Internal combustion Rankine cycle (ICRC) engine uses oxygen instead of air as oxidant during the combustion process, therefore totally eliminates the emission of NOx. CO2 could be captured after separated from the exhaust gas, the latter are mainly water vapor and CO2, through condensation at a relatively low price, and thus an ultra-low emission working cycle is achieved. Moreover, water is heated up by exhaust gas and injected into the cylinder during the combustion process to control combustion temperature, and evaporation of the water mist would increase working fluid inside the cylinder, therefore enhance indicated thermal efficiency. This study investigates the combustion characteristics of a quasi ICRC on a single-cylinder SI engine fueled with propane. Gas mixture of O2/CO2 is employed to simulate EGR in order to control in-cylinder temperature. O2 concentration is set to 40 vol% and water is injected into the cylinder near top dead center to control the oxy-fuel combustion process. The effect of water injection timing, injection duration, as well as injection pressure are studied, and results show that indicted work is enhanced by 7.8% experimentally at engine speed of 2400r/min with IMEP of 0.62 MPa. Cycle performance is better when injection timing is earlier, and combustion phasing is postponed without decreasing peak in-cylinder pressure. The increase of injection duration and pressure has effects on peak in-cylinder pressure but does not affect combustion phasing notably.