G-equation model ignition failed
 

Hello,
When I simulated hydrogen fuel engine combustion with CONVERGE, I'm troubled with some problems.
when I used passive (G-EQN) type to spark mixture, the ignition always failed, as the attachment 1, the heat release rate extremely low.
When I used energy type to spark mixture, the flame can propagate Normally. However, the G=0 isosurface can't propagate normally like flame, as the attachment 2.
the laminar flame speed table is used in G-EQN model. The table is calculated in CONVERGE Studio Table Generation:TLF. I want to know how to determine the calculated temperature、pressure and equivalent ratio range. and in my calculation, some cases is failed as shown in attachment 3. what's the reason?

Hello,

1) We recommend using G source to initiate a flame kernel. Please elaborate on what you mean my ignition failed. Furthermore make sure you have followed the grid resolution consistent with our example case.

2) When sourcing energy, check if the g_eqn_model.temp_cutoff (default is 3500K) is achieved in the cylinder region. It is not clear form the image you attached what is the issue.

3) Laminar flame speed calculations appear to fail at very large temperature which is expected. You may have to play with the solver settings to get these working but I would suggest removing them from the table as these are at very high unburnt temperature.

4) Take a look at engine operating conditions to determine the range of variables in the LFS tables. You can run a motoring case to determine the temperature range while composition and pressure is known to you from the engine data.

Thank you very much for your reply.
When I used G source to initiate a flame kernel, the heat release rate is very low, shown as in attachment (G_HRR.jpg). So I called ignition failed. In my case, the base grid size is 4 mm, the max embed scale is 5 in spark region. And the source setting is shown as attachment (G_soure.jpg).
So why the ignition is failed?

Looks like source modeling may be the culprit. Take a look at our example case for reference. The source file there uses passive/(m3s) as shown in the attached image.



Let me know if that sustains the flame.

Best,
Nitesh

The source modeling has been corrected as example case as shown in the attached image. obviously, the heat release rate is still too low to sustain the flame.

Can you check the following,

1) Ensure that you are using the correct flame speed correlation/table that corresponds to your fuel
2) Ensure that you have activated the turbulent flame speed modeling
3) Check the max temperature and the tke field

If all the above checkouts and makes sense, please reach out to support@convergecfd.com using your office email address so that we can verify your account.

Best,
Nitesh

Thank you very much for your reply. However, I have some questions about No. 4 - LFS tables. Why the temperature range is determined by a motoring case ? I thank in a actual combustion process the temperature of end gas is higher than that in the motoring case.
Do the parameters (temperature, pressure and equivalence ratio) range have to cover the actual range of the temperature, pressure and equivalence ratio of the unburned mixture in a actual combustion process?

I'm looking forward to your reply.

You can use the motoring case to get an estimate of the rage. Ofcourse you need to account for combustion by increasing the upper limit by few 100 K and pressure by few bar.

Thank you very much！

I also use the G equation
 

Would you mind using QQ to communicate with me？（qq:389095952）
thanks!