Engine performance and emission characteristics with late intake valve closing (LIVC) and asymmetric cam profile in a compression ignition engine

Abstract

The objective of the study is to observe the effects of late intake valve closing (LIVC) strategies along with the exhaust gas recirculation (EGR) and intake boosting on the engine performance and the emissions. The effects of LIVC strategies with an intake valve closing (IVC) retardation up to 88 crank angle degrees after bottom dead center (CAD ABDC), which is 60 CAD retarded from the original IVC timing, was examined. Two engine load with fuel quantities of 12.0 and 19.8 mg/stroke was selected for the evaluation. The LIVC strategy improved the conventional NOx-smoke trade-off relationship. NOx reduction was attributed to the lowered adiabatic temperature, while the smoke reduction was attributed to the prolonged ignition delay. Further improvement of the trade-off relationship between NOx and smoke was available with asymmetric cam profile, due to the enhanced swirl flow inside the chamber. The smoke emission and the indicated mean effective pressure (IMEP) were deteriorated with LIVC strategy when the engine load was increased due to insufficient amount of oxygen mass and reduced effective compression ratio, respectively. The intake boosting was required to compensate for the repelled charge from the cylinder caused by the retarded IVC timing. The IMEP was also able to be recovered with intake boosting.