Confined combustion of lean hydrogen-air mixtures with suspended water micro-droplets

Abstract

The present study is devoted to the detailed numerical analysis of the combustion waves propagation through the lean hydrogen-air mixtures with suspended micro-droplets of water. Considered gaseous mixtures are characterized by a relatively low reactivity and so the intensity of the combustion waves is moderate. Herewith, it is found that the flame can be noticeably accelerated in the presence of suspended micro-droplets. In particular, it is shown that the interaction between the flame front and the droplets with a diameter larger than 25~$\mu$m results in the enhancement of the flame instability that provides a substantial acceleration of the mixture burn-out process. At increased number density of water droplets the combustion proceeds in a similar way to the combustion within a porous medium, and similar trends are observed such as the increase in flame speed and intensification of the combustion process with the pressure increasing inside the confined vessel. In such a way it can be concluded that the water should be atomized in a proper way when attempting to use it as hydrogen explosion inhibitor. Otherwise, water droplets could induce flame acceleration via the mechanisms distinguished in this paper.