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Measurements of Formaldehyde Concentrations and Formation Rates in a Methane-Air, Non-Premixed Flame and Their Implications for Heat-Release Rate.


pdf icon Measurements of Formaldehyde Concentrations and Formation Rates in a Methane-Air, Non-Premixed Flame and Their Implications for Heat-Release Rate. (840 K)
Tolocka, M. P.; Miller, J. H.

Combustion Institute, Symposium (International) on Combustion, 27th. Proceedings. Volume 1. August 2-7, 1998, Boulder CO, Combustion Institute, Pittsburgh, PA, 633-640 pp, 1998.

Sponsor:

National Science Foundation, Washington, DC

Keywords:

combustion; formaldehyde; heat release rate; premixed flames; lasers

Abstract:

Tunable diode laser absorption spectroscopy coupled with microprobe sampling was used to quantitatiley determine formaldehyde concentrations in a methane-air non-premixed flame. Resulting concentration profiles are similar in shape and peak locations to previous qualitative measurements, and concentration levels are in line with those predicted by direct numerical simulation of methane-air flames. The resulting concentrations were combined with other data from this flame system in a mixture fraction-based code to predict levels for species whose concentrations are not available experimentally. An analysis was performed of formaldehyde formation and destruction paths to determine HCHO's dependence on specific reaction steps. Formaldehyde formation is dominated by the reaction between methyl radical and oxygen atom, and it is destroyed by hydrogen abstraction. Both processes occur near the stoichiometric surface. The analysis also verified several points made by other researchers about the heat-release rates in methane flames. Heat-release rate correlates well with the destruction rate of methane, the rate of the reaction between methyl radicals and oxygen atoms, and HCO concentrations. A condition of chemical steady state is found for HCO, and the steady-state estimate of HCO concentration may also be used to estimate local heat-release rate in methane flames.