Operation of a DI Diesel Engine With Variable Effective Compression Ratio in HCCI and Conventional Diesel Mode

An experimental investigation was carried out in which an HSDI Common Rail Diesel engine was operated in both HCCI and conventional Diesel combustion modes, using conventional Diesel fuel in both cases. The engine used in the experiments was a single cylinder version of a modern passenger car engine with a displacement of 480 cc. In HCCI mode, the fuel was injected in multiple stages during the compression stroke, using a nozzle with a 60° included angle. To control the phasing and rate of combustion, the effective compression ratio was reduced by retarded intake valve closing. In addition, increased amounts of EGR were used. HCCI operation reduced soot and NO_x emissions significantly. The use of a narrow included angle for conventional Diesel operation increased emissions significantly. The effect of a wider included angle and modifications to the piston were investigated experimentally and numerically. HCCI operation was also possible with a piezo injector with a 140° included angle. Because of the more accurate, shorter injections allowed by the piezo injector, interaction of the spray with the cylinder liner could be avoided, despite the wide included angle.