When a fuel is stored in liquid form (gasoline, diesel, kerosene, but also cryogenic propellants), its spraying in the form of a droplet mist is often necessary before combustion. This involves many complex physical phenomena, including atomization, interaction with the turbulence of the carrier flow, evaporation, mixing and combustion itself. The large eddy simulation (LES) of complex gas flows in realistic geometry is now mature, thanks in particular to the progress made in turbulence modelling and to the power of the machines made available to researchers in the context of high-performance computing. The modelling and simulation of the so-called separate phase before atomisation, then those of the so-called dispersed phase when the spray has been created, still contain many challenges, which will be illustrated during this presentation with examples from the fields of aeronautical and space propulsion.