Specific gas constant; how?

SpaceCrazy5

New member
Joined
Mar 28, 2019
Messages
1
Reaction score
0
Points
0
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!
 

Thunder Chicken

Fine Threads since 2008
Donator
Joined
Mar 22, 2008
Messages
4,327
Reaction score
3,248
Points
138
Location
Massachusetts
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.
 

Linguofreak

Well-known member
Joined
May 10, 2008
Messages
5,017
Reaction score
1,254
Points
188
Location
Dallas, TX
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.
 

n72.75

Move slow and try not to break too much.
Orbiter Contributor
Addon Developer
Tutorial Publisher
Donator
Joined
Mar 21, 2008
Messages
2,687
Reaction score
1,337
Points
128
Location
Saco, ME
Website
mwhume.space
Preferred Pronouns
he/him
Top