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Scaling relations for the length of coaxial oxy-flames with and without swirl

Degenève, Arthur and Vicquelin, Ronan and Mirat, Clément and Labegorre, Bernard and Jourdaine, Paul and Caudal, Jean and Schuller, Thierry Scaling relations for the length of coaxial oxy-flames with and without swirl. (2018) Proceedings of the Combustion Institute, 37 (4). 4563-4570. ISSN 1540-7489

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Official URL: https://doi.org/10.1016/j.proci.2018.06.032

Abstract

An extensive experimental study is carried out to analyze scaling laws for the length of methane oxy-flames stabilized on a coaxial injector. The central methane fuel stream is diluted with N2, CO2 or He. The annular air stream is enriched with oxygen and can be impregnated with swirl. Former studies have shown that the stoichiometric mixing length of relatively short flames is controlled by the mixing process taking place in the vicinity of the injector outlet. This property has been used to derive scaling laws at large values of the stoichiometric mixture fraction. It is shown here that the same relation can be extended to methane oxy- flames characterized by small values of the stoichiometric mixture fraction. Flame lengths are determined with OH∗ chemiluminescence measurements over more than 1000 combinations of momentum ratio, annular swirl level and composition of the inner and outer streams of the coaxial injector. It is found that the lengths of all the flames investigated without swirl collapse on a single line, whose coefficients correspond to within 15% of flame lengths obtained for fuel and oxidizer streams at much larger stoichiometric mixture fractions. This relation is then extended to the case of swirling flames by including the contribution of the tangential velocity in the flow entrainment rate and is found to well reproduce the mixing degree of the two co-axial streams as long as the flow does not exhibit a vortex breakdown bubble. At higher swirl levels, when the flow features a central recirculation region, the flame length is found to also directly depend on the oxygen enrichment in the oxidizer stream.

Item Type:Article
Audience (journal):International peer-reviewed journal
Uncontrolled Keywords:
Institution:Other partners > Air Liquide (FRANCE)
French research institutions > Centre National de la Recherche Scientifique - CNRS (FRANCE)
Université de Toulouse > Institut National Polytechnique de Toulouse - Toulouse INP (FRANCE)
Université de Toulouse > Université Toulouse III - Paul Sabatier - UT3 (FRANCE)
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Agence Nationale de la Recherche
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Deposited On:21 Mar 2019 15:09

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