10 More_Electric_Aircraft_Review_Challenges_and_Opportunities_for_Commercial_Transport_Aircraft

More Electric Aircraft (MEA)

  • Definition & Motivation

    • Similar to developments in electric vehicles, MEA aims to enhance aircraft efficiency.

    • Goals include reducing emissions and fuel consumption.

    • Traditional aircraft utilize a mix of electrical, hydraulic, mechanical, and pneumatic energy, each having drawbacks.

  • Transition Goals

    • Future aircraft designs focus on replacing non-electric systems (e.g., environmental controls, engine start) with electric alternatives.

    • Key improvements targeted: efficiency, emissions reductions, reliability, and maintenance costs.

Current State-of-the-Art in MEA

  • Recent Aircraft Examples

    • Boeing 787 and Airbus A380 integrate main engine generators coupled directly to jet engines.

    • These systems generate power at variable frequencies proportional to engine speed (350 to 800 Hz).

  • Standardization

    • Adoption of constant voltage (115 or 230 Vac) and variable frequency (as per engine speed) for aircraft power systems.

    • Requirements for power conversion (ac to dc and dc to ac) for various loads.

Impact of Electrification on Systems

A. Electric Power Systems

  • Conventional Power Systems

    • Traditional systems operate at 115V, 400Hz, using mechanical drives for constant speed.

    • Electric power mainly supports fans, avionics, and lighting.

  • Modern Developments

    • New aircraft have adopted constant voltage and variable frequency systems.

    • Increased need for power electronic converters and battery chargers.

B. Engine Start Systems

  • Traditional Process

    • The use of pneumatic power through Auxiliary Power Units (APUs) for engine start.

  • New Approaches

    • Boeing 787 utilizes electric starter generators in place of pneumatic systems, reducing equipment weight and complexity.

C. Auxiliary Power Units (APUs)

  • Traditional vs. Electric APUs

    • Conventional APUs provide pneumatic, hydraulic, and electrical power.

    • Electric APUs eliminate pneumatic functions, simplifying design but necessitating larger electric generators.

D. Environmental Control Systems (ECS)

  • Transition from Bleed Air

    • The move from bleed air systems, traditionally used in air conditioning, to electric compressors in contemporary aircraft like the Boeing 787.

    • Challenges include electric power sizing to meet high demand during flight phases.

E. On-Board Inert Gas Generation System (OBIGGS)

  • Functionality Shift

    • Shift from pneumatic to electric compressors for nitrogen generation to prevent explosive conditions in fuel tanks.

    • Active control systems are required to adapt to variations in altitude.

F. Electrification of Hydraulic Systems

  • Replacing Traditional Hydraulic Systems

    • Adoption of Electro-Hydraulic Actuators (EHAs) and Electromechanical Actuators (EMAs) to enhance efficiency and reduce weight.

    • EHAs integrate motors and hydraulic pumps, while EMAs eliminate hydraulic fluid entirely for efficiency.

Future Technologies and Research Opportunities

A. Hybrid Gas–Electric Propulsion

  • NASA Goals

    • Focus on reducing emissions and fuel consumption by 2025.

    • Explore architectures like Hybrid Wing Body (HWB) aircraft configurations.

B. Wide Bandgap Devices

  • Advancements in Power Electronics

    • Introduction of Silicon Carbide (SiC) and Gallium Nitride (GaN) devices for enhanced efficiency and capability in MEA systems.

C. Electric Taxi Technology

  • Emissions Reduction

    • Proposal to integrate electric motors for taxi operations to minimize fuel consumption during ground movement.

    • Potential for battery or fuel cell-powered systems to achieve zero emissions during taxiing.

D. Fuel Cell Applications in MEA

  • Characteristics

    • Lightweight, efficient power sources with zero emissions for aircraft operations.

    • Integration considerations for hybrid systems involving fuel cells and traditional APUs.

E. Power Extraction from Engine Spools

  • Investigating Better Power Distribution

    • Consider using low-pressure spools for additional electrical load capacity.

Conclusion

  • Electrification Trends

    • Focus on enhancing power systems, improving efficiency, and reducing environmental impacts through advanced materials and technologies.

  • Research Focus

    • Developing high-efficiency electric machines, power electronics, and energy storage to realize these goals.