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Air Force Chemical
Equilibrium Specific Impulse
(Isp) Code
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, Pc’s, Ae/At’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
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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
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Example
Continue with our example from class:Oxidizer: O2(l)
Fuel: CH4(l)
Pc = 1000 psi
O/F = 0.1-20.0 (Run a range of mixture ratios)
Ac/At = 3.0
Ae/At = 10.0, 25.0, 50.0
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Input Example (1/8)
Now ready to enterproportions
Enter CH4(l) as Fuel
Follow same steps forO2(g) as Oxidizer
Run INP.exe
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Input Example (2/8)
We want to run a range of mixture ratios from 0.1 to 20.0 by using the optimizer
Mass UnitsWe 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
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Input Example (3/8)
Set the fuel mass fixed at 1
Set up a second relationship as the ratio of CH4 mass to O2 mass
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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’
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Input Example (5/8)
Press ‘Enter’
Input Pc
Input Ae/At
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Input Example (6/8)
Frozen Flow
Setting optimization parameter at ‘constant’ permits code to run through all mass ratios
Press ‘Enter’
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Input Example (7/8)
Press ‘Enter’
Press ‘Enter’
Create Output Summary
Output Options
Select Parameters for Summary
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Input Example (8/8)
View Inputs
Name & Save Input File
Exit Program
Created file ch4o2.in
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Output Example (1/2)
Run ISP.exe
Creates file ch4o2.out
Portion of Output for O/F = 4.0
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Output Example (2/2)
Portion of Output Summary forO/F = 5.1 to 7.7
Tabulated Quantities:1) Mass of CH42) Mass of LOX3) Vacuum Isp at Ae/At = 504) Chamber Temperature5) C* using Chamber Properties6) Thrust Coefficient at Ae/At = 50