Minimum tube diameters for detonation propagation in CH4/H2-air mixtures: implications for natural gas cooktop burners

Abstract

The minimum detonation diameter for methane (CH4) / hydrogen (H2)-air mixtures is numerically evaluated to assess detonation risks in cooktops designed to work with natural gas. A one-dimensional mathematical model that considers heat and friction losses for detonations propagating in pipes is used for that purpose. The initial conditions are selected to emulate the operation of a commercial cooktop working with different CH4 /H2 blends. Results show that for H2 content in the blend higher than 45 %, a conventional cooktop air-fuel mixer may pose a detonation hazard since the minimum detonation diameters predicted by the model are smaller than the diameter of the mixing tube (i.e., dmin < dmixer). Additionally, the individual effect of equivalence ratio, Φ, and hydrogen content, % H2, in the fuel blend are evaluated separately. An increased risk of detonation is present for (i) CH4 /H2-air mixtures with Φ → 1, and (ii) higher % H2 content. Finally, the effect of the natural gas composition was evaluated, showing that 100 % CH4 is not a good surrogate for this fuel since there is a considerable decrease in dmin and in the admissible H2 content in the blend when the real composition is considered.

Fernando Veiga López

Assistant professor of Fluid Mechanics

Passionate researcher on hydrogen combustion for safety and power generation.