Simulation Investigation on the Effects of EGR Ratio and Nozzle Angle on In-Cylinder Combustion and Pollutant Generation of PODE/Methanol Blends

In order to explore effects of coal-based oxygenated fuels polyoxymethylene dimethyl ether (PODE) and methanol on pollutant emissions of diesel engines, in-cylinder combustion numerical model was developed by coupling PODE/methanol reaction mechanism with CONVERGE software. The influences of exhaust gas recirculation (EGR) and nozzle angle on in-cylinder combustion and pollutant generation of PODE/methanol blends were studied. Results show that with the increase of EGR ratio, the fuel-air equivalence ratio increases, the in-cylinder pressure decreases, and the ignition delay period is prolonged. The generation range and rate of NOx gradually decrease, and the final NOx generation decreases by 85.1% at EGR = 20%. However, the peak soot generation rate and the final soot generation increase. With the increase of nozzle angle, the peak in-cylinder pressure and the overall heat release rate increase. When the nozzle angle is adjusted from 148 degrees to 164 degrees, the rich area of fuel-air equivalent ratio in the piston pit decreases, the high temperature area in the piston pit almost disappears. The final in-cylinder NOx generation has been reduced by 29.3%. The soot distribution gradually moves to the upper layer of combustion chamber, and the peak soot generation rate decreases, while the final soot generation increases by almost 49.5%.