Effects of CO2 and N2 mixing into Ambient Air on Flame Temperature and Soot Formation in Intermittent Spray Combustion

In order to study the effects of EGR on diesel combustion fundamentally, the effects of CO₂ and N₂ mixing into ambient air on intermittent spray combustion were examined experimentally. Under the same condition of ambient temperature and pressure, and the same injection pressure, the rates of CO₂ or N₂ mixing were changed from 0 to 15% and the combustion characteristics of diesel spray were examined. Through the systematic experiments, it was explored that the ignition delay and the combustion period became longer with the increase of CO₂ and N₂ mixing, and the effect was larger in the case of CO₂ mixing. The flame temperature became lower with the N₂ mixing mainly due to the dilution effect. In the case of CO₂ mixing, the flame temperature decreased notably, and the flame region with higher temperature became very small. The reason of this tendency was attributed to the dilution effect, the higher heat capacity of CO₂ and the chemical effect of CO₂. Though the combustion delayed and the combustion temperature became lower with the CO₂ mixing, the amount of soot in flame did not change so much.