“…Several potential control methods have been conducted, like fuel–air mixing enhancement, − intake charge heating system, external exhaust gas recirculation (EGR), , internal EGR, variable compression ratio (VCR), , variable valve timing (VVT), , and multiple injection strategies. , One potential methodPCCI engines fitted with the VCR technologywas considered to control the combustion phasing and extend the clean combustion operation range with decreased compression ratio at high loads. However, the practical feasibility, expensive costs, and machining effort are the application constraints of the VCR technology. , VVT was supposed to be another feasible approach to be applied in PCCI combustion. With a late intake valve closing (IVC) timing, the combustion phasing can be retarded, and the range of engine load could also be extended, while the combustion efficiency generally decreases due to the pumping loss. , EGR was often used in diesel PCCI engines .…”