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July 25, 2012, 19:36 |
Unsteady Combustion
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#1 |
Member
NormalVector
Join Date: Oct 2010
Posts: 71
Rep Power: 15 |
Hello,
I'm having a bit of trouble successfully running a hydrogen-air transient combustion case. The basic geometry is a cylinder with a smaller, short concentric cylinder. Oxygen is introduced at the larger cylinder's cross-section while hydrogen is introduced inside of the smaller cylinder and free to flow out. Both are mass flow inlets. I am able to run a steady state simulation and achieve combustion but when I switch over to a transient regime, the mixture never ignites and remains at the species inlet temperature. I've tried increasing the temperature of both species as to induce ignition but no luck. I've also tried timesteps ranging from 1e-05 to 1e-03 and no luck. Some solver specifics:
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July 26, 2012, 00:05 |
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#2 |
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Join Date: Mar 2011
Posts: 64
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Unsteady combustion is really awful. Please use spark model for ignition on a point and also try to patch a small amount of species (reactants and products) around the point. I always use it.
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Saeed Sadeghi Ansys Fluent CFD Consultant |
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July 26, 2012, 02:53 |
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#3 |
Member
NormalVector
Join Date: Oct 2010
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Thanks, at least I know I'm not the only one who has had trouble with transient combustion. Is this a known problem in FLUENT? I tried a spark earlier today but that didn't do anything, it was merely an increase in temperature. Are there any spark parameters you recommend (spark energy, diameter, etc)?
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July 26, 2012, 04:05 |
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#4 |
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You should increase the spark energy to get a temperature of about 2000K at the point. Also there should be at least a small amount of both reactants and products. Don't forget products should also be around the spark point.
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Saeed Sadeghi Ansys Fluent CFD Consultant |
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July 26, 2012, 17:33 |
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#5 |
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NormalVector
Join Date: Oct 2010
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Alright thanks, I'll give it a try.
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July 30, 2012, 19:17 |
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#6 |
Member
NormalVector
Join Date: Oct 2010
Posts: 71
Rep Power: 15 |
Thanks for the help. I was able to get my simulation to combust. Originally, I was using the hydrogen-air mixture template and only included oxygen and hydrogen in the computational domain. When I allowed water to flow into the domain along with the oxygen, the mixture successfully combusted. This was not the case for a steady simulation: the combustion occurred without water present.
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April 23, 2014, 05:35 |
fluent spark ignited
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#7 |
New Member
qiuyonghai
Join Date: Apr 2014
Posts: 4
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hi NormalVector,i have met the same problem to use the spark ignited,
I am able to run a steady state simulation and achieve combustion but when I switch over to a transient regime, the mixture never ignites and remains at the species inlet temperature, i see you have solved the problem,so i am very desired if you could help me thanks very much |
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April 23, 2014, 13:52 |
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#8 |
Member
NormalVector
Join Date: Oct 2010
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See my post above, try adding a small amount of products into your domain.
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April 23, 2014, 14:26 |
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#9 |
New Member
qiuyonghai
Join Date: Apr 2014
Posts: 4
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thanks for your help,i have do it as you said above, rigion a zone around the spark point,and add 0.01productsand some reactants,but it doesnot work,are there other parameters should notice??? desire for your reply
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April 23, 2014, 14:58 |
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#10 |
Member
NormalVector
Join Date: Oct 2010
Posts: 71
Rep Power: 15 |
The only other thing I would suggest is to initialize your entire domain with a small amount of product. That fixed my problem so if that does not work then I don't know what is wrong with your simulation.
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April 24, 2014, 04:23 |
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#11 | |
New Member
qiuyonghai
Join Date: Apr 2014
Posts: 4
Rep Power: 11 |
Quote:
i give the spark energy 2500j and my inlet is 0.05ch4 0.2 o2 ; i wonder if my inlet boundary conditions set is suited i am very glad to see you reply |
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