# Standard Examples

For those with NASA CEA experience, running CEA and reviewing the printed output is standard practice.

The following examples show how to run a case and review the standard CEA output.

RocketCEA always begins with an import statement and an instance of a CEA_obj:

    from rocketcea.cea_obj import CEA_Obj
    ispObj = CEA_Obj( oxName='LOX', fuelName='LH2')

Instead of manually assembling a run deck for CEA, the above is all that is needed to run a CEA rocket case with standard definitions of all the most common rocket propellants.

## LOX/LH2 Performance

The script below is typical to calculate predicted equilibrium performance at a specific chamber pressure, mixture ratio and expansion ratio.

The script uses the short output option. (long-form output is default)

    from rocketcea.cea_obj import CEA_Obj

    ispObj = CEA_Obj( oxName='LOX', fuelName='LH2')
    s = ispObj.get_full_cea_output( Pc=1000.0, MR=6.0, eps=40.0, short_output=1)

    print( s )

Notice that RocketCEA generates the propellant cards and input parameters for the rocket equilibrium problem. (as opposed to a shock or detonation problem)

The propellant temperature and enthalpy are standard, which usually means room temperature for storable or gas propellants and normal boiling point for cryogenic propellants.

See the Temperature Adjust page for modifying the temperature and enthalpy of the reactants.

Notice also that the CEA documentation (shown below) allows for different pressure units to be used for Pc. The default units in RocketCEA are psia, however, bar, atm and mmh are also options.

Pc units can be specified with the input parameter pc_units as shown in the following lines:

    s = ispObj.get_full_cea_output( Pc=1000.0, MR=6.0, eps=40.0, short_output=1, pc_units='psia')
    s = ispObj.get_full_cea_output( Pc=68.948, MR=6.0, eps=40.0, short_output=1, pc_units='bar')
    s = ispObj.get_full_cea_output( Pc=68.046, MR=6.0, eps=40.0, short_output=1, pc_units='atm')
    s = ispObj.get_full_cea_output( Pc=51715., MR=6.0, eps=40.0, short_output=1, pc_units='mmh')

The above script gives the standard output that a typical CEA run from the command prompt would give:

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

            NASA-GLENN CHEMICAL EQUILIBRIUM PROGRAM CEA, OCTOBER 18, 2002
                      BY  BONNIE MCBRIDE AND SANFORD GORDON
         REFS: NASA RP-1311, PART I, 1994 AND NASA RP-1311, PART II, 1996

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

    reac
     fuel H2(L)  H 2
     h,cal=-2154.0      t(k)=20.27       wt%=100.
     oxid O2(L)  O 2
     h,cal=-3102.      t(k)=90.18       wt%=100.

    prob case=LOX_/_LH2
     rocket equilibrium  p,psia=1000.000000, supar=40.000000,
     o/f=6.000000

    outp   calories short

    end

                 THEORETICAL ROCKET PERFORMANCE ASSUMING EQUILIBRIUM

              COMPOSITION DURING EXPANSION FROM INFINITE AREA COMBUSTOR

    Pinj =  1000.0 PSIA
    CASE = LOX_/_LH2

                REACTANT                    WT FRACTION      ENERGY      TEMP
                                             (SEE NOTE)      CAL/MOL       K
    FUEL        H2(L)                        1.0000000     -2154.000     20.270
    OXIDANT     O2(L)                        1.0000000     -3102.000     90.180

    O/F=    6.00000  %FUEL= 14.285714  R,EQ.RATIO= 1.322780  PHI,EQ.RATIO= 1.322780

                    CHAMBER   THROAT     EXIT
    Pinf/P            1.0000   1.7351   459.06
    P, ATM            68.046   39.216  0.14823
    T, K             3483.35  3291.03  1440.95
    RHO, G/CC       3.2038-3 1.9758-3 1.7690-5
    H, CAL/G         -235.74  -509.81 -2372.54
    U, CAL/G         -750.09  -990.49 -2575.47
    G, CAL/G        -15090.3 -14544.2 -8517.40
    S, CAL/(G)(K)     4.2644   4.2644   4.2644

    M, (1/n)          13.458   13.606   14.111
    (dLV/dLP)t      -1.02525 -1.01954 -1.00000
    (dLV/dLT)p        1.4496   1.3682   1.0001
    Cp, CAL/(G)(K)    2.0951   1.9171   0.7308
    GAMMAs            1.1401   1.1403   1.2388
    SON VEL,M/SEC     1566.3   1514.4   1025.6
    MACH NUMBER        0.000    1.000    4.123

