Quantification of HCl in Solid Propellant Combustion Products

Heavy weight space launchers often use solid propellant boosters to propel the first phase of their ascending trajectory. Combustion gases contain a consistent fraction of hydrogen chloride, which readily becomes hydrochloric acid, once in contact with atmospheric moisture. Hydrochloric acid is potentially toxic for the environment and takes part to ozone layered pletion processes, at stratospheric level. Lab-scale research and development of solid propellants characterized by lower HCl emissions need a quick and reliable method for quantification of hydrogen chloride in the combustion products. This paper documents a method for collection and quantification of hydrogen chloride released from small solid propellant samples. The technique is based on an apparatus for underwater sample combustion and an acid-base titration procedure. Good agreement with ideal data has been obtained in verification tests. The method has been used to verify the performance of two neutralized propellant formulations based on Al/Mg fuel blends. All the Mg-based compositions demonstrated very high neutralization efficiency, without strong alterations of the ballistic behavior.