Aero Engine Concepts Beyond 2030: Part 1 — The Steam Injecting and Recovering Aero Engine

Abstract Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. This first part focuses on the steam injecting and recovering aero engine concept. In the second part, the free-piston Composite cycle engine concept is presented. A third publication, building upon those two concepts, presents the project which aims for demonstrating the proof of concept with numerical simulation and test-bench experiments up to a technology readiness level of three. In the steam injecting and recovering aero engine concept, exhaust heat generated steam is injected into the combustion chamber. The humidified mass flow contains significantly more extractable energy than air. Furthermore, the pumping of liquid water up to the necessary pressure requires a magnitude less power than the compression of air, which reduces the internal power demand. Both lead to a noticeable increase in specific power compared to a conventional gas turbine and, foremost, to a significant increase in thermodynamic efficiency. By use of a condenser, installed behind the steam generator, the water is recovered from the exhaust gas-steam mixture. The proposed concept is expected to reduce fuel burn and CO2 emissions by about 15 % and NOx formation can be almost completely avoided compared to state-of-the-art engines of the same technology level. Moreover, the described concept has the potential to drastically reduce or even avoid the formation of condensation trails. Thus, the steam injecting and recovering aero engine concept operated with sustainable aviation fuels offers the potential for climate-neutral aviation. Based on consistent thermodynamic descriptions, preliminary designs and initial performance studies, the potentials of the concepts are analyzed. Complementarily, a detailed discussion on concrete engineering solutions considers the implementation into aircraft. Finally, the impact on emissions is outlined.