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

TL;DR

This study uses detailed numerical analysis to show that suspended water micro-droplets can accelerate combustion in lean hydrogen-air mixtures, highlighting the importance of proper water atomization to prevent unintended flame acceleration.

Contribution

It reveals how water micro-droplets larger than 25 μm can enhance flame instability and accelerate combustion, providing insights for safer hydrogen explosion mitigation.

Findings

Water droplets >25 μm accelerate flame propagation.

Increased droplet density mimics porous medium combustion.

Proper atomization of water is crucial for safety.

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.