Burning and flameholding characteristics of a miniature solid fuel ramjet combustor

Abstract

The objective of this research was to characterize the combustion and flameholding limits in solid fuel ramjet combustors of particularly small size (10mm i.d.). The main combustion characteristics, as well as the specific effects resulting from the special size range, are pointed out. Several hundred static tests were performed with three different fuel types, polymethylmethacrylate (plexiglass), polyethylene, and polybutadiene. Air inlet temperatures of 800 K, 520 K, and room temperature were tested to simulate flight Mach numbers of 3, 2, and low subsonic, respectively. All three fuels exhibited very good flameholding capability at the higher air temperature (800 K). The flammability limits decreased at 520 K and became very narrow at room temperature. The flameholding capability also deteriorated with decreasing combustor size. The flow-reattachment distance, coinciding with the maximum fuel regression rate zone, was shown to be proportional to the inlet step height and was independent of fuel type and port-flow Reynolds number. Nomenclature A — area d = diameter F = thrust G = mass flux H = step height k = thermal conductivity M = Mach number m = exponent m = mass flow rate n = exponent p = pressure Q = heat capacity (sensible enthalpy) Q = heat loss rate q = heat flux Re = Reynolds number r = fuel regression rate T — temperature V = volume xr = reattachment distance Subscripts