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Previously published data for nonmetalized and metalized fuels exhibited a strong dependence on oxidizer flow rate and burner pressure. In this study, the observed pressure dependence was investigated further. Butyl rubber, lithium hydride, and polyurethane fuels were investigated using a laboratory slab burner; the gaseous oxidizers were fluorine, oxygen, and nitrogen. Using oxygen or nitrogen as a diluent, the partial and total pressures of fluorine were varied independently from 4 to 130 psi and 20 to 165 psi, respectively, and the flow rate was varied from 0.014 to 0.21 lb/in. 2 -sec. Measured rates were independent of total pressure for all flow rates; they increased with increasing oxidizer pressure for the higher flow rates but were nearly independent of the partial pressure, while increasing with flow rate for the lower flow rates. Dilution of fluorine with oxygen or nitrogen gave essentially the same results, indicating that oxygen acted only as a diluent. Partial pressure and flow-rate dependence were correlated with a simple model based on turbulent transport processes competing with fluorine kinetic processes.Nomenclature BI = blowing parameter, B\ = rp//(GC/ 0 /2) Cf 0 = friction coeff without blowing, (7/ 0 G = total specific flow rate through port, lb/in. 2 -sec k c = local mass transfer coeff, in./sec k = kinetic rate const, sec" 1 Poo = total gas pressure in freestream, psia P 0oo = partial oxidizer pressure in freestream, psia Pow = partial oxidizer pressure at the wall, psia r = regression rate, in./sec R = specific gas const, in.-lbf/lbm-°R Re = Reynolds number, (GaoX/n) Sc = Schmidt number T = gas temperature, °R C/oo = freestream velocity, in./sec x = distance from leading edge of grain, in. X = weight fraction of gaseous products from wall decompositionPresented as Preprint 66-113 at the AIAA 3rd Aerospace

Abstract. Streamers are rapidly extending ionized finger-like structures that dominate the initial breakdown of large gas volumes in the presence of a sufficiently strong electric field. Their macroscopic parameters are described by simple scaling relations, where the densities of electrons and of excited molecules in the active streamer front scale as the square of the density of the neutral gas. In this work we estimate the absolute density of nitrogen molecules excited to the C 3 Π u state that emit photons in the 2P-N 2 band, by radiometrically calibrated short exposure intensified imaging. We test several pressures (100, 200 and 400 mbar) in artificial air at room temperature. Our results provide a first confirmation for the scaling of the density of excited species with the gas density. The method proposed here is particularly suitable to characterize the excitation densities in sprite streamers in the atmosphere.

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