Flame mode allows for furnaces to heat up with a well-developed and anchored flame that is easily detected by UV sensors.  

Flameless mode can be switched on when the furnace temperature is above the self-ignition temperature of the fuel. This operating mode can minimize NOx emissions levels to as low as 40 mg/Nm³. 

CFD simulation of a TSX burner showing the development of the temperature field in flameless mode.