Mathematical study of methods to reduce emission of nitrogen oxides and particulate from a compression ignited, direct injection engine .

摘要

A phenomenological model based on the multizone concept and a three-dimensional CFD model were used to predict the effect of engine modification on particulated and NO_x emission from a compression ignited direct injection (CIDI) engine. The phenomenological model consisted of a spray model, an evaporation model, a heat release model, NO_x formation, soot formation, and oxidation model, and can be used to predict the combustion process and pollutant emission in a CIDI diesel engine. The advantage of the multizone model over the 3-D CFD model is the small CPU and memory it requires for a simulation.; In this study, the phenomenological model was used to investigate (1) the effect of increasing the intake-air O₂ content on soot and NO _x emission as a function of power level and wall temperature; and (2) the effect of exhaust gas recirculation (EGR) and split fuel injection on pollutant emission, and compare their soot penalty at a given NO_x emission. The results indicate that EGR with a relatively low temperature can reduce NO_x emission with a minimum penalty of soot particle emission. The use of EGR is promising for significantly reducing NO_x emission with small or no penalty of soot particle emission.; The effect of auxiliary gas injection (AGI) on diesel engine combustion and emission was studied using KIVA 3V, a multidimensional computation fluid dynamics code. AGI enhances the diesel combustion via mixing to reduce the emission of pollutants.; The simulation of a high-speed gas jet model with a relatively coarse computational grids was described. The choice of turbulent length scale for optimum simulation suitability is dependent of local mesh grid. The results demonstrate that AGI creates a second-way flow in the cylinder, which improves the mixing of charge in the cylinder. The effect of AGI on combustion and flow movement is significant. The use of exhaust gas on the AGI can reduce soot emission, while NO_x emission also can be decreased to some degree.; To reduce soot and NO_x emission effectively, the combination effect of EGR and AGI on pollutant emission was analyzed. The results showed that soot and NO_x emission were reduced more than 50%, respectively.