Date of Award
Mechanical, Automotive, and Materials Engineering
Sobiesiak, Andrzej (Mechanical, Automotive & Materials Engineering)
CC BY-NC-ND 4.0
A geometry and reactant delivery method relevant to burners with low emission of nitrogen oxides is studied at the laboratory-scale. The design is an inverse diffusion flame of methane, with a central air jet discharging into a jet of fuel. Surrounding the fuel is an additional co-flow of either air or co-flowing combustion products. The location of the central air discharge is raised above the burner, to allow the fuel to mix with the co-flowing gas before reacting with the central air stream. Characteristics of these flames are studied experimentally with excited-state CH* chemiluminescence imaging. Numerical simulations are validated through comparison with the experimental measurements. Simulation results are post-processed to account for chemiluminescent emission and to model the non-ideality of the imaging system. At low velocities of the central air jet, hysteresis behaviour of the inner flame is observed. A partially-premixed flame is formed on the centreline at a constant fraction of the outer diffusion flame height. When the central air velocity reaches a critical level, this flame propagates upstream and stabilizes closer to the burner face. The spread in velocity between this transition, and the extinction of the inner flame is larger with co-flowing combustion products. Simulation results are analyzed to explain the characteristics of the flames observed in the experimental images, and how these characteristics affect the heat release and pollutant emissions from the flames. As the central air velocity is increased, emission of nitric oxide is decreased, as more of the combustion takes place in a premixed versus a diffusion flame, but this is offset by increased emissions of CO and unburned fuel that are entrained into the central air jet and exit the simulation domain. Raising the discharge location of the central air stream tends to increase the emissions of nitric oxide, as the fuel is displaced outwards and more of it reacts in the diffusion flame.
Johnson, Michael, "Methane Inverse Diffusion Flames with Co-flowing Air and Combustion Products" (2009). Electronic Theses and Dissertations. 460.