The Study Of Mixture Formation And Combustion Process In A Methanol Fueled Directly-Injection Engine

This paper presents results of a CFD study of the flow field, charge stratification and ignition stabilization inside the cylinder of a direct-injection methanol engine.The calculations and analysis of the in-cylinder flow near TDC were performed and the effects of initial swirl and initial tumble on the in-cylinder flow field are studied.Based on the results obtained in terms of swirl, squish and turbulence intensity fields, in the second part, the fuel injection and subsequent charge stratification process inside the engine cylinder is modeled. In particular, the effect of the nozzle position, spray parameters and initial tumble ratio on the mixture formation are discussed and some conclusions drawn. For the part of ignition stabilization, the ignition position is optimized, The combustion characteristics of methanol and NOx emission are studied with different injection timing and ignition timing. The main results are as follows:1. When there is no initial swirl or tumble, a longitudinal vortex is formed in the entrance of the combustion chamber on the effect of the squish, and the initial tumble has a stonger effect on the vortex than the initial swirl;2. By matching the spray and the in-cylinder flow, the mixture can be stratified reasonably and get a stable ignition area where there is suitable equivalent ratio concentration and flow velocity;3. Based on the methanol spray strategy, when the engine works at low load, spray process is nearly finished before the combustion process starts, the premixed combustion plays an important role; when the engine works at high load, only about a half of the methanol is injected into the combustion chamber, which is burned in a premixed way, then the combustion process is mainly controlled by spray, the diffusion combustion plays a main role.