What is Fuel Cell Aircraft: 11 Interesting Facts To Know

What is a Fuel Cell Aircraft ?

Hydrogen Fuel Cell Aircraft

Aviation industry has been extensively trying to go green in terms of fuel usage. Study and analysis are being extensively carried out to identify hydrogen as a viable alternative. Concept designs and models have been demonstrated by some of the top aviation companies, so it’s important that we update ourselves with their research. Let’s start with the terminology ‘Fuel Cell Aircraft’.

An aircraft that uses hydrogen fuel as a main source of energy is called fuel cell aircraft. Either jet engine or other type of internal combustion engine can burn hydrogens or use them to power a fuel cell to generate power for a propeller. In contrast to most aircraft which use fuel storage wings, hydrogen fuel cell aircraft are typically developed in the fuselage in hydrogen fuel tanks.

fuel cell aircraft
Fuel Cell Aircraft HY4; Image Source: DLR, CC-BY 3.0, HY4 2016-09-29 ueber Flughafen StuttgartCC BY 3.0 DE

What is Hydrogen Fuel Cell?

Hydrogen Fuel Cell

This is an important technology with potentiality that offers a range of industries, including automotive and heavy transmission, considerable energy efficiency and de-carbonization benefits. Today hydrogen petroleum technology is used for various purposes, which comprises providing emergency backup capacity for critical facilities like hospitals, replacing grid electricity for essential facilities of load such as data centres.

Can hydrogen fuel cells be used in planes? | Do airplanes use fuel cells ?

In the near future, everything from low-carbon urban areas to portable computers to future zero-emission fuel cell aircraft could potentially be powered. Different Research studies has shown that large commercial hydrogen fuel cell aircraft is practical to be built within 2020 . However, it will probably only be in service near the year 2030. The interest in using fuel cell aircraft as personal aircraft has grown in the near future.

In the European research project, the technical and mechanical feasibility, safety perspective, environmental compatibilities, and economic viabilities of the use of fluid Hydrogen (H2) as an aviation fuel were assessed in cooperation with Airbus, together with 33  partner organization contained in a fuel cell aircraft and dubbed as CRYOPLANE, a detail report was published in the year 2003.

How did Hydrogen Fuel Cell come into existence?

History of Hydrogen fuel Cell

Sir William Grove, a judge-turned-scientist, devised a unique idea in 1838: to build a cell with two independent sealed compartments, each fueled by hydrogen or oxygen gas. He named his device a “gas voltaic battery” at the time. Regrettably, it did not generate enough electricity to be useful. After some time, English engineer Francis Thomas Bacon grew interested in it and, in 1932, created the world’s first hydrogen-oxygen fuel cell to make it a reality, which is used today to build the concept of the fuel cell aircraft. Bacon’s fuel cell became a success in the space industry, where it was used to power satellites and rockets for space exploration operations such as Apollo 11.

In February 1957, a NACA Martin B-57B was experimented and flown for 20 minutes on hydrogen instead of jet fuel for one of its two Wright J65 engines. The Tu-155, an upgraded Tu-154 airliner, flew for the first time on April 15, 1988, as the first hydrogen-powered experimental fuel cell aircraft.

Boeing Hydrogen Fuel Cell Aircraft | Boeing Fuel Cell Aircraft

Boeing produced and operated the world’s first hydrogen-powered aircraft in 2008. During takeoff and climb, the single-person plane’s fuel cells were augmented with electricity from lithium-ion batteries. The Phantom Eye (meant to perform four-day reconnaissance missions at the height of 20,000 meters), a liquid-hydrogen-powered unmanned aerial vehicle, was unveiled four years later. However, Boeing could not sell the UAV to the military, and it is now on exhibited in a museum only as a liquid-hydrogen-powered aerial vehicle.

aircraft fuel cells bladders

Why aren’t fuel cells replacing jet engines?

