On the initiation of blow-out from cooktop burner jets: A simplified energy-based description for the onset of laminar flame extinction in premixed hydrogen-enriched natural gas (HENG) systems

Abstract

Due to the prohibitive financial expense and logistical difficulties of a wholesale changeover from natural gas to hydrogen, hydrogen-enriched natural gas (HENG) offers a more viable intermediate solution for offsetting the carbon dioxide output of domestic gas usage and reducing the blow-out susceptibility of natural gas flames. In order to formulate a practically useful description of the blow-out threshold, the present work addresses the minimum energy per unit volume of premixed gas required for the sustained combustion of HENG fuels with molar hydrogen concentrations between zero and 50 mol%. By considering a ring burner comprising circular burner jet apertures with diameters in the range 1.0–2.4 mm, this critical energy density was demonstrated to increase linearly with the mean velocity of the admitted gas premixture, approaching a value that was common to all of the investigated HENG compositions in the limit of zero flow. Furthermore, despite flame morphology varying substantially as a function of flow conditions, the visible surface area of critically stable flames consistently exhibited an empirical squared dependence on the power generated by combusting fuel. By combining these correlations, the onset of blow-out was shown to be well-approximated by a formula that relates the critical surface-averaged laminar burning velocity to the mean velocity of gas molecules at the burner jet. This model provides a simplified means of predicting blow-out conditions from measurable input parameters and could serve as an invaluable asset for the design of new HENG burner systems or the retrofitting of existing natural gas appliances.