Effect of pressure on structure and NOx formation in CO-Air diffusion flames
Howard G. Maahs, Irvin M. Miller, United States. National Aeronautics and Space Administration. Scientific and Technical Information Branch, Langley Research Center
National Aeronautics and Space Administration, Scientific and Technical Information Branch, 1979 - Science - 55 pages
A study has been made of flame structure and nitric oxide formation in confined laminar CO-air diffusion flames over a pressure range from 1 to 50 atm. The shape of the flames changed from wide and convex at 1 atm to slender and concave at 50 atm, with the greatest change occurring below about 10 atm. Flame height decreased with increasing pressure from 1 atm to about 10 atm, but was independent of pressure at higher pressures. The regimes of stable burning decreased with increasing pressure up to 50 atm, with the greatest reduction occurring between 1 atm and 20 atm. The molar emission index (the moles of nitrogen oxides formed per mole of carbon monoxide consumed) increased as the pressure was increased above 1 atm, reached a maximum at approximately 28 to 30 atm, and thereafter decreased slowly up to 50 atm. Circumstantial evidence is offered to support the proposition that the concentrations of nitrogen oxides in the flames approach their equilibrium values for pressures above about 20 atm. (Author).
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146-sccm CO flame 73-sccm CO flame adiabatic flame temperature air flow rate approximately atm Figure average equivalence ratio calculated carbon monoxide carbon particles CH4 flame CO-air diffusion flames CO2 and N2 Combustion Inst combustion reactions decrease diameter diffusional rate elementary reaction equation equilibrium with molecular estimate experimental average rate figure 10(a flame height flame zone formation of nitrogen formation of NOX formation rates function of pressure gases high-pressure chamber higher pressures igniter Im,eq kinetics lower pressures mass flow rate maximum Methane methane-air diffusion flame methane-air flame molar emission index mole fraction molecular oxygen moles/cm^-sec NASA Nitric Oxide Formation nitrogen oxides NOX formation obtained oxygen atoms oxygen-atom concentrations plotted in figure ppm H2 premixed flame pressure is increased rate expression rate of formation reaction rate constant reaction volume reaction zone reactions approach equilibrium reference sccm stability and extinction stoich stoichiometric thermocouple Tref volumetric flow rate Zeldovich mechanism