I have been working on a rocket engine and I have cad models and everything and I am getting ready to build it. Then, I was running over the numbers one more time and I realized that the thrust I was getting was completely different from what I should have been getting.
The big problem is the nasa equations. It uses the variables Ttotal and Ptotal. NASA states, "pt is the total pressure in the combustion chamber, Tt is the total temperature in the combustion chamber." However, when I plug in 300 psi and 5742 degrees fahrenheit and the exhaust values for each variable as given by NASA's isentropic equations, I get a thrust of 735 pounds, whereas the first time I ran the numbers I got 32 pounds of thrust.
Here is my data, most of it was from a formula. The top ten rows are all givens. I got that information from https://risacher.org/rocket/eqns.html as I am building a gasoline-GOX engine.
What it is
Value
Unit
Combustion pressure (Pc)
300
PSI
Mixture Ratio
2.5
n/a
Flame Temp
5742
Fahrenheit
ISP
261
Seconds
GOX Density
0.083
lb/ft^3
Gas Density
44.5
lb/ft^3
Nozzle Throat Cross Sectional Area
0.00173611
ft^2
Gas constant (R)
65
ftlb/lb
Gamma (heat ratio)
1.2
gc (gravitation)
32
ft/second/second
Tt (temperature of gasses at nozzle throat)
5637.618
Fahrenheit
Tc (temperature of cumbustion flame)
6202
Rankine
Pt (gas pressure at nozzle throat)
169.2
PSI
Me (mach number of gasses at exit)
2.55
Area Exhaust/Area throat
3.65
Temperature Exhuast/Temperature combustion
0.606
Thrust
31.84104294
Pounds
Mass flow rate
0.0009229501076
pounds per second
Exhaust velocity
1380.669321
ft/second
Temperature Exhuast
3479.652
Fahrenheit
Exhaust pressure
24.4297
psi
As you might imagine, I would really appreciate someone going over and double checking my numbers. Thank you so much!
