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As I understand it, coking in kerolox engines occurs when the engine shuts down and fuel flow stops, causing fuel still in the coolant channels to overheat and decompose.

Can this problem.be avoided by using a battery powered pump to keep the fuel flowing for a few seconds after shutdown? If so, how much fuel would be required, and how heavy would the additional equipmemt?

Organic Marble
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Abdullah is not an Amalekite
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    No, coking does not only happen after shutdown. If that were true, it would not be a problem for single-use engines. Coking is possible any time the temperature of hydrocarbon fuel gets too high. Where did you get the idea it's only post shutdown? – Organic Marble Nov 15 '23 at 12:33
  • Read some references linked here - these authors know their subject https://space.stackexchange.com/a/59099/6944 – Organic Marble Nov 15 '23 at 12:35
  • Without any acceleration, it's impossible to suck fuel from the tank. – user3528438 Nov 15 '23 at 12:55
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    @user3528438 then how do they ever start engines in free fall? – Organic Marble Nov 15 '23 at 13:00
  • Coking in regenerative cooling passages occurs both before and after shutdown. If it were technically possible to continue fuel flow after shutdown of oxidizer (the ultimate fuel-rich mixture!) you could reasonably expect reduced post-shutdown coking. Data from test bed firing could confirm (or refute) this. But it would make a sooty mess of your test stand. – Woody Nov 15 '23 at 14:10
  • @OrganicMarble Woody told me... – Abdullah is not an Amalekite Nov 15 '23 at 16:44
  • @OrganicMarble It's called "ullage", and it's a nontrivial problem. They have to do something to settle the fuel in the "bottom" of the tank before firing. The Apollo upper stage used tiny solid rockets for the purpose, Falcon 9 uses cold gas thrusters prior to relighting for the boostback, and so on. Hypergolic RCS thrusters use a balloon style fuel tank to avoid the problem by just not having any space in the tank that isn't full of fuel, but I think those didn't work real well on large-scale turbopumped tanks. Some satellites use a tiny ion drive for the purpose. – Darth Pseudonym Nov 15 '23 at 21:19
  • @DarthPseudonym I've written answers here about it. https://space.stackexchange.com/a/38270/6944 My comment was challenging the assertion that it's impossible. – Organic Marble Nov 15 '23 at 22:00
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    Yeah, I thought it was rather strange that you were challenging user3528438 when their statement was correct -- you DO need some kind of acceleration to settle your fuel, with the oddball exception of a balloon diaphragm tank. I'm not sure what it has to do with the question at hand, but it wasn't untrue. – Darth Pseudonym Nov 15 '23 at 22:00
  • @DarthPseudonym or those other devices shown in my answer. You don't need acceleration, it's certainly not "impossible". – Organic Marble Nov 15 '23 at 22:01
  • At least for a large engine like we're discussing, you kinda do need acceleration. IIRC surface-tension systems can only guarantee a small amount of fuel before potentially ingesting bubbles, so they only work for relatively low-flow engines, and bladders don't cooperate with large tanks very well. – Darth Pseudonym Nov 15 '23 at 22:24
  • @DarthPseudonym once you get a little prop to the engine, then you have acceleration. It's kind of what they do. Those galleries etc for the OMS engine just held enough to get started. – Organic Marble Nov 16 '23 at 01:48

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