Ethanol has been used either as an alternative fuel or in blends with gasoline in spark ignition (SI) engines for many years. However, the existing method of using ethanol fuel by blending gasoline and ethanol fuel does not fully exploit the ethanol fuel's potential in improving engine thermal efficiency and reducing pollutant emissions. The dual-fuel injection strategy, ethanol direct injection plus gasoline port injection (EDI+GPI), offers a potentially new way to make the best use of ethanol fuel. In this paper the potential of EDI+GPI is investigated based on experiments conducted on a single cylinder SI research engine equipped with EDI+GPI. The leveraging effect of EDI+GPI on engine performance was investigated at different ethanol/gasoline energy ratios (EERs) and speeds. Then further investigation to the leveraging effect enhanced by ethanol injection timing and spark timing was performed. Experimental results showed that the IMEP increased with the increase of EER. Engine combustion characterized by initial, early and major durations was improved with the increase of EER until the EER was 42.4%. HC and CO decreased with the increase of EER until the EER was 24.2% and increased with further increase of EER. Experimental results for leveraging effect enhanced by ethanol injection timing and spark timing showed that the later ethanol direct injection after the inlet valve was closed was effective in suppressing engine knock and enabling more advanced spark timing. Earlier ethanol direct injection before the inlet valve was closed could effectively increase the volumetric efficiency. However its effect on knock suppression was less than that with later ethanol direct injection. The combined effects of spark advance and improved volumetric efficiency in early ethanol direct injection led to higher IMEP and engine efficiency than that in later ethanol direct injection.