Accelerated study of CO2-ultrafine water mist to inhibit the compound flame at the early stage of gas/coal dust explosion

• Experimentally investigated the inhibition characteristics of methane/coal dust by CO 2 and ultrafine water mist. • Flame velocity, pressure, flame structure, flow field characteristics and functional groups were analysed. • The effects of CO 2 concentration and ultrafine water mist concentration on methane/coal dust explosion suppression were obtained. • Inhibition mechanism of CO 2 and ultrafine water mist revealed. A 20 L spherical test system with a large viewing window was used to investigate the suppression characteristics of CO 2 -uitraultrafine water mist on the propagation of a composite flame in a gas/coal dust explosion. The results show that when CO 2 and ultrafine water mist act together, the flame propagation speed, maximum explosion pressure and maximum pressure rise rate are monotonically reduced, indicating that their synergistic inhibition of gas/coal dust explosions is significantly better than the single action, and the amount of coal dust particles ignited at the initial stage of the explosion is significantly reduced, which in turn reduces the explosion hazard level. It was found that the addition of CO 2 and ultrafine water mist affects the vortex distribution of the gas/coal dust explosion flow field, with large vortices moving towards the centre of the flame, indicating a strong reaction within the flame, slow flame expansion, low flame propagation speed, and weakening of the explosion intensity. Product analyses showed that CO 2 and ultrafine water mist reduced the cleavage of chemical functional groups in coal dust particles and inhibited the involvement of coal dust in the explosion.