To decrease even eliminate Carbon Dioxide (CO2) emissions for mitigating global warming, various technologies are being developed on combustion engines. In the research presented in this paper, a numerical investigation of Oxy-Fuel Combustion (OFC) technology on an ethanol-gasoline Dual-Fuel Spark Ignition (DFSI) engine under economical oxygen consumption at low and mid-high loads was performed by one-dimensional computer simulation. It is demonstrated that under OFC mode without other optimisation, Brake Mean Effective Pressure (BMEP) can meet the requirement at mid-high load, but it has a considerable decline at low load compared to Conventional Air Combustion (CAC) mode. Moreover, there is a considerable deterioration in Brake Specific Fuel Consumption (BSFC) compared to that of CAC mode. A practical method is proposed to optimise the DFSI engine performance under OFC mode by changing intake charge components and utilising appropriate Water Injection (WI) strategies. BMEP increases approximately 0.05 bar at low load. BSFC has a reduction of 3.35% and 1.82% at low load and mid-high load, respectively.