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. The first part focuses on the novel steam injecting and recovering aero engine concept. In the second part, the free-piston composite cycle engine concept is presented. Complementary to the two technical publications, this third part describes the cooperative project, which was initiated by an interdisciplinary consortium, aiming at the demonstration and the proof of concept of both aforementioned aero engine concepts. At the beginning of the project, simulations on propulsion, aircraft system, and test bench level will be conducted. On this basis, preliminary tests and fundamental experiments are planned in order to establish a solid basis for the demonstration. Finally, a system demonstration will be carried out at the laboratory level. Thus, the project allows for a final judgement on both the feasibility of the new concepts and the attainability of the requirements for future aircraft propulsion systems.
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.
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. Part one focuses on the steam injecting and recovering aero engine concept. This second part presents the free-piston composite cycle engine concept. 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. The free-piston composite cycle engine concept is composed of a gas turbine topped with a free-piston system. The latter is a self-powered gas generator in which the internal combustion process drives an integrated air compressor. Here, several free-piston engines replace the high-pressure core of the gas turbine. Through the ability to work at much higher temperatures and pressures, the overall system efficiency can be increased significantly, and fuel burn as well as CO2 emissions reduce. The proposed free-piston composite cycle engine design is described in detail, and the sources of thermodynamic benefits are stated. Concrete engineering solutions consider the implementation into an aircraft. The free-piston design enables lower weight and size compared to a crankshaft-bound piston engine, as no mechanical transmission and lubrication system is required. The absence of a crankshaft and connecting rods eliminates reactive forces, reduces mechanical losses, and allows higher mean piston velocities. Facilitated through air lubrication, higher cylinder temperatures are viable. The reduction of heat losses enables cooling of the piston-cylinder with core fluid. The use of a sequential combustion chamber can enhance operability and tailor the production of NOx in low-altitude operation. A discussion of emissions affecting the environment shows the potential to reduce the climate impact of aviation.
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. Exhaust heat generated steam is injected into the combustion chamber. By use of a condenser, installed behind the steam generator, the water is recovered from the exhaust gas-steam mixture. Both lead to a noticeable increase in specific power compared to a conventional gas turbine and, foremost, to a significant increase in thermodynamic efficiency. 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.
Aviation faces increasing pressure not only to reduce fuel burn, and; therefore, CO2 emissions, but also to provide technical solutions for an overall climate impact minimization. To combine both, a concept for the enhancement of an aircraft engine by steam injection with inflight water recovery is being developed. The so-called Water-Enhanced Turbofan (WET) concept promises a significant reduction of CO2 emissions, NOx emissions, and contrail formation. Representative missions for an A320-type aircraft using the proposed new engine were calculated. Applying a first-order one-dimensional climate assessment prospects the reduction of more than half of the Global Warming Potential over one hundred years, compared to an evolutionarily improved aero-engine. If CO2-neutrally produced sustainable aviation fuels are used, climate impact could be reduced by 93% compared to today’s aircraft. The evaluation is a first estimate of effects based on preliminary design studies and should provide a starting point for discussion in the scientific community, implying the need for research, especially on the formation mechanisms and radiation properties of potential contrails from the comparatively cold exhaust gases of the WET engine.
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