Just what it says on the tin. I need to know either the "stay time" (Ts) or characteristic length (L*) that would be used to figure combustion chamber dimensions used with a LOX/LCH4-fuelled rocket engine. I'm having a difficult time finding this little datum, online or in the literature (although I admit, I'm still collecting "the literature.")

  • $\begingroup$ I thought that residence time and chamber length was used in combination with injector efficiency, not just for a particular fuel $\endgroup$
    – R. Hall
    Commented Jul 28, 2021 at 7:01
  • 1
    $\begingroup$ Half marks. You are correct that some tuning is involved (R&N, CFD simulation, burn tests,) but every fuel/oxidizer combination has a base set of values that can cut down sharply on the R&D spend. This value may take fhe form of either the "characteristic length" (of the combustion chamber,) or "L*," or the "stay time" (time the fuel needs to mix and fully combust,) generally in seconds. Onw may be calculated from the other, and either will get you your chamber dims. Either way, you're avoiding a performance penalty. $\endgroup$
    – JDKelley
    Commented Jul 28, 2021 at 10:12

1 Answer 1


The LOX/CH4 engine described in the paper EXPERIMENTAL STUDIES ON COMBUSTION INSTABILITIES IN A MULTI-ELEMENT, RECTANGULAR ROCKET CHAMBER is stated to have an L* between 113–339 cm.

The paper Comprehensive Design Method for LOX/Liquid-Methane Regenerative Cooling Combustor with Coaxial Injector gives a Ts between 0.97 and 1.71 ms.


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