Adding a new mechanism into cantera

[Ambuj Punia]

Hi all

I am a new user to cantera. 

My query is that I want to add a new reaction mechanism for methane pyrolysis into cantera(version 2.3.0) and use it like GRI3.0(in python 3.6). Earlier I was using GRI3.0 , but I was not able to get the results I was expecting. Now I have a reaction mechanism which I want to use in cantera but I am not sure as how to create that in cantera. How can I access the properties for the species and the reactions so that it can be converted into CHEMKIN format and eventually to cantera format(this is what I am thinking but I am not sure).

Request you to please help.

Regards

Ambuj

[Ruinan Yang]

Hi Ambuj,

I'm not quite sure whether I understand your question correctly. Do you mean you want to convert a mechanism to Cantera format? I guess you can try ck2cti function.

Best regard,

Ruinan

在 2018年5月25日星期五 UTC-4上午11:42:50，Ambuj Punia写道：

[Ambuj Punia]

Hi Yang

I am sorry that you misinterpreted my question ( or may be I didn't asked properly).

What I want to do is to take a new mechanism which is not there in chemkin (basically a methane pyrolysis mechanism) which first I can write down in chemin format and then I convert that in cantera format and eventually use that like GRI.

So right now I just have the mechanism containing the elementary reactions with which I want to create the chemkin format file using the database which right now I am figuring out how to do that. Once I am done with the Chemin file then I can use the cktocti for conversion to cantera.

I hope this makes my prob more clear. 

Request you to please help on this.

Regards

Ambuj

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[Alex K]

Hi Ambuj,

It's still a little unclear. Are you saying that you have a list of chemical reactions, in some plain-text format? That is, you just have a list of elementary reactions from a PDF document or something like that?

If so, you're best bet may be to write a script (say, in python or bash) to parse the text information that you have and to spit that out into the CHEMKIN format. You can see the specification for what a chem.inp file should look like here. You could then combine that with therm.dat and tran.dat files that include all of the species that you are interested (and that you deem to be appropriately up-to-date, accurate, relevant for your target conditions et cetera...), at which point you could run the ck2cti command and get a cti file for cantera.

If you were asking a different question, you might need to clarify that a little more.

Best of luck,

Alex

[Ambuj Punia]

Hi Alex

I think you interpreted my question correctly. I have a reaction mechanism containing the elementary reactions and I want to first make a chem.inp file and then I can run cktocti for converting to cantera format.

Can you please tell me from where  should I extract the thermodynamic, transport and reaction data based on my reaction mechanism(like data for each species, data for individual elementary reaction)?

Is there any software that can do that for me or I will have to write the file on my own?

Regards

Ambuj

[Alex K]

There are quite detailed databases for thermo and transport data publicly available. For examples Lawrence Livermore National Labs (LLNL) combustion chemistry group has a very exhaustive database available here. I can't comment on how suitable these databases are for your needs, that may require specific knowledge to your exact problem. I'm not sure what is required for methane pyrolosis (by which I assume you mean the thermal decomposition of CH4 in an anaerobic environment). But, it seems reasonable that the species thermo and transport data should be OK to use, so long as you are within the intended range of temperatures and pressures.

The trickier part are the elementary reactions. It sounds like you only have access to the set of stoichiometric equations, and not to any of the Arrhenius parameters. I would advise caution in taking Arrhenius parameters from some chemical mechanism not intended for your conditions of interest. It is extremely common for the Arrhenius parameters to be optimized for a particular set of target conditions (often some type of engine combustion). The danger is that when you apply the Arrhenius parameters to other conditions there is no expectation that the results will be at all accurate.

It's hard to provide further guidance without knowing more specific details of your problem. It sounds like the first step would be to determine if there are any chemical kinetic mechanisms (including the Arrhenius parameters) that are suitable for your target conditions (so, potentially some more literature review).

