Species Mole Fractions¶
RocketCEA version 1.1.6 and greater provide access to the combustion species mass fractions and mole fractions.
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.
A Display of the contents of those two dictionaries is shown below:
ROCKETCEA MOLE FRACTIONS (frozen=0, frozenAtThroat=0)
*H 0.03417 0.02810 0.00001 MW=1.00794
HO2 0.00003 0.00002 0.00000 MW=33.0067
*H2 0.24832 0.24538 0.24401 MW=2.01588
H2O 0.66590 0.68751 0.75598 MW=18.0153
H2O2 0.00001 0.00001 0.00000 MW=34.0147
*O 0.00334 0.00217 0.00000 MW=15.9994
*OH 0.04478 0.03446 0.00000 MW=17.0073
*O2 0.00345 0.00236 0.00000 MW=31.9988
=======================================================
ROCKETCEA MOLE FRACTIONS (frozen=1, frozenAtThroat=0)
*H 0.03417 0.03417 0.03417 MW=1.00794
HO2 0.00003 0.00003 0.00003 MW=33.0067
*H2 0.24832 0.24832 0.24832 MW=2.01588
H2O 0.66590 0.66590 0.66590 MW=18.0153
H2O2 0.00001 0.00001 0.00001 MW=34.0147
*O 0.00334 0.00334 0.00334 MW=15.9994
*OH 0.04478 0.04478 0.04478 MW=17.0073
*O2 0.00345 0.00345 0.00345 MW=31.9988
=======================================================
ROCKETCEA MOLE FRACTIONS (frozen=1, frozenAtThroat=1)
*H 0.03417 0.02810 0.02810 MW=1.00794
HO2 0.00003 0.00002 0.00002 MW=33.0067
*H2 0.24832 0.24538 0.24538 MW=2.01588
H2O 0.66590 0.68751 0.68751 MW=18.0153
H2O2 0.00001 0.00001 0.00001 MW=34.0147
*O 0.00334 0.00217 0.00217 MW=15.9994
*OH 0.04478 0.03446 0.03446 MW=17.0073
*O2 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 0.00208 0.00000 MW=1.00794
HO2 0.00008 0.00004 0.00000 MW=33.0067
*H2 0.03720 0.03636 0.03486 MW=2.01588
H2O 0.89139 0.91033 0.96514 MW=18.0153
H2O2 0.00003 0.00001 0.00000 MW=34.0147
*O 0.00397 0.00255 0.00000 MW=15.9994
*OH 0.05658 0.04308 0.00000 MW=17.0073
*O2 0.00820 0.00555 0.00000 MW=31.9988
=======================================================
ROCKETCEA MASS FRACTIONS (frozen=1, frozenAtThroat=0)
*H 0.00256 0.00256 0.00256 MW=1.00794
HO2 0.00008 0.00008 0.00008 MW=33.0067
*H2 0.03720 0.03720 0.03720 MW=2.01588
H2O 0.89139 0.89139 0.89139 MW=18.0153
H2O2 0.00003 0.00003 0.00003 MW=34.0147
*O 0.00397 0.00397 0.00397 MW=15.9994
*OH 0.05658 0.05658 0.05658 MW=17.0073
*O2 0.00820 0.00820 0.00820 MW=31.9988
=======================================================
ROCKETCEA MASS FRACTIONS (frozen=1, frozenAtThroat=1)
*H 0.00256 0.00208 0.00208 MW=1.00794
HO2 0.00008 0.00004 0.00004 MW=33.0067
*H2 0.03720 0.03636 0.03636 MW=2.01588
H2O 0.89139 0.91033 0.91033 MW=18.0153
H2O2 0.00003 0.00001 0.00001 MW=34.0147
*O 0.00397 0.00255 0.00255 MW=15.9994
*OH 0.05658 0.04308 0.04308 MW=17.0073
*O2 0.00820 0.00555 0.00555 MW=31.9988
=======================================================