The use of hydrogen as an aircraft fuel has been shown by Boeing through its concept of Phantom Eye. However, according to Mike Sinnett (VP, Product Development, Boeing Aviation) commented that additional research is needed to evaluate the factor safety for an aircraft’s structure and fuel tanks to function as securely as today’s airliners.

So this imply that the hydrogen fuel will not be employed in Boeing fuel cell aircraft for more than two decades from now, and that engines for aircraft a decade from now are already being built.

Development of Phantom Eye

The Phantom Eye developed Boeing’s previous achievement with the piston-powered Boeing Condor, which established multiple altitudes and endurance records in the late 1980s. Boeing also worked on the Phantom Ray UAV as a flying test bed for innovative technologies, as well as a larger HALE unmanned aerial vehicle that can fly for over ten days and carry payloads of 900 kilogram or more.

The Phantom Eye’s propulsion system (Designed in connection with the propulsion system and the air frame) passed an 80-hour altitude chamber test on March 1, 2010.  The Ball Aerospace, Aurora Flight Sciences, Ford Motor Company, and MAHLE Power train collaborated together in technological advancement to create the Phantom Eye, finally unveiled on July 12th, 2010.

Darryl Davis, the head of Boeing’s Phantom Works advanced ideas section, believes that ‘Phantom Eye demonstrator ’ is a 60-70 % accurate scale model of an objective system.  With as few as four planes, the Phantom Eye prototype might lead to an objective system capable of providing year-round coverage of a large area.

How will Hydrogen Fuel Cell work?

A conventional hydrogen fuel cell for a fuel cell aircraft is made up of two electrodes (an anode and a cathode) detached by an electrolytic membrane. This functions as follows:

  1. Hydrogen steps in the fuel cell through the anode. Electrons and protons are formed through division of Hydrogen atoms, owing to their reaction with a catalyst. The cathode, on the other hand, allows oxygen from the adjacent air to enter.
  2. The positively charged protons travel to the cathode through the permeable electrolyte membrane. The negatively charged electron exit from the cell, providing a current that capable to power an electric or hybrid electric propulsion system.
  3. Protons and oxygen combine in the cathode to form water.

Properties of Hydrogen

The specific energy of hydrogen is three times that of ordinary jet fuel, although it has a lower energy density. Carbon fibre tanks, which can withstand a pressure of 700 bar, are utilized in aircraft. It’s also possible to employ cryogenic liquid hydrogen.

Suppose hydrogen is readily available from low-carbon energy source like wind or nuclear. In that case, it will emit fewer greenhouse gases, which includes water vapour and a small amount of nitrogen oxide in aircraft than in existing cases. Presently, only a small amount of H2 is produced using low-carbon energy source, and there are different significant obstruction to hydrogen’s use in air-crafts. The Hydrogen is more expensive than fossil fuels owing to its production method and its relative inefficiencies using current technologies.

The LH2 is one of the most effective engineering coolants. It has been proposed to cool in take air for very fast aircraft or even the aircraft’s skin itself, especially for the scram jet aircrafts.

Weight and Energy Density

Whether in gaseous or liquid form, the extra weight necessary for fuel storage is the main hurdle to hydrogen-powered flight in fuel cell aircraft. Making lightweight vacuum-insulated tanks that keep liquid hydrogen below its boiling point of 20 Kelvin will be the issue for liquid hydrogen. Because the tanks must endure high pressures of 250 to 350 bar, gas has a higher weight penalty.

The energy density of liquid hydrogen is 2.8 times that of aviation gasoline. However, according to Argonne National Laboratory, aviation fuel outperforms hydrogen by a factor of 1.6 in terms of combined fuel and tank weight. Unlike aviation fuel, which makes up roughly 78% of the overall weight of the tank and fuel, liquid hydrogen only makes up 18% of the total weight in modern storage systems. It is claimed that the fuel weight fraction must reach at least 28% to compete with fossil fuels. Liquid hydrogen has a lot lower energy per unit volume than hydrocarbons.

