The superior fuel economy and power density of direct injection internal combustion engine (diesel and gasoline) is related to use of high compression ratio to auto ignite the fuel and the overall lean combustible mixture. Two of the major problems in diesel engine emissions are the NOx and soot emissions, which are caused by the heterogeneity of the charge and the properties of the diesel fuel. Convention Direct Injection Gasoline engines don't have these problems because of the fuel properties particularly its volatility. However its efficiency and specific power output are limited by the knock, knock produced pre- ignition and sporadic pre- ignition phenomenon. Gasoline Direct Injection Compression Ignition (GDICI) engine combine the superior features of the two engines by increasing the compression ratio and use of gasoline as a fuel. One of the main advantages of GDICI engine is the low temperature combustion for low engine out emissions of NOx and Particulates. This paper presents results of an investigation using a high compression ratio, single cylinder, naturally aspirated, high speed, HATZ diesel engine modified to operate as a GDICI engine. Experimental Setup included High response CAMBUSTION analyzer for NOx, CO and CO2 and Unburned Hydrocarbons and A&D high speed data acquisition system and combustion analyzer. A comparison was made between auto- ignition, combustion characteristics, performance, fuel economy and engine out emission parameters using gasoline and ULSD fuels at different operating conditions including cold start transients and part load steady state.