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Jens September 29, 2002 16:43

Problem with Combustion

I am trying to setup a combustion process for propane. But I have an error when solving. There are no residuals for H2O and CO2 ??? e.g. no reaction. The fluid is setup as a reacting mixture.

Any hints ?



Astrid September 29, 2002 18:11

Re: Problem with Combustion
Although you see no residuals for H2O and CO2, are their equations being solved? Did you set-up the file REACTIONS correctly, with the multifluid settings?

What usually helps is to set an reasonable initial mass fraction for both H2O and CO2. Something like 1e-5.


Bob September 30, 2002 05:08

Re: Problem with Combustion
Hi Jens, which version of the software are you using and is your combustion a steady state simulation or transient ? Bob

Karl September 30, 2002 16:37

Re: Problem with Combustion
Is the temperature high enough for the reaction to start?

Jens October 1, 2002 03:01

Re: Problem with Combustion

I will try to answer all the question in this post:

Yes the eqn. for H2O and CO2 are being solved.

Yes the multifluid are setup in the correct way.

I am using CFX 5.5 and my combustion are solved as transient.

The temperatur at the beginning are only about 300 K.

But I have found that sometime there are a problem with the setup. Although all the physics are setup in the right way. Combustion will not happen.

I have started from the begining again, doing the geometry(import iges), putting on the physics, mesh etc. And this time the combustion starts. But the setup are fully the same as the previous one. So at some stage CFX did not understand the input correct. Or manybe the way to input was set up.



Karl October 1, 2002 11:06

Re: Problem with Combustion
Astrid is right, having a tiny fraction of products does help he numerics. A test you could do is to increase the initial temperature to see whether the reaction kicks start as sometimes it will not manage to get started, hence the temperature remains (low) constant and nothing happens...

Bob October 2, 2002 14:18

Re: Problem with Combustion
It also may be worth contacting CFX if you can not sort out the problem as I think there is something you need to set to start the ignition in CFX5.5.1 for a transient simulation, I believe it may be a bug ? Bob

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