Long tunnel fire flame problem consultation

[yinyaolong]

In the self-extinguishing simulation of long tunnel fire, I often encounter that when the fire is about to die out, the flame moves to both sides, and then the heat release rate suddenly increases. I want to know how to solve this problem.

[rmcdermo]

When you are looking at flame extinction, you probably need to incorporate a realistic ignition threshold so that you do not get spurious "ghost flames" when fuel and air meet at low temperatures. You can set this value with AUTO_IGNITION_TEMPERATURE on REAC. In theory, this value is fuel dependent, but in practice I think there is too much uncertainty to really expect the handbook values of AIT to be precise for coarse grids and the myriad other assumptions at play. Something in the range of 300 C to 500 C is reasonable. I'd start with 300 C and see if your results make sense.

Note that you are in research territory! Validation of the model is your responsibility.

If you use AIT you will need to set an exclusion zone around the burner to light the initial flame. Search AIT_EXCLUSION_ZONE in the user guide. This too is research.