Silicon hydrides as high-energy fuels: facts and perspectives

The history and potential use of silicon hydrides for air- and spacecraft propulsion is summarized. Silanes burn vigorously with most oxidizers, releasing a high amount of usable energy because they have highly positive heats of formation. Monosilane is an extremely effective combustion enhancer and is used as an ignition aid in NASA scramjet ground testing and flights and is reported to have been used in RBCC (Rocket Based Combined Cycle) research programs. Recent thermochemical data, obtained from ab initio calculations, have enabled estimating ideal performance of lower, gaseous silanes and also of the hitherto relatively unknown higher, liquid silanes as rocket and scramjet fuels. Limitations of these performance predictions are identified and discussed and several research activities are proposed in order to come to a more realistic description and assessment.