Comment by littlestymaar
3 months ago
It's not liquid at the point of ignition, that's the thing: if you mixed liquid oxygen and fuel nothing would happen expect the fuel would freeze. For a fire to take place the temperature must reach the fire point temperature, and if you manage to get your fire below this temperature then the fire stops. I don't know how low this temperature can be when the oxidizer is pure oxygen and maybe it's so low water wouldn't be enough, but then you can imagine using other fluids. The problem being the mass burden it adds to a spacecraft, I'm not it'd make any sense given that such q leak should happen in the first place.
I believe LOX is injected into the engine as a liquid, it gets atomised rather than boiled?
And you can have fires where both fuel and oxidiser are solid: thermite reactions.
"Fire point" seems to be more of a factor for conventional fire concerns, albeit I'm judging a phrase I've not heard before by a stub-sized Wikipedia page: https://en.wikipedia.org/wiki/Fire_point
It's not about the state itself, but about temperature. For things to burn you need to have three elements:
- a fuel
- an oxidizer
- enough heat
It's the fire triangle.
> but about temperature
Which is why I said water would raise the temperature because the oxygen is liquid oxygen — i.e. very cold.
I mentioned solid phase because you were saying "if you mixed liquid oxygen and fuel nothing would happen". There are also videos of people starting fires by pouring LOX onto things.
The fuel and oxidiser in a rocket are often pumped around the outside of the engine bell before reaching the injectors, in order to keep the engine bell itself from melting due to the heat of combustion. I'm not sure exactly what temperature the fuel and oxidiser are at when they hit the injector, but I've seen ground tests where there's frost on the outer wall while the engine is running.
Also, one of the (rare) Falcon rocket failures was due to ice (IIRC oxygen ice) building up around the plumbing during flight: https://www.adastraspace.com/p/spacex-falcon-9-grounded
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