I am under the assumption that higher chamber pressure results in increase in exhaust velocity. Is this true?

  • 1
    $\begingroup$ I first read it "camembert pressure" and it was very strange. I think you meant to say chamber (please correct the title and the body of your post) $\endgroup$
    – Antzi
    Commented Feb 1, 2019 at 0:20
  • $\begingroup$ Increasing the pressure of the fuel increases its enthalpy (the energy content of the fuel). The Isp is a function of the enthalpy of the fuel and the efficiency of the engine which is given by the injector, chamber and nozzle. The biggest advantage of a higher pressure is that you can increase the nozzle expansion ratio during atmospheric flight which greatly increases efficiency or allows for a smaller/lighter nozzle at the same expansion ratio. That's why upper stage engines tend to have lower chamber pressures. $\endgroup$
    – Christoph
    Commented Feb 1, 2019 at 8:40

1 Answer 1


Yes, it is absolutely true.

enter image description here

On this graph you can see the ISPs (aka exhaust velocity) at different mixture ration and chamber pressure.

The higher the pressure the higher the velocity and thus delta/v per unit of fuel.

A few other parameters come into play:

  • The shape of the nozzle
  • The pressure ratio between the combustion chamber and the outside (the higher the ambiant pressure the lower the ratio the lower the exhaust velocity)

Source: https://www.researchgate.net/figure/ISP-as-a-function-of-propellant-mixture-ratio-and-chamber-pressure-for-nitrous-oxide-and_fig4_305620863


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