Energy density of fuels – horizontal per mass, vertical per volume; Image Source: Scott DialEnergy density, marked as public domain, more details on Wikimedia Commons

However, according to Phillip Ansell, director of the University of Illinois at Urbana-NASA-funded Champaign’s Center for High-Efficiency Electrical Technologies for Aircraft, Different parts of the aircraft like the wings and the fuselage can be modified individually or collectively to counter the increase in aerodynamic drag, resulting from the extra external surface required to accommodate larger hydrogen tanks.

Advantages of Hydrogen Fuel Cell

Fuel cells (that utilize pure hydrogen, hence carbon-free ), are a clean source of energy since they produce electricity thru an electro chemical reaction.  The following are some more important benefits of fuel cells:

  1. Fuel cells, unlike batteries, do not require recharging and can continue to create energy as long as a fuel source (hydrogen) is available.
  2. Individual fuel cells can be “stacked” to create bigger systems that can generate more power, allowing for scalability. Fuel cell stacks can be coupled to form large-scale, multi-megawatt systems, while a single fuel cell capable to generate sufficient electricity to empower specified application.
  3. Fuel cells are quiet and dependable since they have no moving parts.

Is hydrogen a viable fuel for aircraft?

Three unique concepts have been brought into existence by Airbus for hydrogen fuel cell aircraft that can carry up to 200 passengers and cover a range closing to 2000 nautical miles (3700 kilometres). Each one of them comprises of a conceptual hybrid system containing combustion turbines and fuel cell driven motors. In a turboelectric system, a hydrogen-fueled gas turbine powers an electric generator, while an electric motor drives the fan.

Airbus plans to power its future long-range 300 to 400-seater airliners using synthetic fuels derived from renewable sources rather than hydrogen. Adapting hydrogen to planes that will be emptied and replenished numerous times a day will be a new challenge for the corporation, even if it is already experienced with the fuel in aerospace applications.

Aircraft Fuel Cell Repair | Aircraft Fuel Cell Maintenance

The presence of fuel spilling on the aircraft’s bottom is usually the first sign of a leak. While looking for the source of the leak, it is necessary to note that fuel might travel quite a distance before reaching an exit location. It can be difficult to pinpoint the source of the leak as a result of this. One must follow the leak path before catering to any suspicion, without assuming that the leaking fuel cell is in close proximity to the visible leak.

Leaks should be checked in the connections, hoses, and vent regions. It’s also worth noting that just because a fuel cell is leaking doesn’t give rise to the necessity of replacement.  On a fuel cell, there are some leaks that can be repaired like:

  1. Hose clamps are too loose
  2. The screws on the transmitter are loose.
  3. Faulty gaskets
  4. Bolts with a loose plate or a filler neck
  5. The filler neck or tubing has cracks in it.

Double clamping fuel cell connections avoid leaks in older cells, but it’s also useful for newer cells with big interconnects. The rubber will settle after the clamps are tightened. As a result, an hour after the initial installation, it’s a good idea to re-tighten all of the clamps.

Aircraft Fuel Cell Tape

Examine the region around the fuel cell bay for corrosion loss. Remove any remaining tape and residue. MEK can be used to remove tape residue easily. Remove all FOD, particularly metal shavings, which can quickly damage a newly installed fuel cell.

Make careful to use fuel cell tape while taping the liner. Suitability of duct tape or electrical tape does not justify the substitution of fuel cell tape. The tape and adhesive utilized in fuel cell are remarkably intact during the event of a fuelspill, in this situation, duct tape, electric tape, and other tapes will not work.

All rivets and edges should be taped with fuel cell tape. Working with short sections of tape (about 6-inches long) is usually easier than working with long sections, particularly true if taping are in difficult to reach regions blindly. In challenging places, a mirror might also help you see what you’re doing.

