Using sulfur / H2S as aircraft fuel

[Andrew Lockley]

I've been thinking about the energetics of distribution of sulfur by aircraft (fixed wing and rockets. Both liquid sulfur and H2S are flammable. In principle, they can be used as fuels - albeit potentially only as a blend, due to unfavourable energetics. 

For comparison, the exothermic heat of combustion is 

Sulfur 316 kJ/mol = 9.87 MJ/kg (to SO2; sulphur is burned industrially in furnaces not wholly unlike jet engine flame cans)

H2S 519 kJ/mol = 15.2MJ/kg

Jet fuel 43.5 MJ/kg

So S has roughly 1/4 the energy of jet fuel, and H2S has roughly 1/3.

My thinking is therefore that using either of these chemicals as a fuel additive has two potential advantages 

1) the energy of combustion can be captured by a jet or rocket engine, lightening the fuel load.

2) by injecting S atoms directly into the flame can, they're likely to form a well-mixed blend of water (steam), CO2 and SO2, diluted in air. This may help form H2SO4. However, I'm unclear how the acid will form, in these circumstances (perhaps combustion to SO3 without a catalyst is possible, as catalyst poisoning is an issue). 

The disadvantages of this approach appear to be 

1) difficulties in handling two different fuels, or creating a stable blend 

2) need to switch fuel at altitude, even if a blend is used 

3) engine performance may be limited by lack of oxygen, necessitating higher energy fuel blends 

4) mass flow rates for sulfur may be >> fuel mass flow rates, thus rendering the whole thing a distraction 

5) engines may perform poorly

I'd welcome thoughts 

Andrew 

[Douglas MacMartin]

Jordan Smith did a bit on this a couple years back (with David Keith)

https://keith.seas.harvard.edu/publications/production-sulfates-onboard-aircraft-implications-cost-and-feasibility

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[Russell Seitz]

Andrew, I'd worry less about  hydrogen sulfide  poisoning catalysts,  and more about it  poisoning the crew and everybody in the airport.

H2S  is  as toxic as hydrogen cyanide.