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[augustas83]

Hi,
I'm doing my firs simulation with PyroSim, can anybody help me with some answers? (I'm simulating peat burning.) If so please write me at augustas83@yahoo.com i will explain the whole thing.

[Charlie Thornton]

If you wanted to have a long talk about peat modeling right here in the forum, that would be wonderful too.

What is giving your trouble?  (I'm guessing material properties...)

- Charlie

[augustas83]

Well it's a bit more complicated  than material properties... Ok, i'll try to explain everything in details:
Aim of my simulation is to simulate a fire of a peat burning which could have started from peat self ignition - exothermic chemical reactions. Peat is mound in piles in bins.
Any way, my biggest problem now is how to define a combustion, because if self ignition is possible (if not, ignition source can be applied) it would start in the lowest layers, and would spread in shape of 1/4 sphere. Burning should start from smoldering and later, when all of neighboring oxygen is consumed and consumption is faster then oxygen supply to reaction zone, pyrolysis will start. Main question - can i model such a situation with Pyrosim? Is it possible to create such conditions, that burning is starting in the middle of material and spreading in it, consuming oxygen and releasing smoke and heat? I have some more questions, so to be continued...

[Charlie Thornton]

I haven't been able to find any documentation addresses this.  That surprises me a bit since I'm sure I've heard of peat fires and FDS before but I can't seem to find the reference.  I did try to put together a simulation where I had a stack of pine blocks and one of the internal blocks was a heater, but I wasn't able to get the temperature to propagate outward - probably bad material properties on my end.

However, I have located a picture of a peat mound, so, there's that anyway.

[augustas83]

I still want to know, is it possible to make FDS with PyroSim in powder materials, according to conditions i have mentioned before(fire starts inside burning material)? If yes, what are the main parameters I should pay my attention?

[Charlie Thornton]

Unfortunately, I don't know the answer.  You may have more luck at the FDS discussion group:

http://groups.google.com/group/fds-smv

It can be a good source of information about the capabilities of FDS.

[augustas83]

I have found the answer
Starting in FDS5, the solid material can be given an ABSORPTION_COEFFIENT (1/m) that allows the radiation penetrate and absorb into the solid. Correspondingly, the emission of the material is based on the internal temperatures, not just the surface.

[Charlie Thornton]

Hey, great, thanks for following up.  Maybe that mixed with TMP_FRONT will get heat spreading inside the pile?  It seems like the next challenge is to get the heat to spread to the opposite side of obstructions - but maybe the ABSORPTION_COEFFICIENT used with the correct BACKING option takes care of that.

[augustas83]

Hello,
i was able to make peat burn and made the simulation,
but not from inside, i applied 350kW ignition source on top.

[Charlie Thornton]

Hey, great.  Does the heat spread down into the peat the way you think it should?

- Charlie

[augustas83]

Well I'm not shore about that, because i wasn't been able to get it burn from inside... , but peat bin gets on flame after 5 min., and it fits my expectations.