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Rocket engine ignition!


DerpenWolf

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/me imagines a janitor placing a burning candle below every bell at T-15 minutes...

Seriously though, the only thing I ever heard of were

a) some kind of fireworks (sorry, my english fails me here). It resembled a shotgun shell.

B) fuels that will ignite on contact, no spark required.

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AFAIK they are either ignited externally(look at a space shuttle launch, shortly before ignition you will see it sparkling) or by injecting a Hypergolics. Hypergolics are fuels that will already ignite when they are just touching, requiring no external ignition. After that either the main fuel is injected into the chamber or the Hypergolics are the main fuel.

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Well, it depends on the kind of fuel / oxydizer you have, and the type of engine (turbopump / pressure fed)

Also depends if you ignite it inflight or on the ground :)

On the ground, for Lh2/lox for example, they can use sparkles to ignite the h2/o2 mix.

For other kind of fuels, they can use an additive which will react as an hypergol to either your fuel or your oxydizer, the ignition of the hypergol then igniting the fuel / oxydizer mix.

Using hypergolic fuels + oxydizer, you won't need an ignition system.

I think there's also the possibility to use pyrotechnics.

The key point, is they need to have an uniform ignition to prevent combustion instabilities.

Of course, for turbopumps engines, you first need to start the the gas generator which drives the turbopumps.

For pressure fed engines, you just need to open the valves (especially as they generally use hypergolics)

Aditionally, for inflight ignitions, you may need to settle the fuels in the tanks (especially before starting the turbopumps)

For that, you can use various ullage methods (either small SRBs, or hypergolic pressure fed RCS systems) or hot-staging, like the russians (the engines are ignited before the previous stage is stopped and separated)

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Recent SpaceX launches have given a great view on the engine ignition method they use: an ignitor fluid named triethylaluminum-triethylborane (TEA-TEB). It's the same method that was used on the Saturn V, but it wasn't nearly as visible there.

Quoting wikipedia: "Triethylborane is strongly pyrophoric, igniting spontaneously in air, burning with an apple-green flame characteristic for boron compounds."

And therefore, you get something called the "Green Flash" on rockets that use it. The Falcon 9 always shows this extremely well at roughly T-3 of every launch:

Other methods include: pad-based ignition systems, spark plugs, and laser ignition.

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Sparkling you see under rockets aren't for igniting the mixture. It's to prevent hydrogen buildup and to avoid detonation.

Don't worry I knew about that, I've seen it before on shuttle launches! But I didn't know that they used hypergolic fuels for ignition for the most part, Very cool!

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