Multi-dimensional Numerical Simulation On Stratified Charge Combustion Ignition Engine Combustion Mechanism

Stratified Charge Combustion Ignition (SCCI) is a promising combustion mode that can expand the operate range of Homogeneous Charge Combustion Ignition (HCCI). It is a key strategy to achieve high efficiency and low emissions in a bigger operate range.A multi-dimensional model is adopted to investigate the combustion mechanisms and emission processes of n-Heptane SCCI combustion processes. The multi-dimensional model couples the reduced chemistry and the CFD model. First of all, the quondam n-Heptane reduced chemistry mechanism expanded through the sensitivity analysis. The new chemistry mechanisms adapt to SCCI combustion simulation, improved the calculation precision. Base on this reduced chemistry mechanism; a multi-dimensional model is adopted to investigate the SCCI combustion mechanisms. Simulation results indicate that the SCCI high temperature reaction occurs ahead of the HCCI combustion processes. The high temperature reaction regions for SCCI combustion process are located in the area where the equivalence is high. In the SCCI combustion process the oxidizing reaction speed of CO reduced, combustion process gently. It is advantageous in expanded the high efficiency and low emissions combustion operation range to the high load areas. There will appear a partial high temperature area in the SCCI combustion process, so the NOx increases.Author used port/direct injection to achieve different stratified charge, and simulated how different stratified charge influenced the combustion and emission. The simulation results of exchange the timing of injection shows that 40°BTDC is a dividing line. When the injection time is before 40°BTDC, the combustion process is more like HCCI combustion process. The rate of high temperature reaction increases, the partial high temperature area reduces, NOx decreases; when the injection time is after 40°BTDC, the rate of high temperature reaction increases, the partial high temperature area extend, NOx increases. Especially when the injection time is 13°BTDC, the high temperature reaction of homogeneous charge and the proliferation burning overlapped. The pressure and the combustion rate are high and NOx is the highest. The simulation results of exchange the mass of injection shows that along with the inject fuel increase; the high temperature reaction occurs advanced, the oxidizing reaction speed of CO reduced, the partial high temperature area in the cylinder enlarged, NOx increased.The result of this research opened out the combustion mechanism of SCCI. It has important theory significance to the stratified charge control.