Stochastic characterisation of unstable lean hydrogen–air annular premixed flames

Abstract

This study is devoted to the characterisation of lean premixed hydrogen–air laminar flames stabilised on an annular burner. The flames studied are chosen to lie close to the lean flammability limit, spanning a range of Damköhler and Reynolds numbers, and correspond to situations where instabilities arise. The experimental characterisation is achieved by examining the statistical moments of the flame hydroxyl radical (OH*) chemiluminescence and schlieren. The standard deviation and the skewness, that are needed to fully characterise the measured probability density functions, are shown to exhibit a non-monotonic behaviour with the distance from the burner surface, first increasing, then decreasing downstream the flame tip. An exponentially modified Gaussian distribution model is proposed to describe the skewed schlieren fluctuations probability density function. This model is closed by developing relations for the probability density function parameters based on the Damköhler and Reynolds numbers, and then used to describe the OH* stochastic behaviour. The relation between the distribution parameters and the transport equation of a reactive scalar gradient is addressed also.

Keywords:

• skewed probability density function
• lean hydrogen flames
• premixed combustion
• annular burner
• unstable flames

Acknowledgments

This work has been performed while the author was on leave from Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio, Brazil). The author is grateful for the experimental support provided by V. Montassier and A. Claverie and to L. Pirateque Henao and N. Lopes M. B. Junqueira for performing the premixed flame computations. This work pertains to the French government programme ‘Investissements d'Avenir’ (EUR INTREE, reference ANR-18-EURE-0010). For the purpose of Open Access, a CC-BY public copyright license has been applied by the authors to the present document and will be applied to all subsequent versions up to the Author Accepted Manuscript arising from this submission.

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Disclosure statement

No potential conflict of interest was reported by the author(s).