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So I've been researching about designing a rocket engine, when I came across the specific heat ratio. I found on the Braeuig.us website that they were able to get a number by finding the heat capacity $C_p$ and the constant volume specific heat $C_v$.

Shouldn't the size of the combustion chamber pressure be taken into account? As it gets smaller, won't the fuel/oxydizer combustion be hotter due to the high pressure? I'm pretty much a novice in rocketry so please excuse my question if it's a little dumb. Thanks in advance!

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    $\begingroup$ The specific heat ratio is a physical property of the gas mixture, independent of equipment the gas is passing through. $\endgroup$ – Chet Miller Feb 7 '18 at 1:00
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Regardless of the pressure, the fuel/oxygen mixture contains a certain amount of energy per unit mass and can therefore only reach a certain temperature (because if has a certain heat capacity per unit mass). If you compress the mixture before combustion, you have to do work to get there.

Imagine dividing a chamber into two equal ones that are half the size; the temperature will be no different if you insert a "virtual septum".

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