The superior fuel economy of direct injection internal combustion engines (diesel and gasoline) is related to use of a 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. Conventional Direct Injection Spark Ignition 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 preignition and the sporadic preignition phenomenon. The Gasoline Direct Injection Compression Ignition (GDICI) engine combines 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 the GDICI engine is the low combustion temperature and associated 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 analyzers 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 during the cold start transients and under part load steady state operation.