Entrainment of mainstream flow in a trapped-vortex combustor

Abstract

A laboratory-scale combustor is described. To provide good flame stabilization the combustor uses a vortex formed and trapped inside an annular cavity introduced into a centerbody that is placed in a concentric, axially flowing mainstream which is confined by a circular duct. Separately-controlled primary air and gaseous propane are directly injected unpremixed into the cavity for combustion purposes. The stability of the vortex in a driven-cavity is determined by the cavity dimensions. For a cavity that is additionally pumped by the directly-injected primary air and fuel flows, the relative momenta of the mainstream and injected cavity flows will also determine the combustion stability through the entrainment of mainstream flow into the cavity. Direct measurements of cavity entrainment are difficult to make. However, indirect assessments of enlrainment are possible from other measurements with a few plausible assumptions. Indirect estimates of entrainment are provided over wide ranges of operating conditions at atmospheric temperature and pressure for several cavity sizes.