Closed-loop control of HCCI combustion for DME using external EGR and rebreathed EGR to reduce pressure-rise rate with combustion-phasing retard

This study experimentally investigates the effects of the combustion phasing on the homogeneous charge compression ignition (HCCI) combustion, and implements a closed-loop control of HCCI combustion to reduce pressure-rise rate (PRR) with combustion-phasing retard. The experiments were conducted using dimethyl ether (DME) in a single-cylinder HCCI research engine equipped with an exhaust gas recirculation (EGR) loop for external EGR and a two-stage exhaust cam for rebreathed EGR. The results show that a maximum PRR (PRR_max) and a maximum in-cylinder charge temperature decreases with combustion-phasing retard. However, excessive combustion-phasing retard leads to unacceptable coefficient of variation (COV) of CA50 and IMEP with partial-burn and/or misfire cycles. To dampen increasing cycle-to-cycle variations around the limit of combustion-phasing retard, the closed-loop control of HCCI combustion was implemented using three feedback variables. Finally, stable stoichiometric HCCI operation could be achieved with extensive combustion-phasing retard while maintaining acceptable PRR_max with the higher level of IMEP.