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Introduction
As the world strives to reduce its carbon footprint and transition towards more sustainable energy solutions, the aviation industry faces a significant challenge. Aircraft have long been notorious for their substantial greenhouse gas emissions. However, recent advancements in hydrogen fuel cell technology have ignited a glimmer of hope for electric flight. From small drones to commercial aircraft, hydrogen fuel cells are emerging as a promising alternative to traditional fossil fuel-powered aviation. In this article, we will explore the progress of hydrogen fuel cell technology and its potential to revolutionize the future of air travel.
The jet engine in all its variations has revolutionized air travel, but with airline profit margins running wafer-thin in these ecologically conscious times, there’s a lot of interest in moving away from aircraft powered by fossil fuels and toward emission-free electric propulsion systems that aren’t dependent on petroleum and its volatile prices.
As the need to reduce gas emissions, optimize aircraft performance, and decrease operating and maintenance costs becomes more urgent, the industry is progressing towards more electric aircraft (MEA) and ultimately an All-Electric Aircraft. These electric systems offer higher efficiency and better reliability compared to conventional combustion engines, with no greenhouse gas emissions, and low noise and vibration.
Numerous airlines made strides towards reducing carbon emissions and investing in next generation air transportation technologies in 2021. Several airlines, including Virgin Atlantic, GOL, and Japan Airlines have pre-ordered electric vertical take-off and landing (eVTOL) vehicles from the company Vertical Aerospace.
Fuel cells have gained considerable attention as a potential power source for aircraft. Unlike traditional internal combustion engines, which burn fossil fuels to generate power, fuel cells produce electricity through a chemical reaction between hydrogen and oxygen, with the only byproduct being water. This makes them an attractive option for aircraft, as they have the potential to drastically reduce emissions and noise levels. However, implementing fuel cells in aircraft requires overcoming significant technological and logistical challenges, such as developing lightweight and efficient fuel cell systems and establishing a reliable hydrogen supply chain. Despite these challenges, ongoing research and development efforts are paving the way for the adoption of fuel cells in the aviation industry.
United Airlines, has invested in electric aircraft startup Heart Aerospace and ZeroAvia, the hydrogen-electric aircraft engine company. The agreement brings the total investment in ZeroAvia up to $115 million, and it also includes a provision for United to purchase up to 100 of ZeroAvia’s hydrogen-electric engines.
Dan Steingart, an associate professor of chemical metallurgy at Columbia University, explained that “in a single hydrogen molecule, there is somewhere between one-fourth and one-eighth the total energy available in a single typical jet fuel molecule.” So, for the same amount of fuel, “planes would go one-fourth the distance.”
Obviously, that’s not ideal. So large aircraft meant to go any substantial distance would need much larger fuel tanks. And those tanks would need to be frozen to minus 420 degrees Fahrenheit — close to absolute zero — to liquefy the hydrogen. That is almost as cold as anything in the universe can get.
In today’s planes, wings are where the fuel is stored, and they are in no way large enough to store the hydrogen that would be needed for a long flight. “Yes, as far as hydrogen-powered, the planes will definitely look different,” said Bhupendra Khandelwal, an associate professor at the University of Alabama. So the hydrogen planes of the future could have extra-large fuselages, but more likely they will be what’s called blended wing, in which the planes are shaped like large triangles. This would allow them to store more fuel, “but also reduce fuel consumption to make the aircraft aerodynamics even better,” Khandelwal said.
It’ll be sometime in the 2030s that the cost of hydrogen becomes comparable to jet fuel, according to ICF, and the infrastructure to help make that happen would probably develop outside of aviation, said Eliot Lees, ICF’s vice president for clean transportation. “What you’ll see is the infrastructure for hydrogen becoming important for the on-road fleet of heavy- and medium-duty trucks, and from there it will make its way into aviation.”
Airbus has announced plans for the world’s first zero-emission commercial aircraft models that run on hydrogen and said they could be flying by 2035. Boeing, meanwhile, has done several tests of hydrogen-powered aircraft — both manned and unmanned.