Best,

Alex

[Ambuj Punia]

Hi Alex

Thank you very much for your reply. I checked the link you sent and yes there are lots of detailed mechanisms but for methane pyrolysis I couldn't find one. I will check for some other group databases while if you have some more groups in your mind please share.

And yes you got the problem correctly that methane is decomposed without oxygen in the temperature range of 1000 to 1800K eventually forming hydrogen and carbon soot, but for now I am keeping myself restricted till gas phase products.

Once again thank you for the help.

Regards

Ambuj

[Alex K]

Hi Ambuj,

I don't have specific knowledge on methane pyrolosis, unfortunately. Groups that study gasification would also need to include pyrolosis sub-mechanisms, so that's another place to look.

In your search, keep in mind the following:

1. Most chemical mechanisms that include methane will be targeting combustion conditions, i.e., plenty of oxygen available. They (the elementary reactions and Arrhenius rates) may not be suitable for your needs. 
2. I would guess that the pyrolosis of methane is a subset problem of higher alkane pyrolosis, in the same way that C0-C1 chemistry is a subset of higher alkane combustion chemistry. So, it might be that you could use a pyrolosis mechanism designed for more complex fuels (like propane or heptane), if they have to treat the ultimate pyrolosis of methane (that would be created from the decomposition of bigger molecules). So, you many not be restricted to only looking specifically for methane pyrolosis mechanisms.

Good luck!

[Ambuj Punia]

Hi

Thank you very much Alex for your time and help.

Regards

Ambuj

[Steven DeCaluwe]

Hi Ambuj,

If you have a mechanism that is neither in Chemkin nor cti format, you do not need to begin by making a Chemkin input file - you can proceed straight to writing the mechanism directly into a cti file.

I would suggest taking an existing file, saving it under a new name, and then editing the contents to incorporate your new material.  If you will be preserving many of the reactions from GRI3.0, you could use this as your ''starter'' file.  Otherwise, if you will be creating most of the content from scratch, start with the smallest mechanism file you can find.

Save and test the file often by trying to import it into Cantera.  That way it will be easier to diagnose and the typos and formatting errors that will (rather unavoidably, imo) occur.

Best of luck!

Steven

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From: canter...@googlegroups.com [canter...@googlegroups.com] on behalf of Ambuj Punia [ambu...@gmail.com]
Sent: Friday, May 25, 2018 9:42 AM
To: Cantera Users' Group
Subject: [cantera-users] Adding a new mechanism into cantera

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[Ambuj Punia]

Hi Steven 

Thanks for your reply. I did the same the same thing and it's working fine.

I have one more query. In the reaction mechanism which I want to write in cti file there are some elementary reactions for which only rate constants are given and not the Arrhenius parameters. So can I remove those reactions if there is some way to include them also in cantera?

Regards

Ambuj

[Steven DeCaluwe]

Hi Ambuj,

So you have a rate constant `k,` is that right?  This is the same as just providing the pre-exponential Arrhenius parameter A.  So you could just give the parameters as [k, 0, 0], where k is the rate constant that you have.

It could still  be problematic in that these reactions would have no temperature dependence (at least in the forward direction. If they are reversible reactions, the reverse reaction would have an activation energy equal to -1 times the enthalpy of reaction [I think]).

Anyway, feel free to include them, using the method above.

Best,

Steven

——————————————————————————————————

Steven DeCaluwe, PhD

Assistant Professor of Mechanical Engineering

Colorado School of Mines

Brown Building W410B

Golden, CO 80401

email: deca...@mines.edu

phone: (303) 273-3666

Twitter: @DeCaluweGroup

[Ambuj Punia]

Hi Steve

I will try that for sure. Yes I have only forward reactions in the mechanism with only rate constant values. Thanks for helping me out. 

Regards

Ambuj

[arthur gilles]

Dear Ambug,

Would you be OK to share your mechanism of methane pyrolysis, or maybe is it already available elsewhere?

Thank you in advance to support open research,

Sylvain