Methane oxygen combustion in a tube

student85 · June 19, 2011, 15:42

Hello
I am new to the forum and i am also new to the cfx software. My task is to create a Tube, to fill the tube with methane/oxygen mixture and to ignite it in order to study the temperature changes, velocity, reaction rate etc. (transient simulation). I created the mixture but i do not know if i have to put in the option reacting mixture or variable composition mixture. i would like to put a heat source in the inlet in order to increase the temperature above the autoignition point and to propagate to the rest of the tube. BUT the problem is that if i put reacting mixture i do not have propagation because regardless of the heat source the mixture ignites, on the other hand if i put variable composition mixture i do not have ignition at all. Is there any suggestions????
Thank you very much for you time.
Student85

canopus · July 8, 2011, 11:14

I guess you want to study premixed combustion.
Then you should use Temperature or other parameter at one end to trigger the combustion.
And then the flame front should propagate from burnt to unburnt side.

student85 · July 8, 2011, 13:48

Thank you so much for your reply. i managed to simulate fire propagation in the tube. Now my main problem is the validation of my model. ANY IDEAS of any papers that could help are very much appreciated.

canopus · July 11, 2011, 05:30

What is your model?
What do you want to validate?

student85 · July 16, 2011, 07:43

I am sorry for the delayed answer. I would like to validate the fire propagation in a tube with heat loss. Methane/ oxygen of methane air one stage reaction. ANY SUGGESTIONS??????????

canopus · July 18, 2011, 09:08

1. Dis you validate for laminar flame speed of methane air flame for various equivalence ratios?

student85 · July 18, 2011, 13:18

I am sorry but i do not understand... why i have to validate for laminar flow??? i use Eddy dissipation model and i read in the manual that this model is only used for Turbulent flow. Isnt that right????????

student85 · July 18, 2011, 13:44

I am sorry i did not understand the question...can you be more specific please?????

canopus · July 19, 2011, 08:37

Quote:

Originally Posted by student85

I am sorry but i do not understand... why i have to validate for laminar flow??? i use Eddy dissipation model and i read in the manual that this model is only used for Turbulent flow. Isnt that right????????

Yes you are right.
I did not have details about your test case so i presumed it being a laminar flame. Also flame in a tube is one of the ways to estimate laminar burning velocity experimentally.

About turbulent combustion of methane air there is lot of literature using various numerical models. You can google for the set up with BCs which comes near to your case.

student85 · July 19, 2011, 08:42

Thank you very much for your reply... can you answer another question???????????? how i can calculate the burning velocity???? In the cfx post which is the flame speed and which the velocity of the unburnt gas????????

June 19, 2011, 15:42	Methane oxygen combustion in a tube	#1
student85 New Member Student85 Join Date: Jun 2011 Posts: 10 Rep Power: 14	Hello I am new to the forum and i am also new to the cfx software. My task is to create a Tube, to fill the tube with methane/oxygen mixture and to ignite it in order to study the temperature changes, velocity, reaction rate etc. (transient simulation). I created the mixture but i do not know if i have to put in the option reacting mixture or variable composition mixture. i would like to put a heat source in the inlet in order to increase the temperature above the autoignition point and to propagate to the rest of the tube. BUT the problem is that if i put reacting mixture i do not have propagation because regardless of the heat source the mixture ignites, on the other hand if i put variable composition mixture i do not have ignition at all. Is there any suggestions???? Thank you very much for you time. Student85

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July 8, 2011, 11:14		#2
canopus Member SM Join Date: Dec 2010 Posts: 97 Rep Power: 15	I guess you want to study premixed combustion. Then you should use Temperature or other parameter at one end to trigger the combustion. And then the flame front should propagate from burnt to unburnt side.

July 8, 2011, 13:48		#3
student85 New Member Student85 Join Date: Jun 2011 Posts: 10 Rep Power: 14	Thank you so much for your reply. i managed to simulate fire propagation in the tube. Now my main problem is the validation of my model. ANY IDEAS of any papers that could help are very much appreciated.

July 11, 2011, 05:30		#4
canopus Member SM Join Date: Dec 2010 Posts: 97 Rep Power: 15	What is your model? What do you want to validate?

July 16, 2011, 07:43		#5
student85 New Member Student85 Join Date: Jun 2011 Posts: 10 Rep Power: 14	I am sorry for the delayed answer. I would like to validate the fire propagation in a tube with heat loss. Methane/ oxygen of methane air one stage reaction. ANY SUGGESTIONS??????????

July 18, 2011, 09:08		#6
canopus Member SM Join Date: Dec 2010 Posts: 97 Rep Power: 15	1. Dis you validate for laminar flame speed of methane air flame for various equivalence ratios?

July 18, 2011, 13:18		#7
student85 New Member Student85 Join Date: Jun 2011 Posts: 10 Rep Power: 14	I am sorry but i do not understand... why i have to validate for laminar flow??? i use Eddy dissipation model and i read in the manual that this model is only used for Turbulent flow. Isnt that right????????

July 18, 2011, 13:44		#8
student85 New Member Student85 Join Date: Jun 2011 Posts: 10 Rep Power: 14	I am sorry i did not understand the question...can you be more specific please?????

July 19, 2011, 08:42		#10
student85 New Member Student85 Join Date: Jun 2011 Posts: 10 Rep Power: 14	Thank you very much for your reply... can you answer another question???????????? how i can calculate the burning velocity???? In the cfx post which is the flame speed and which the velocity of the unburnt gas????????