Problem with Non-Premixed model (coal burner)

Nando

Hello:

I´m modeling a coal burner with non-premixed model. I´ve got one fuel stream (coal) and two oxidizer stream with different compositions.

I must apply two-mixture-fraction approach.(three stream with different composition).DPM iteraction every 25 continuous phase iteraction.

I´ve a problem about this approach:

Fluent update properties continuous phase every ten iterations. I plot some variables (temperature,O2,mass flow rate).

When Fluent do this update properties, these variables increase or decrease its value too much (example: Tempearture changes from 2000 K to 500 K approximately, it changes from 500 to 2000 at the next update it happens every 10 iterations).

The solution can´t converge because of these great changes of the fluid properties.I don´t understand this approach.

Could somebody explain me two mixture fraction approach?

How can i converge my case?

My english is so bad.I´m sorry.

Thanks