reactingFoam - Laminar premixed case - methane+air

Foamer7 · January 7, 2022, 04:40

Hi,

I have been running a case in reactngFoam for a month. It's laminar premixed ignition of methane + air. I created a setFieldDict for spherical ignition kernal, set T as 1600 K. I'm using 1 step reaction mechanism. But the temperature is dropping till 900K and then stabilising in and around 1000K. Ignition temp is 1600 K and Mixture temp is 298 K. I've changed the boundary condition, mesh resolution. However, temperatures falling instead of going up. I 've few questions

1) Can setFieldDict only be used to achieve flame ignition in reactngFoam? Does it actually ignite the mixture? Or do i need to givefvOptions?

2) Why temp. is falling instead of raising? Is this a limitation of one - step mechanism?

3) How can i set different grid size in the domain according to the area of interest? Is that complicated? Could you direct me?

All forms of helps are much appreciated. Thanks

Foamer7 · January 7, 2022, 12:07

Any idea guys?

JulioPieri · January 11, 2022, 11:08

1) yes it does ignite the flame
2) many factors can cause this.
- the flow might not be developed enough prior to ignition (and after it),
- the mixture proportions might not be ideal,
- the parameters in reactions file might be wrong (what is very easily done with all the confusing units).
- the surrounding of the flame is to cold for radiation.
check if the flame is actually there (see the Qdot variable). also, you could try a two-step mechanism and assess the CO concentration.
If the flame is there but the temp is low, check the BC, the arrhenius parameters, etc. Remember that flame height and swirl (therefore inlet velocities) also affects the flame temperature.
3) you can use snappyHexMesh with refinement boxes. check tutorials online (I recommend the wolf dynamics one, google it and you will find)

January 7, 2022, 04:40	reactingFoam - Laminar premixed case - methane+air	#1
Foamer7 New Member Appu Join Date: Jan 2022 Posts: 2 Rep Power: 0	Hi, I have been running a case in reactngFoam for a month. It's laminar premixed ignition of methane + air. I created a setFieldDict for spherical ignition kernal, set T as 1600 K. I'm using 1 step reaction mechanism. But the temperature is dropping till 900K and then stabilising in and around 1000K. Ignition temp is 1600 K and Mixture temp is 298 K. I've changed the boundary condition, mesh resolution. However, temperatures falling instead of going up. I 've few questions 1) Can setFieldDict only be used to achieve flame ignition in reactngFoam? Does it actually ignite the mixture? Or do i need to givefvOptions? 2) Why temp. is falling instead of raising? Is this a limitation of one - step mechanism? 3) How can i set different grid size in the domain according to the area of interest? Is that complicated? Could you direct me? All forms of helps are much appreciated. Thanks

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January 7, 2022, 12:07		#2
Foamer7 New Member Appu Join Date: Jan 2022 Posts: 2 Rep Power: 0	Any idea guys?

January 11, 2022, 11:08		#3
JulioPieri Senior Member Julio Pieri Join Date: Sep 2017 Posts: 109 Rep Power: 9	1) yes it does ignite the flame 2) many factors can cause this. - the flow might not be developed enough prior to ignition (and after it), - the mixture proportions might not be ideal, - the parameters in reactions file might be wrong (what is very easily done with all the confusing units). - the surrounding of the flame is to cold for radiation. check if the flame is actually there (see the Qdot variable). also, you could try a two-step mechanism and assess the CO concentration. If the flame is there but the temp is low, check the BC, the arrhenius parameters, etc. Remember that flame height and swirl (therefore inlet velocities) also affects the flame temperature. 3) you can use snappyHexMesh with refinement boxes. check tutorials online (I recommend the wolf dynamics one, google it and you will find)