Mechanism of Oxygen Concentration Effects on Combustion Process and Emissions of Diesel Engine

Abstract

The mechanism of oxygen concentration effects on the combustion process of diesel combustion and the effects of injection pressure and intake pressure on low-temperature combustion are investigated by CFD simulation. The oxygen concentration is modulated by CO2. The results indicate: with the decrease of oxygen concentration, the peak of the average in-cylinder pressure decreases and the ignition delay becomes long. Decreasing oxygen concentration is the most effective method to control NOx emissions. With the decrease of oxygen concentration, soot emissions increase first and then decrease. It is the essential reason of low soot emissions at low oxygen concentrations that the low in-cylinder combustion temperature leads to the inhibition of soot formation. With the increase of injection pressure, the flow velocity and turbulent kinetic energy in the cylinder increase, which are beneficial to improving the mixing of fuel and air; soot emissions decrease; and NOx emissions increase. The enhancement of intake pressure improves the condition of oxygen lack at lower oxygen concentration. With the increase of intake pressure, ignition delay becomes long. Soot and NOx emissions decrease.