1. 1 Air Force Chemical Equilibrium Specific Impulse (Isp) Code

2. 2/14 Overview The Air Force ISP code is a DOS-based thermochemistry code designed for rocket combustion/performance evaluation Performs similar functions as ‘Rocket’ mode of CEA Why use this code over CEA? Has optimization feature which allows code to be run over a large range of O/F’s, P c ’s, A e /A t ’s, etc. with minimal input effort by user Produces tabular summary of data which can easily copied into Excel, Matlab, etc. Drawbacks to ISP Code? Does not calculate thermal transport properties Does not have additional functional capabilities that CEA has such as shocks, detonations, etc. Software is available for download on AAE 539 course website

3. 3/14 Overview There are two exectuable files that must be run to perform calculation: INP.exe – Run this first – sets up inputs, desired outputs, and asks for input file name ISP.exe – Run this second – asks for input file name, desired output file name, and executes code *.DAT files contain propellant libraries, equilibrium reaction data, etc. HLP.doc – Details the Optimizer functionality Program has a fairly extensive library of propellants however not everything is there – you may have to enter some on your own

4. 4/14 Example Continue with our example from class: Oxidizer: O 2(l) Fuel: CH 4(l) P c = 1000 psi O/F = 0.1-20.0 (Run a range of mixture ratios) A c /A t = 3.0 A e /A t = 10.0, 25.0, 50.0

5. 5/14 Input Example (1/8) Now ready to enter proportions Enter CH 4(l) as Fuel Follow same steps for O 2(g) as Oxidizer Run INP.exe

6. 6/14 Input Example (2/8) We want to run a range of mixture ratios from 0.1 to 20.0 by using the optimizer Mass Units We are running a ratio of oxidizer mass to fuel mass – must indicate this here We will fix the fuel mass at 1 and vary ox mass Can enter fixed proportions here

7. 7/14 Input Example (3/8) Set the fuel mass fixed at 1 Set up a second relationship as the ratio of CH 4 mass to O 2 mass

8. 8/14 Input Example (4/8) Set initial mass ratio at 0.1 Set range of mass ratios from 0.1 to 20.0 with a step size of 0.1 Summary of relationships Press ‘Enter’

9. 9/14 Input Example (5/8) Press ‘Enter’ Input P c Input A e /A t

10. 10/14 Input Example (6/8) Frozen Flow Setting optimization parameter at ‘constant’ permits code to run through all mass ratios Press ‘Enter’

11. 11/14 Input Example (7/8) Press ‘Enter’ Create Output Summary Output Options Select Parameters for Summary

12. 12/14 Input Example (8/8) View Inputs Name & Save Input File Exit Program Created file ch4o2.in

13. 13/14 Output Example (1/2) Run ISP.exe Creates file ch4o2.out Portion of Output for O/F = 4.0

14. 14/14 Output Example (2/2) Portion of Output Summary for O/F = 5.1 to 7.7 Tabulated Quantities: 1) Mass of CH4 2) Mass of LOX 3) Vacuum I sp at A e /A t = 50 4) Chamber Temperature 5) C* using Chamber Properties 6) Thrust Coefficient at Ae/At = 50