A new DISC combustion system with a pilot flame for ignition was analyzed by using a model combustion chamber of a Wankel type rotary engine. A two-stroke diesel engine's cylinder head was replaced with this combustion chamber to simulate temporal changes of air flow and pressure fields inside the chamber as in actual engines. Two types of fuel injection systems were tested to obtain combustion characteristics such as the heat release rate. Direct photographs of spray and combustion were analyzed to understand the mixture-formation process of the main spray and to see the flame temperature distribution and flame moving velocity vectors. In order to understand the mixture-formation process, numerical calculations were made using a gaseous fuel. Finally, the effect of the fuel characteristics on combustion was examined using diesel fuel and n- hexane.