Multi-dimensional Numerical Simulation On DME/MEOH Dual Fueled HCCI Engine Combusiotion Mechanism

Homogeneous Charge Combustion Ignition (HCCI) is a promising combustion mode that can achieve high efficiency and low emissions simultaneously, and it is also a key strategy to meet future emission regulations.A multi-dimensional model is adopted to investigate the combustion mechanisms and emission processes of Dimethyl Ether(DME) and Dimethyl Ether(DME)/Methanol(MEOH) dual fuel HCCI combustion processes. The multi-dimensional model couples the reduced chemistry and the CFD model.Simulation results indicate that low temperature reaction timing predicted by zero-dimensional model is the same as that predicted by multi-dimensional model. However, high temperature reaction timing predicted by multi-dimensional model is later than that predicted by zero-dimensional model, and rate of heat release is also lower, because the heat transfer and in-cylinder turbulence flow are considered in the multi-dimensional model. Cylinder temperature throughout the combustion process undergoes a process from inhomogeneity till homogeneity. Both low and high temperature reactions don't occur simultaneously. Dual fuel not only changes the paths of DME reaction, but also the initial locations of combustion process. Low temperature reaction regions for DME HCCI combustion process are located near piston surface and squish region, and high temperature reaction occurs in the combustion chamber core zone. Quasi-low temperature reaction region for DME/MEOH HCCI combustion process resides in the combustion chamber core zone, and high temperature reaction is initiated in the combustion chamber core zone near the cylinder axis. DME and Methanol undergoes one stage oxidization process respectively. Emission analysis indicates that unburned fuel and CH2O account for the majority of unburned hydrocarbon (HC), and unburned fuel shares greater part. Much of unburned fuel resides in the piston-ring crevice region, which is the main reason of low thermal efficiency for dual fuel combustion process. Compared with pure DME HCCI combustion process, unburned fuel account for greater portion of HC for DME/MEOH HCCI combustion process. For DME HCCI combustion process, unburned fuel, CH2O and CO mainly resides in the bottom, middle and top of piston-ring crevice region respectively. For dual fueled HCCI combustion process, unburned fuel mainly resides in the piston-ring crevice region; the majority of CH2O is located next to...