Commercial Aircraft Propulsion and Energy Systems Research Reducing Global Carbon Emissions (2016) / Chapter Skim
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4 Electric Propulsion
4 Electric Propulsion
Pages 51-70
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From page 51... ...
With a series hybrid system, only the electric motors are mechanically connected to the fans; the gas turbine is used to drive an electrical generator, the output of which drives the motors and/or charges the batteries. Series hybrid systems are compatible with distributed propulsion concepts, which 1 In this report, "specific power" and "specific energy" refer to power and energy per unit mass, respectively, and "power density" and "energy density" refer to power and energy per unit volume.
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From page 52... ...
Turboelectric propulsion research is one of the four high-priority approaches identified in this report for developing advanced propulsion and energy system technologies that could be introduced into service during the next 10 to 30 years to reduce CO2 emissions. As detailed in the section Technology Needs, below, hybrid-electric and all-electric systems are not recommended as a high-priority approach because the committee determined that batteries with the power capacity and specific power required for commercial aircraft at least as large as a regional jet are unlikely to be matured to the point that products satisfying FAA certification requirements can be developed
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From page 53... ...
For large commercial aircraft it is likely that fuel cell applications will be limited to secondary systems such as auxiliary power units and starter systems. Considerable improvements in the specific power of batteries and fuel cells will have to be attained before these power sources would be considered for large aircraft.
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From page 54... ...
electrical performance, time frame, whether cost and environmental impact were considered, and overall level of detail. Each of these studies contributes to the body of knowledge for electric aircraft and has been used by the committee to identify overall trends and establish electric component performance levels that could enable various types of electric aircraft.
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From page 55... ...
In addition, the improvements arising from electric propulsion are often in comparison to current aircraft, not to future conventional aircraft of the same time period that could also benefit from many of the improvements from these other areas. Tables 4.2 and 4.3 were created to relate levels of electrical power component performance requirements to various propulsion architectures and aircraft types.
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From page 56... ...
However, the committee is unaware of any systems studies that show that any electric propulsion system that relies on less-advanced batteries to augment the propulsion system of large commercial aircraft will reduce CO2 emissions more than would a partial turboelectric or conventional propulsion system. Turboelectric concepts are not dependent on advances in energy storage technologies.
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From page 57... ...
TECHNOLOGY NEEDS: STATUS AND PROJECTIONS Electric Machines and Power Conditioning Introduction Turboelectric propulsion concepts are heavily dependent on advances in aircraft electrical power system technologies. These technologies include generator systems for electrical power generation; power electronics for power conversion, conditioning, and distribution; high power aircraft distribution that includes circuit protection;
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From page 58... ...
This section includes a discussion of aircraft electrical power technologies and challenges that are critical to enabling turboelectric propulsion concepts. The state of the art and 20-year projections for these electrical power system technologies are summarized in Table 4.3.
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From page 59... ...
using state-of-the-art equipment. It is envisioned that in 20 years SiC-based power electronics systems for aircraft applications will have a specific power of 9 kW/kg for power conversion and circuit protection using electronic components up to 200 A at ±270 V (essentially 540 V, for a power capacity of 108 kW)
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From page 60... ...
The preceding section, Power Electronics, describes current and future projected capabilities of circuit protection components. Cryogenic/superconducting power distribution is discussed in a later section, Cryogenic Electric Aircraft Power Systems.
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From page 61... ...
power systems. Approaches for thermal management of MW-class turboelectric aircraft propulsion systems have not been addressed in detail in system trade studies to date.
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From page 62... ...
In addition, a fleet of large commercial all-electric aircraft would only be possible with new or upgraded power transmission lines to airports and, potentially, new generating capacity. Fuel Cells Fuel cells convert the chemical energy in a fuel into electrical power without any combustion.
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From page 63... ...
There are no currently certified fuel cell systems on a commercial aircraft. The current technology readiness level for PEM fuel cells and SOFCs is TRL 4/TRL 5.7 Because of the challenges and concerns outlined here, while fuel cells may contribute as a power source for auxiliary power units, the committee does not foresee their contribution as an aircraft propulsion source in the timeline of this study.
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From page 64... ...
In summary, cryogenic technologies have the ability to greatly reduce the specific power of electrical systems for a wide variety of applications, including aviation. However, there are substantial barriers to the implementation of these technologies in the challenging operational environment of a commercial aircraft, and it is not envisioned that technology for cryogenic power generation or power distribution will be ready for incorporation in an aircraft propulsion system within the 30-year time frame addressed by this report.
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From page 65... ...
The SUGAR Volt concept features a twin-engine aircraft (see Figure 4.6) and relies upon projected advances in battery technology to enable a parallel hybrid electric propulsion system.
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From page 66... ...
Figure 4.6 shows the primary SUGAR Volt airframe architecture. Another element of the SUGAR project, the SUGAR Freeze, considered the viability of using fuel cells, cryogenic technologies, and boundary layer ingestion (using a propulsor in the aft fuselage)
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From page 67... ...
These propulsors could be either electrically powered by turbogenerators mounted on the wings or shaft driven. The study evaluated an electrical power distribution system based on electrical technologies available at TRL 4 today.
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From page 68... ...
68 COMMERCIAL AIRCRAFT PROPULSION AND ENERGY SYSTEMS RESEARCH FIGURE 4.8 STARC-ABL (150 passenger) concept being developed by NASA.
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From page 69... ...
While fuel cells may contribute as a power source for auxiliary power units, the committee does not foresee their contribution as a source of aircraft propulsion in the timeline of this study. To be considered as a propulsion source, vast improvements in specific power would have to be achieved.
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From page 70... ...
RECOMMENDED HIGH-PRIORITY RESEARCH PROJECTS Turboelectric Aircraft System Studies Conduct more encompassing studies of aircraft powered by turboelectric systems in order to better understand the benefits, component performance sensitivities, certification issues, and trade-offs related to key aircraft systems, such as thermal management and energy storage. Establishing cost targets, thermal management targets, and reliability targets at an early stage would help define the research plan.
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