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To improve an energy optimization issue of ECS for MEA, we propose our concept in which ACS is replaced with VCS. A VCS is generally evaluated as auxiliary or limited cooling system of an aircraft. Cooling demand of commercial aircraft usually becomes large due to ventilation air at hot day conditions. In case of using conventional VCS for whole cooling demand, the ECS becomes too heavy as aircraft equipment. Though ACS's light weight is advantageous, the issue that VCS will be available for aircraft ECS is important for saving energy. ECS of commercial aircraft should work for three basic functions, i.e. pressurization, ventilation, and temperature control. The three functions of the ECS for bleed-less type of MEA can be distributed among equipment of the ECS. MDFAC works for pressurization and ventilation. Therefore, we should select appropriate system for only temperature control.

The authors are currently developing the MEE (More Electric Engine) electric motor-driven fuel pump system for aircraft engines. The electric fuel system will contribute to the reduction of engine power extraction to drive the fuel pump; thus, an improvement in engine efficiency will be expected. In addition, the engine system reliability will be improved by introducing advanced electric architecture, and the reduction of hydraulic components, fuel tubes and fittings is effective to enhance the maintainability of the engine. Although it is considered that the MEE electric fuel system will realize several benefits, there are technical challenges to introduce such new electric system into aircraft. One of the key technical challenges is to construct a redundant and simplified electric fuel system, because continuous operation of the fuel pump system is crucial for aircraft safety.