Abstract
Recently VVT (Variable Valve Timing) has been regarded as one of the most feasible methods for implementing HCCI (Homogeneous Charge Compression Ignition) combustion on both gasoline and diesel engines. In this paper, a numerical investigation of the application of late IVC (Intake Valve Closure) for controlling diesel HCCI combustion is described. The investigation was carried out with a full-cycle 3D (Three-Dimensional) CFD (Computational Fluid Dynamics) model coupled with detailed chemical kinetics. The results for diesel HCCI combustion and emission characteristics demonstrated that late IVC could successfully assist diesel engines to run HCCI combustion by decreasing the efficient compression ratio. It could provide efficient control of ignition timing and significant reduction of NOx (Nitrogen Oxides), but need careful adjustment for maintaining a low level of soot, HC (Hydrocarbon) and CO (Carbon Monoxide) emissions. The model was also used to evaluate the influence of intake valve profiles on engine combustion and emissions. It was found that changing intake valve profile during the delayed IVO (Intake Valve Opening) period or reopening intake valve around TDC (Top Dead Center) doesn’t significantly affect NOx and soot emissions, compared to the strategy of late IVC realised by retarding IVC timing.
Keywords: HCCI, CFD, VVT (Variable Valve Timing), late IVC (Intake Valve Closure), diesel engine