Lifting and Splitting of Nonpremixed Methane/Air Flames Due to Reactant Preheating

In order to assess the impact of initial reactant temperature on the occurrence of local extinction (LE) and the subsequent lifting process of non-premixed attached flames with increasing fuel injection velocity, hydroxyl radical planar laser-induced fluorescence (OH-PLIF) and high-speed CH*-chemiluminescence visualizations were conducted in a methane/air jet-flame, with preheating up to 1000 K. LE occurrence probability increases when approaching lifting, and the preheating level (Tox,ref) affects the probability density function (PDF) shape of LE axial origin. At low Tox,ref, partial lifting events occur near the burner lip, eventually leading the flame to lift directly from the very flame base. At higher Tox,ref, partial lifting events no longer occur, and LE is mostly witnessed in the flame breakpoint zone (axially from 1 to 3 jet diameters), resulting in a breakpoint lifting process. For very high Tox,ref (1000 K), local extinctions become widespread in the breakpoint zone so that a stable split flame is achieved prior to the lifted regime.