Thermodynamic cycles used with external combustion are typically based on compression, heating, expansion and cooling, admitting variants to enhance efficiency or power. This paper carries out a thorough theoretical study of isochoric heating and non-adiabatic expansion processes and proposes a new thermodynamic cycle based on three instead of four stages. The compressor is removed because the working fluid (a gas) is pressurized by heating it isochorically. A novel concept of an engine is proposed (patent ES2992009A, WO 2025/257447), and it shows potential for power generation that has to be explored.
Martínez-Val et al. (2026) studied this question.