def calculate_combustion_parameters_at_chamber(self, phi):
""" Uses RocketCEA, which wraps NASA CEA, to calculate 4 parameters at
the combustion chamber:
OF_ratio : Oxidizer/fuel mass ratio.
k : exhaust gasses cp/cv = gamma.
M : exhaust gasses moleculaer weight.
To : adiabatic flame temperature.
Parameters
----------
phi : float
Equivalence ratio: phi = (fuel-to-oxidizer ratio) /
(fuel-to-oxidizer ratio)st.
Returns
-------
OF_ratio : float
Oxidizer/fuel mass ratio based on given phi.
gamma : float
Exhaust gasses cp/cv.
molecular_weight : float
Exhaust gasses moleculaer weight.
flame_temperature : float
Adiabatic flame temperature.
"""
cea_analysis = CEA_Obj(
oxName=self.oxidizer.name,
fuelName=self.fuel.name,
isp_units="sec",
cstar_units="m/sec",
pressure_units="bar",
temperature_units="K",
sonic_velocity_units="m/sec",
enthalpy_units="kJ/kg",
density_units="kg/m^3",
specific_heat_units="kJ/kg-K",
viscosity_units="millipoise",
thermal_cond_units="W/cm-degC",
)
# Get OF ratio based on equivalence ratio
OF_ratio = cea_analysis.getMRforER(ERphi=phi)
# Calculate outputs
area_ratio = cea_analysis.get_eps_at_PcOvPe(Pc=self.p_chamber,
MR=OF_ratio,
PcOvPe=self.p_chamber /
self.Pa)
(
Isp,
cstar,
flame_temperature,
molecular_weight,
gamma,
) = cea_analysis.get_IvacCstrTc_ChmMwGam(Pc=self.p_chamber,
MR=OF_ratio,
eps=area_ratio)
return OF_ratio, gamma, molecular_weight, flame_temperature
def optimize_combustion_parameters_at_chamber(self):
""" Uses RocketCEA, which wraps NASA CEA, to calculate 4 parameters at
the combustion chamber:
OF_ratio : Oxidizer/fuel mass ratio.
k : exhaust gasses cp/cv = gamma.
M : exhaust gasses moleculaer weight.
To : adiabatic flame temperature.
OF_ratio is calculated by optimizing the specific impulse of the motor.
Returns
-------
optimal_OF_ratio : float
Optimized oxidizer/fuel mass ratio generating optimum specific
impulse.
gamma : float
Exhaust gasses cp/cv.
molecular_weight : float
Exhaust gasses moleculaer weight.
flame_temperature : float
Adiabatic flame temperature.
"""
# ---------------Calculated Inputs----------------#
# Calculate input parameters from oxidiser and fuel combustion
# Initialize CEA analysis
cea_analysis = CEA_Obj(
oxName=self.oxidizer.name,
fuelName=self.fuel.name,
# Units
isp_units="sec",
cstar_units="m/sec",
pressure_units="bar",
temperature_units="K",
sonic_velocity_units="m/sec",
enthalpy_units="kJ/kg",
density_units="kg/m^3",
specific_heat_units="kJ/kg-K",
viscosity_units="millipoise",
thermal_cond_units="W/cm-degC",
)
# Get stoichiometric equivalence ratio
stoichiometric_OF_ratio = cea_analysis.getMRforER(ERphi=1.0)
# Find optimal specific impulse
def minus_specific_impulse_function(OF_ratio):
area_ratio = cea_analysis.get_eps_at_PcOvPe(Pc=self.p_chamber,
MR=OF_ratio,
PcOvPe=self.p_chamber /
