Pyrolysis-gas chromatography mass spectroscopy and pipe combustor analysis of the ignition and mass regression characteristics of a sulfur doped polysulfide ramjet fuel

The autoignition and low pressure combustion characteristics of five candidate polysulfide (LP-33) based ramjet solid fuel formulations are evaluated using pyrolysis-gas chromatography mass spectroscopy and a subscale pipe combustor. The polysulfide based fuels are oxidatively cured using p-quinone dioxime and manganese dioxide. The fuel formulations differ by the amount of elemental sulfur that is added to alter the decomposition temperature, mass burning rate, and to modify the mass fraction of low ignition temperature sulfur based decomposition gasses. The objectives of this research are to demonstrate that the autoignition temperature and the mass regression rate of the candidate fuels can be tailored as function of the sulfur doping fraction. The results of the analysis show that the mass fraction of low autoignition temperature decomposition gasses that include carbon disulfide and hydrogen disulfide increase as the mass fraction of elemental sulfur increases in the fuel formulation. Pipe combustor test results demonstrate repeatable autoignition temperatures less than 400°C at ambient pressure for all formulations. The results also show that the primary effect of sulfur doping is to lower the mass burning rate of the fuel in direct correlation to the Shore-A hardness of the material which increases the time to ignition with no appreciable change to the mean autoignition temperature.