Effect of Damkohler number on superequilibrium OH concentration in turbulent nonpremixed jet flames
Journal Article
·
· Combustion and Flame; (USA)
- Combustion Research Facility, Sandia National Lab., Livermore, CA (US)
Simultaneous, spatially resolved measurements of mixture fraction and absolute hydroxyl radical concentration are obtained for the first time in nonpremixed, turbulent, hydrogen-air-flames. This is accomplished by combining spontaneous Raman scattering with linear, laser-induced fluorescence (LIF). The Raman scattering data define the instantaneous, local collisional quenching environment of the OH molecules, allowing quenching corrections to be applied for each laser shot and making the linear LIF measurements quantitative. The effect of Damkohler number on OH superequilibrium is determined by performing measurements at selected locations in two argon-diluted hydrogen flames (Reynolds number 8,500 and 17,000). Results demonstrate that departures from chemical equilibrium in these flames are a consequence of the fact that time scales for turbulent transport are competitive with time scales for three-body radical recombination reactions. Due to the slow characteristic time for the radical recombination, convective histories, as well as instantaneous local conditions, determine hydroxyl concentrations. Damkohler numbers are not sufficiently low for the rapid bimolecular reactions to be strongly affected. Comparison of turbulent flame data with results from strained laminar flame calculations indicates that partial equilibrium of the bimolecular reactions is a good approximation near the stoichiometric mixture fraction.
- OSTI ID:
- 5799618
- Journal Information:
- Combustion and Flame; (USA), Journal Name: Combustion and Flame; (USA) Vol. 82:3-4; ISSN CBFMA; ISSN 0010-2180
- Country of Publication:
- United States
- Language:
- English
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