Intialization v/s Patch Region for combustion problem
 

I am using diesel for gas turbine combustion and therefore it requires a high temperature for the mixture to ignite.

In my experimental setup, I am using a spark ignition source to ignite a local flame and then the main fuel supply is turned on which then catches the local flame and a swirl stabilized flame is achieved.

Now, for my numerical simulation I implemented two methods.

1) While initializing, I selected 'all zones', and under that I set the temperature to 2500K. The mixture did ignite after 80 iterations.

2) During my second simulation, I gave a patch of 2500K under entire zone. The mixutre ignited here as well.

My question is which approach is numerically correct. Am I making a mistake here??

Whats the difference between Initialization and Patching a zone with high temperature??

For simulation, air inlet and fuel are both at 300K (same in experiment)

Any help with be appreciated. Thanks.

Both are correct. In steady simulations it is not important how to ignite.

Can you please brief me on this so as to why it is not important?

Thanks.

Because the only important thing is your last result, the steady result. It is not important what happens before being steady. It is steady when converged.

please help with combustion divergence !!
 

Dear msaed;

I am simulating a steady flame of lean methane/air mixture in a swirl stabilized dump combustor. Because of similarity, i took only quarter section of combustor with periodic boundary condition in the azimuthal direction. my equivalence ratio is 0.65. the problem is that when i used finite rate/eddy dissipation model i have no ignition despite i tried both patching and initialization. i tried eddy dissipation model alone and i have divergence error in AMD solver and temperature exceeds 5000. i tried patching the entire domain with 2500 k and i have the same errors. i tried patching with products in the entire domain and i got same errors. i tried without patching at all and i got same errors!!!

of course this all were done either with initializing the solution or starting with steady cold flow solution.

kindly advice what to do, shall i check the grid or what, knowing that i use pressure based solver, second order schemes and courant number of 1.