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Air Force Chemical

Equilibrium Specific Impulse

(Isp) Code

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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