This paper focuses oil the effects of early stage injection and two-stage injection oil the combustion characteristics and engine performances of an indirect injection (IDI) diesel engine. In a direct injection (DI) diesel engine, HC emission increases with early stage injection because some of the fuel spray adheres to the cylinder wall and burns in the gap between the piston and the cylinder. On the other hand. since the fuel spray of early stage injection in an IDI diesel engine is injected into an auxiliary combustion tion chamber such as a swirl chamber, the IDI diesel engine could reduced the HC emission produced from the gap compared with a DI diesel engine. In a two-stage injection IDI diesel engine. NO and smoke emissions are improved when the amount of fuel in the first stage injection is small and small first stage injection timing is advanced over -80degrees TDC. And 20% improvement in fuel consumption Is achieved when the first stage injection timing is advanced over -80degrees TD TDC. Conversely. HC and CO emissions of two-stage injection increases compared with that of conventional injection of an IDI diesel engine. However, CO emission can be improved a little when the first stage Injection timing is advanced over -100degrees TDC and the second stage injection timing is retarded over TDC. (C) 2004 Elsevier Ltd. All rights reserved.