External EGR Combined with Internal EGR for High Load Extension on a Gasoline HCCI Engine

Homogeneous charge compression ignition(HCCI) is a combustion concept with high efficiency and low NO x emissions.Compared with spark ignition(SI) engine,HCCI engine faces the problem of narrow operation range.It is limited by occurring knocking and high NO x emission level.For the natural aspirated HCCI engine,the max.IMEP has been up to 0.5 MPa.The investigation to extend HCCI high load operation limit using internal and external EGR was conducted in a four-stroke gasoline direct injection engine.The experimental results show the HCCI high load limit increases,the max.load rises from 0.41 MPa IMEP to 0.59 MPa IMEP.Under a fixed fuel delivery,with the external EGR increasing,the combustion duration extends and combustion temperature decreases.As a result,the NO x emissions are obviously reduced.The HCCI combustion can be optimized by adjusting the rate of external EGR and internal EGR.