Despite ongoing efforts to curb CO₂ emissions with electric and hybrid vehicles, other forms of transportation remain significant contributors of greenhouse gases. To address this issue, old technologies are being revamped to make them greener, such as the reintroduction of sailing vessels in shipping and new uses for hydrogen in aviation. Now, researchers reporting in ACS Sustainable Chemistry & Engineering have used computer modeling to study the feasibility and challenges of hydrogen-powered aviation.
尽管通过电动车和混合动力车持续努力遏制二氧化碳排放，其他交通形式仍是温室气体的重要来源。为解决这一问题，旧技术正被改造以更环保，例如航运中帆船的重新引入和航空中氢能的新应用。如今，研究人员在《ACS可持续化学与工程》中报告称，他们利用计算机建模研究了氢能航空的可行性与挑战。

"While there is a long way to go for hydrogen aviation to be realized at scale, we hope that our analysis of both onboard system design and enabling infrastructure will be used to prioritize development efforts," says Dharik Mallapragada, one of the study's coauthors.
“虽然实现氢能航空规模化应用还有很长的路要走，但我们希望这项关于机载系统设计与配套基础设施的研究分析能帮助明确研发优先级，”该研究的合著者之一Dharik Mallapragada表示。

The aviation industry's energy-related CO₂ emissions have grown faster than those of rail, road and shipping in recent decades, according to the International Energy Agency. To reduce the potential climate impacts of this growth, scientists are improving aircraft design and operation, and developing low-emission fuels such as hydrogen, which is used for direct combustion or to power electric fuel cells. Hydrogen's appeal as a fuel source is that its use produces no CO₂ and provides more energy per pound than jet fuel. To understand the potential impact of switching from traditional jet fuel to hydrogen fuel in aviation, Anna Cybulsky, Mallapragada and colleagues modeled its use in the electrification of regional and short-range turboprop aircraft.
国际能源署的数据显示，近几十年来，航空业能源相关的二氧化碳排放量增速快于铁路、公路和Ship行业。为减少这一增长对气候的潜在影响，科学家们正改进飞机设计与运营，并开发氢等低排放燃料——氢既可用于直接燃烧，也能为电动燃料电池供能。氢作为Gas源的吸引力在于其使用时不产生二氧化碳，且每磅提供的能量高于航空燃油。为了理解从传统航空燃油转向氢燃料在航空领域的潜在影响，Anna Cybulsky、Mallapragada及其同事模拟了氢燃料在区域性和短程涡轮螺旋桨飞机电气化中的应用。

The researchers calculated that the extra bulk of a hydrogen fuel tank and fuel cells retrofitted to an existing plane would need to be offset by weight reductions elsewhere, such as reducing the aircraft's payload (cargo or passengers). This could mean that more flights would be needed to deliver the same payload. The team's model suggested, however, that improvements in fuel cell power and the fuel system's gravimetric index (the weight of the fuel in relation to the weight of the full fuel tank) could eliminate the need to reduce payload, thus eliminating the environmental impact of additional flights. At the same time, they noted that shifting to hydrogen-powered flight may reduce the aviation industry's CO₂ emissions by up to 90%.
研究人员计算出，对现有飞机进行改装，加装氢燃料箱和燃料电池所增加的重量需要通过减少其他地方的重量来抵消，比如减少飞机的有效载荷（货物或乘客）。这可能意味着需要更多航班才能运送相同的有效载荷。然而，该团队的模型表明，燃料电池功率和燃料系统重量指数（燃料重量与满燃料箱重量之比）的提升可消除减少有效载荷的需求，从而避免额外航班对环境的影响。与此同时，他们指出转向氢动力飞行或能使航空业的二氧化碳排放量减少高达90%。

A bigger challenge than switching aviation fuel types may be providing the infrastructure needed to generate and distribute hydrogen in a low-carbon and cost-effective manner. One low-carbon production method uses natural gas reforming (extracting hydrogen from methane gas) coupled with carbon capture, but it requires access to CO₂ infrastructure and sequestration sites. Another green option is electrolysis, which splits water into hydrogen and oxygen, and could be done by using electricity from a nuclear plant or renewable resources. But this would add substantial demand to electrical grids. Cybulsky and colleagues noted that because grid electricity prices can be highly variable across a region, it may be more cost-effective to transport hydrogen from a low-cost production facility to end-users.
比起改用航空燃料类型，更大的挑战或许是以低碳且经济高效的方式提供生产和分配氢气所需的基础设施。一种低碳生产方法采用天然气重整（从甲烷中提取氢气）结合碳捕集技术，但这种方法需要配套的CO₂基础设施和封存场地。另一种绿色选择是电解法——通过核电站或可再生能源提供的电力将水分解为氢气和氧气。但这将给电网带来巨大的需求压力。Cybulsky及其同事指出，由于电网电价在一个地区内可能差异很大，将氢气从低成本生产设施运输到终端用户可能更具成本效益。

For these reasons, the researchers suggest that the rollout of hydrogen-based aviation might start at locations that have favorable conditions for hydrogen production, such as Hamburg, Germany, or Barcelona, Spain. The infrastructure required to support hydrogen use in aviation would also benefit decarbonization efforts in other industries, including road transportation and shipping, by making hydrogen fuel more available.
基于这些原因，研究人员建议，氢动力航空的推广可以从具备有利制氢条件的地区开始，例如德国汉堡或西班牙巴塞罗那。支持航空业使用氢燃料所需的基础设施还将通过提高氢燃料的普及度，助力公路运输和Shipping等其他行业的脱碳进程。

The authors acknowledge funding from the Massachusetts Institute of Technology Energy Initiative Low-Carbon Energy Centers for Energy Storage and Future Energy Systems Center.
作者感谢麻省理工学院能源倡议低碳能源中心（能源存储与未来能源系统中心）提供的资金支持。