Effects of liquid water addition on turbulent premixed hydrogen/air combustion

Statistically planar premixed hydrogen/air flames with and without liquid water injection are numerically investigated through Direct Numerical Simulations. The approach used for studying the interaction of the liquid dispersed phase with the gaseous carrier phase is a hybrid Eulerian–Lagrangian scheme with two-way coupling. The results show that the water injection acts to attenuate the differential diffusion effects arising from non-unity Lewis number and thermal expansion effects, especially under stoichiometric conditions. Furthermore, the size effect of the water droplets is considered by comparing the simulation results for two different initial droplet diameters of the water mist. In a second series of simulations, the effect of preferential diffusion is analysed in isolation. In these cases, the fuel has the same properties as hydrogen but a unity Lewis number. It is observed that the combined action of preferential diffusion and turbulence-induced wrinkling acts to increase the turbulent burning velocity in the regime considered here, while flame thickening acts to decrease the turbulent flame area in the fuel-lean cases and as a consequence weakens the effectiveness of preferential diffusion effects.