Key results from the EU H2020 project CENTRELINE are presented. The research activities undertaken to demonstrate the proof of concept (technology readiness level—TRL 3) for the so-called propulsive fuselage concept (PFC) for fuselage wake-filling propulsion integration are discussed. The technology application case in the wide-body market segment is motivated. The developed performance bookkeeping scheme for fuselage boundary layer ingestion (BLI) propulsion integration is reviewed. The results of the 2D aerodynamic shape optimization for the bare PFC configuration are presented. Key findings from the high-fidelity aero-numerical simulation and aerodynamic validation testing, i.e., the overall aircraft wind tunnel and the BLI fan rig test campaigns, are discussed. The design results for the architectural concept, systems integration and electric machinery pre-design for the fuselage fan turbo-electric power train are summarized. The design and performance implications on the main power plants are analyzed. Conceptual design solutions for the mechanical and aero-structural integration of the BLI propulsive device are introduced. Key heuristics deduced for PFC conceptual aircraft design are presented. Assessments of fuel burn, NOx emissions, and noise are presented for the PFC aircraft and benchmarked against advanced conventional technology for an entry-into-service in 2035. The PFC design mission fuel benefit based on 2D optimized PFC aero-shaping is 4.7%.

A fuel cell—gas turbine hybrid propulsion concept is introduced and initially assessed. The concept uses the water mass flow produced by a hydrogen fuel cell in order to improve the efficiency and power output of the gas turbine engine through burner steam injection. Therefore, the fuel cell product water is conditioned through a process of condensation, pressurization and re-vaporization. The vaporization uses the waste heat of the gas turbine exhaust. The functional principles of the system concept are introduced and discussed, and appropriate methodology for an initial concept evaluation is formulated. Essential technology fields are surveyed in brief. The impact of burner steam injection on gas turbine efficiency and sizing is parametrically modelled. Simplified parametric models of the fuel cell system and key components of the water treatment process are presented. Fuel cell stack efficiency and specific power levels are methodically derived from latest experimental studies at the laboratory scale. The overall concept is assessed for a liquid hydrogen fueled short-/medium range aircraft application. Block fuel savings of up to 7.1% are found for an optimum design case based on solid oxide fuel cell technology. The optimum design features a gas turbine water-to-air ratio of 6.1% in cruise and 62% reduced high-level NO_x emissions.

In the paper, options for mechanically integrated parallel hybrid propulsion are evaluated, and a conceptual sizing and performance study of a mechanically integrated parallel hybrid electric turbofan engine for a short-range aircraft application is presented and discussed. Through a methodical down-selection procedure, a most promising power plant system architectural concept is identified from an initial cloud of concept candidates. The design of the preferred configuration is conceptualized including initial performance analyses, both at the isolated power plant as well as at the integrated aircraft level. Beside the basic power plant definition, the multidisciplinary concept elaboration includes solutions proposed for the electric systems architectural layout, the major electrical components involved as well as important airframe integration aspects. The components of the electrical power management and distribution system are sized, and efficiency and weights are evaluated under special consideration of thermal management requirements. In result, a best and balanced degree of power hybridization is determined for the studied mechanically integrated parallel hybrid power plants taking account of electric system design and weight impacts as well as power plant operational robustness in case of electric system failure. The overall system assessment includes the evaluation of fuel reduction potentials through a parametric aircraft sizing study including the derivation of key technological requirements for onboard electrical energy storage. In the paper, essential design and sizing strategies for mechanically integrated parallel hybrid aero propulsion systems are derived, and a brief characterization of the associated key technological challenges is provided.

Hybrid-Electric Propulsion (HEP) could be part of the solution to decrease emissions associated with regional commercial aviation. This study presents results for the aircraft level fuel reduction potential of a regional turboprop concept with an HEP architecture and Entry-Into-Service (EIS) in 2035+. The configuration specifically tackles the elaborated challenges of introducing an additional electrical energy source to the configuration by employing a twofold electrical assistance to a turboshaft engine in combination with an innovative thermal management concept. Relevant components and disciplines were modeled and incorporated into an integrated aircraft design environment. The behavior and interaction of the HEP architecture with the aircraft was thoroughly investigated. A best-performing configuration was derived and compared with a conventional reference configuration following a State-of-the-Art (SoA) reference aircraft approach. For a typical mission with 200 nmi range, a block fuel reduction of 9.6% was found. However, the assumed battery performance characteristics limited the reduction potential and led to a fuel burn increase for the 600 nmi design mission. Furthermore, sourcing the non-propulsive subsystems directly from the on-board battery was detrimental. The innovative Thermal Management System (TMS) located in the propeller slipstream showed a synergistic effect with the investigated configuration.

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 (FP-CCE) 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 judgment on both the feasibility of the new concepts and the attainability of the requirements for future aircraft propulsion systems.