Controlling mechanisms of ignition of solid fuel in a sudden-expansion combustor

Abstract

Ignition of solid fuel by a hot oxidizing flow in a sudden-expansion combustor was investigated experimentally. The controlled variables of the experiments were concentration of oxygen (12-25%), gas temperature (750-850°C), and flow velocity (19-46 m/s). The step height was 29 mm. The corresponding Reynolds numbers based on the flow velocity and the step heights were 12 x 10 4 -31 x 10 4 . The controlling mechanisms of ignition in the flow with abundant oxygen were distinct from those with little oxygen. The initial flame kernels formed near the reattachment point and adjacent to the surface of solid fuel when the oxygen concentration was large. The process was controlled by diffusion and the ignition delay decreased with increased flow velocity. For the flow containing oxygen at a small concentration, the initial flame kernels formed within the recirculation zone and away from the surface of the solid fuel. The process was then controlled by the chemical kinetics and the ignition delay increased with increased flow velocity.

Cooling transients in a sudden-expansion channel with varied rates of wall transpiration

“…Various flow patterns are involved, including corner eddy, recirculation vortex, shear layer, reattachment zone, and re-developing boundary layer. By incorporating additional fluid transpiration from the bottom wall downstream the backstep, the flow may either simulate the pyrolysis of solid fuel in an axial dump combustor (Richarson et al [6]; Yang and Wu [7]), or serve as an efficient cooling approach that protects the wall from the hot inlet stream. The injected flow not only carries positive momentum into the reverse stream of the recirculation vortex, but also induces a favorable pressure gradient to counteract the adverse one downstream the backstep.…”

Transient flame spread during convective ignition of solid fuel in a sudden-expansion combustor

“…Except the research in Ref. [8][9][10][11][12][13], literatures dedicated to the phenomena of solid fuel ignition within the sudden-expansion combustors are rare. A review of the fundamentals for solid propellant ignition may be referred to [14], in which the ignition were categorized into the head-end and aft-end modes.…”