20 January/February 2024 | E-Mobility Engineering Commercial aviation is one of the world’s fastestgrowing sources of pollution, responsible for about 2% of global greenhouse gas (GHG) emissions and 2.5% of carbon emissions. These levels are projected to reach around 20% by 2050. As airlines emit CO2, NOx and contrails at high altitudes, their impact on global warming is more complex and probably more severe than simple metrics indicate. Sustainability in aviation is therefore critical to keeping Earth habitable, and humans connected across oceans and continents. However, so-called sustainable aviation fuels (SAFs) remain many times more expensive than kerosenes, and producing them often depends on diverting land use away from food production or acquiring new farmland through deforestation, and burning them may still release NOx, contrails and other pollutants. For many, e-mobility presents a more achievable means of sustainable flight, with a focus on lighter batteries to suit aircraft weight and enable zero-emission flight. However, as battery innovations can take decades to scale and certify, many chemistry ‘breakthroughs’ have failed over the last century. Further downstream in electric vehicles (EVs), there is underused potential for reducing the weight of propulsion systems to make extra room for onboard energy storage, which could increase aircraft ranges considerably without needing new advances in batteries or fuel cells. Today’s complete electric propulsion units (EPUs) – encompassing motor, inverter, gearbox and all related housings – typically have cumulative thermally-continuous power densities of about 3 kW/kg. But the US’s Advanced Research Projects Agency-Energy (ARPA-E) has determined that a powertrain of at least 12 kW/kg and 93% power efficiency could enable all-electric flights for single-aisle, 150- to 200-passenger commercial aircraft, such as Boeing 737s, on today’s H3X formed after its founders learned via ARPA-E that EPUs of 12 kW per kg could enable electric passenger aircraft (Images courtesy of H3X) H3X is meeting the challenge of maximising continuous power output against high operating temperatures. Rory Jackson reports Power of three
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