Tag: Hydrogen

The Revolutionary Role of Hydrogen

Hydrogen has a history with aviation. What could be better. A gas that is so light. So easily produced and with no need heat it up. With a lightweight gas-tight bag and a fair amount of rope, balloon construction took-off. Literally. The proof that hydrogen gas could lift a balloon goes back to the 1780s in France.

Sadly, the downside of this gaseous element is its propensity to combine with other elements. In fact, where would we be without liquid water. On this planet, that most basic and prolific combination of hydrogen and oxygen. Not so much sadly but more luckily.

Step forward about 250 years and we have a different vision for hydrogen in aviation. If it’s combined with the oxygen in the air that we breath, we get nothing more noxious than water. Since, the other forms of combustion, that populate our everyday lives, is distinctly noxious, surely hydrogen has a lot to offer. Talk about downsides. Burning fossil fuels is distinctly unsustainable. Polluting the atmosphere.

This week, I was looking out to sea. At the English Channel (No name changes there, I see). Standing on the pebble beach at Budleigh Salterton. They ought to have an award just for that name. It’s a small seaside town in Devon. The towns cliffs are part of a World Heritage Site, namely The Jurassic Coast[1]. 

Forget the 250 years of humans flying, cited above. About 185 million years of the Earth’s history is for all to see on the Devon and Dorset coast. When we say “fossil fuels” what we mean is that we are living off the back of Earth’s history. Society powers modern life on dinosaur juice. Well, not exactly but plant and animal life from hundreds of millions of years ago. How crazy is that?

Hydrogen, on the other hand, is one of the most abundant elements. It’s everywhere.

Modern day dinosaurs (politicians and pundits) insist that we continue to exploit dinosaur juice until it’s all gone. That’s putting aside any concerns about returning all that carbon to the Earth’s atmosphere. Carbon accumulated over millions of years.

Hydrogen can be a clean fuel. The problem is that saying that and then doing it are two different things. There are complexities that come with using Hydrogen as a fuel. It might be reasonably easy to produce, in multiple different ways, but it’s not so easy to transport.

Producing leak proof systems for transport and storage requires innovative thinking. We can’t just treat it with the familiarity of conventional fuels. Whole new regimes are going to be needed to get Hydrogen from where it’s produced to where it’s needed.

Producing leak proof systems for aircraft is a challenge. Given the odourless and invisible nature of this light gas, accurate and extensive detection systems are going to be needed. If the gas is to be consumed by fuel cells to produce electricity, then there’s going to be a constant struggle against complexity and significant expenditures.

What is reassuring is that none of the above is insolvable. At this time in history, we have the materials technology and control systems that make Hydrogen a viable clean fuel.

[1] https://jurassiccoast.org/

H2 Aircraft Design

Cards on the table. I’m a believer. Despite the immense technical challenges, Hydrogen is a viable fuel for future large civil aircraft. That said, operational service of such revolutionary aircraft isn’t going to happen in a hurry.

Reading the history, Concorde was an incredible test of the boundaries of what was possible and that was met, but it didn’t come easy. Breaking new ground is never easy. [A common saying that’s maybe open to challenge]. In aviation making step-changes happens every decade. What’s nearly always required is exceptional determination, almost beyond reason, large sums of money and special people.

Control systems – no big deal. Mechanical components – evolution possible. Turning a gaseous fuel into high-levels of propulsive thrust – can be done. Building a one-off technology proving research vehicle. It’s happening. At least for the light and commuter class of aircraft.

None of this is enough. Because the gap between an aircraft that can fly and an aircraft that can be produced in the thousands and go on to make an operational living and build an impressive safety and reliability reputation, that’s still a million miles off.

Today, there’s artist impressions of all sorts of different H2 aircraft configurations. It’s like people painted pictures of Mars with imaginary canals, long before anyone knew what the planet looked like in reality. Innovation starts with ideas and not all of them are sound.

As I expressed in my last article, crashworthiness must be given much consideration when speculating about future designs. It’s not always explicit in aircraft certification, cabin safety being the exception, but studying the history of accidents and incidents is essential. One of the successes of the authorities and industry working together is to take lessons learned seriously.

I remember looking at the pictures of the wreckage of Air France Flight 358, which crashed on landing in Toronto, Canada[1]. The fact that there were no fatalities from that accident is a testament to good operations and good design practices. The Airbus aircraft burned out but there was enough time for passengers and crew to get away.

My thought is what kind of H2 aircraft configurations would permit the same opportunity?

Considering this large aircraft accident, and others like it, then there’s a message as to where fuel tanks might best be placed. There’re some aircraft configurations that would have little hope of providing the opportunity for rapid evacuation of hundreds of people.

So, in my mind, don’t attached large pressurised cryogenic fuel tanks to the underbody structure of an aircraft fuselage. However robust the design and build of such fuel tanks they would be unlikely to survive as well as the cabin passenger seats, namely 9g[2]. That would not provide a good outcome post-accident.

Maybe, like aircraft engines sitting on pylons off the wings, that too is a good place for fuel tanks.

