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Engine system reliability can be improved by advanced electric architectures, while the reduction of hydraulic components, fuel tubes, and fittings can enhance the maintainability of the engine and minimize pilot workload.

This proposed schematic of the integrated fuel feed system concept is for an assumed 150-200-seat single-aisle aircraft with twin engines, such as a Boeing 737 or Airbus A320.
Fuel connecting chart of the proposed system shows the fuel line among the tanks, electric pump units, and engines. Redundant electric fuel pump units are connected to each engine.
The engine fuel system consists of an AGB (accessory gear box)-driven fuel pump, FMU (fuel metering unit), and FPV (fuel pressurizing valve) at a minimum. Performance characteristics of the fuel pump are determined so that the pump supplies sufficient fuel flow with the obtained fuel inlet condition and engine operating condition.

Typically, the fuel pump consists of an LP (low pressure) impeller pump and HP (high pressure) gear pump. The LP pump increases fuel pressure at the HP pump inlet for the proper suction of fuel.

A more electric architecture supports the integration, simplification, and reconstruction of the aircraft and engine fuel system because of increased controllability, a modular design, and flexibility of component installation.

The MEE electric fuel system simplifies the engine fuel system by eliminating the fuel bypass circuit and complicated FMU. In addition, the MEE fuel system increases the flexibility of the engine fuel pump installation, because it is not necessary any more to attach the motor-driven fuel pump to the engine AGB. The location of the pump may be moved to an area other than the external surface of the engine. It means that the engine fuel pump is possibly considered as one of the components within the aircraft fuel system, and a possible location would be in the nacelle, fuselage, or wing.

Current aircraft fuel systems and engine fuel systems have duplicated functions, such as a boost pump, which enables the provision of proper suction of fuel from the tank, and a shutoff valve that shuts off fuel to the engine combustor. An integrated fuel system would remove the burden of the aircraft and engine interface condition, removing the duplicated function as much as possible and simplifying the system construction.

Integrated Fuel System Benefits

Table. LRU Comparison
A reduction in fuel burn is expected through the introduction of the MEE electric fuel system, which eliminates the loss in fuel system efficiency caused by the AGB-driven pump system.

Also, the number of components in the fuel system would be minimized. In the conventional aircraft fuel system and engine fuel system, which are separated from each other, there is a duplicated function between the aircraft components and the engine components. One of the typical examples is the pressure boosting function to ensure that the engine fuel pump properly suctions fuel from the aircraft fuel tank.

In the conventional system, electric motor-driven fuel boost pumps, which are usually submerged in the fuel tank, pressurize fuel to provide the minimum pressure required by the engine fuel system. Typically, the aircraft boost pump is the impeller type and adds about 50 psi to the tank pressure. However, the engine fuel pump also has a LP impeller pump to boost fuel pressure at the engine inlet because the engine fuel pump is required to supply fuel even though the aircraft boost pump is in operational condition.

In the proposed integrated system, the boosting function is accomplished by the LP impeller pump in the electric fuel pump unit. The feasibility study of the small-size turbofan MEE fuel pump shows that the single shaft electric pump, which drives both the LP impeller pump and HP gear pump by the same shaft, can suction fuel during an aircraft boost pump failure. The submerged aircraft fuel boost pumps can be removed, which will not only contribute to a reduced number of components, but also remove the submerged components in the fuel tank.

Another possible approach to reduce the number of components is to remove the cross feed valves and electric transfer pumps. In a conventional fuel system, the cross feed valve is necessary to have fuel mass balance between the left and right wing tanks in case one of the engines is shut down. In the proposed integrated fuel system, the left main pump unit has fuel inlets connecting to both left and right wing tanks. It is the same for the right main pump unit. The left and right main pump units always suction fuel from both the left and right wing tanks, so the fuel mass balance between the tanks will be maintained automatically, allowing the cross feed valve to be removed.