Effect of gravity on premixed methane–air flames

Premixed flames under different levels of gravity were studied experimentally and numerically. The experiments were carried out in the Bremen Drop tower. The object of investigation were conical premixed rich, lean, and stoichiometric $\rm CH_4$–air flames with wide range of flow regimes, at Reynolds numbers of $600$–$2000$, which were generated on specially designed cone nozzle and premixed cylinder chamber with grids and beads. Planar laser-induced fluorescence $\rm OH$ radicals and high-speed video recording was performed under microgravity, terrestrial conditions, and inverted gravity. All the experiments were performed at atmospheric pressure. Our experiments confirm that gravity has a complex influence on laminar and weakly turbulent premixed flames. Gravity causes flame flickering, while under reduced gravity flames are stable and almost not flicker. Based on the experimental data and numerical simulation, a correlation of flickering frequency with different mixture equivalence ratio and gravity is formed.