For in depth understanding on Fuel cells technology and applications please visit: Fuel Cells 101: An Introduction to the Basics of Fuel Cell Technology
Fuel cells for Aircraft and UAV missions
Propulsion systems are essential for Aircraft and UAV missions, providing them the necessary power to propel them for forward flight or hover. The flight time or endurance of a UAV is influenced by the propulsion technology used, the aerodynamic design, and the amount of fuel carried. To meet the energy requirements of a large variety of UAVs, market players have designed several variants of piston engines and electric motors. Electric propulsion is also gaining interest in UAVs as they are increasingly employed by various industries, including Defense and Security missions.
Electric propulsion can be powered by rechargeable batteries, fuel cells, or solar energy. While newer research promises the possibility of higher energy densities, typically lithium-ion batteries in use today have a maximum energy density of around 1,000,000 joules of energy per kilogram. In comparison, aviation fuel has a density of 43 million joules per kilogram. Therefore, swapping fuel tanks for a battery weighing 43 times as much is not a viable option. Solving this storage problem is essential before electricity can power large aircraft over long distances.
A fuel cell is a device that generates electricity through a chemical reaction, converting hydrogen and oxygen into water and producing electricity. Fuel cells are environment friendly, as they don’t produce pollutants or greenhouse gases, and provide high energy efficiency (up to 80% when generating both heat and electricity). They are scalable and can readily be combined with other energy technologies, such as batteries, wind turbines, solar panels, and super-capacitors.
Hydrogen fuel cells have a broad range of applications such as cars, buildings, electronic devices, trucks, backup power systems, telecommunication towers, data centers, emergency response systems, hospitals, and military applications.
Benefits of fuelling drones with Hydrogen
Hydrogen fuel cells are demonstrated as the propulsion system for long-endurance, small, electric unmanned air vehicles (UAVs). UAVs are typically used for military operations where manned flights would be too risky or difficult. They send back real-time imagery of activities on the ground and are usually powered by batteries that last up to 30 minutes before needing to recharge. Hydrogen fuel cells can increase UAV airtime to approximately eight hours and can be refueled in less than 15 minutes. Additionally, fuel cell-powered UAVs require less maintenance and no lubricants due to the absence of moving parts.
There are several benefits to using hydrogen as an energy source for drones. Firstly, hydrogen is a clean energy source that won’t produce acid rain, deplete the ozone, or produce harmful emissions. When converted to energy, it only has one byproduct: water, making it an incredibly clean fuel source.
Secondly, hydrogen is the most abundant resource on Earth, and throughout the entire Universe, ensuring its availability for future use. Even on Mars hydrogen is still the most abundant resource.
Thirdly, fuel cells have a higher energy density than batteries, producing more energy for their weight. This means a hydrogen tank attached to a drone will generate more energy than a Lithium powered (LiPo) battery of the same weight.
Fourthly, hydrogen fuel cells enable longer flight times than traditional batteries, already demonstrated up to two and a half hours. In comparison, most LiPo-powered drones have a maximum flight time of 25-30 minutes. Fifthly, hydrogen fuel cells refuel quickly, taking only a few minutes to complete.
Finally, hydrogen-fueled drones function well in low temperatures, expanding their use in northern and southern latitudes. Hydrogen fuel cells require the constant presence of oxygen but are not affected by low temperatures. The ability to function in low temperatures will open up new applications for drones.
Since hydrogen-fueled drones have longer-flight times and can operate in lower temperatures, they’re more reliable for beyond-visual-line-of-sight (BVLOS) flights. However, changes in regulation around BVLOS flights will need to occur first before we reap the full benefits of hydrogen-fueled drones.
For deeper understanding of Fuel cell technology in Aviation please visit: Fuel Cell Hydrogen Revolution in Aviation: From Drones to Commercial Aircraft
Towards Commercial Aviation: Hurdles and Hope
The real game-changer for hydrogen fuel cells lies in their application to commercial aviation. While small drones, regional aircraft, and eVTOLs demonstrate the feasibility of the technology, commercial aircraft present unique challenges. Larger airplanes demand significantly higher power output and energy storage capacity to sustain long-haul flights. Additionally, the weight and size of hydrogen storage systems remain critical obstacles to overcome.
Despite these hurdles, researchers and industry leaders remain optimistic. Advancements in lightweight materials and innovative hydrogen storage solutions, such as cryogenic or solid-state hydrogen storage, are being explored. Moreover, collaborative efforts between aviation stakeholders, governments, and fuel cell manufacturers are accelerating the pace of development.
