Aspects of Flame Stability in a Research Dump Combustor

The lean blowout process is studied in a simplified, nominally diffusion flame research combustor that incorporates the essential features of the combustor primary zone for an aircraft gas turbine engine. The research combustor is provided with extensive optical access. To investigate the blowout, a variety of diagnostic techniques are employed, including direct flame observation, laser-Doppler anemometry, spontaneous OH-imaging, thin-filament pyrometry, laser-induced fluorescence OH-imaging, coherent anti-Stokes Raman spectroscopy, and computational fluid dynamics. Lean blowouts in the research combustor are related to well-stirred reactor blowout. A blowout sequence is found to initiated by the loss of a key flame structure in the form of an attached pilot flame. The behavior of this attached flame is investigated. It is concluded that a major contribution to the existence of the attached flame is near-field, non-stationary radial transport of reactants directly into the recirculation zone, rather than by mean flow recirculation of hot products. “Lift” of the attached flame is the reason that lean blowout in the research combustor is related to well-stirred reactor blowout since it allows at least partial premixing of reactants to take place.