Global synergistic enhancement of thermo-diffusive effects by turbulence in lean premixed hydrogen flames

This study experimentally investigates the e!ect of turbulence on thermodi! usive (TD) behavior in lean premixed hydrogen/air flames at an equivalence ratio of 0.34. The Karlovitz number (Ka) was varied from 38.6 to 99.2 by changing the reactant flow rate at fixed burner geometry. Mie scattering and OH-PLIF were used to measure the global and local responses. As Ka increases, the wrinkling term, the normalized global consumption speed, and the stretch factor increase by 6.4%, 47.4%, and 38.6%, respectively. Thus, the burning is enhanced more than the flame area increases. The mean OH intensity and its fluctuation increase with Ka, but the sensitivity of the OH gradient to the curvature and their Pearson correlation decrease. The fraction and OH-gradient-weighted contribution of strongly positively curved (leading-point-like) detected-front segments also increase. These results support a positive global turbulence–TD interaction in the investigated Ka range, although the local OH-gradient response to curvature becomes weaker.