In DLN (9FA) combustion, we are mixing air & gas before combustion in premix mode. In this mode gas temperature will be around 180 deg c & air temperature will be around 400 deg c. While mixing itself, why fire is not taking place?

 

In order for there to be combustion the mixture of air and fuel has to be within certain limits. Generally, in GE-design heavy duty gas turbine DLN combustors operating in premix mode the amount of air is very, very high in relation to the amount of fuel.

You can think of it like the hydrogen in the generator. Hydrogen is combustible, explosive even--in the right proportion to the presence of air (oxygen). If the purity of the hydrogen is kept high then even if there is a spark there will be no explosion or combustion.

If the proportion of fuel in the combustor is kept low enough with the respect to the amount of air there will be no diffusion flame.