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Jonathan Lemay February 26, 2008 14:15

combustion of 2 differents fuels
 
Dear CFX users

I am currently trying to model a bluff-body burner in which my fuels is composed 50% volume of H2 and 50% volume of CH4 (both gaz). Is there somebody who already performed this task of modeling combustion of 2 different fuels?

What I did up until now was to create a reacting mixture material in which I chose Hydrogen Air and Methane Air WD1 as reactions. Unfortunately it is not converging when I run it non-reacting. The goal of running non converging is for helping the convergence process and give initial value for the reacting case.

I either created a CFX-RIF flamelet library and run a flamelet combustion model instead of choosing and Eddy Dissipation Model. I had the same convergence problem on cold flow...

Is there somebody that already work with combustion of 2 different fuel in hte same domain (but homogeneous in mixture) could help me?

Best regards

Glenn Horrocks February 26, 2008 16:32

Re: combustion of 2 differents fuels
 
Hi,

I doubt you will get help on a detailed technical area like this on the forum (but you never know your luck I guess). I would think the best thing to do is to talk to CFX support.

Do I read you correctly when I see that the flow does not converge even when the reactions are turned off? Have you read the section in the documentation titled "Tips for obtaining convergence"?

Glenn Horrocks

Jonathan Lemay February 27, 2008 12:04

Re: combustion of 2 differents fuels
 
Hi Glenn

Your are right! The flow does not converge even when the reactions are turned off. What I performed on next step was to use EDM model with a two step reaction of Methane-Air. The advantage of using a two step reactions is that it allowed to included other fuels (such as H2) when the whole burning substance is made of a mixture of fuel.

I did follow the convergence tips on the CFX manuals for combustion, but unfortunately it has not help. I run single and multi steps reaction but both of the case where not converging.

All the case I an up until now where non-reacting flows. Should I try to run directly with combustion?

Regards

Glenn Horrocks February 27, 2008 16:44

Re: combustion of 2 differents fuels
 
Hi,

I would forget about turning the reactions/combustion on until it runs successfully as simple gasses flowing through the domain. Have you run it as a simple single phase model with air flowing through it? This would be the first really simple model to get right. After that works reliably then go to multiple gasses, then after that is OK then turn on reactions/combustion.

Glenn Horrocks

Jonathan Lemay February 27, 2008 22:01

Re: combustion of 2 differents fuels
 
Hi Glenn

Yes I have been able to run a success case with air-air mixture as you suggest me. After that I ran a non reacting case using a flamelet library of Methane-Air and I achieve it.

My problem is when I am using a Eddy Dissipation Model instead of a flamelet library. Using typical reaction such as Methane-Air WD1 or Methane-Air WD2, I do not converge. I really need to you use this EDM model with Methane-Air WD2 as my fuel is composed of methane and hydrogen.

It is strange because EDM model normally converge without to much problem? Got an idea why?

regards

Jonathan Lemay February 28, 2008 12:02

Re: combustion of 2 differents fuels
 
Hi Glenn

I finally resolved my problem!!! For the initial conditions of my domain I predefined some values for H2 and CH4. Instead of letting it Automatic for those value, I chose Automatic with value. I think it was not converging because the initial guess was wrong... Anyway thanks for your tips.


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