Ignition and combustion control of HCCI (Homogeneous Charge Compression Ignition) in DI (Direct Injection) Diesel Engine were examined. In this study, double injection technique was used by Common Rail injection system. The first injection was used as an early injection for fuel diffusion and to advance the changing of fuel to lower hydrocarbons (i.e. low temperature reaction). The second injection was used as an ignition trigger for all the fuel. It was found that the ignition of the premixed gas could be controlled by the second injection when the early injection was maintaining low temperature reaction.
It was found that as the boost pressure increased, ignition timing advanced slightly and the rate of pressure increase markedly decreased. The rate of pressure increase is one of the factors concerning operation limit in this combustion. Therefore, the VNT (Variable Nozzle Turbo-charger) was applied to the production engine to allow boost pressure control. Spray characteristics and combustion analysis images were investigated by the shadowgraph method. Luminous flame was not observed. The fluctuation due to the low temperature reaction was observed from the shadowgraph images. Many ignition points appeared in the combustion chamber. Low NOx and smoke were possible both in the first injection and in the second injection by this combustion. This HCCI concept was named as UNIBUS (Uniform Bulky Combustion System) by the author et al. and applied to the production engine (1KD-FTV, 3 liter-4cylinder) in August 2000 in the Japanese market.