reactingFoam: ignition point?
 

Hi,

I'm just a beginner with OpenFoam and I would appreciate any help very much. I am currently trying to find out the influence of temperature in reactingFoam, but the result of my case confuses me:

i am mixing methane and air. when setting the inlet temperature to 800K for both methane and air, i can see that the temperature rises up to over 2000 K when both gases start mixing. Witih an inlet temperature of 293K the temperatur stays at 293K. I thought it was because of the ignition temperature of methane, but i found that it lies at 600°C. As 800K=527°C, the temperature isn't reached in my case. Why then it rises to 2000K when the gases converge? Or did I miss something and it doesn't depend on the ignition point?

Thanks for any clues
Jui

There are way too many things that can go wrong here, so without your cases setup it's very hard to give you any help.
Most importantly, which reaction mechanism are you using?

But something you can (and should) test on your own is the non-reacting case. Just switch off the chemistry (in constant/chemistryProperties).
Additionally you can test how it works when you have only methane and nitrogen (no oxygen => no combustion).
These tests are a good exercise in any case to verify that your flow solver settings are correct. Once you are sure everything is working correctly, go on with the reacting case.

Also, which OpenFOAM version are you using?

-Armin

Hi, thanks for your fast reply!

i already tested the case when switching off combustion. in this case, it doesn't react (no co2 or h2o) and the temperature doesn't rise but stays at 293K.

The second possibility (only nitrogen instead of air) could be interesting. i will try that!

as to your question which reaction mechanism i use, i don't exactly know what you mean: do you need to know what reactions take place? or some setting/model?

and: i am using version 2.3.0

thanks

no oxygen --> no reaction products, no rise of temperature, i just tried it.
but still, i don't know at which temperature reaction starts and why. i wished i could look it up somewhere.

Good! One source of error ruled out, for the first trials at least. ;)

Otherwise, I don't even understand your problem. Your ignition point and your whole combustion depends so much on your reaction mechanism that without knowing which one you use nobody can really help you any further!

Hi,

sorry, I didn't know where to find the reaction mechanism.

Now I found that in the file "reactions" is written "irreversableArrheniusReaction". when setting up my case, I just changed the reaction equation but copied that reaction type from the example of reactingFoam, that's why I didn't remember it.

There is also written "Ta=14904" which seems far too high for an activation temperature.. I just changed my temperature to 15000K for a try but the calculation seems to fail: no results at all. Or is Ta something else?
(beta=0, A=5.2e16)

Or maybe Ta is the activation ENERGY and in cal/mol?

I think you have there some ground work on combustion modeling to do before you start with CFD simulation. ;)

I would strongly recommend you to start with a basic course on combustion and book studies. Here some recommendations:

• Peters, Norbert. Turbulent Combustion. Cambridge University Press, 2000. http://dx.doi.org/10.1017/CBO9780511612701.
• Warnatz, Jurgen, Ulrich Maas, and Robert W. Dibble. Combustion - Physical and Chemical Fundamentals, Modeling and Simulation, Experiments, Pollutant. 4th ed. Springer, 2006. http://www.springer.com/engineering/...-3-540-25992-3.
• Poinsot, Thierry, and Denis Veynante. Theoretical and Numerical Combustion. Third., 2012. http://elearning.cerfacs.fr/combustion/index.php.
• Echekki, Tarek, and Epaminondas Mastorakos, eds. Turbulent Combustion Modeling. Vol. 95. Fluid Mechanics and Its Applications. Dordrecht: Springer Netherlands, 2011. http://link.springer.com/10.1007/978-94-007-0412-1.

Yes :o thanks for the literature, i'll start with that ;)