Analysis of Effect of Water on NO Formation in DI Diesel Engines

The effect of water on NO formation was analyzed theoretically from the point of view of changes in the entrained air rate and specific heat of the burned gas in the combustion chamber. The specific heat was calculated accurately based on the chemical equilibrium composition analysis considering the absolute humidity of the inducted air, the amount of water in the emulsified fuel and the residual gas fraction. It is clarified by the two-zone combustion model analysis that about 20% reduction in NO_x is attained by an increase of only 0. 01 kg/kg in the absolute humidity, and the NO_x reduction due to the water-emulsified fuel is caused by increases in both gas weight and specific heat of the burned gas whereas the entrained air rate is hardly affected by the water in the emulsified fuel