This paper focuses on a novel combustion mode that is developed from the original concept of homogeneous charge compression ignition (HCCI) combustion. Experiments on iso-octane thermo-atmosphere combustion were carried out on a modified single-cylinder engine. n-Heptane was induced from the intake manifold to promote the ignition of iso-octane spray that was directly injected into the cylinder, through HCCI combustion of n-heptane. The combustion and emission characteristics of this novel combustion strategy were analyzed, and the effects of the iso-octane supply advance angle and n-heptane premixed ratio were investigated. The results show that the influence of the thermal effect and active radical produced by n-heptane HCCI combustion on the iso-octane ignition and emission is varied, depending upon the iso-octane supply advance angle. With the advancing of this fuel supply angle, the ignition of iso-octane is enhanced at first but then suppressed. At an iso-octane supply advance angle of 25 °CA BTDC, ...