Visualization of Fuel Jet in Conditions of Highly Preheated Air Combustion

Abstract

During highlypreheatedaircombustion,fuelandairareintroducedseparately intoa furnace.High-temperature air is injected into the furnace and mixed with the already present combustion products to generate a hot gas with low oxygen concentration into which fuel issupplied directly. Theway thefuel and airare injected into thefurnace chamber is of primary importance for the distributions of furnace temperature, oxygen, and fuel that thus affects NOx emission and combustion efe ciency. Fuel directly injected into a crosse owof a highly preheated (up to900 ± C) oxidizer with variable oxygen content was studied experimentally. For still and high-speed photography, direct and schlieren color visualizations were used to record images of e ames. Flamesize, visibility, color, liftoff distance, and e ow structure were investigated. The oxygen concentration in the highly preheated oxidizer was found to have a substantial effect on e ame size, liftoff distance, and e ame-base e uctuation. A lower oxygen concentration increases the e ame size and the liftoff distance, and for the high-velocity fuel jet it also increases the e uctuation and liftoff distance. Temperature has the opposite effect of decreasing the e ame size but not in the same proportions as an increase in oxygen concentration. The e ame visibility decreases with decreasing oxygen concentration and increases with temperature. Also, e ame color changes from bright white/yellow to blue/green/yellow and is primarily ine uenced by oxygen concentration.