Effects of air dilution on highly preheated air combustion in a regenerative furnace

Air dilution in highly preheated air combustion has been found to be effect ive in controlling the NOx emission and improving the temperature uniformit y. In this study, the effects of air dilution with different diluents on hi ghly preheated air combustion have been numerically investigated. A regener ative furnace was simulated, where nitrogen, carbon dioxide, helium, argon, and flue gas were adopted as air diluents. It was found that the flame tem perature, the temperature uniformity, and the NOx emission are different wh en different air diluents were adopted under the same preheated air tempera ture and oxygen concentration. On the basis of the analysis and comparison, it is deduced that the heat capacity of the diluted air, represented by th e product of the density and specific heat, plays a main role in the effect of air dilution on the combustion process. The turbulent intensity, repres ented by the kinetic energy, also plays a role but less significant compare d with the heat capacity. The difference in the momentum of diluted air flo ws with different diluents results in a change in the flame shape.