HCCI operation of a passenger car common rail DI Diesel engine with early injection of conventional Diesel fuel

Artikel i vetenskaplig tidskrift, 2004

The possibilities of operating a direct injection Diesel engine in HCCI combustion mode with early injection of conventional Diesel fuel were investigated. In order to properly phase the combustion process in the cycle and to prevent knock, the geometric compression ratio was reduced from 17.0:1 to 13.4:1 or 11.5:1. Further control of the phasing and combustion rate was achieved with high rates of cooled EGR. The engine used for the experiments was a single cylinder version of a modern passenger car type common rail engine with a displacement of 480 cc. An injector with a small included angle was used to prevent interaction of the spray and the cylinder liner. In order to create a homogeneous mixture, the fuel was injected by multiple short injections during the compression stroke. The low knock resistance of the Diesel fuel limited the operating conditions to low loads. Compared to conventional Diesel combustion, the NOx emissions were dramatically reduced. The smoke emissions also showed a significant reduction, while CO and HC emissions increased substantially. The HCCI combustion mode is characterized by a much more rapid heat release and higher fuel consumption, due to the lower compression ratio and the high HC and CO emissions.