Version: 1.0.5 (Under development), December 26, 2022
Short Description: Python library that automates analysis of rocket problems in
CEA-NASA, which for now only works on Windows.
Author: Julio C. R. Machado
Undergraduate student in the last period of the aerospace engineering course
at Federal University of Maranhão - Brazil.
Emails: [email protected], [email protected], [email protected]
pip install CEApy
The library was developed to be embedded in other libraries, allowing automatic analysis
of the combustion process in rocket engine chambers. In its first version, it is possible to
analyze all combinations of compounds available in the thermodynamic library of CEA, which h
as a method called search_specie to search for all available chemical species.
The library works by taking the parameters passed by the user through the settings, input
_propellants, input_parameters and output_parameters methods, and creating the input .inp fil
e, for subsequent execution of the fortran code developed by (Mcbride and Gordon, 1994.) For
now only available on Windows by using the CEA2.exe executable and not the cea.f code. After
execution, the library takes the desired parameters and exports the data in a Pandas datafr
ame through the get_results method.
For now, only rocket problems are available in the library, and methods that allow analyz
ing new specific mixtures by the number of atoms and their junction have not yet been created.
Methods that allow inserting, omitting or selecting species are not yet available, as well as
the option trace specie values and the parameters of Champman-Jouquet Detonation. These featu
res will be implemented in future versions.
from CEApy import CEA
combustion = CEA("My_first_Analysis")
combustion.search_specie()
combustion.show_all_species()
combustion.settings()
combustion.input_propellants()
combustion.input_parameters()
combustion.output_parameters()
combustion.show_inp_file()
combustion.run()
combustion.get_results()
combustion.show_out_file()
combustion.get_simulation_file()
combustion.remove_analysis_file()
def search_specie(self, words):
- words: Specie to be searched
def show_all_species(self):
- Show all species in the thermodynamical data of CEA
def settings(self, frozen='yes', freezing_point='exit',
equilibrium='yes', short='yes', transport='yes'):
- frozen: enable or disable freeze condition, 'yes' or 'no'
- freezing_point: can be 'combustor' or 1, 'throat' or 2, 'exit' or 3,
or it can be an integer equal to or greater than 1. For better understanding,
see (McBride and Gordon, 1994) and (McBride and Gordon, 1996 ).
- equilibrium: enable or disable equilibrium condition, 'yes' or 'no'
- short: enable or disable short condition in the output file .out 'yes' or 'no'
- transport: enable or disable transport properties in the CEA analysis
def input_propellants(self, oxid=None, fuel=None):
- oxid: should be a list like: oxid=[oxid1,oxid2]
oxid1 = [name,massfraction,temperature]
name: name of propellant, massfraction: mas fraction of propellant (0 to 100),
temperature: temperature of propellant in Kelvin.
- example of two oxids:
oxid1 = ['O2(L)',50,54.36], oxid2 = ['N2O4(L)',50,298.15]
oxid = [['O2(L)',50,54.36],['N2O4(L)',50,298.15]]
if one:
oxid = [['N2O4(L)',50,298.15]]
- fuel: fill in the same way as the oxidizer.
def input_parameters(self, combustion_temp=3800, chamber_pressure=None, acat=None, sub_aeat=None,
sup_aeat=None, pipe=None, of_ratio=None, chem_ratio=None,
phi_ratio=None, fbyw_ratio=None):
- Parameters must be a list, lik: sup_aeat = [10,20,150], of = [1,2,3,5]
if one: sup_aeat = [100], of = [3]
- fbyw: fuel by weight ratio, for better undertanding of parameters, see
McBride and Gordon, 1994) and (McBride and Gordon, 1996 ).
- acat: contraction ratio from stagnation values to throat
- sub_aeat: subsonic expansion ratio
- sup_aeat: supersonic expansion ratio
- example:
CEA.input_parameters(chamber_pressure=[10],sup_aeat=[10,20],of_ratio=[1,2,3])
def output_parameters(self, user_outputs):
- user_outputs: Must be a string 'all' to evaluate all available output parameters,
or a list of parameters, like: ['isp','cf','gam','mach','pipe']
List of output parameters available:
output_list = [
'p', 't', 'rho', 'h', 'u', 'g', 's', 'm', 'mw', 'cp', 'gam', 'son', # thermo prop
'pipe', 'mach', 'aeat', 'cf', 'ivac', 'isp', # rocket performance
'vis', 'cond', 'condfz', 'pran', 'pranfz', # transport properties
'%f', 'o/f', 'phi,eq.ratio', 'r,eq.ratio'] # fuel-oxidant mixture parameters
For a better understanding of all parameters, see McBride and Gordon, 1994) and
(McBride and Gordon, 1996 ).
def show_inp_file(self, type_f='logical'):
type_f: if 'logical': it shows the file being made by the code.
if 'file': it shows the file written in the folder where
the analysis is done, if it exists.
def run(self):
- Runs the CEA analysis
def get_results(self, column_names='all', condition=3):
- Returns the CEA simulation results, the parameters that were
defined in the output_parameters method
Column names: Must be a string 'all' to returns all available output parameters,
or a list of parameters, like: ['isp','cf','gam','mach','pipe']
condition: Is the parameter that says which lines should be skipped.
For example if condition = 3 and the results have 9 lines, the method will return
lines 3, 6, 9. If condition = 3 and the results have 14 lines, the method will
return lines 3, 6, 9 and 12. If condition = 4 and the results have 14 lines, the
method will return lines 4, 8 and 12. This parameter is important to get only results
that are of interest in certain analyses. for example, evaluating a range of
o/f = [1,2,3,4], the method will return all results in the combustor (1), throat (2)
and exit (3) section of all o/f considered. To get only the results in the output,
for example, make:
condition =3 (this is the default).
