Rocket-propellant characteristics of silanes/O₂

We present a theoretical analysis of the applicability of various silicon hydrides (silanes) as rocket propellants. Thermodynamic data sets for 12 different silanes ranging from monosilane SiH4 to pentasilane Si5H12 were generated based on existing data. They were derived from empirically corrected thermochemical ab initio calculations and used in conjunction with the well-known computer packages NASA CEA2 and CHEMKIN to calculate equilibrium compositions and rocket performance indices. The thermodynamic datasets are now publicly available online for future calculations. Chemical equilibrium combustion compositions and adiabatic flame temperatures in rocket combustion chambers and the specific impulses at the nozzle exit assuming shifting equilibrium were calculated for several silane fuels using oxygen as oxidizer. The computational results created by CEA2 and CHEMKIN are in very good agreement to each other and are compared to conventional fuels such as liquid hydrogen (LH), hydrocarbons and hydrazines. Compared to alkane fuels, the combustion of silanes with oxygen-despite the much higher average molecular mass of the combustion products-results in similar maximum specific impulses and adiabatic flame temperatures due to the high positive values of the heats of formation of the silanes, indicating that silanes may be interesting candidates as rocket propulsion fuels.