Effects of water sprays on flame propagation in hydrogen/air/steam mixtures

Different aspects of the interaction between droplets and flame propagation have been studied. First, flammability limits of H2/air/steam mixtures at 100 kPa for 3 temperatures between 358 and 383 K. the flammability domain was marginally modified by increasing the temperature. The mixtures were not flammable for H2O mol% ⩾ 55. The presence of water mist in initially dry H2/air mixtures at 100 kPa and 298 K did not shift the lower flammability limit as long as the droplets density number was below a critical value. The slight shift in the limit was essentially due to the saturated water vapor pressure. The effect of dispersed large droplets (SMD = 200-250 μm) on laminar H2/air flames was also marginal except when the droplet velocity is of the same order of magnitude as the flame speed in the same direction. Non-flammable H2/air/steam mixtures at 358 K and 383 K were made explosive by aspersion with cold water spray. However, the pressure increase was limited when ignition occurred for mixtures close to the flammability limit. In this case, the burned gas bubble was rapidly dragged downward by the spray. The water mist effect on the deflagration of H2/air mixtures were studied for various equivalence ratios. With droplets diameter <10 μm, the violence of explosion was mitigated except for lean mixtures in the domain where the combustion was not complete. In this case, the turbulence generated by the spray was sufficient to increase the combustion rate.