Most of the time it is difficult to evaluate the results, so it is better to get
all the available results, visualize and evaluate later. To get all results do:
condition = 'all'
def show_out_file(self):
Show the output file '.out' after executing the run method
def get_simulation_file(self, type_file='out'):
Returns the file as a string for later saving in a specified folder.
- type_file = 'inp': returns the .inp file
- type_file = 'out': returns the .out file
def remove_analysis_file(self, name=None):
- Delete the analysis file from the folder
- Always indicated after completing the analyzes and saving the relevant
files in the working folder.
1 - To save data, To save data, such as simulation results, images, or .inp and
.out files, the absolute path of the folder must be passed, for example:
C:/users/user/desktop/file.csv
not: 'file .csv'.
Otherwise the files will be saved in the library installation folder.
2 - In case of doubt or error in the results, or empty results, it is always
good to look at the output file name of the analysis.out and see if there are
errors, through the show_out_file method.
Code:
from CEApy import CEA
import matplotlib.pyplot as plt
# Evaluating Isp behavior as a function of propellant mixing rate
# creating
reaction = CEA()
reaction.settings()
# STUDY 1
# adding propellants
reaction.input_propellants(oxid=[['O2(L)', 100, 90.17]], fuel=[['H2(L)', 100, 20.27]])
# adding input parameters
exp_ratio = 20 # nozzle expansion rate
p_c = 100 # chamber pressure, bar
of_ratio = [0.5, 1, 2, 3, 4, 5, 6, 7, 8] # propellant mixing rate
reaction.input_parameters(sup_aeat=[exp_ratio],
chamber_pressure=[p_c],
of_ratio=of_ratio)
# adding output parameters
reaction.output_parameters(user_outputs=['isp', 'cf', 'o/f'])
# input file of CEA engine
reaction.show_inp_file()
# running analyses
reaction.run()
# output file of cea engine
reaction.show_out_file()
# getting results
df = reaction.get_results()
print('df.head() of simulation results')
print(df.head())
# plotting o/f x isp
df['isp'] = df['isp']/9.81
print('simulation results')
print(df)
plt.plot(df['o/f'], df['isp'],label='Isp (s)',color='red')
plt.title('O/F x Isp (s), Supersonic expansion ratio = {}, Pc = {} bar'.format(exp_ratio,p_c))
plt.xlabel('O/F')
plt.ylabel('Isp (s)')
plt.legend()
plt.savefig("study1_100bar.png",dpi=300,format="png")
plt.show()
plt.close()
# getting output file to save if necessary
strings = reaction.get_simulation_file('out')
#*********************************************
# RUNNING NEW STUDY
reaction.input_propellants(oxid=[['O2(L)', 100, 90.17]], fuel=[['H2(L)', 100, 20.27]]) #same
p_c2= 200 # chamber pressure, bar, modification 100 -> 200 bar
reaction.input_parameters(sup_aeat=[exp_ratio],
chamber_pressure=[p_c2],
of_ratio=of_ratio)
reaction.output_parameters(user_outputs=['isp', 'o/f'])
# running
reaction.run()
# getting results
df_study2 = reaction.get_results()
df_study2['isp'] = df_study2['isp']/9.81
print("df_study2 head")
print(df_study2.head())
# comparing
plt.plot(df['o/f'], df['isp'],label='pressure = {}'.format(p_c))
plt.plot(df_study2['o/f'], df_study2['isp'],label='pressure = {}'.format(p_c2))
plt.title('O/F x Isp (s), Supersonic expansion ratio = {}'.format(exp_ratio))
plt.xlabel('O/F')
plt.ylabel('Isp (s)')
plt.legend()
plt.savefig("study2_200bar.png",dpi=300,format="png")
plt.show()
plt.close()
#*******************************************
# RUNNIG STUDY WITH FUEL MODIFICATION
# configuring propellants
liq_hydrogen = ['H2(L)', 50, 20.27] # half the total amount of propellant
RP_1 = ['RP-1', 50, 298.15] # half the total amount of propellant
# configuring analysis
reaction.input_propellants(oxid=[['O2(L)', 100, 90.17]], fuel=[RP_1,liq_hydrogen])
reaction.input_parameters(sup_aeat=[exp_ratio],chamber_pressure=[p_c2],of_ratio=of_ratio)
reaction.output_parameters(user_outputs=['isp', 'o/f'])
# running
reaction.run()
# getting results
df_study3 = reaction.get_results()
df_study3['isp'] = df_study3['isp']/9.81
print("df_study3 head")
print(df_study3.head())
# comparing
plt.plot(df['o/f'], df['isp'],label='fuel = H2(L), pressure = {}'.format(p_c))
plt.plot(df_study2['o/f'], df_study2['isp'],label='fuel = H2(L), pressure = {}'.format(p_c2))
plt.plot(df_study3['o/f'], df_study3['isp'],label='fuel = [H2(L),RP-1], pressure = {}'.format(p_c2))
plt.title('O/F x Isp (s), Supersonic expansion ratio = {}'.format(exp_ratio))
plt.xlabel('O/F')
plt.ylabel('Isp (s)')
plt.legend()
plt.savefig("study3_H2_RP1_200bar.png",dpi=300,format="png")
plt.show()
plt.close()
# deleting analysis files
reaction.remove_analysis_file()
Output images:
![Study 3 - O2(L),[H2(l), RP-1], Pc = 200Bar](doc_images/study3_H2_RP1_200bar.png)
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