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
=======================================================
