K. L. Maxwell and M. K. Hudson
ABSTRACT: A labscale hybrid rocket was used to study spectral bands produced by metal combustion. Bands in the ultraviolet-visible region (300–750 nm) are of interest. The rubber-like fuel, hydroxyl-terminated polybutadiene (HTPB), was doped with a metallic salt for introduction into the plume during combustion. When introduced, the metals produce atomic line emissions as well as molecular bands due to excited forms of metallic molecules in combustion. The most likely molecular band emissions are from the excited states of metal oxides or metal hydroxides formed by these metals in the presence of the oxygen flow of the hybrid rocket. As the concentration of metallic dopants increases in the flame, the molecular band emissions also increase. The fashion by which they increase is observed here. The high concentrations observed for these metals result in intensity versus concentration curves that diverge from the expected linear progression for manganese, magnesium and strontium. The molecular band emissions observed for calcium, barium and copper in this study followed linear progression, as does the atomic line emission for barium. The line emissions for manganese, strontium and calcium lean toward the concentration axis. The curves are attributed to selfabsorption or increased interactions among mixing species as metal concentration increases in the plume. This study indicates that molecular bands are useful for monitoring engine health and for plume diagnostics.
Keywords: combustion diagnostics, hybrid rocket, plume emissions, spectral signature, rocket exhaust, atomic spectroscopy, molecular spectroscopy, emission spectroscopy
Ref: JPyro, Issue 21, 2005, pp59-69
(J21_59)
© Journal of Pyrotechnics and CarnDu Ltd
