Characterization of inverse diffusion flames with methane and hydrogen

Francisco Maria Machado Rosa Neves Vaz

Key information

Authors:

Francisco Maria Machado Rosa Neves Vaz (Francisco Maria Machado Rosa Neves Vaz)

Supervisors:

Filipe João Marques Quintino (Filipe João Marques Quintino); Edgar Caetano Fernandes (Edgar Caetano Fernandes)

Published in

12/06/2019

Abstract

Greenhouse gas emissions and their climate impact are forcing the combustion industry to devise clean and more efficient solutions. Contrary to conventional flame configurations, Inverse Diffusion Flames (IDF) combine benefits of premixed and diffusion flames, exhibiting extended lean flammability range and low soot production. Hydrogen, in turn, when blended with hydrocarbon-based fuels, can significantly enhance combustion processes and reduce emissions due to its unique properties. In this thesis, an experimental study was conducted to assess the impact of H2 enrichment on the flame structure and emissions of a methane IDF in a multi-slit rectangular burner, under fuel-lean conditions. Fuel blends containing 0%, 25% and 50% H2 were tested, the global equivalence ratio was varied between 0.2 and 1.0 and flame power fixed at 236 W. A PIV (Particle Image Velocimetry) analysis was performed and measurements of the UHC, CO, CO2 and NOx emissions were attained. Two distinct flame structures were identified (Type I and II). It was found that \ce{H2} addition does not create new flame structures but affects the stability range of Type I and II. PIV analysis demonstrated that a significant fraction of the central air jet escapes combustion in flame structure II. Efficiency was found to be dependent on flame structure, with Type I exhibiting better performance overall. Hydrogen enrichment lowered carbon-related emissions for both flame structures and reduced NOx for flame Type I whereas the opposite was found for flame Type II. Finally, hydrogen enabled to maintain flame structure Type I for leaner conditions.