[Marpole]

Hello,

I'm running reactingFoam for simulating methane combustion. I'm using OpenFOAM v9 and Westbrook-Dryers one-step reaction. The computation ran without crashing. However, I noticed that the gas temperature cannot be above 3,500K. It ends up with 3,500K in all combustion domain. Is there any reason the temperature is capped at 3,500K?

Thanks in advance,

[matejfor]

You are burning methane with oxygen, or at elevated inlet temperature or pressure? And it is a physical behaviour that the whole domain is reaching the temperature in the whole domain?

[Marpole]

Thanks Matej. Thank you for responding. It is simulating burning methane with oxygen in a constant volume. Inside the volume at the centre, I made an ignition.

From the simulation results, in the domain after the flame, the temperature is constant and at 3500K. I think that is odd; it can be high temperature but may not necessary to be exactly at 3500K.

[matejfor]

I see my answer got lost in other tabs today.
OK, so the limit 3500 K is suspiciously the same number used in many thermo files as the limit for the max. temp when specifying thermodynamics properties of individual species.

therefore check your thermo file and maybe replace it with one of these coming with the installation located at $FOAM_ETC/thermoData/therm.dat

hope this helps

[Marpole]

Thanks Matej. I made changes to Thigh in thermo.dat as you suggested. The maximum temperature is now able to move over above 3500K and reach 4050K, which is what I hope.

I found that I have to change Thigh for all species. For some species, I can find coefficients for a wider temperature range (e.g. from 200K to 6000K) from the new GRI mechanism and Caltech mechanism. For some, for example, CH4, the species will decomposed at temperature higher than 3500K. The temperature range cannot be over than 3500K. I reluctantly change its Thigh to 6000K. But if I keep it at 3500K, OpenFOAM will keep the temperature maximum at 3500K. So I have to change it to 6000K to keep the computation run.

It works but I get new question. Thanks again for your help.

[alainislas]

You can refer to the JANAF thermodynamic tables, they are available over the internet. Cp, Hf, and Sf are calculated from a 2 piecewise polynomial function, where in most cases the coefficients are valid for a range between Tlow = 200K and Thigh = 5000 K for all species.

[Marpole]

Thanks Alain. I found a JANAF table from NIST website : https://janaf.nist.gov/tables/C-067.html

The temperature range for methane goes to 6,000K. I will look for a method to convert JANAF table to OpenFOAM input form.

[alainislas]

Look at the Nasa Technical Memorandum 4513 - Coefficients for calculating thermodynamic and transport properties of individual species. There you'll find the polynomial coefficients you looking for

[Marpole]

Thanks Alain. I will give it a try.