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