Controller-Observer Implementation for Cycle-by-Cycle Control of an HCCI Engine

This paper presents experimental cycle-by-cycle control of a single cylinder HCCI engine. The controller is developed from a discrete-time nonlinear model presented in previous work. The model captures the behavior of a gasoline direct-injection engine with an exhaust-recompression strategy used to achieve HCCI. This model is linearized about an operating point so as to enable the synthesis of linear controllers. The model states are represented by the temperature and oxygen content of the retained exhaust, and so are not measurable in practice. Therefore, an observer is used to estimate the states based on a measured ignition proxy. The state estimates are then used by a reference-input tracking controller to track a desired system trajectory. Experimental results show tracking of the model outputs that is comparable to tracking achieved in simulation. The controller is also seen to reduce the cycle-to-cycle variability of combustion significantly, particularly at later combustion phasing. This stabilizes combustion, lowers the instances of misfires, and enables steady operation at points that are normally unstable.