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
