In this thesis the use of electric machines and a DC link to transfer power between aircraft engine spools is evaluated. The power transfer influences the part load performance of turbofan engines and reduces fuel consumption as well as bleed air requirements at low part load. The main objective of the work is to determine the potential decrease of fuel consumption of an engine for a narrow-body aircraft and of a significantly larger engine for a wide-body aircraft. Besides the evaluation at propulsion system level, the potentials for different flight missions are calculated using aircraft models. An objective associated with the assessment is the development of a methodology for aircraft engine performance calculation that enables both the design calculation and the steady-state and transient off-design calculation of the electrical system in the same level of detail as for conventional engines. This methodology then enables the determination of the fuel saving potentials. A further objective is to determine potential improvements in engine design when using power transfer. The highest requirements for the electric system occur when the aircraft is flying at low altitude with the highest permissible equivalent airspeed. For the substitution of the handling bleed of the narrow-body aircraft engine at these ambient conditions, a maximum power of approximately 1.0MW must be taken off the low-pressure spool and – minus losses – supplied to the high-pressure spool. Approximately 1.6MW is sufficient for the wide-body aircraft engine, although the maximum thrust is two and a half times as high. Transient operating conditions with higher power requirements can be covered while using the thermal capacity of the electrical machines. The combined off-design calculation of the engine and the electrical system also reveals the challenges in realizing such an overall system, because the electric machines have to provide full power far below their maximum speed. Thus, the achievable power densities of the electric machines are lower than in many other applications. The power transfer leads to increased surge margins for the two engine types, both in steady-state and transient operation. The engines also respond more quickly during acceleration. During deceleration however, they are exposed to a slightly higher risk of combustion chamber weak extinction, which could be reduced by short-time usage of handling bleed. The additional surge margin allows for a slightly improved design of the engines. Thus, the power transfer is largely beneficial at engine level. For the narrow-body aircraft, power transfer enables fuel savings on approximately 90% of the passenger kilometres. The duration of taxiing and total distance of the mission have the greatest impact on savings. For example, for a mission with a total distance of 250NM and an average duration of taxiing for U.S. airports, savings of up to 5.9% are calculated. When the duration of taxiing decreases, the savings decline and with total distances above approximately 2000NM, additional fuel consumption consistently occurs. For wide-body aircraft, the threshold is located at slightly longer total distances. Nevertheless, the additional mass of the electric system leads to increased fuel consumption for the vast majority of missions here.
Bewertung elektrischer Systeme zur Verbesserung des Betriebsverhaltens von Flugtriebwerken
Assessment of electric systems for the improvement of aircraft engine off-design performance
2023-01-01
1 Online-Ressource : Illustrationen pages
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2023). doi:10.18154/RWTH-2024-04245 = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023
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