Reference Governor for Load Control in a Multicylinder Recompression HCCI Engine

This paper presents a model-based control strategy designed to regulate combustion phasing during load transitions in a recompression homogeneous charge compression ignition (HCCI) engine. A low-order discrete-time control-oriented model for recompression HCCI combustion is developed that represents the strong thermal and composition coupling between engine cycles. A baseline two-input single-output controller is designed to regulate combustion phasing, using the amount of negative valve overlap and the fuel injection timing as actuators. This controller is augmented by a reference or fuel governor, which modifies transient fuel mass commands during large load transitions, when future actuator constraint violations are predicted. This approach is shown in experiments to improve combustion phasing and load responses, preventing engine misfires in some cases. The fuel governor enables larger load transitions than were possible with the baseline controller alone. The governor acts only when future actuator constraint violations are predicted. The complexity and computational overhead of the governor are reduced by developing a linearized fuel governor. Satisfactory performance is demonstrated experimentally for a range of engine speeds.