Exploration of the Load Range of HCCI Operation of a DI Diesel Engine

Magazine article, 2005

A passenger car type DI Common Rail Diesel engine was operated in HCCI mode in a load range from 0.1 to 0.5 MPa IMEP and an engine speed range from 1000 to 2500 rpm. Conventional Diesel fuel was injected in up to six subsequent injections during the compression stroke by a piezo injector. For most load cases, soot and NOx emissions were reduced to near zero levels, but HC and CO emissions were significantly higher, when compared to conventional Diesel operation. The improved accuracy of the piezo injector enabled short injections and consequently short spray penetration lengths, which made it possible to use a nozzle with a wide included angle, without excessive cylinder liner wetting. Maintaining the wide included angle meant that operation of the same engine in Diesel operation was not compromised by the injector geometry. EGR and the intake valve closing angle were used as control parameters to properly phase the combustion. Delaying the intake valve closing angle to 90 CAD BTDC reduced the effective compression ratio which allowed the EGR rate to be reduced.