Closed-Loop Combustion Control of a HCCI Engine with Re-Breathing EGR System

This study experimentally investigates the control system and the algorithm after constructing a HCCI combustion control system for the development of a small HCCI engine fuelled with Dimethyl Ether (DME). This system can control four throttles for the mixing ratio of three gases of in-cylinder (stoichiometric pre-mixture, hot EGR gas and cold EGR gas). At first, the combustion behavior for combustion phasing retarded operation with cold and hot EGR was examined. Then, the potential of model-based and feed back control for HCCI combustion with change of the demand of IMEP was investigated. In the end, the limit of combustion-phasing retard for IMEP and PRR was explored. Results shows that to get high IMEP with acceptable PRR and low coefficient of variation of IMEP, crank angle of 50% heat release (CA50) should be controlled at constant phasing in the expansion stroke. CA50 can be controlled by changing the ratio of pre-mixture, hot EGR gas and cold EGR gas with throttles. Due to the cycle-to-cycle variation, the change of total mass of fuel in cylinder has a big effect on IMEP. After misfire, unburned fuel and intermediates remain in exhaust gas, which is re-breathed as hot EGR gas, and unburned fuel and intermediates are supplied to next cycle. This leads to the total mass of fuel changes cycle-to-cycle. As a result of feedback control, transient performance is realized but high sensitivity of response cannot be achieved under the constant engine speed.