Silanes as Fuels for Scramjets and Their Applications

Abstract

In the light of recently revived interest in scramjet propulsion, a new look is being given at unconventional new fuels. Among the latter are, or could be included, hydrides. These contain hydrogen in variable amounts, suggesting their use for airbreathing applications in which a much higher density compared to that of L H 2 would be beneficial. In particular, this paper deals with silicon hydrides (silanes), because of their interesting combustion and energetic properties as fuels for scramjets. Silanes in combination with air seem, at this preliminary stage of analysis, an interesting conceptual alternative to L H 2 and, perhaps, also to LCH 4 for scramjet application. Accordingly, this paper explores the practical limits of application of silanes and their performance along cruiser and accelerator trajectories. Equilibrium composition of the combustion products of silanes, from monosilane up to pentasilane, were calculated. Ideal scramjet performance (specific thrust and specific impulse) were evaluated along a constant dynamic pressure trajectory from 21,350 to 30,500 m and compared to that with CH 4 /air and H 2 /air mixtures. High specific thrust is obtained as the equivalence ratio is increased; the I sp trend is the reverse, but still very appealing when weighted with the bulk density of silanes.