Experimental study on turbulent flame speed scaling of expanding premixed flames

Characterization of the turbulent flow field in a constant-pressure, dual-chamber, expanding flame apparatus is reported, with the flow field measured by a high-resolution particle image velocimetry system. Eight symmetrically located fans with rotation speed range of 3000 ∼ 7000 rpm generate nearly homogeneous and isotropic turbulent flow with fluctuation velocity linearly ranging from 0.70 to 1.77g m/s, and the integral length scale maintaining about 10 mm. The homogeneity and isotropy of turbulence are verified by statistically analyzing the probability density functions of the instantaneous velocity. Turbulent flame speeds for ethylene/air and ammonia/methane/air mixtures were measured over a range of the turbulent Reynolds number (Re_T = uR_f/S_u⁰δ_f ) from 29 to 2706, and from 69 to 2560, respectively. An extended turbulent flame speed scaling correlation is proposed, applicable to both the corrugated flame and thin reaction zone regimes. The extended model accounts for the geometry and history effects of the interaction between turbulence and flame propagation. For ethylene/air and ammonia/methane/air turbulent flame speeds, the Mean Absolute Percentage Error between the experimental and predicted values is 7.8% and 8.5%, respectively, which shows higher accuracy compared to existing scaling models.