Cryogenic High-Efficiency Electrical Technologies for Aircraft (CHEETA) project
The University of Illinois has announced that NASA is underwriting a project to develop a cryogenic hydrogen fuel cell system for powering all-electric aircraft. Funded by a three-year, US$6 million contract, the Center for Cryogenic High-Efficiency Electrical Technologies for Aircraft (CHEETA) will investigate the technology needed to produce a practical all-electric design to replace conventional fossil fuel propulsion systems.
The CHEETA project is a consortium of eight institutions that include the Air Force Research Laboratory, Boeing Research and Technology, General Electric Global Research, Ohio State University, Massachusetts Institute of Technology, the University of Arkansas, the University of Dayton Research Institute, and Rensselaer Polytechnic Institute. Although the project is still in its conceptual stage, the researchers have a firm vision of the technology and its potential.
“Essentially, the program focuses on the development of a fully electric aircraft platform that uses cryogenic liquid hydrogen as an energy storage method,” says Phillip Ansell, assistant professor in the Department of Aerospace Engineering at Urbana-Champaign who is the project’s principal investigator. “The hydrogen chemical energy is converted to electrical energy through a series of fuel cells, which drive the ultra-efficient electric propulsion system.
The low temperature requirements of the hydrogen system also provide opportunities to use superconducting, or lossless, energy transmission and high-power motor systems. “It’s similar to how MRIs work, magnetic resonance imaging. However, these necessary electrical drivetrain systems do not yet exist, and the methods for integrating electrically driven propulsion technologies into an aircraft platform have not yet been effectively established. This program seeks to address this gap and make foundational contributions in technologies that will enable fully electric aircraft of the future.”
World’s First Hydrogen-Electric Passenger Aircraft: Element One, unveiled in 2018
Singapore’s HES Energy Systems developed Element One, the world’s first regional hydrogen-electric passenger aircraft. The ultra-light Element One can take up to four passengers and is envisioned for fully autonomous flying. Element One is designed to fly 4 passengers for 500 km to 5000 km depending on whether hydrogen is stored in gaseous or liquid form. This performance is several orders of magnitude better than any battery-electric aircraft attempt so far, opening new aerial routes between smaller towns and rural areas using an existing and dense network of small-scale airports and aerodromes. HES Energy Systems said that it worked on the project for 12 years and intends to build the first flying prototype before 2025.
Designed as a zero-emissions aircraft, Element One merges HES’ ultra-light hydrogen fuel cell technologies with a distributed electric aircraft propulsion design. With virtually no change to its current drone-scale systems, HES’ distributed system allows for modularity and increased safety through multiple system redundancies.
Fuel cell demonstration on UAVs
Flight times of >24 hours have been demonstrated for the 35-lb Ion Tiger fuel cell UAV while carrying a 5-lb payload. The promise of hydrogen-electric power could shape the future of aviation. “It’s now possible to break past the endurance limits of battery-electric flight using HES’ ultra-light hydrogen energy storage in a distributed propulsion arrangement,” says Taras Wankewycz, founder of HES. “Element One’s design paves the way for renewable hydrogen as a long-range fuel for electric aviation.”
At InterDrone exhibition in Las Vegas, two FCHEA member companies showcased hydrogen fuel cell power packs for commercial UAVs. Doosan Mobility Innovation’s fuel cell powerpack is refueled using a single, detachable hydrogen container, and the powerpack can keep UAVs flying for two hours on a single charge of hydrogen.
Intelligent Energy’s new 800W Fuel Cell Power Module (FCPM) was shown with the company’s 650W model, which was unveiled at the 2017 InterDrone exhibition. The 800W FCPM is 10% more power dense than the 650W model, and multicopter UAVs will be able to carry one kilogram of cargo for two hours, or two kilograms for one hour. Intelligent Energy will also work with customers who have the capability to combine two of the 800W models to provide 1.6 kW of continuous power building on the success and interest in UAVs, FCHEA member Alakai Technologies is going one step further, developing a hydrogen fuel cell-powered, four-passenger, long-duration, all-electric vertical takeoff and landing (eVTOL) aircraft in 2019.
