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xulixian April 14, 2009 03:28

Problems on H2/air CFX simulation
am puzzled by the simulation of H2/air combustion using CFX. I could not get the expected temperature, the maximum flame temperature is always below 980K. I use stoichiometric mixture of hydrogen and air, but after the reaction, their always a lot of O2 left. It looks like a lean combustion. And the in the beginning of the simulation, CFX tell me
Reactants and products do not balance for a reaction.
| Products will not be scaled for conservation of mass. |
| |
| Reaction : Hydrogen Oxygen |
| Products scale = 2.7750
My reaction chamber is a tube with 0.2 mm in diameter and 1.55mm in length, the inlet diameter is 0.1mm. Adiabatic wall condition.The boundary is the following:

Inlet: 300K, 6 m/s, Mass fraction H2: 0.02857 O2: 0.22857 N2: constraint,

Outlet: static pressure 1 bar

Initial temperature: 1000K

I use the default stoichiometric coefficient, so the reaction is H2 + 0.5 O2 = H2O,

Pre-Exponential Factor : 3.12e7 [m^1.5 s^-1 mol^-0.5] **(the value in Fluent is 9.87e8, I change the value since I have to switch the uint from "kmol" in Fluent to "mol" in CFX.)
Temperature Exponent : 0
Activation Energy : 3.1e+04 j/mol.

In the begining of the simulation, I use the time step of 1 e-7 s, then I increase the time step to 1 e-5 s.

Can you help me to diagnose the simulation? I appreciate for your help.

kerstin April 14, 2009 14:29

you should read the thread about wall heat flux in CFX answered by Bernhard.

Seems to become more and more people stumbling in the wrong forum. So we can start having fun now? ;-)

xulixian April 14, 2009 15:00

Hi Kerstin,
thank you for your reply. Acctually I proposed my question in CFX forum, but I didn't get any answers from them, so I tried my luck here, and it looks not bad! ^_^
I will check the thread you mentioned. thanks again.

regards, Lixian

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