Numerical study on steam-added mild combustion

Abstract

Numerical study on flame structure and NO emission is conducted covering a wide range of atmospheric temperature, high temperature, and mild combustion regimes in H2-Air laminar flames diluted with steam. Special concern is focused on the difference of flame structure and NO emission behaviour between high-temperature combustion and mild combustion modes. The important role of chemical effects of added steam in flame structure and NO emission behaviour is also discussed. It is seen that there exists an oxidizer-side temperature limit which the combustion mode changes from high temperature combustion to mild combustion. In high temperature combustion modes the OH production via the reaction step, (-R23) is suppressed while in mild combustion modes is enhanced by the increase of oxidizer-side temperature. It is also found that chemical effects of added steam are influenced by the competition between both the reaction steps, (R21) and (-R23). NO emission index increases with increasing oxidizer-side temperature and decreases with mole fraction of added steam. The remarkably produced OH due to chemical effects of added steam does not contribute to the increase of NO but plays a role of holdback on NO in thermal mechanism. It is also seen that in both the high temperature combustion and mild combustion modes NO emission indicates a consistently similar tendency, and is consequently recognized that in the whole ranges steam addition suppresses NO emission. Copyright © 2004 John Wiley & Sons, Ltd.