Progress in knowledge of flamelet structure and extinction

NOx formation in two-stage methane–air flames

Soot and NO formation in methane-oxygen enriched diffusion flames

Effects of diluents on NOx formation in hydrogen counterflow flames

A laminar counterflow configuration is investigated in which a fuel-rich methanol spray is transported by air against an apposing air stream. The fuel-stream equivalence ratio ranges from 1.6 to 3.0, and the fuel-side strain rate from 50 s −1 to 100 s −1 . Under these conditions, there is a vaporization plane in the fuel stream at which the spray disappears, a pale green fuel-rich premixed flame in the fuel stream, and a brighter blue diffusion flame in the vicinity of the stagnation plane. Temperature profiles are measured by thermocouples, and concentration profiles of stable species are measured by gas chromatography of samples withdrawn by a fine probe. Computational methods are employed to calculate the flame structure, with detailed chemistry and transport included. Chemical-kinetic descriptions available in the literature predict the premixed flame to be more than 0.5 mm closer to the diffusion flame than observed experimentally and give nearly twice the measured peak CH 4 concentration and more than twice the measured concentration of C 2 H 2 in the premixed flame. Modification of the rate data by introducing a temperature-dependent branching ratio to the isomers CH 3 O and CH 2 OH, in the H attack on CH 3 OH, patterned after the known variation in the OH attack and by including the step CH 3 O+M→CH 2 OH+M, produces good agreement between all experimental and computational results. A reaction path for methanol in these flames is suggested, including routes to CH, important for prompt NO formation.

Experimental and numerical studies of two-stage methanol flames

Staged combustion can be employed to reduce the formation of CO and NO{sub x}, stabilize the flame, decrease the flame temperature, and create better working conditions in gas turbine combustors. To help understand influences of partial premixing and addition of water on NO{sub x} formation, the authors study two-stage flames in a counterflow spray burner. This paper reports experimental and theoretical results concerning two-stage combustion in which one feed stream is composed of a fuel-rich mixture of methane and air and the other is air. Water sprays are added to the air stream. This two-phase laminar counterflow configuration exhibits a green premixed flame, a blue diffusion flame, and a vaporization plane. All three are flat and parallel. The separation distances between them decrease with increasing equivalence ratio and strain rate. Flow visualization is provided through illumination by an argon ion laser sheet, velocity fields and spray structure are measured by a phase-doppler particle analyzer, concentration fields of major stable species are measured by gas chromatography of samples withdrawn from the flame, and temperature fields are measured by a thermocouple. Numerical integrations that employ a recent chemical-kinetic data base are performed to model the flame structure and NO{sub x} formation. Comparisonsmore » of experimental results with numerical predictions are made to test agreement. This work provides information on hydrocarbon combustion in both premixed flames and diffusion flames, indicates how NO{sub x} is formed in fuel-rich flames, and suggests how the pollutants can be reduced.« less

Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames

Staged combustion can be employed to reduce the formation of CO and NOx, stabilize the flame, decrease the flame temperature and create better working conditions in gas turbine combustors. To help understand influences of partial premixing and addition of water on NOx formation, we study two-stage flames in a counterflow spray burner. This paper reports experimental and theoretical results concerning two-stage combustion in which one feed stream is composed of a fuel-rich mixture of methane and air and the other is air. Water sprays are added to the air stream. This two-phase laminar counterflow configuration exhibits a green premixed flame, a blue diffusion flame and a vaporization plane. All three are flat and parallel. The separation distances between them decrease with increasing equivalence ratio and strain rate. Flow visualization is provided through illumination by an argon ion laser sheet, velocity fields and spray structure are measured by a phase-doppler particle analyzer, concentration fields of major stable species are measured by gas chromatography of samples withdrawn from the flame, and temperature fields are measured by a thermocouple. Numerical integrations which employ a recent chemical-kinetic data base are performed to model the flame structure and NOx formation. Comparisons of experimental results with numerical predictions are made to test agreement. This work provides information on hydrocarbon combustion in both premixed flames and diffusion flames, indicates how NOx is formed in fuel-rich flames and suggests how the pollutants can be reduced.Copyright © 1996 by ASME

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N. Ilincic

Papers

Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames

Reduction of NOx Formation by Water Sprays in Strained Two-Stage Flames