Error in flame speed value - Propane + Air premixed freely propagating flame using USC Mech Version II: High-Temperature Combustion Reaction Model of H2/CO/C1-C4 Compounds*

[LOKESH KALATHI]

I downloaded the USC Mech Version II: High-Temperature Combustion Reaction Model of H2/CO/C1-C4 Compounds* mechanism, thermal and transport data from USC website (http://ignis.usc.edu/Mechanisms/Model%20release.html) and converted them into a .cti file which is required for the cantera program and then I simulated the freeflame program for methane (CH4)+Air and butane (C4H10)+Air. But surprisingly, I am getting very high values of burning velcoity for both the cases.

For Methane I got 5 m/s for stoichiometric (CH4:1, O2:2, N2:7.52)
For Butane I got 8 m/s. for stoichiometric (C4H10:1, O2:6.5, N2:24.4)

Can anyone please help me to find out the solution for this problem?

Thanks inadvance

[Bryan W. Weber]

Hi Lokesh,

You need to provide some more information. One of the primary things that can go wrong is if the gradients near the boundaries are non-zero. You should check that the gradients of the temperature and species are zero at the boundaries. Can you please provide the script that you used to calculate the flame speeds, and the CTI file as well?

Best,

Bryan

[LOKESH KALATHI]

Thanks Bryan

Please find attached the script and .cti file which I used

please help me to sort out the problem

Regards,

Lokesh

[Bryan W. Weber]

Hi Lokesh,

Which version of Cantera are you using? You are importing the old interface (import Cantera with capital C), but you should not use this interface any more, it will be deleted in the next version of Cantera. Instead, you should use the new interface with import cantera, lowercase c. You can find information about migrating here: http://cantera.github.io/docs/sphinx/html/cython/migrating.html

In addition, I do not think you will have a fully flat profile at the boundaries. Your slope and curve values are very large, they should be closer to 0.1 in the final solution. Did you check your output file to see what the boundaries looked like?

Bryan

[LOKESH KALATHI]

Hi Bryan,

As per your suggestion I tried with the latest version of cantera and I used very low slope values. But still, I am not getting the correct results (It is again 5 m/s for methane for stoichiometric).

Please find attached the script and my result. Kindly go through this and help me to get good results.

Thanks and Regards,

Lokesh

[Ray Speth]

Hi Lokesh,

You appear to have used an old version of the ck2cti program to convert this mechanism to the CTI format. This version of ck2cti (from Cantera 2.0 or older) has a number of bugs which have been fixed in the more recent ck2cti.py that is included with Cantera 2.0 and newer. The problem is caused by the fact that the transport data for the USC mechanism contains some additional non-standard data, which the old converter mistakenly interprets as coefficients for the standard transport properties. The new converter will generate an error unless this non-standard data is removed from the input file.

After correcting this and a number of other issues with the input files, I get 0.36 m/s as the flame speed for the CH4/air flame, which is a lot more reasonable. I think the lesson here is (and this goes for everyone, really) don't use old versions of Cantera.

Regards,

Ray

[LOKESH KALATHI]

Thanks a lot Ray for your valuable reply,

Currently, I am trying with "ck2cti.cpython-33.pyc" for converting the ck files to .cti file. I would like to know whether this approach is correct or not?. Morever, I am facing difficultly in generating the .cti file for the USC high temp mechanism. If possible, please provide me the clear methodology to convert ck file to .cti file with some examples.

I attached the file for which I am facing difficulty in converting to cti format.

Thanks in advance.

Regards,

Lokesh

[Bryan W. Weber]

Lokesh,

See here for some instructions I gave to another user about a similar mechanism: https://groups.google.com/d/msg/cantera-users/91JvCtoOjks/fvqQB4wgK6MJ

The advice is the same as Ray gave you - there are lines in the transport file that cannot be interpreted by Cantera because they should be comments. You need to either comment out those lines or delete them. Cantera is usually quite good about giving an error message that tells you what is wrong.

Hope it helps,

Bryan

[LOKESH KALATHI]

Thank you Ray

I updated my cantera to 2.1.1 and I tried the conversion to .cti for the USC High Temp Mechanism and then I ran my python script with this mechanism but still I am getting very high value of flame speed for Methane (5 m/s). So can u please send your .cti file of this mechanism so that I will find out the error, as well as I can get the correct value of flame speed.

Thanks in advance

Regards,

Lokesh D

On Sunday, 7 September 2014 08:49:00 UTC+5:30, Ray Speth wrote:

[Bryan W. Weber]

Dear Lokesh,

Can you please provide us with the CTI file **and the script you use to calculate the flame speed**? That will be the easiest way for us to help.

Best,

Bryan

[LOKESH KALATHI]

Brayan,

Sorry for delay in reply.

Please find attached my .cti file which I used in my script. The script is same as the example script provided in the C:\cantera\python\ example folder

Regards,

Lokesh

[Bryan W. Weber]

Dear Lokesh,

There are 10 scripts in the C:\PythonXX\Lib\site-packages\cantera\examples\onedim folder alone, not to mention all the other folders in the examples directory. Which example are you using? You need to be explicit so that we can help you. Otherwise we have to guess and we may get it wrong. Also, all of us here are volunteering our time, so every little bit of help you can give makes it easier for someone to give you help and makes it more likely that you will get a correct answer quickly.

Best,

Bryan

[LOKESH KALATHI]

I regret for not mentioning the correct file.

This is the script which I used.

Please help me to sort out the issue. I think the problem is with the .CTI file because the other mechanisms are giving good results with the same script.

Thanks in advance,

Lokesh

[Ray Speth]

Lokesh,

Despite what you said, this CTI file was created using the old converter which handles non-standard input files badly, as I previously described. I have no idea how you're actually trying to run the ck2cti.py converter, but you need to examine this again.

You also appear not to have corrected the transport data input file to remove the non-standard parameters. You need to look at the transport data in your CTI file and make sure it is correct before using it to run a simulation. One easy way to see that the transport data in the CTI file you generated is invalid is that the geometry for species such as N2 and H2 is listed as "atom" when those species have a linear geometry. Note that the other transport parameters for these species are also wrong, so it's not sufficient to just fix the geometry flag.

Regards,

Ray