Presumably liquid rocket combustion is never 100% efficient, so what proportion of fuel does typically remain unburnt, venting into the atmosphere, and does this vary for different rocket designs and fuel types - hydrogen, methane etc?

  • $\begingroup$ Accounting for what is leftover in the tanks or only the one which remain unburnt after passing through the engine ? $\endgroup$
    – Antzi
    Sep 29, 2016 at 14:02
  • 1
    $\begingroup$ This varies for each engine design. An important factor is the mixture ratio, there's usually a slight excess of fuel over oxidizer. $\endgroup$
    – Hobbes
    Sep 29, 2016 at 16:39
  • $\begingroup$ Yes Antzi, I was really thinking about how much ends up in the atmosphere, but perhaps sources do in the end? For hydrogen it's not a problem, but methane is an extremely strong greenhouse gas. $\endgroup$ Sep 29, 2016 at 17:13
  • $\begingroup$ I think the incident of russian rocket falling up over canadian island/waters rich waters. The hydrazine in tank burnt up but it wasn't regular rocket. $\endgroup$
    – Isrorian
    Sep 30, 2016 at 16:58

1 Answer 1


I managed to track down one reference online, in the SSME (Shuttle) engine, which uses liquid hydrogen/oxygen, "two-stage combustion approximately 99.6% efficient"


Also see, Modern Engineering for Design of Liquid-Propellant Rocket Engines by Dieter K. Huzel


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