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If liquid fuel and oxdizer is injected in a rocket combustion chamber, the mixture will be moving relatively slow before reaching the nozzle, preventing the flame front from escaping outside the engine.

But if the fuel and oxidizer come from gas generators, they should be injected at high speeds since they are lighter, so they should be at a temperature higher than the self-ignition point, have some kind of catalyst or a very high flame front speed to keep the flame inside.

How does the combustion chamber in a full-flow staged combustion engine manage to keep the combustion inside it?

ElEmparuMC
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    Are the two not injected separately. The combustion chamber is the first place where they mix (apart from what has already mixed and combusted in the turbines). – Steve Linton Jan 28 '21 at 17:58
  • @SteveLinton It's really unclear, but I think it's asking how the flame front is kept from being blown out of the throat. I can't tell if there's some kind of misconception that gases will mix and burn slower (reality being quite the opposite), or an expectation that something special has to be done to prevent it. – Christopher James Huff Jan 28 '21 at 21:42
  • @ElEmparuMC I don't know how to answer this other than "they're designed to do so". The propellants have to vaporize before they can burn anyway, and they do this very rapidly. You're actually giving them a head start by injecting them as a gas. – Christopher James Huff Jan 28 '21 at 21:46
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    Proper injection results in complete combustion within the first cm of the injector surface (I have a citation based on FEA modeling but can't track it down in my lit folder). Many engines use gaseous fuel despite not being full-flow staged combustion--eg: expander cycle engines. The injection velocity (equiviliantly, pressure) is negilgable compared to the effects of full combustion, and is ignored entirely in many energy analyses of rocket engiens – Anton Hengst Jan 28 '21 at 22:12

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