Numerical simulation of the effect of the air-fuel ratio on NO emission reduction in a gas turbine combustor with a double swirler

The purpose of this study is investigating the effect of fuel to air ratio on the flow characteristics and NO emission in a model double swirler combustion chamber. The air in this combustion chamber passes inversely through the liner. In this research, by defining the boundary conditions and producing adequate mesh, and using standard K-Ɛ model for methane fuel, combustion simulations have been performed. The simulations are performed in four different equivalence ratios, all of which are for the dilute phase of the fuel. The physics of the flow inside the chamber showed that in the higher equivalence ratios than 1, the mass flow air in entrance is not enough to keep the vortex breakdown and the stability of the flame, and thus prevents the formation of flame. By examining the vorticity and the amount of power of each vortex breakdown inside the chamber, the results showed that reducing the equivalence ratio increases the intensity of the vortex. It was found that reducing the equivalence ratio not only reduces the maximum flame temperature, but can also reduce the flame length to some extent. Finally, it was concluded that the NO production behavior is highly depend on the fluid temperature and its change graph is very similar to the temperature change diagram in the chamber, which results in a significant positive effect of decreasing the equivalence ratio on reduce the production of combustion emissions.