Work with multiple mechanisms#

PyChemkin can facilitate multiple mechanisms in one project. However, only one chemistry set can be active at a time. This example shows how to use the activate() method to switch between multiple chemistry sets (mechanisms) in the same Python project. You can use this method to compare results from two different mechanisms, such as the base and reduced mechanisms.

Import PyChemkin packages and start the logger#

from pathlib import Path

import ansys.chemkin.core as ck  # Chemkin
from ansys.chemkin.core import Color
from ansys.chemkin.core.logger import logger

# check working directory
current_dir = str(Path.cwd())
logger.debug("working directory: " + current_dir)
# set verbose mode
ck.set_verbose(True)

Create the first chemistry set#

The first mechanism to load is the GRI 3.0 mechanism for methane combustion. This mechanism and its associated data files come with the standard Ansys Chemkin installation in the /reaction/data directory.

# set mechanism directory (the default Chemkin mechanism data directory)
data_dir = Path(ck.ansys_dir) / "reaction" / "data"
mechanism_dir = data_dir

# specify the mechanism input files
# including the full file path is recommended
chemfile = str(mechanism_dir / "grimech30_chem.inp")
thermfile = str(mechanism_dir / "grimech30_thermo.dat")
tranfile = str(mechanism_dir / "grimech30_transport.dat")
# create a chemistry set based on GRI 3.0
My1stMech = ck.Chemistry(chem=chemfile, therm=thermfile, tran=tranfile, label="GRI 3.0")

Preprocess the first chemistry set#

# preprocess the mechanism files
ierror = My1stMech.preprocess()
print()
if ierror != 0:
    # encountered error during preprocessing
    print(f"Preprocessing error encountered. Code = {ierror:d}.")
    print(f"See the summary file {My1stMech.summaryfile} for details.")
    exit()
else:
    # Display the basic mechanism information
    print(Color.GREEN + "Preprocessing succeeded.", end=Color.END)
    print("Mechanism information:")
    print(f"Number of elements = {My1stMech.mm:d}.")
    print(f"Number of gas species = {My1stMech.kk:d}.")
    print(f"Number of gas reactions = {My1stMech.ii_gas:d}.")

Set up a gas mixture#

Set up a gas mixture based on the species in this chemistry set. Create a gas mixture named mymixture1 based on the My1stMech chemistry set. The species mole fractions/ratios are given in the recipe format. The X property is used because the mole fractions are given.

mymixture1 = ck.Mixture(My1stMech)
# set mixture temperature [K]
mymixture1.temperature = 1000.0
# set mixture pressure [dynes/cm2]
mymixture1.pressure = ck.P_ATM
# use the "X" property to specify the molar compositions of the mixture
mymixture1.x = [("CH4", 0.1), ("O2", 0.21), ("N2", 0.79)]

Perform an equilibrium calculation#

The equilibrium state is stored as a mixture named equil_mix1_hp. You can get the equilibrium temperature from the temperature property of this mixture. You can learn more about the PyChemkin equilibrium() method by either typing ck.help("equilibrium") at the Python prompt or uncommenting the following line.

# ck.help("equilibrium")

# find the constrained H-P equilibrium state of ``mymixture1``
equil_mix1_hp = ck.equilibrium(mymixture1, opt=5)
# print the equilibrium temperature
print(f"Equilibrium temperature of mymixture1: {equil_mix1_hp.temperature} [K]")

Create the second chemistry set#

The second mechanism is the C2 NOx mechanism in the /reaction/data directory. Here, a different process for setting up a chemistry set is used. The chemistry set instance is created before the mechanism files are specified. You can make changes to the files to include in the chemistry set before running the preprocessing step.

The C2 NOx mechanism file, in addition to the reactions, contains the thermodynamic and transport data of all species in the mechanism. Thus, you must only specify the mechanism file, that is, chemfile. If your simulation requires transport properties, you must use the preprocess_transportdata() method to tell the preprocessor to also include the transport data.

# set the second mechanism directory (the default Chemkin mechanism data directory)
mechanism_dir = data_dir
# create a chemistry set based on "C2_NOx" using an alternative method
My2ndMech = ck.Chemistry(label="C2 NOx")
# set mechanism input files individually
# this mechanism file contains all necessary thermodynamic and transport data
# thus, there is no need to specify thermodynamic and transport data files
My2ndMech.chemfile = str(mechanism_dir / "C2_NOx_SRK.inp")

# direct the preprocessor to include the transport properties
# only when the mechanism file contains all the transport data
My2ndMech.preprocess_transportdata()

Preprocess the second chemistry set#

The C2 NOx mechanism also includes information about the Soave cubic Equation of State (EOS) for real-gas applications. The PyChemkin preprocessor indicates the availability of the real-gas model in the chemistry set processed. For example, during preprocessing, this is printed: real-gas cubic EOS 'Soave' is available. As soon as the second chemistry set is preprocessed successfully, it becomes the active chemistry set of the project. The first chemistry set, My1stMech, is pushed to the background.

# preprocess the second mechanism files
ierror = My2ndMech.preprocess()
print()
if ierror != 0:
    # encountered error during preprocessing
    print(f"Preprocessing error encountered. Code = {ierror:d}.")
    print(f"See the summary file {My2ndMech.summaryfile} for details.")
    exit()
else:
    # Display the basic mechanism information
    print(Color.GREEN + "Preprocessing succeeded.", end=Color.END)
    print("Mechanism information:")
    print(f"Number of elements = {My2ndMech.mm:d}.")
    print(f"Number of gas species = {My2ndMech.kk:d}.")
    print(f"Number of gas reactions = {My2ndMech.ii_gas:d}.")

Set up the second gas mixture based on the species in the second chemistry set#

Create a gas mixture named mymixture2 based on the My2ndMech chemistry set.

mymixture2 = ck.Mixture(My2ndMech)
# set mixture temperature [K]
mymixture2.temperature = 500.0
# set mixture pressure [dynes/cm2]
mymixture2.pressure = 2.0 * ck.P_ATM
# set mixture molar composition
mymixture2.x = [("H2", 0.02), ("O2", 0.2), ("N2", 0.8)]

Run the detonation calculation#

You can now compute the detonation wave speed with the mymixture2 gas mixture. The CJ_mix2 represents the mixture at the Chapman-Jouguet state. The speed of sound and the detonation wave speed are returned in the speeds_mix2 tuple.

speeds_mix2, cj_mix2 = ck.detonation(mymixture2)
#  print the detonation calculation results
print(f"Detonation mymixture2 temperature: {cj_mix2.temperature} [K]")
print(f"Detonation wave speed = {speeds_mix2[1] / 100.0} [m/sec]")

Switch to the first chemistry set and gas mixture#

Use the activate() method to reactivate the My1stMech chemistry set and the mymixture1 gas mixture.

My1stMech.activate()

Run the detonation calculation#

You can now compute the detonation wave speed with the mymixture1 gas mixture. The CJ_mix1 represents the mixture at the Chapman-Jouguet state. The speed of sound and the detonation wave speed are returned in the speeds_mix1 tuple.

Note

The mymixture1 and mymixture2 gas mixtures have different initial conditions.

speeds_mix1, cj_mix1 = ck.detonation(mymixture1)
# print the detonation calculation results
print(f"Detonation 'mymixture1' temperature: {cj_mix1.temperature} [K]")
print(f"Detonation wave speed = {speeds_mix1[1] / 100.0} [m/sec]")

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