Impact of CH4/H2 Blends on the Entrainment Ratio of Domestic Cooktop Burners

Hydrogen addition to methane increases mixture reactivity, potentially affecting flame stability and promoting flashback. Previous studies on partially premixed domestic burners, where the equivalence ratio 𝜑 cannot be imposed a priori, have analysed equivalence ratio and flashback phenomena, but the analysis of 𝜑 in cooktop burners fed with CH4/H2 blends remains largely unexplored. Since the equivalence ratio 𝜑 is determined by the entrainment of ambient air, its estimation is useful both for phenomenological understanding and validation of numerical simulations. In this study, 𝜑 and the entrainment ratio 𝑅 were estimated for two domestic cooktop burners operating with CH4/H2 blends from 0 to 50% vol H2. In all cases, 𝜑 decreased with increasing H2 content while remaining fuel-rich: starting from 𝜑≈2 with pure methane and reaching about 𝜑 = 1.55− 1.65 at 50% vol H2. The estimated entrainment ratio 𝑅𝑚 and the geometrical entrainment ratio 𝑅𝑔, calculated using a theoretical model from the literature, showed qualitative agreement, with a decreasing trend with increasing H2 content. Finally, no macroscopic flame instabilities were observed during steady operation under the adopted