Non Dependence of Chemical reactions written on YAML file

[Gibin Varghese]

Hi all,

 I am working with gri30.yaml file and I am trying to understand how Cantera deals with the yaml file. 

 In total there are 325 reactions written in the gri30.yaml file. But even if I cancel out all reactions except the first 2 reactions, I am still getting the same plots of Cp, Cv, ratio of Cp and Cv, viscosity, thermal conductivity, enthalpy, Entropy, Gibbs Energy and so on.

 Then I thought of keeping only one reaction which is the 325th reaction. Still I was able to get the same results.

 Without keeping any reactions, the program shows error.

 Corresponding YAML files are attached herewith.

 1. gri30_Test_1_Original_File.yaml  :- All 325 Reactions are included. Original gri30.yaml file

2. gri30_Test_2_React1and2.yaml  :- Only reactions 1 & 2 is present. Rest is deleted.

3. gri30_Test_3_Reaction325.yaml :- Only Reaction no. 325 is present. Rest is deleted.

 So, my question is why the change in those reactions doesn't affect the plot results at all. Does Cantera has any internal calculations or does these parameters (Cp, Cv...)doesn't get affected by the chemical reactions.

 Any suggestions will be highly appreciated.

Thanks and regards,

Gibin varghese

[Mark E. Fuller]

On Wednesday, July 13, 2022 at 4:21:40 PM UTC+3 gibi...@gmail.com wrote:

Hi all,

 I am working with gri30.yaml file and I am trying to understand how Cantera deals with the yaml file. 

 In total there are 325 reactions written in the gri30.yaml file. But even if I cancel out all reactions except the first 2 reactions, I am still getting the same plots of Cp, Cv, ratio of Cp and Cv, viscosity, thermal conductivity, enthalpy, Entropy, Gibbs Energy and so on.

None of these are dependent on the kinetics (reactions) - they are dependent on the mixture composition 

 Then I thought of keeping only one reaction which is the 325th reaction. Still I was able to get the same results.

 Without keeping any reactions, the program shows error.

 Corresponding YAML files are attached herewith.

 1. gri30_Test_1_Original_File.yaml  :- All 325 Reactions are included. Original gri30.yaml file

2. gri30_Test_2_React1and2.yaml  :- Only reactions 1 & 2 is present. Rest is deleted.

3. gri30_Test_3_Reaction325.yaml :- Only Reaction no. 325 is present. Rest is deleted.

 So, my question is why the change in those reactions doesn't affect the plot results at all. Does Cantera has any internal calculations or does these parameters (Cp, Cv...)doesn't get affected by the chemical reactions.

If you don't change what species are in the mixture and their proportions as well as the thermodynamic state (temperature, pressure, ...) then none of these things will change.

The species available to you and their thermodynamic properties are also encoded in the YAML file, which is the source of the information used to compute the properties you mention, above.

[Gibin Varghese]

Hi, many thanks for your response.

May I ask you one more thing. Lets say I am actually analyzing air getting decomposed into its various thermal decomposition products. And I haven't included any relevant chemical reactions.

I ran my test from 300 to 3000Kelvin. So how the cantera predicts the decomposition products, if there are no chemical reactions in the system (But it predicts).

My other question is "Why we have to include the reactions in the YAML file, if it doen't require at all'. 

Thanks in advance.

With best regards,

Gibin Varghese

[Mark E. Fuller]

If you are running equilibrium calculations, equilibrium is determined by thermodynamics, not kinetics (kinetics are time-dependent and equilibrium is at infinite time, effectively).

I believe you can run a file with an empty kinetics section - you reduced a mechanism down to 1 reaction already, and you don't have to have reaction data for all calculations as you saw in your original posting.

[Gibin Varghese]

Thanks a lot for your response.  Now I have a better understanding level on this area.