Species Mole Fractions

Use RocketCEA versions 1.1.9 and greater to access to the combustion species mass fractions and mole fractions.

Warning

Only use >= version 1.1.9 for Species Fractions. (Versions 1.1.6 through 1.1.8 have a bug.)

Notice at the bottom of the sample run at Standard Examples LOX/LH2 Performance that the combustion species mole fractions are displayed.

CEA prints those values as:

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

RocketCEA provides the function get_SpeciesMoleFractions that returns two dictionaries. One with with species molecular weights and one with the combustion species mole fractions. The user can specify equilibrium or frozen values.

Note

RocketCEA returns 4 columns of species concentrations.

Columns are: (1) Injector Face, (2) Combustion Chamber, (3) Throat and (4) Exit

For a Finite Area Combustor , the Injector Face and Combustion Chamber will differ, otherwise the two are identical.

A Display of the contents of those two dictionaries is shown below:

   ROCKETCEA MOLE FRACTIONS (frozen=0, frozenAtThroat=0)
 *H               0.03417  0.03417  0.02810  0.00001   MW=1.00794
 HO2              0.00003  0.00003  0.00002  0.00000   MW=33.0067
 *H2              0.24832  0.24832  0.24538  0.24401   MW=2.01588
 H2O              0.66590  0.66590  0.68751  0.75598   MW=18.0153
 H2O2             0.00001  0.00001  0.00001  0.00000   MW=34.0147
 *O               0.00334  0.00334  0.00217  0.00000   MW=15.9994
 *OH              0.04478  0.04478  0.03446  0.00000   MW=17.0073
 *O2              0.00345  0.00345  0.00236  0.00000   MW=31.9988
=======================================================
   ROCKETCEA MOLE FRACTIONS (frozen=1, frozenAtThroat=0)
 *H               0.03417  0.03417  0.03417  0.03417   MW=1.00794
 HO2              0.00003  0.00003  0.00003  0.00003   MW=33.0067
 *H2              0.24832  0.24832  0.24832  0.24832   MW=2.01588
 H2O              0.66590  0.66590  0.66590  0.66590   MW=18.0153
 H2O2             0.00001  0.00001  0.00001  0.00001   MW=34.0147
 *O               0.00334  0.00334  0.00334  0.00334   MW=15.9994
 *OH              0.04478  0.04478  0.04478  0.04478   MW=17.0073
 *O2              0.00345  0.00345  0.00345  0.00345   MW=31.9988
=======================================================
   ROCKETCEA MOLE FRACTIONS (frozen=1, frozenAtThroat=1)
 *H               0.03417  0.03417  0.02810  0.02810   MW=1.00794
 HO2              0.00003  0.00003  0.00002  0.00002   MW=33.0067
 *H2              0.24832  0.24832  0.24538  0.24538   MW=2.01588
 H2O              0.66590  0.66590  0.68751  0.68751   MW=18.0153
 H2O2             0.00001  0.00001  0.00001  0.00001   MW=34.0147
 *O               0.00334  0.00334  0.00217  0.00217   MW=15.9994
 *OH              0.04478  0.04478  0.03446  0.03446   MW=17.0073
 *O2              0.00345  0.00345  0.00236  0.00236   MW=31.9988
=======================================================

The script that produces the above output is:

from rocketcea.cea_obj import CEA_Obj

ispObj = CEA_Obj( oxName='LOX', fuelName='LH2')

for frozen, frozenAtThroat in [(0,0), (1,0), (1,1)]:
    molWtD, moleFracD = ispObj.get_SpeciesMoleFractions( Pc=1000.0, MR=6.0, eps=40.0, 
                                            frozen=frozen, frozenAtThroat=frozenAtThroat )
                                            
    print('   ROCKETCEA MOLE FRACTIONS (frozen=%i, frozenAtThroat=%i)'%(frozen, frozenAtThroat)  )
    for species, mfL in moleFracD.items():
        
        s = '  '.join( [ '%7.5f'%mf for mf in mfL ] )
        print( ' %-15s '%species, s, '  MW=%g'%molWtD[species] )
    print('='*55)

Species Mass Fractions

If mass fractions are preferred, that can be obtained by calling the method get_SpeciesMassFractions.

Modifying the above mole fraction script to return mass fractions is shown below.

from rocketcea.cea_obj import CEA_Obj

ispObj = CEA_Obj( oxName='LOX', fuelName='LH2')

for frozen, frozenAtThroat in [(0,0), (1,0), (1,1)]:
    molWtD, massFracD = ispObj.get_SpeciesMassFractions( Pc=1000.0, MR=6.0, eps=40.0, 
                                            frozen=frozen, frozenAtThroat=frozenAtThroat )
                                            
    print('   ROCKETCEA MASS FRACTIONS (frozen=%i, frozenAtThroat=%i)'%(frozen, frozenAtThroat)  )
    for species, mfL in massFracD.items():
        
        s = '  '.join( [ '%7.5f'%mf for mf in mfL ] )
        print( ' %-15s '%species, s, '  MW=%g'%molWtD[species] )
    print('='*55)

This script produces the following:

   ROCKETCEA MASS FRACTIONS (frozen=0, frozenAtThroat=0)
 *H               0.00256  0.00256  0.00208  0.00000   MW=1.00794
 HO2              0.00008  0.00008  0.00004  0.00000   MW=33.0067
 *H2              0.03720  0.03720  0.03636  0.03486   MW=2.01588
 H2O              0.89139  0.89139  0.91033  0.96514   MW=18.0153
 H2O2             0.00003  0.00003  0.00001  0.00000   MW=34.0147
 *O               0.00397  0.00397  0.00255  0.00000   MW=15.9994
 *OH              0.05658  0.05658  0.04308  0.00000   MW=17.0073
 *O2              0.00820  0.00820  0.00555  0.00000   MW=31.9988
=======================================================
   ROCKETCEA MASS FRACTIONS (frozen=1, frozenAtThroat=0)
 *H               0.00256  0.00256  0.00256  0.00256   MW=1.00794
 HO2              0.00008  0.00008  0.00008  0.00008   MW=33.0067
 *H2              0.03720  0.03720  0.03720  0.03720   MW=2.01588
 H2O              0.89139  0.89139  0.89139  0.89139   MW=18.0153
 H2O2             0.00003  0.00003  0.00003  0.00003   MW=34.0147
 *O               0.00397  0.00397  0.00397  0.00397   MW=15.9994
 *OH              0.05658  0.05658  0.05658  0.05658   MW=17.0073
 *O2              0.00820  0.00820  0.00820  0.00820   MW=31.9988
=======================================================
   ROCKETCEA MASS FRACTIONS (frozen=1, frozenAtThroat=1)
 *H               0.00256  0.00256  0.00208  0.00208   MW=1.00794
 HO2              0.00008  0.00008  0.00004  0.00004   MW=33.0067
 *H2              0.03720  0.03720  0.03636  0.03636   MW=2.01588
 H2O              0.89139  0.89139  0.91033  0.91033   MW=18.0153
 H2O2             0.00003  0.00003  0.00001  0.00001   MW=34.0147
 *O               0.00397  0.00397  0.00255  0.00255   MW=15.9994
 *OH              0.05658  0.05658  0.04308  0.04308   MW=17.0073
 *O2              0.00820  0.00820  0.00555  0.00555   MW=31.9988
=======================================================