A fundamentally new concept of a heat engine on the basis of heterogeneous working body, consisting of liquid and lyophobic towards it capillary-porous matrix was proposed in the middle 1980's. The unusualness of the new thermodynamic cycle and engine is that the interface of condensed heterogeneous lyophobic systems (HWB), "liquid-rigid solid capillary-porous matrix", the carrier of free surface energy, serves as a working body (in a thermodynamic sense) instead of traditional gas/steam. In this paper the main advantages, challenges and prospects for use of HWB as the working fluid for external combustion engine are discussed.