CPep 1.2

CPep Version 1.2 – Propellant Evaluation Program

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CPep is an implementation in standard C of the chemical equilibrium algorythm presented by GORDON and McBRIDE in the NASA report RP-1311: Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications

CPep is based on Cpropep, Copyright (c) 2000 by Antione Lefebvre
with modifications and improvements. It is being released under the GPL and is free of charge.

CPep is aimed at solving 4 problems:

  1. Adiabatic flame temperature
  2. Frosen equilibrium
  3. Shifting equilibrium
  4. Fixed pressure and temperature equilibrium


The development of cpep is based on the theory pesented in:
S. Gordon and B.J. McBride, Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications: I. Analysis , NASA Reference Publication 1311, October 1994.
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The thermochemical data were provided by Bonnie McBride of NASA Gleen Research Center.

CPepshell provides a graphical userinterface to operate CPep under Windows. Install CPepshell in the same working directory as the CPep.exe. CPepshell uses the CPep.conf to locate the propellant data file – just as CPep.exe does.

CPepshell allows setting up calculations for all 4 types of problems. When only one problem is selected then the conditions for that particular problem is defined by the user. If more than one problem is solved at a time, the conditions are coupled in the following way:

  • Fixed pressure and temperature equilibrium takes its own independent values for chamber pressure and temperature.
  • Adiabatic flame temperature and frosen equilibrium and fixed equilibrium shares the same value of the chamber pressure.
  • Frozen equilibrium and shifting equilibrium shares the same exit conditions.


CPep is based on Cpropep, an open source project created and maintained by Antoine Lefebvre (antoine.lefebvre@polymtl.ca). Original GPL source code for Cpropep is available here cpropep-src.tar.gz and thesource for the mathematical library can be found here libnum-src.tar.gz.

CPepshell is free to use for anyone who finds it useful and is based on Cpropepshell by Hans Olaf Toft