Stochastic characterisation of unstable lean hydrogen-air annular premixed flames

Overview & Synopsis

This study is devoted to the characterization of lean premixed hydrogen-air laminar flames stabilized on an annular burner. The flames studied are chosen to lie close to the lean flammability limit, spanning a range of Damkohler and Reynolds numbers, and correspond to situations where instabilities arise. The experimental characterization 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 characterize the measured probability density functions, are shown to exhibit a non monotonic behavior 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 Damkohler and Reynolds numbers, and then used to describe the OH* stochastic behavior. The relation between the distribution parameters and the transport equation of a reactive scalar gradient is addressed also.