (HCCI) the switch. The linearized HCCI model is used to synthesize a closed-loop controller to track a desired combustion phasing, with fuel injection timing as the controlled input. The control strategy is tested on a single-cylinder HCCI engine with direct injection. Experimental results at different operating points show that the controller is able to maintain a desirable phasing transient during the mode switch, prevent cycles with very early or late phasing and enable smooth transitions with minimal load fluctuations.