Check reactions for balance of surface sites

[speth]

• Cantera version: b20c0c6
• Operating System: all
• Python/MATLAB version: all

Expected Behavior

A reaction such as:

CH4(s) + 2 O2 => CO2 + 2 H2O

where CH4(s) is a surface species and all others are gas phase should be identified as problematic because it does not balance the number of surface sites.

Actual Behavior

Incorrect rates are computed in reactor calculations -- if the only surface species are CH4(s) and a species representing open sites, then the coverages will not change.

Proposed resolution

When validating surface reactions, require that sum(species.size) over the surface species is the same for the reactants and products.

Originally reported at https://groups.google.com/forum/#!topic/cantera-users/wlww4-RUC_E

[santoshshanbhogue]

Fundamentally, does creation of a reaction even check for stoichiometry? I mean, I can execute this line in the dev-version with Py2.7 without any error:

r = ct.Reaction.fromCti(''' reaction('HO2 + O <=> H2O + O2',[1.0, 2, 3.4E+5] )''')

Not that there is an imbalance of H on both sides

[santoshshanbhogue]

Ok, Cantera does when a solution object is created...

[bryanwweber]

I think the reason the first one is valid is because there is no atomic composition information associated with the species in a Reaction, that's stored in the Species, which has the thermo data.

[santoshshanbhogue]

Yup, but why do this much later in Kinetics and not when the Reaction object is created. This way depending on what the reaction type is, one can run a battery of tests during immediately upon creation of an object (elemental balance for all rxns, site balance for surface, charge balance for electrochem., etc) ?

[speth]

As Bryan says, when you create a Reaction object, all it knows is the name of the species, not its composition, or any other data that is contained in a Species object. So these checks are only possible at the point where the Reaction is added to a Kinetics object.