This paper experimentally and numerically studied the effects of fuel combination and intake valve opening(IVO)timing on combustion and emissions of an n-heptane and gasoline dual-fuel homogeneous charge compression ignition(HCCI)engine.By changing the gasoline fraction(GF)from 0.1 to 0.5 and the IVO timing from-15℃A ATDC to 35℃A ATDC,the in-cylinder pressure traces,heat release behaviors,and HC and CO emissions were investigated.The results showed that both the increased GF and the retarded IVO timing delay the combustion phasing,lengthen the combustion duration,and decrease the peak heat release rate and the maximum average combustion temperature,whereas the IVO timing has a more obvious influence on combustion than GF.HC and CO emissions are decreased with reduced GF,advanced IVO timing and increased operational load.