Destruction of liquid and gaseous waste surrogates in an acoustically excited dump combustor

Abstract

Destruction of gaseous and liquid waste surrogates is studied in a two-dimensional dump combustor configuration. Two different waste surrogates are examined: sulfur hexafluoride, which is injected in the gaseous phase and pyrolyzed at high temperatures, and acetonitrile, which is injected in the liquid phase and can be burned in the presence of high concentrations of oxidizing species. Waste surrogates are injected through movable ceramic plugs into the recirculation zones within the dump combustor cavity. The movable plugs allow the combustor cavity length to be altered, in turn exciting or damping various acoustic modes of the device. Strong coupling among the fluid mechanics, acoustics, and combustion/incineration processes are observed in this device; these processes are representative of dump combustors in general. Among the important observations in this study is that waste destruction is strongly affected by the flame and recirculation zone stability. When the flame is perturbed by large vortical structures corresponding to low-frequency “chugging” oscillations, or when it is chaotically destabilized (while acoustically quiet), the recirculation zones into which waste is injected can be destabilized, and DREs for the surrogate are reduced. When the flame is stabilized under conditions which are acoustically quiet, or when the flame is only slightly wrinkled or disturbed, as under high-frequency mode conditions, the recirculation zones are stable and waste is usually destroyed well. Waste destruction itself, however, is also observed to affect recirculation zone and flame stability in addition to affecting the device's acoustic signature.