    PERFORMANCE PARAMETERS

    Ae/At                     1.00000   40.000
    CSTAR, FT/SEC              7560.0   7560.0
    CF                         0.6572   1.8351
    Ivac,LB-SEC/LB              289.8    451.7
    Isp, LB-SEC/LB              154.4    431.2

    MOLE FRACTIONS

    *H               0.03417  0.02810  0.00001
    HO2              0.00003  0.00002  0.00000
    *H2              0.24832  0.24538  0.24401
    H2O              0.66590  0.68751  0.75598
    H2O2             0.00001  0.00001  0.00000
    *O               0.00334  0.00217  0.00000
    *OH              0.04478  0.03446  0.00000
    *O2              0.00345  0.00236  0.00000

     * THERMODYNAMIC PROPERTIES FITTED TO 20000.K

    NOTE. WEIGHT FRACTION OF FUEL IN TOTAL FUELS AND OF OXIDANT IN TOTAL OXIDANTS

## Transport Properties

New in RocketCEA version 1.06, to include transport properties, set the show_transport flag.

    from rocketcea.cea_obj import CEA_Obj

    ispObj = CEA_Obj( oxName='LOX', fuelName='LH2')
    s = ispObj.get_full_cea_output( Pc=1000.0, MR=6.0, eps=40.0,
                                    short_output=1, show_transport=1)

    print( s )

which adds the following lines to the output:

    TRANSPORT PROPERTIES (GASES ONLY)
      CONDUCTIVITY IN UNITS OF MILLICALORIES/(CM)(K)(SEC)

    VISC,MILLIPOISE   1.0588   1.0153  0.43328

     WITH FROZEN REACTIONS

    Cp, CAL/(G)(K)    0.9029   0.8950   0.6859
    CONDUCTIVITY      1.3519   1.2760   0.4369
    PRANDTL NUMBER    0.7071   0.7121   0.6803

To access transport properties, each of the following calls return a tuple of (Heat Capacity, Viscosity, Thermal Conductivity and Prandtl Number):

    Cp, visc, cond, Pr = ispObj.get_Chamber_Transport(Pc=1000.0, MR=6.0)
    Cp, visc, cond, Pr = ispObj.get_Chamber_Transport(Pc=1000.0, MR=6.0, frozen=1)

    Cp, visc, cond, Pr = ispObj.get_Throat_Transport(Pc=1000.0, MR=6.0)
    Cp, visc, cond, Pr = ispObj.get_Throat_Transport(Pc=1000.0, MR=6.0, frozen=1)

    Cp, visc, cond, Pr = ispObj.get_Exit_Transport(Pc=1000.0, MR=6.0, eps=40.0)
    Cp, visc, cond, Pr = ispObj.get_Exit_Transport(Pc=1000.0, MR=6.0, eps=40.0, frozen=1)

where the frozen flag determines equilibrium or frozen output.

The standard units will be the same as the printout, namely:

    Cp   = CAL/(G)(K)
    visc = MILLIPOISE
    cond = MILLICALORIES/(CM)(K)(SEC)
    Pr   = dimensionless

If different units are desired, use the cea_obj_w_units wrapper, for example:

    from rocketcea.cea_obj_w_units import CEA_Obj
    C = CEA_Obj( oxName='LOX', fuelName='LH2',
                 specific_heat_units='kJ/kg-K',
                 viscosity_units='poise',
                 thermal_cond_units='BTU/s-in-degF')

## Frozen Performance

To run the same LOX/LH2 case above, but with frozen composition during expansion, the following script is used.

Notice here that the flag to freeze the composition at the throat is set. Otherwise, the chamber composition is used.

Also notice that without the short output flag, the long form of output results.

    from rocketcea.cea_obj import CEA_Obj

    ispObj = CEA_Obj( oxName='LOX', fuelName='LH2')
    s = ispObj.get_full_cea_output( Pc=1000.0, MR=6.0, eps=40.0, frozen=1, frozenAtThroat=1)

    print( s )

The result are shown below:

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

            NASA-GLENN CHEMICAL EQUILIBRIUM PROGRAM CEA, OCTOBER 18, 2002
                      BY  BONNIE MCBRIDE AND SANFORD GORDON
         REFS: NASA RP-1311, PART I, 1994 AND NASA RP-1311, PART II, 1996

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

    reac
     fuel H2(L)  H 2
     h,cal=-2154.0      t(k)=20.27       wt%=100.
     oxid O2(L)  O 2
     h,cal=-3102.      t(k)=90.18       wt%=100.

