High spatiotemporal evolution of flame-droplet interactions in KHCO3 enhanced water mist fire suppression

This study presents near-field measurements of potassium bicarbonate (KHCO 3 ) enhanced water mist suppression of buoyant turbulent fires, observing near-field interactions between water mist droplets and the turbulent flame front. The water mist is doped with varying concentrations of KHCO 3 , providing enhanced chemical fire suppression capabilities. Joint OH-PLIF and Mie scattering of droplets is employed with high spatial and temporal resolution (5000 Hz) to elucidate flame-droplet interactions resulting in extinction. A 20 kW turbulent buoyant diffusion flame is stabilised above the Sydney Turbulent Buoyant Fire Burner, surrounded by a water mist laden co-flow with droplet sizes d 32 ∼ 50 μm. The experimental operating conditions are chosen such that it is possible to delineate between the effects of increasing purely the inhibitor concentration and/or increasing the flow rate of water mist. Localised flame extinction and reconnection events are observed with increasing concentrations of KHCO 3 , demonstrating the opposing effects of radical pool depletion and edge flame propagation. The frequency of flame front breakages and thinning of the reaction front is also identified. Droplet positions in space relative to the flame front are quantified, showing distributions of droplet penetration depth from the air into the fuel side with increasing number of droplets traversing the flame front with increasing inhibitor concentration. A phenomenon known as droplet fragmentation is directly imaged, showing the explosive breakup of droplets doped with KHCO 3 .