Frequently Asked Questions — Cantera 3.2.0 documentation

If your question isn’t answered here, consider asking us on the Cantera Users’ Group.
Install the Dependencies tool.
If you are using Conda: Run this tool from a terminal where your Cantera Conda environment is active. That is, run the command:
from that terminal, replacing the path with the path to DependenciesGUI.exe on your computer. This step is necessary to have the PATH environment variable set correctly.
Use Dependencies to open the Cantera Python extension module. If you installed Mambaforge at C:\mambaforge and Cantera in an environment named ct-env, then this file would be named something like C:\mambaforge\envs\ct-env\Lib\site-packages\cantera\_cantera.cp312-win_amd64.pyd.
Identify any DLLs that the tool is unable to find, or if there are methods that are not being resolved. One thing to keep an eye out for is if there are any libraries that are being loaded from unexpected locations (for example, other than from your conda installation and the Windows system directories).
There are a few sites that distribute mechanisms in the Cantera YAML format:
The Caltech Explosion Dynamics Laboratory provides a number of mechanisms for combustion applications.
CollectionOfMechanisms is a user-maintained GitHub repository of mechanisms that have been obtained from scientific publications and other sources.
Stanford University provides the Foundational Fuel Chemistry Model Version 2.0 (FFCM-2) for combustion of H₂, CO, CH₂O, and C₁-C₄ hydrocarbons.
Many research groups maintain pages with mechanisms they developed, provided in the Chemkin format. These mechanisms can be converted to the Cantera YAML format using the ck2yaml tool. The following is an incomplete list:
The University of Galway Combustion Chemistry Centre provides mechanisms for combustion
DETCHEM provides a variety of mechanisms for catalytic systems that were developed by the research group of Olaf Deutschmann at the Karlsruhe Institute of Technology.
Lawrence Livermore National Laboratory provides a number of combustion mechanisms
The inclusion of a site in the above lists does not constitute an endorsement of the chemical mechanisms provided there. You must use your own judgement to determine if a mechanism is appropriate for any particular scientific or engineering purpose.
See our documentation on Debugging common errors in CK files. If you’re encountering an issue not described there, please post a question on the Cantera Users’ Group.
Reference states in thermodynamics are arbitrary, since the observable quantities of interest (work done, heat transferred) do not depend on absolute quantities but on differences between states. Different data sources use different conventions for the reference state. Cantera uses the convention commonly used in reaction thermodynamics, where pure elements in their natural state (for example, oxygen as O₂ gas and carbon as graphite) have zero enthalpy at a temperature of 298.15 K and a pressure of 1 atm. This convention provides a consistent treatment for the change in enthalpy associated with chemical reactions. In contrast, it is common for tabulated data for a single pure substance to use a different reference state, such as CO₂ where the enthalpy may be referenced to the saturated liquid at 273.15 K.
Cantera’s definition of \(c_p\) is the partial derivative of enthalpy with respect to temperature, with pressure and composition held constant. The value returned by CEA is the derivative while holding the system at chemical equilibrium. The former definition is the one that appears in governing equations for multi-species systems, such as well-stirred reactors. While the latter property is of interest in certain physical situations, it is of somewhat limited use computationally, since it is only defined for mixtures at equilibrium.
You can use Cantera to compute a value like what’s returned by CEA by computing \(dh/dT\) using a finite difference method where the mixture is equilibrated at constant \(T\) and \(P\) at each point before calculating the enthalpy. sound_speed.py presents a related example.
CEA provides a value consistent with Cantera’s definition which it calls the \(c_p\) “with frozen reactions.”
Chemical equilibrium is not defined in terms of reactions. For whatever set of species are allowed in a phase or multi-phase mixture, it is defined as the composition that minimizes a particular thermodynamic state variable while holding two others constant (for example, for equilibrium at constant temperature and pressure, the Gibbs free energy is minimized). This optimization is independent of any reactions that are defined, and the resulting composition may be different from what you would get, for example, from integrating a reactor network using a set of irreversible chemical reactions or a set of reactions that does not form a complete basis set for the defined species.
Cantera defines reactor flows in terms of inlet and outlet mass flow rates, with residence time being an output that can be calculated:
To achieve a specified residence time, you can define the mass flow rate to be a function of the combustor state. For example, the following approach is used in the example combustor.py:
Calls to ReactorNet.step or ReactorNet.advance may result in error messages like the following:
The list labeled “Components with largest weighted error estimates” provides a list of component indices followed by their corresponding error estimates. Large error estimates tend to be associated with rapidly changing variables which require very small time steps. If you are using the Python interface and the ReactorNet object is named net, you can identify the variables associated with these indices:
It is sometimes the case that a reaction mechanism will contain one or more reactions where at some temperatures, either the forward or reverse rate constant becomes high and nonphysical, particularly if the mechanism has not been designed for use at in a particular temperature range. For this exampl