    prob case=LOX_/_LH2
     rocket frozen nfz=2   p,psia=1000.000000, supar=40.000000,
     o/f=6.000000

    outp   calories

    end

    OPTIONS: TP=F  HP=F  SP=F  TV=F  UV=F  SV=F  DETN=F  SHOCK=F  REFL=F  INCD=F
    RKT=T  FROZ=T  EQL=F  IONS=F  SIUNIT=F  DEBUGF=F  SHKDBG=F  DETDBG=F  TRNSPT=F

    TRACE= 0.00E+00  S/R= 0.000000E+00  H/R= 0.000000E+00  U/R= 0.000000E+00

    Pc,BAR =    68.947304

    Pc/P =

    SUBSONIC AREA RATIOS =

    SUPERSONIC AREA RATIOS =    40.0000

    NFZ=  2  Mdot/Ac= 0.000000E+00  Ac/At= 0.000000E+00

       REACTANT          WT.FRAC   (ENERGY/R),K   TEMP,K  DENSITY
           EXPLODED FORMULA
    F: H2(L)            1.000000  -0.108393E+04    20.27  0.0000
             H  2.00000
    O: O2(L)            1.000000  -0.156098E+04    90.18  0.0000
             O  2.00000

     SPECIES BEING CONSIDERED IN THIS SYSTEM
    (CONDENSED PHASE MAY HAVE NAME LISTED SEVERAL TIMES)
     LAST thermo.inp UPDATE:    9/09/04

     g 6/97  *H               g 4/02  HO2              tpis78  *H2
     g 8/89  H2O              g 6/99  H2O2             g 5/97  *O
     g 4/02  *OH              tpis89  *O2              g 8/01  O3
     g11/99  H2O(cr)          g 8/01  H2O(L)           g 8/01  H2O(L)

    O/F =   6.000000

                          EFFECTIVE FUEL     EFFECTIVE OXIDANT        MIXTURE
    ENTHALPY                  h(2)/R              h(1)/R               h0/R
    (KG-MOL)(K)/KG       -0.53769505E+03     -0.48782395E+02     -0.11862706E+03

    KG-FORM.WT./KG             bi(2)               bi(1)               b0i
     *H                   0.99212255E+00      0.00000000E+00      0.14173179E+00
     *O                   0.00000000E+00      0.62502344E-01      0.53573438E-01

    POINT ITN      T            H           O
      1    9    3483.350      -9.273     -16.160
    Pinf/Pt = 1.734909
      2    4    3291.075      -9.450     -16.510
    Pinf/Pt = 1.735136
      2    1    3291.030      -9.450     -16.510

              THEORETICAL ROCKET PERFORMANCE ASSUMING FROZEN COMPOSITION
                                    AFTER POINT 2

    Pinj =  1000.0 PSIA
    CASE = LOX_/_LH2

                REACTANT                    WT FRACTION      ENERGY      TEMP
                                             (SEE NOTE)      CAL/MOL       K
    FUEL        H2(L)                        1.0000000     -2154.000     20.270
    OXIDANT     O2(L)                        1.0000000     -3102.000     90.180

    O/F=    6.00000  %FUEL= 14.285714  R,EQ.RATIO= 1.322780  PHI,EQ.RATIO= 1.322780

                    CHAMBER   THROAT     EXIT
    Pinf/P            1.0000   1.7351   539.53
    P, ATM            68.046   39.216  0.12612
    T, K             3483.35  3291.03  1149.39
    RHO, G/CC       3.2038-3 1.9758-3 1.8194-5
    H, CAL/G         -235.74  -509.81 -2255.83
    U, CAL/G         -750.09  -990.49 -2423.71
    G, CAL/G        -15090.3 -14544.2 -7157.33
    S, CAL/(G)(K)     4.2644   4.2644   4.2644

    M, (1/n)          13.458   13.606   13.606
    Cp, CAL/(G)(K)    2.0951   1.9171   0.6859
    GAMMAs            1.1401   1.1403   1.2705
    SON VEL,M/SEC     1566.3   1514.4    944.7
    MACH NUMBER        0.000    1.000    4.352

    PERFORMANCE PARAMETERS

    Ae/At                     1.00000   40.000
    CSTAR, FT/SEC              7560.0   7560.0
    CF                         0.6572   1.7843
    Ivac,LB-SEC/LB              289.8    436.7
    Isp, LB-SEC/LB              154.4    419.3

    MOLE FRACTIONS

    *H              0.02810   HO2             0.00002   *H2             0.24538
    H2O             0.68751   H2O2            0.00001   *O              0.00217
    *OH             0.03446   *O2             0.00236

     * THERMODYNAMIC PROPERTIES FITTED TO 20000.K

       PRODUCTS WHICH WERE CONSIDERED BUT WHOSE