Boeing’s Insitu advances its fuel cell technology; LH2 fueling, reported in March 2021
Insitu, a subsidiary of Boeing, is making significant advancements in hydrogen fuel-cell propulsion for Unmanned Aerial Vehicles (UAVs). In December 2020, Insitu successfully completed the first flight of the ScanEagle3 UAV powered by an all-electric, hydrogen-fueled, PEM fuel cell, confirming its performance characteristics. Now, the company is preparing for test flights using a 3D-printed Liquid Hydrogen (LH2) storage tank on the aircraft, which is expected to provide 10+ hours of endurance for ScanEagle3.
The Liquid Hydrogen (LH2) flight tank has undergone successful testing for liquid hydrogen fill, pressure, and vapor generation at Washington State University’s Hydrogen Properties for Energy Research (HyPER) Lab. These tests verify the operation performance metrics of the LH2 tank, leading up to the upcoming flights of ScanEagle3 equipped with a PEM fuel cell power system.
The defense industry is increasingly interested in the benefits of hydrogen fuel cell technology due to its environmental and operational advantages. PEM fuel cell stack emissions are minimal, with only small amounts of water and trace amounts of hydrogen produced. Additionally, the thermal and acoustic signatures of fuel cells and electric motors are much lower than traditional internal combustion engines, allowing for missions closer to targets. The combination of PEM fuel cells and electric motors also reduces platform vibration and enables greater payload diversity. Fuel cells offer improved reliability and lower logistics costs compared to small internal combustion engine propulsion solutions.
ZeroAvia says it has achieved record-breaking performance while testing the high-temperature proton exchange membrane (HTPEM) systems in its hydrogen fuel cells.
Hydrogen-electric aircraft propulsion developer, ZeroAvia, has achieved groundbreaking results in testing its high-temperature proton exchange membrane (HTPEM) systems in hydrogen fuel cells. The pressurized, 20-kilowatt HTPEM fuel cell stack demonstrated a specific power level of 2.5 kW/kg at the cell level, and ZeroAvia anticipates reaching power densities exceeding 3 kW/kg in the next two years. This advancement makes hydrogen fuel cells powerful enough to enable electric propulsion systems for larger aircraft like the Boeing 737 and Airbus A320 families.
Earlier this year, ZeroAvia successfully conducted the first flight test of a 19-seat Dornier 228 regional airliner retrofitted with one of its hydrogen propulsion systems. The company acquired HyPoint, a hydrogen fuel cell systems developer, with plans to integrate the turbo-air-cooled HTPEM fuel cells into its propulsion systems. The HTPEM fuel cells, capable of operating at up to 200 degrees Celsius (392 degrees Fahrenheit), are ideal for powering ZeroAvia’s ZA2000 powertrain for 40- to 80-seat aircraft and could enable new electric propulsion systems for eVTOL aircraft and rotorcraft.
Traditional low-temperature PEM fuel cells have limitations at higher temperatures, making HTPEMs more suitable for transportation applications. HTPEMs are also expected to have a life cycle of 20,000 hours or about four times longer than that of LTPEMs. With these advancements, ZeroAvia aims to deliver zero-emission flight across various aircraft categories, offering hydrogen-electric powertrains for retrofits and future aircraft designs.
ZeroAvia has received provisional order commitments for approximately 1,500 of its hydrogen propulsion systems, with a significant portion intended for aircraft with up to 19 passenger seats. The company plans to start accepting deposits for delivery slots soon.
As hydrogen fuel cell technology continues to advance and become more accessible, we can expect to witness the integration of hydrogen fuel cells in various aircraft, further contributing to sustainable aviation solutions.
Conclusion
From the humble beginnings of hydrogen-powered drones to the promising advancements in eVTOLs and regional aircraft, hydrogen fuel cell technology has come a long way in revolutionizing electric flight. They have become a promising solution for powering UAVs, providing longer airtime, faster refueling, and a cleaner energy source than traditional batteries
While hurdles remain for its widespread application in commercial aviation, the industry’s determination and the world’s growing focus on sustainability provide a strong impetus for continued research and development.
As technology progresses, we can envision a future where hydrogen-powered commercial aircraft take to the skies, enabling eco-friendly air travel and ushering in a new era of sustainable aviation. With collective efforts, the aviation industry can soar towards a cleaner, greener, and more responsible future in the skies.
References and Resources also include:
https://newatlas.com/nasa-cheeta-funding-aircraft-fuel-cell/59725/
https://uavcoach.com/hydrogen-drone/
https://www.marketplace.org/2021/10/28/how-close-are-hydrogen-planes-really/
