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Custom reaction rates#
An example demonstrating how to use custom reaction objects.
For benchmark purposes, an ignition test is run to compare simulation times.
Requires: cantera >= 3.1.0
Average time of 100 simulation runs for 'gri30.yaml' (CH4)
- Built-in rate parameterizations: 30.31 μs/step (T_final=2780.21)
- Two Custom reactions (Python): 33.06 μs/step (T_final=2780.21) ... +9.06%
- Two Custom reactions (C++): 30.23 μs/step (T_final=2780.21) ... -0.27%
- Two Extensible reactions: 31.64 μs/step (T_final=2780.21) ... +4.36%
from timeit import default_timer
import numpy as np
from math import exp
import warnings
import cantera as ct
mech = 'gri30.yaml'
fuel = 'CH4'
gas0 = ct.Solution(mech)
species = gas0.species()
reactions = gas0.reactions()
# construct reactions based on CustomRate: replace two reactions with equivalent
# custom versions (uses Func1 functors defined by Python lambda functions)
reactions[2] = ct.Reaction(
equation='H2 + O <=> H + OH',
rate=lambda T: 38.7 * T**2.7 * exp(-3150.1542797022735/T))
reactions[4] = ct.Reaction(
equation='H2O2 + O <=> HO2 + OH',
rate=lambda T: 9630.0 * T**2.0 * exp(-2012.8781339950629/T))
gas1a = ct.Solution(thermo='ideal-gas', kinetics='gas',
species=species, reactions=reactions)
# construct reactions based on CustomRate: replace two reactions with equivalent
# custom versions (uses Func1 functors defined by C++ class Arrhenius1)
reactions[2] = ct.Reaction(
equation='H2 + O <=> H + OH',
rate=ct.Func1("Arrhenius", [38.7, 2.7, 3150.1542797022735]))
reactions[4] = ct.Reaction(
equation='H2O2 + O <=> HO2 + OH',
rate=ct.Func1("Arrhenius", [9630.0, 2.0, 2012.8781339950629]))
gas1b = ct.Solution(thermo='ideal-gas', kinetics='gas',
species=species, reactions=reactions)
# construct reactions based on ExtensibleRate: replace two reactions with equivalent
# extensible versions
class ExtensibleArrheniusData(ct.ExtensibleRateData):
__slots__ = ("T",)
def __init__(self):
self.T = None
def update(self, gas):
T = gas.T
if self.T != T:
self.T = T
return True
else:
return False
@ct.extension(name="extensible-Arrhenius", data=ExtensibleArrheniusData)
class ExtensibleArrhenius(ct.ExtensibleRate):
__slots__ = ("A", "b", "Ea_R")
def set_parameters(self, params, units):
self.A = params.convert_rate_coeff("A", units)
self.b = params["b"]
self.Ea_R = params.convert_activation_energy("Ea", "K")
def get_parameters(self, params):
params.set_quantity("A", self.A, self.conversion_units)
params["b"] = self.b
params.set_activation_energy("Ea", self.Ea_R, "K")
def validate(self, equation, soln):
if self.A < 0:
raise ValueError(f"Found negative 'A' for reaction {equation}")
def eval(self, data):
return self.A * data.T**self.b * exp(-self.Ea_R/data.T)
extensible_yaml2 = """
equation: H2 + O <=> H + OH
type: extensible-Arrhenius
units: {length: cm, quantity: mol, activation-energy: cal/mol}
A: 3.87e+04
b: 2.7
Ea: 6260.0
"""
extensible_yaml4 = """
equation: H2O2 + O <=> HO2 + OH
type: extensible-Arrhenius
units: {length: cm, quantity: mol, activation-energy: cal/mol}
A: 9.63e+06
b: 2
Ea: 4000
"""
reactions[2] = ct.Reaction.from_yaml(extensible_yaml2, gas0)
reactions[4] = ct.Reaction.from_yaml(extensible_yaml4, gas0)
gas2 = ct.Solution(thermo="ideal-gas", kinetics="gas",
species=species, reactions=reactions)
# construct test case - simulate ignition
def ignition(gas, dT=0):
# set up reactor
gas.TP = 1000 + dT, 5 * ct.one_atm
gas.set_equivalence_ratio(0.8, fuel, 'O2:1.0, N2:3.773')
r = ct.IdealGasReactor(gas)
net = ct.ReactorNet([r])
net.rtol_sensitivity = 2.e-5
# time reactor integration
t1 = default_timer()
net.advance(.5)
t2 = default_timer()
return t2 - t1, net.solver_stats['steps']
# output results
repeat = 100
print(f"Average time of {repeat} simulation runs for '{mech}' ({fuel})")
sim0 = 0
sim0_steps = 0
for i in range(repeat):
elapsed, steps = ignition(gas0, dT=i)
sim0 += elapsed
sim0_steps += steps
sim0 *= 1e6 / sim0_steps
print(f'- Built-in rate parameterizations: {sim0:.2f} μs/step (T_final={gas0.T:.2f})')
sim1a = 0
sim1a_steps = 0
for i in range(repeat):
elapsed, steps = ignition(gas1a, dT=i)
sim1a += elapsed
sim1a_steps += steps
sim1a *= 1e6 / sim1a_steps
print('- Two Custom reactions (Python): '
f'{sim1a:.2f} μs/step (T_final={gas1a.T:.2f}) ... '
f'{100 * sim1a / sim0 - 100:+.2f}%')
sim1b = 0
sim1b_steps = 0
for i in range(repeat):
elapsed, steps = ignition(gas1b, dT=i)
sim1b += elapsed
sim1b_steps += steps
sim1b *= 1e6 / sim1b_steps
print('- Two Custom reactions (C++): '
f'{sim1b:.2f} μs/step (T_final={gas1b.T:.2f}) ... '
f'{100 * sim1b / sim0 - 100:+.2f}%')
sim2 = 0
sim2_steps = 0
for i in range(repeat):
elapsed, steps = ignition(gas2, dT=i)
sim2 += elapsed
sim2_steps += steps
sim2 *= 1e6 / sim2_steps
print('- Two Extensible reactions: '
f'{sim2:.2f} μs/step (T_final={gas2.T:.2f}) ... '
f'{100 * sim2 / sim0 - 100:+.2f}%')
Total running time of the script: (0 minutes 34.898 seconds)