Numerical Simulation On The Flashback Character For Lean Premixed Combustion

Lean-premixed combustion is facing the problem of flashback under low or high load, though with the advantage of low NOx emissions of gas turbine combustor. In this paper the flashback characteristics of laminar cone-shaped premixed flame stabilized on a ring and turbulent swirling premixed flame with methane as fuel are studied by numerical simulation method, and the feasibility and reliability of this method are validated. On the basis of above research, the main factors affecting the flashback characteristics of premixed combustion are investigated.Firstly, laminar finite-rate model was used to simulate the process of flashback of cone-shaped premixed flame and the numerical results are compared with published experimental data. It is show that the calculated flashback characteristics are qualitatively consistent with experimental data. The flashback speed increases with the increment of equivalent-ratio and it reaches its maximum value when the equivalent-ratio is about 1.0. The numerical results also proved that the critical velocity gradient neat the wall is just slightly lower than the ratio of laminar flame speed to extinguishment distance, which accorded with classical boundary layer flashback theory of laminar flame which can quantitatively predict the flashback characteristics of laminar premixed flame.Secondly, the flashback characteristics of turbulent premixed flame burning methane are simulated using validated realizable k-e turbulent model and eddy-dissipation concept turbulent combustion model and the effects of swirling strength on flashback are investigated. The numerical results indicate that the flashback characteristics of weak swirling flow are better than that of strong one. Moreover, the radial velocity profile of the burner exit is also a key factor affecting flashback characteristics.