Flame dynamics analysis of highly hydrogen-enrichment premixed turbulent combustion

The highly hydrogen blended turbulent natural gas flames were stabilized on a nozzle-type Bunsen burner and measured with laser diagnostic technique. Flame topology characteristics and turbulent burning velocities for the lean turbulent combustion and uniform laminar flame speed of S_L ≈ 40 cm/s were investigated and compared. Hydrogen effect of high diffusivity on combustion properties was analyzed. The local flame structure parameters were obtained and analyzed. Results show that finer wrinkled structure is not only induced by increasing turbulence intensity u’/S_L, but also there is a significant enhancement due to the increasing hydrogen ratio. At large turbulence intensities for lean combustion, more elongated flame folds are formed and small scale structures are generated inducing flame pockets detaching from the main flame, which may largely due to the strong thermo-diffusive effect. However, when fixing S_L ≈ 40 cm/s, the flame front shows cusp structure with large negative curvature at high hydrogen ratio when u’/S_L is low, which mainly result from Darrieus-Landau instability in influencing the flame-turbulence interaction. Moreover, hydrogen addition apparently enhances turbulent burning velocity and the enhancement is more evident for higher intensities. S_T/S_L seems to follow the power law relation for lean flames while showing a quadratic relation for flame of S_L ≈ 40 cm/s. The PDF profile widens encompassing a larger range with increasing hydrogen ratio, indicating that the scale of wrinkled structure is getting smaller. This can be further verified by the profile of local radius of curvature. Hydrogen has an evident effect in enhancing flame surface density which may connect to turbulent burning velocity. And a slightly decreasing trend is found when ZH2 is beyond 0.6 at high u′/S_L.