Has methylsilane (CH₆Si) ever been considered as fuel in rocketry?

Question

Methylsilane CH₆Si seems to have some useful properties for rocket fuel:

• high hydrogen content, 6 atoms per molecule, 13% of overall mass;
• high combustion energy, -2612 KJ/mol or 56.8 MJ/kg (better than methane 55 MJ/kg);
• decent liquid density, 0,628 kg/l (better than liquid methane 0.422 kg/l); 11% higher hydrogen content per volume than liquid hydrogen itself;
• non cryogenic, self pressurizing storage, 14 bar of pressure at 21°C, critical temperature 79.3°C;
• low average molar mass of gaseous stoichiometric combustion products 21.7 g/mol (better than methane 23.2 g/mol). Fuel rich combustion has even lower average gas mass because CH₆Si decomposes to SiC and 3H₂.

But there are some drawbacks:

• solid particles of SiO₂ and traces of SiC in exhaust, but less solid residue in exhaust than in solid fuels;
• possibly pyrophoric in high humidity atmosphere, but non pyrophoric in standard conditions;
• non toxic, but harmful to inhalation and skin exposure.

Considering all of data, they show promise, but are there any works related to its use in rocketry?

Answer 1

tl;dr: I see that comments below the question by the OP argue against this being a deal-breaker problem but I'm going to point it out anyway as a partial answer. Any engine using "sand" as a reaction mass will have to avoid any significant production of silica nanoparticles so large that they are not accelerated in the nozzle.

---

Assuming a perfect, stoichiometric reaction with H, C, O and Si masses of 1, 12, 16, and 28, I get the following:

2CH₆Si + 7O₂ → 2CO₂ + 6H₂O + 2SiO₂

with the exhaust mass fractions of 0.28, 0.34 and 0.38 for the CO₂, H₂O and SiO₂ products, having masses of 44, 18 and 60.

The exhaust is potentially almost 40 percent sand!

The boiling point of silica (SiO₂) is about 2950 °C, so when the exhaust cools below that temperature condensation of tiny nano- or even micro-particles of liquid glass is possible. Because they are much heavier than molecules, it is not guaranteed that they will be accelerated in the nozzle to the same exhaust velocity.

If a significant amount of reaction mass does not accelerate properly, the Isp will be lower than you'd expect for the amount of energy being produced.

This is not comparable to soot production in KeraLOX engines because this is the main reaction product, not a side-product from incomplete combustion. Nearly 40% of the reaction mass is SiO₂!

As a side note, "glass soot" is what optical fibers and other high purity silica products (e.g. CMP slurries) are made from, though it's a different silicon precursor (sometimes SiCl₄).