So it is clear that kerosene fueled engines use two fluids for film cooling via injection in the combustion chamber, throat, or nozzle. (That is "true film cooling" and not just a fuel rich outer ring at the injector plate.) First fluid is exhaust from gas generator. Second fluid is plain RP-1 from propellant tank.

Q: For the second case of RP-1 film cooling what is a typical value for the mass fraction of total RP-1 mass flow that is used for the film cooling? What, for example, of total RP-1 flow did an F-1 use for film cooling?

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    $\begingroup$ I don't believe the premise is correct. As far as I know, the F-1 only used gas generator exhaust for film cooling. Any injection of RP-1 into a combustion chamber or nozzle would immediately combust anyway. Do you have a citation for an engine which injects RP-1 further down the engine than the injector face? $\endgroup$ Aug 21, 2019 at 19:21
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    $\begingroup$ "So it is clear that..." Welcome to Stack Exchange! can you add some supporting links or cite some sources that demonstrate how clear these things are? Thanks! $\endgroup$
    – uhoh
    Aug 21, 2019 at 22:58
  • $\begingroup$ For example here: arc.aiaa.org/doi/pdf/10.2514/6.2016-2149 but this is a theoretical study. I think that the Merlin uses this method but I could be wrong. I know Merlin does not use GG exhaust because you can see it being dumped overboard but it must use something. $\endgroup$
    – Superfort
    Aug 22, 2019 at 16:54
  • $\begingroup$ GG exhaust can never be useful for combustion chamber cooling, it's at too low pressure. $\endgroup$ Aug 23, 2019 at 2:56

1 Answer 1


I don't know of any RP-1/kerosene fueled engines that used two fluids for film cooling. The only instance of film cooling was of the gas generator exhaust fluid being fed into the nozzle to insulate it from the hot combustion products streaming out of the chamber. This btw was responsible for the F-1 exhaust gases always looking brighter in the center of the plume than on the plume's outer layer. The ratio of gas generator RP-1 flow to total RP-1 flow was around 1.4%. I can add sources later when I have access to my (physical) library, as it sports a book with the exact specs.

  • $\begingroup$ Thanks for comments! So let's narrow the discussion to nozzle film cooling from the throat to back up into the combustion chamber. We know that GG exhaust pressure is too low and in some case (Merlin) is dumped over board in any case. We are left with the direct injection of the (high pressure) RP-1 as the only mechanism (as in the AIAA paper)? (It does not combust because it never mixes inside the engine.) So can anyone quote a "typical" flow fraction for the RP-1 used for throat film cooling for a large kerosene engine? $\endgroup$
    – Superfort
    Aug 26, 2019 at 14:17
  • $\begingroup$ @Superfort I am more than willing to answer questions here on space.stackexchange.com, that's what I am here for. A "discussion", though...? A last thing I can do is look up the RP-1 cooling flow fraction in the Huzel and Huang classic book, for the A1 stage; that one has a - hypothetical - engine suspiciously close to the F-1, at about half its thrust IIRC. As soon as I have physical access to my library again (am travelling), can do that. But I'm not going to "discuss" or chat here for ever, as I don't get the impression that that is what this site was meant for. $\endgroup$ Aug 27, 2019 at 9:55
  • $\begingroup$ @Superfort And, btw, be polite please and either accept my answer, or otherwise tell us why you won't accept it ? $\endgroup$ Aug 27, 2019 at 9:57
  • $\begingroup$ I am sorry for appearing to be not polite! I am sorry. $\endgroup$
    – Superfort
    Oct 14, 2019 at 18:15

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