New conceptual solutions are required to significantly increase the internal combustion engine efficiency. Introducing external spool combustion chamber of constant volume and structural separation of the compression and expansion processes in its design are able to provide multi-fuel capacity, qualitative increase in the efficiency and significantly simplify the gearbox. In order to qualitatively improve characteristics of the internal combustion engine, systematic analysis of the created scientific and technical potential is required, followed by comprehensive implementation. The paper considers a concept of an internal combustion engine with continued expansion and ability to approach the gas turbine engine cycle implementation at constant volume with high efficiency on the example of such a basis using the rotary piston engine (CIAM) with the spool combustion chamber of constant volume (PJSC “UEC-Saturn”). The proposed concept makes it possible to effectively implement promising technologies for nitrogen separation and STIG technologies for further increase in the efficiency.