Numerical investigation of the effect of late intake valve closing on diesel HCCI combustion and emissions

A full-cycle three-dimensional computational fluid dynamics (CFD) model coupled with detailed chemical kinetics was developed to investigate the effect of late intake valve closing (IVC) on combustion and emission characteristics in a diesel homogeneous charge compression ignition (HCCI) engine. Utilization of late IVC provides effective ignition timing controlling and significant reduction of nitrogen oxides (NOx) by decreasing effective compression ratio, but it increases soot, hydrocarbon (HC) and carbon monoxide (CO) emissions due to low combustion temperature and lack of oxygen. Parametric studies by varying intake pressure, exhaust gas recirculation (EGR) rate and start of injection (SOI) timing by changing IVC timing were conducted to explore the potential of late IVC on emission reduction of diesel HCCI engines. Results show that, late IVC and boosting intake pressure realize ultra-low NOx while maintain low soot, HC and CO emissions if sufficient EGR and optimized SOI timing are set. By retarding IVC timing to 260°CA and employing 0.18 MPa intake pressure, 50% EGR and 20°CA BTDC SOI, both NOx and soot formation regions can be suppressed under partial engine load.