I'm modeling a tubular combustor with swirler& vane passage fuel injection as part of my PhD and I'm having big problems with the combustion model.

For these swirling combustion flows the finite rate/eddy dissipation model is essential but when I use it the flame goes out eventually after around 25 iterations even when having the outer wall at 1500K and patching in the temp of 1300K.

The boundary conditions were worked out by my supervisor and previous theses confirm them. The aerodynamics are spot on but when adding combustion (methane) the flame keeps going out for this model. The eddy dissipation model can be used but combustion occurs where the flow velocity is very high so flame should be quenched. I wrote a UDF to halt reactions > 80,100,120m/s but results are still not great but more sensible.

hi,

did u add products (co2 and h2O) in the reaction zone? To initiate the reaction, you need to do this.....add say 0.01 of h2O and co2 just to artificially begin the reaction. These values will eventually vanish after a few iterations. This should help. If not, let me know

James

The reaction still goes out after around 20 iterations. The only way I've found to keep it going is to have a hot wall at the reaction zone. I'm hoping it's just a drawback of using the basic species transport - finite rate/eddy dissipation models. It does mention difficulties with maintaining the reaction in the documentation.

regards phil

is your mixture lean or rich? If it is lean, then i suspect you are very close, if not below the lean flammability limit.....in that case, you will have to consider increasing your fuel mass flow a bit...yes your equivalence will go up a bit but that could solve the problem.

You might be experiencing lean blow-out problems....this is the case when the mixture is too lean

Let me know how it goes James

i'm pleased to know you,please help me to find the following: all files is required: data base,mesh,case,data and analysis file

James,

I was using the wrong model - I needed the finite rate combined with eddy dissipation model because where the fuel is injected the flow velocities are too high for combustion to occur.

I may experience the problem you suggested when I move to detailed reaction mechanisms though.

Thanks for helping.

Phil

Hi Phil,

Pleased to know that you've been able to figure out the problem. I thought from the onset, you were using both the finite rate/eddy dissipation model. I guess you know why this model works best with gas turbine combustion?

I am using the same model for my work. The finite rate chemistry model works too but it doesn't account for turbulent-chemistry interaction, even though it is better with regards to chemistry and can capture very well the effect of varying equivalence ratio on the flame speed. The combined model cannot do that since after the ignition, the turbulent mixing rate is almost always bigger than the arrhenius rate and so the rate is taken as the former.

Good luck.

James

James,

I've just read over my messages and at this point I was using the finite rate/eddy diss model but the flame keeps going out.

I tried what you suggested with initialization but the only way I found to keep the flame going was to have the outer wall at roughly the flame temp, or just below it to avoid affecting the temp scale in the contour plots.

I'm moving on to detailed reaction mechs soon and then onto biofuel so I'm leaving these problems behind for now but I'd be very interested to hear what you are doing for your work.

Where are you based? Will you publish any papers? I think I'm going to try and publish my first paper in the ASME journal this year as the next conference is in Monte Carlo!

Phil