Species settings in combustion

Kenzhia3310 · April 28, 2020, 08:02

Hi, there.
I am currently doing the premixed combustion in bunsen burner.
I have applied the reduced mechanism of Grimech 3.0 in my system.
Fluent always set the remaining species as N2, for example: I set my coflow inlet with pure nitrogen so I no need to put the mole fraction value in the boundary condition of coflow.
For my pressure outlet, I cannot put 0.209(mole fraction) for O2 because it implies that only 0.209 of O2 and 0.791 of N2 will extract from the system. However, if I didn't put anything on pressure outlet, it seems like my outlet condition will become a region with pure nitrogen.
My question is: What kind of species should I put on the pressure outlet region?

vinerm · April 28, 2020, 11:54

The species fraction at the outlet is determined by Fluent depending on the reactions or mixing inside the domain. The value that user specifies at the outlet is used only in case of flow reversal at the outlet. Otherwise, it has no effect. So, specify realistic values but do not worry much about it.

Kenzhia3310 · April 28, 2020, 11:57

Thanks for your clarification

April 28, 2020, 08:02	Species settings in combustion	#1
Kenzhia3310 New Member Koo How Boon Join Date: Mar 2020 Posts: 13 Rep Power: 6	Hi, there. I am currently doing the premixed combustion in bunsen burner. I have applied the reduced mechanism of Grimech 3.0 in my system. Fluent always set the remaining species as N2, for example: I set my coflow inlet with pure nitrogen so I no need to put the mole fraction value in the boundary condition of coflow. For my pressure outlet, I cannot put 0.209(mole fraction) for O2 because it implies that only 0.209 of O2 and 0.791 of N2 will extract from the system. However, if I didn't put anything on pressure outlet, it seems like my outlet condition will become a region with pure nitrogen. My question is: What kind of species should I put on the pressure outlet region?

April 28, 2020, 11:54	Outlet	#2
vinerm Senior Member Vinerm Join Date: Jun 2009 Location: Nederland Posts: 2,946 Blog Entries: 1 Rep Power: 35	The species fraction at the outlet is determined by Fluent depending on the reactions or mixing inside the domain. The value that user specifies at the outlet is used only in case of flow reversal at the outlet. Otherwise, it has no effect. So, specify realistic values but do not worry much about it. __________________ Regards, Vinerm PM to be used if and only if you do not want something to be shared publicly. PM is considered to be of the least priority.

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April 28, 2020, 11:57		#3
Kenzhia3310 New Member Koo How Boon Join Date: Mar 2020 Posts: 13 Rep Power: 6	Thanks for your clarification