Orbiter-Forum Specific gas constant; how?
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 03-28-2019, 11:49 AM #1 SpaceCrazy5 Orbinaut Specific gas constant; how? I've been researching a lot about rocketry, specifically rocket engines. I decided to give designing one a go, but I'm slightly stuck; how am I supposed to calculate the Specific Gas Constant of the combustion chamber gas? It's mostly confusion to do with the molecular mass, and how that relates in terms of the oxidizer/fuel ratio, and other factors. Sorry if I've posted this in the wrong place, I'm just confused!
 03-28-2019, 11:20 PM #2 Thunder Chicken Fine Threads since 2008 Well, first thing to know is that the combustion gases are not ideal gases, so use of a gas constant and constant specific heats is a gross simplification. It can be used as a crude and simple approximation, but I wouldn't expect anything more from it.
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 03-29-2019, 01:58 AM #3 Linguofreak Orbinaut Quote: Originally Posted by SpaceCrazy5  I've been researching a lot about rocketry, specifically rocket engines. I decided to give designing one a go, but I'm slightly stuck; how am I supposed to calculate the Specific Gas Constant of the combustion chamber gas? It's mostly confusion to do with the molecular mass, and how that relates in terms of the oxidizer/fuel ratio, and other factors. Sorry if I've posted this in the wrong place, I'm just confused! There may be a few people on the forum who can help, but in general this is a fairly deep subject. In general, the specific gas constant depends mostly on the structure of the molecule: all monatomic gasses tend to have about the same specific gas constant, all diatonic gasses share (more or less) a different gas constant, and so forth. The problem in a combustion chamber is that the chemical composition of the gas changes rapidly as the fuel burns.

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