Showing papers by "Preeti Aghalayam published in 1998"

The role of radical wall quenching in flame stability and wall heat flux: hydrogen-air mixtures

Abstract: The role of wall quenching of radicals in ignition, extinction and autothermal behaviour of premixed H2–air flames impinging on a flat surface was studied using numerical bifurcation techniques, with detailed gas-phase chemistry and surface radical recombination reactions. Quenching out of radicals was found to retard the system at ignition due solely to the kinetics of the surface reactions. While kinetically extinction is also retarded, the thermal feedback from the wall recombination of radicals can render the flame more stable and lead to a higher wall heat flux as a function of wall temperature compared to an inert surface under some conditions. It is also shown that the combined kinetic and thermal effects of wall radical quenching can expand the autothermal regime. Implications for estimating flammability limits near reactive surfaces of tubes are finally discussed. M This article features multimedia enhancements available from the abstract page in the online journal; see http://www.iop.org.

Roles of thermal and radical quenching in emissions of wall‐stabilized hydrogen flames

Abstract: A numerical study of the combustion of H{sub 2}/air mixtures impinging on surfaces has been performed, using detailed chemistry and multicomponent transport, in order to elucidate the roles of surface thermal and chemical quenching in pollutant emissions For extinguishable fuel/air mixtures, the thermal coupling with the surface has been found to be strong, and surface thermal quenching reduces NO{sub x} emissions However, nonextinguishable mixtures are practically unaffected by changes in surface temperature, except for an increase in NO{sub 2} at low surface temperatures It is shown that radical wall quenching can affect emissions for all flames, with H being the most important one primarily for NO{sub 2} near the surface, due to the reaction NO{sub 2} + H {leftrightarrow} NO + OH A new method to elucidate the dominant paths for NO formation is also presented

NOx and fuel emissions in combustion of hydrogen/air mixtures near inert surfaces

Abstract: Combustion of premixed H 2 /air flames near inert surfaces was studied numerically using detailed chemistry and multicomponent transport. The roles of inlet composition, radiative loss from the surface, and thermal quenching by cold walls in NO x and fuel emissions were analyzed. It is shown that the bifurcation behavior in terms of extinguishability strongly determines the role of thermal quenching in emissions. For weak, extinguishable flames, thermal quenching at the surface effectively reduces NO x emissions, although at the cost of higher fuel emissions. Strong, nonextinguishable flames at low strain rates are practically unaffected by thermal quenching except for an increased NO 2 mole fraction near the surface.