  Solid and liquid sodium combustion with liquid water occurs through a thin
gas layer where exothermic reactions happen with sodium and water vapors. It
thus involves multiple interfaces separating liquid and gas in the presence of
surface tension, phase transition and surface reactions. The gas phase reaction
involves compressible effects resulting in possible shock wave appearance in
both gas and liquid phases. To understand and predict the complexity of sodium
combustion with water a diffuse interface flow model is built. This formulation
enables flow resolution in multidimension in the presence of complex motion,
such as for example Leidenfrost-type thermo-chemical flow. More precisely
sodium drop autonomous motion on the liquid surface is computed. Various
modelling and numerical issues are present and addressed in the present
contribution. In the author's knowledge, the first computed results of such
type of combustion phenomenon in multidimensions are presented in this paper
thanks to the diffuse interface approach. Explosion phenomenon is addressed as
well and is reproduced at least qualitatively thanks to extra ingredients such
as turbulent mixing of sodium and water vapors in the gas film and delayed
ignition. Shock wave emission from the thermo-chemical Leidenfrost-type flow is
observed as reported in related experiments.
