An experimental study of pulsating instability in near-limit laminar nonpremixed flames

    Authors

    M. Chaos;R. H. Chen

    Comments

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    Abbreviated Journal Title

    Combust. Sci. Technol.

    Keywords

    diffusive-thermal effects; Lewis number; extinction; pulsation; instability; nonpremixed flames; laminar flames; DIFFUSIONAL-THERMAL INSTABILITY; OSCILLATING EDGE-FLAMES; DILUTED; PROPANE; LEWIS NUMBERS; JET FLAME; STABILITY; THERMOCOUPLES; TEMPERATURE; EXTINCTION; METHANE; Thermodynamics; Energy & Fuels; Engineering, Multidisciplinary; Engineering, Chemical

    Abstract

    Pulsating instability of near-limit C3H8, CH4, and H-2 nonpremixed flames was experimentally investigated. The criterion of an effective Lewis number (Le(eff)) (Chen, R.-H., Mitchell, G.B., and Ronney, P.D., Proc. Combust. Instit., vol. 24, pp. 213-221, 1992) based on the premixed burning regime described by Linan (Linan, A., Acta Astronaut., vol. 1, pp. 1007-1039, 1974), which successfully explained the cellular instability of near-limit nonpremixed flames with Le(eff) < 1, is extended for pulsating instability in this study. In this criterion, near-extinction diffusion flames exhibit fuel-lean or-rich burning and the Lewis number of the deficient species is Le(eff). Pulsating instability of nonpremixed flames was found to occur near extinction limits and for Le(eff) sufficiently greater than 1. Pulsating modes were observed near both the heat-loss and blowout limits. Present experimental results suggest that Le(eff) greater than or equal to 2.6 for pulsating instability to occur in near-limit flames. Flames with Le(eff) as large as 1.8 did not exhibit pulsating instability. A criterion recently proposed by Kim and Lee (Kim, J.S. and Lee, S.R., Combust. Theory Model., vol. 3, pp. 123-146, 1999), where a Lewis number (L-e) is a weighted average of the fuel and oxidizer Lewis numbers with the mixture strength (A(F)) as the weighting factor, is also examined. The theoretical criterion is found to be supported by the experimental results. For all values of A(F), no pulsation was observed for L-e < 2.0. For A(F) -- > 1, pulsation was not observed for L-e as large as 2.21, while for A(F) sufficiently greater than 1 pulsating instability was observed for L-e > 2.0. This suggests that larger values of L-e are necessary for pulsating instability to occur in near-limit flames for A(F)-- >1, in agreement with the theoretical prediction.

    Journal Title

    Combustion Science and Technology

    Volume

    176

    Issue/Number

    8

    Publication Date

    1-1-2004

    Document Type

    Article

    Language

    English

    First Page

    1191

    Last Page

    1215

    WOS Identifier

    WOS:000222990800002

    ISSN

    0010-2202

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