Aircraft Fuel Cell Cleaner

Scrub off any remaining fuel from the fuel cell before packing for the shipment. The fuel cell should be cleaned using warm water and liquid dish soap, according to Hartwig Aircraft Fuel Cell Repair. The cleaning and drying process must be followed by folding and packing of the cell for the shipment to the repair facilities. Before shipping, some mechanics add an oil film to the cell to preserve the cell. Eagle Fuel Cells strongly advises against doing so, stating that it is not required to coat the cell with oil at the expense of additional labour.

Aircraft Fuel Cell Welding | Aircraft Aluminum Fuel Cell Welding

The common oxy-fuel torch (oxy-fuel welding or OFW) has been an important mainstay in the aluminium joining process. In the 1850s, oxy-hydrogen created by electrolysis was used to flame weld metals with low melting points, such as gold, silver, copper, and platinum. The discovery of acetylene is noteworthy because it was linked to the hunt for a new method of making aluminium metal.

In the aircraft industry, oxy-hydrogen is more commonly linked with OFW than oxy-acetylene, but not because of any technical benefit. Acetylene was rationed expressly for shipyard usage due to wartime economics, leaving hydrogen as the only alternative. Because mixing acetylene leftovers with hydrogen gas can result in a accidental disaster, using hydrogen as fuel demands a whole separate tank, regulator, hose, and torch.

Furthermore, hydrogen does not produce soot, which might be useful as a temperature indicator during the annealing of aluminium sheet. Fuel production costs (with feasible electrolysis facility) and a somewhat cleaner weld zone appearance (because of the absence of carbon in the flame region) maybe advantages of hydrogen.

What is the shelf life of fuel cell ?

Aircraft Fuel Cell Shelf Life

The majority of airplanes in use today have outlived their intended design lives. Many of these planes have undergone one or more changes to the airframe or avionics. The service life of a fuel cell, on the other hand, is frequently overlooked because it is not included in numerous government papers, aircraft manuals, or aircraft TOs.

The crucial varying factors amongst fleets comprise of the flight hours, environmental conditions, and removal and reinstallation cycles. As a result, predicting a fuel cell’s service life is impossible. Remanufactured, refurbished, or overhauled fuel cells are not possible. The depiction of fuel cells like such is erroneous.

However, we can say that any fuel cell that is more than 15 years old in a fuel cell aircraft should be evaluated for replacement. This is especially crucial if the aircraft is undergoing any major modifications that necessitate the removal of the cell. It should be emphasized that, depending on the aircraft program, US forces have concluded that the typical service life should be 10 to 12 years. In general, extensive repairs on any fuel cell that is older than 12 years and expected to remain in service for more than 12 months are a waste of money.

What is the future fuel for airplanes?

Emerging aviation fuel

The benefits of hydrogen have recently come to light, and the airline industry is taking notice. According to Fymat, Airbus wants to produce the world’s 1st  zero emission commercialized aeroplane by 2035.

According to sources, ZeroAvia, a US-based firm, wants to produce a hydrogen fuel cell aircraft for approximately 20 passengers by 2024. It has already secured $5 million in subsidies from three UK government programmes and has successfully attracted the interest of 12 regional carriers from the United Kingdom, the United States, and the European Union.

Now that you have learnt about hydrogen as a prospective aviation fuel, navigate to learn about the storage system of the fuel- Aircraft Fuel Tank System.

Esha Chakraborty

I have a background in Aerospace Engineering, currently working towards the application of Robotics in the Defense and the Space Science Industry. I am a continuous learner and my passion for creative arts keeps me inclined towards designing novel engineering concepts. With robots substituting almost all human actions in the future, I like to bring to my readers the foundational aspects of the subject in an easy yet informative manner. I also like to keep updated with the advancements in the aerospace industry simultaneously. Connect with me with LinkedIn - http://linkedin.com/in/eshachakraborty93

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