I am doing non-premixed combustion for coal using single mixture fraction method. I have two inlets. Primary inlet is for the coal+air, and secondary inlet is for the air. I have DPM injection set to be 0.03 kg/s, based on the HCV of coal for 70kW thermal input as surface injection at primary inlet.
When setting up boundary conditions for the inlets, I have set mean mixture fraction set as 0 (air in gaseous phase) for the primary and secondary inlets. However, the flame produced is very tiny as compared to the flame I have produced using EDM combustion.
I am under the assumption that the volatiles are introduced after the devolatilization in the system, which is why I set the mean mixture fraction as 0. Is it a right approach ? Or do I have to set the mean mixture fraction in the primary inlet to a value >0 to accommodate for the volatiles produced during devolatilization ?