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Typically engines built are repeatedly hot fired to analyses their performance.

In between tests, what are the review that the engine undergoes? How is an engine gauged suitable for a hot fire static test?

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  • $\begingroup$ The F-1 engine of the first stage of the Saturn V were cleaned with solvents to remove any deposits from the fuel rocket petrol. If deposits within the cooling system would accumulate over several test runs, the combustion chamber walls and the nozzle may overheat and melt. Deposits are impossible when liquid hydrogen is used as fuel. $\endgroup$ – Uwe Sep 11 '18 at 20:23
  • $\begingroup$ @Uwe what is the solvent typically used for cleaning the soot deposit? $\endgroup$ – karthikeyan Sep 11 '18 at 20:52
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    $\begingroup$ I don't know for this specific case, but acetone is often used for de-greasing. If it's strong enough I would imagine they used that. $\endgroup$ – Rikki-Tikki-Tavi Sep 16 '18 at 7:56
  • $\begingroup$ @Rikki-Tikki-Tavi oh. Is it due to the fact that acetone is polar and can dissolve a lot of organic substances? $\endgroup$ – karthikeyan Sep 16 '18 at 8:24
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    $\begingroup$ Yes. It's also not terribly poisonous and readily available in any quantity. $\endgroup$ – Rikki-Tikki-Tavi Sep 16 '18 at 15:28
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There are a couple of things that wear out in rocket engines. What exactly wears out first depends on the design of the rocket engine. Some design choices put more load on a particular component, which increases the likelyhood of a compnent failure.

Therefore it's imortant to be familliar with typical problems with a specific design when deciding if the engine can be fired up again.

Four examples:

  • self-lubricated turbopump bearings may fail if an Armalon cage is worn down, and the glas fibers are laid bare
  • the interpropllant floating ring seals may wear out and leak
  • a turbine may have cracks forming at blade roots
  • in a hydrogen-oxygen-fuled engine, the chamber wall/nozzle extension may have so many cracks that the ISP suffers noticeably

The three turbopump related things can be checked with a boroscope.

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  • $\begingroup$ Thanks for the turbo-pump specific information. Would the chamber wall/nozzle extension cracks common in any engine? Are they typically inspected visually? $\endgroup$ – karthikeyan Sep 11 '18 at 19:40
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    $\begingroup$ @karthikeyan yes, you can just have a look. They're pretty obvious. Maybe it's because of my background, but I think most wear happens in the turbopumps. $\endgroup$ – Rikki-Tikki-Tavi Sep 12 '18 at 1:07

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