self.Pa)
Isp, cstar, To, M, k = cea_analysis.get_IvacCstrTc_ChmMwGam(
Pc=self.p_chamber, MR=OF_ratio, eps=area_ratio)
return -Isp
res = minimize(
fun=minus_specific_impulse_function,
x0=stoichiometric_OF_ratio,
method="Powell",
bounds=[[
stoichiometric_OF_ratio * 0.5, stoichiometric_OF_ratio * 2
]],
)
# Optimization sequence complete, store results
optimal_OF_ratio = res.x[0]
optimal_area_ratio = cea_analysis.get_eps_at_PcOvPe(
Pc=self.p_chamber,
MR=optimal_OF_ratio,
PcOvPe=self.p_chamber / self.Pa)
(
optimal_Isp,
cstar,
flame_temperature,
molecular_weight,
gamma,
) = cea_analysis.get_IvacCstrTc_ChmMwGam(Pc=self.p_chamber,
MR=optimal_OF_ratio,
eps=optimal_area_ratio)
return optimal_OF_ratio, gamma, molecular_weight, flame_temperature
def getPerformanceParameters(self, combustionPressure, ambientPressure,
oxidizerTemperature, expansionRatio,
mixtureRatio):
CpAve = CP.PropsSI('CP0MOLAR', 'T', oxidizerTemperature, 'P',
combustionPressure, "N2O")
MolWt = CP.PropsSI('M', 'T', oxidizerTemperature, 'P',
combustionPressure, "N2O") * 1e3
HMOLAR = CP.PropsSI('HMOLAR', 'T', oxidizerTemperature, 'P',
combustionPressure, "N2O") / 1e3
RHO = CP.PropsSI('D', 'T', oxidizerTemperature, 'P',
combustionPressure, "N2O") * 1e3 / (1e2 * 1e2 * 1e2)
# print(HMOLAR, RHO)
card_str = """
oxid=NITROUS wt=1.0 t,K={:.4f} h,kj/mol={:.4f} rho,g/cc={:.4f} N 2 O 1
""".format(oxidizerTemperature, HMOLAR, RHO)
add_new_oxidizer('NITROUS_COOLPROP',
card_str.format(oxidizerTemperature))
fuelTemperature = 293
card_str = """
fuel=C(gr) wt=0.02 t,K={:.4f}
fuel=SASOL907 wt=0.98 t,K={:.4f} h,kj/mol=-1438.200 rho,g/cc=0.720 C 50 H 102
""".format(fuelTemperature, fuelTemperature)
add_new_fuel('SASOLWAX907_CARBONBLACK', card_str)
# cea = CEA_Obj(
# oxName="NITROUS_COOLPROP",
# fuelName="SASOLWAX907_CARBONBLACK"
# )
# s = cea.get_full_cea_output(Pc=combustionPressure/1e5, MR=mixtureRatio, eps=expansionRatio, pc_units="bar", output='siunits')
# print(s)
#
# pass
with hiddenPrints:
cea = CEA_Obj_W_Units(oxName="NITROUS_COOLPROP",
fuelName="SASOLWAX907_CARBONBLACK",
pressure_units='Pa',
cstar_units='m/s',
temperature_units='K',
sonic_velocity_units='m/s',
enthalpy_units='J/kg',
density_units='kg/m^3',
specific_heat_units='J/kg-K',
viscosity_units='poise',
thermal_cond_units="W/cm-degC")
Isp, mode = cea.estimate_Ambient_Isp(Pc=combustionPressure,
MR=mixtureRatio,
eps=expansionRatio,
Pamb=ambientPressure)
IspVac, Cstar, Tc, MW, gamma = cea.get_IvacCstrTc_ChmMwGam(
Pc=combustionPressure, MR=mixtureRatio, eps=expansionRatio)
# cea = CEA_Obj(
# oxName=oxidizerCard,
# fuelName="SASOLWAX907_CARBONBLACK"
# )
# s = cea.get_full_cea_output(Pc=combustionPressure/1e5, MR=mixtureRatio, eps=expansionRatio, pc_units="bar", output='siunits')
# print(s)
return Isp, CpAve, MolWt, Cstar, Tc, gamma