Introduction to CEA

The online program CEARUN has been written to facilitate the use of the iconic NASA chemical equilibrium code CEA(Chemical Equilibrium with Applications), published in 1994 by Sanford Gordon and Bonnie J. McBride at the NASA Lewis Research Center (now the Glenn Research Center). CEA is part of a long evolution in chemical equilibrium codes written at Lewis Research Center and used worldwide. Its predecessors, CEC and CET89, were the first practical computer programs to use equilibrium chemical thermodynamics to analyze combustion and rocketry problems. Subsequent developments have extended these capabilities to the analysis of shock waves, Chapman-Jouget detonations and other important applications. With a thermodynamic database containing over 1900 species both gaseous and condensed, CEA remains the gold standard for detailed analysis of problems involving combustion, rocketry, shock and detonation.

The state of a thermodynamic system consisting of a multispecies compressible gas in equilibrium can be described by the overall chemical composition (Duhem's Law) and two independent thermodynamic variables, such as (temperature, pressure) or (enthalpy, pressure). The choice of which two independent variables to be held constant is determined by the problem to be solved. An example is adiabatic combustion at constant pressure. Here the system pressure and enthalpy are held constant and the Gibbs Free Energy is minimized through variation in the system temperature and overall chemical composition. This is called an 'hp' problem because the independent variables H and P are held constant. It is the first pick at the top of the portal page ( http://cearun.grc.nasa.gov) on CEARUN.

Use of CEARUN

The first thing to do is download the User's Guide pdf file. It has many examples. It is found at http://www.grc.nasa.gov/WWW/CEAWeb/RP-1311P2.htm .

The portal page ( http://cearun.grc.nasa.gov) allows the user to specify which of the several applications are to be solved. CEA finds the most stable composition and properties for thermodynamic states specified by the user. The choice of which two independent variables to be held constant is determined by the problem to be solved.


I. The portal page

http://cearun.grc.nasa.gov

A pick at the top of this page reads 'rocket'. Rocket operation is modeled by a combustion (hp) process followed by an isentropic expansion through the rocket nozzle. CEA can determine performance based either on a continuous equilibrium adjustment during the expansion or on a composition 'frozen' at the throat values. CEA determines and lists the rocket thrust, c*, Isp, Ivac and other important design variables, for equilibrium or frozen expansion.

Other picks at the top of the page, 'det', 'uv', 'tp' et al. are discussed in the User's Guide. It is very informative to set up and run the sample problems, and to experiment with the input parameters to see the effects of changes.

The theoretical underpinnings of the CEA program can be downloaded from http://www.grc.nasa.gov/WWW/CEAWeb/RP-1311.htm .

**********************************************************************************************************

II. Example: Running a constant-pressure combustion (hp) problem with CEARUN

(1) http://cearun.grc.nasa.gov

(2) Use the radiobutton 'hp', fill in the code box and click 'Submit'

(3) Choose your pressures. This page is self-expanatory.

(4) You will choose your fuel(s) here. Commonly used species are on the page as radiobuttons. If your fuel is not one of these, you must use the Periodic Chart option.

(5) To use the Periodic Chart, specify all elements in the compound of interest,(e.g. for Jet-A, check C and H), Click Submit.

(6) You will see a list of species containing the elements you have checked. Click on the compound(s) you wish to use. Click Submit.

(7) Self-explanatory-Do you want to specify more compounds?

(8) If you have specified more than one compound, you will be asked to fill in the relative amounts.

(9) Now fill in the boxes for the fuel temperatures.

(10) Repeat for the oxidizer(s).

NOTE: For Air at T not equal to 298.15K, you must use the Periodic Table and select N, O, C and Ar.

(11) Now fill in the relative amounts(mass)of oxidizer to fuel. This can be expressed as an O/F ratio or as an equivalence ratio.

(12) Definitions:

(a) Use 'omit' to exclude possible species from the calculation.

(b) Use 'only' if you wish to consider in the calculation only some of the possible species from the CEA database.

(c) Use 'insert' to start the convergence process with one or more condensed species present. This option sometimes helps with convergence. It will not change the overall composition. C(gr) is often inserted for hydrocarbon oxidation problems. AL2O3(a) is often inserted if aluminum has been added to rocket fuels.

(d) 'Trace' is the minimum concentration that will be reported in your output.

**********************************************************************************************************

Privacy Policy and Important Notices