Fuel governor augmented control of recompression HCCI combustion during large load transients

A control strategy designed to track desired combustion phasing for a homogeneous charge compression ignition (HCCI) engine during large load transitions is presented in this work. Three inputs are controlled, namely valve timings, fuel injection amount and fuel injection timing. The valve and fuel injection timings are manipulated to track combustion phasing using a mid-ranging control strategy. A fuel governor is then added on to the compensated system to modify the fuel injection amount by enforcing pointwise-in-time actuator constraints. The fuel governor is shown to improve the transient response of combustion phasing and load during large load transitions, when the possibility of future constraint violations exists. The use of the fuel governor during large load reductions can prevent engine misfire. Moreover, the fuel governor strategy simplifies the overall controller design by decoupling the phasing controller from the constraint enforcing mechanism. System complexity is reduced by approximating the nonlinear fuel governor as a set of linear algebraic expressions. This is solved with very little computational overhead and without incurring a significant loss in performance, as presented in simulations.