Study on Model-Based Control for HCCI Engine

In order to realize stable and fuel-efficient operation with homogeneous charge compression ignition (HCCI) combustion, it is necessary to precisely control in-cylinder conditions such as gas temperature and oxygen concentration according to the target load set for each cycle. The HCCI combustion discussed in this study utilizes internal exhaust gas recirculation (EGR). For this type of combustion, the exhaust gas temperature and composition in the last cycle should be accurately estimated, and the internal EGR rate and the fuel injection quantity should be appropriately commanded to generate in-cylinder conditions that ensure combustion in the next cycle. To implement this effectively, the authors constructed a control-oriented model for the HCCI combustion which utilizes internal EGR with the negative valve overlap method, and developed a model-based feedforward controller based on this model. Firstly, the model-based feedforward controller was validated by simulations in which a change in the target load was given to the controller. Secondly, engine experiments were conducted to validate the controller in the same way. The results confirmed that the model-based feedforward controller was able to generate in-cylinder conditions suitable for the target load given to each cycle and thus realize stable HCCI combustion while following the target load.