[1] https://asn.flightsafety.org/asndb/322361

[2] https://www.easa.europa.eu/sites/default/files/dfu/NPA%202013-20.pdf

Challenges of Hydrogen Fuel in Civil Aviation

This week has been a Hydrogen week. It’s great to learn more of the projects that are out there and the ambitions of those developing systems. Hydrogen is a live subject. Looking at the possible pathways for civil aviation to take there’s a myriad of choices. However, when it comes to the fuel for propulsion there are not so many potentials.

It’s surely the case that at some time in the future the use of fossil fuels to propel us across the skies will no longer be acceptable. Even if I’m talking to climate change sceptics the point must be made that fossil fuels are a limited resource. Not only that but the air quality around airports is a matter of concern.

It’s there in our basic education. Water is H2O. It’s that combination of Hydrogen and Oxygen that is essential to life on Earth. So, if we have a process that provides aircraft propulsion by using Hydrogen it should be a whole lot better for the environment than using Jet A1.

The problem is, and there’s always a problem, to carry enough Hydrogen it will need to be pressurised and in liquid form. That means extremely low temperatures, robust storage containers and extensive leak free plumbing.

Today, we have cars on the road that run on liquefied petroleum gas (LPG). It’s a novelty. It’s less harmful to the environment and can cost less. However, LPG systems need regular servicing. The point of mentioning this pressured gas in a transport system is that it has been integrated into regular everyday usage. That’s knowing that escape of even small quantities of the liquefied gas can give rise to large volumes of gas / air mixture and thus a considerable hazard[1].

Any analogy between the car and the aircraft can be forgotten. That said, one or two of the issues are similar. Yes, what happens when an escaped volume of gas / air mixture is ignited?

What scenarios would bring about conditions whereby a destructive explosion is possible?

Let’s start with the situations where aircraft accidents most often occur. Take-off and landing are those phases of flight. A surprising number of accident scenarios are survivable. The important part being to get an aircraft in trouble on the ground in such a way that an evacuation is possible. That can mean hitting the ground with a great deal of force[2].

Here’s the matter of concern. An aircraft with large cryogenic tanks and associated complex plumbing hits the ground at a force of many “g”. What then happens? Certainly, pressurised liquefied gas would escape. Being a very light gas, the uncontained Hydrogen would rise rapidly. However, trapped amounts of gas / air mixture would remain a hazard. Would that be ignited?

There are a lot of unknowns in my questions. Although there are unknowns, any post impact situation is likely to be very different from a situation with a conventionally fuelled aircraft.

Today’s, burn through requirements ensure that an external fuel fire is held back. Thereby ensuring enough time to evacuate. For a hydrogen aircraft ventilation may be essential to stop build-up of a gas / air mixture inside a fuselage. That means a whole different approach.

[1] https://youtu.be/AG4JwbK3-q0

[2] https://skybrary.aero/accidents-and-incidents/b772-london-heathrow-uk-2008

Hydrogen in Aviation

The potential for LH2 (liquid hydrogen) is enormous. That’s matched by the logistical and technical difficulties in exploiting this gas’s great potential. It offers energy for a means of propulsion that is nowhere near as environmentally damaging as existing means.

Society already integrates hazardous liquids and gases into everyday life. Each one has been through several iterations. It has been a rollercoaster. Each one has been at the root of disasters, at one time or another.

  • We use gas for cooking and heating in domestic settings. Periodically explosions demolish buildings. Leaks cannot be ignored. Harm can be done.
  • We use light and heavy oils widely in transport systems. Periodically intense fires burn vehicles. Care in handling is essential. Harm can be done.

Without having to say it, both above harm the environment. The search for non-CO2 emitting ways of flying is urgent. Here, I’m writing about harm to people. Physical harm. The business of aviation safety.

Often the physical harm is not associated with the design of the systems used but to the maintenance of those systems. Naturally, there was a learning curve. If we look at early versions of those systems, fatal accidents and incidents were far more regular. So, here’s the challenge for aviation. How do we skip the dangers of the early learning phase? How do we embed rigorous maintenance practices from day one? Big questions.

On the first one of these, lots of fine minds are engaged in putting together standards and practices that will address good design. If this works, and it will be tested extensively, the chance opens for introduction to service with a great deal of confidence that the main risks will be managed.

On the second of these, there’s not much happening. You might say there’s an element of chicken and egg. The shape and form of future LH2 systems needs much more work before we can think deeply about how they will be maintained.

I think that’s wrong. It’s old-fashioned thinking. As the industry has often practiced, making the systems first and then devising ways of maintaining them while in-service. That’s yesterday’s reasoning.

Making aviation system maintenance the Cinderella in the LH2 world is to invite failure. This is a situation where advancing the consideration of how the in-service realm could work, day by day, is necessary. It’s advantageous.

Here’s my reasons.

  1. There are generic approaches that can be tested without knowing the detailed design. That can take existing learning from other industries, like chemical and space industries, and consider their application in aviation.
  2. Emerging technologies, like machine learning, coupled with large scale modelling can provide ways of simulating the operational environment before it exists. Thereby rapidly testing maintenance practices in a safe way.
  3. It’s imperative to start early given the mountain that needs to be climbed. This is particularly true when it comes to education and training of engineers, flight crew, airport and logistics staff and even administrators.

Everyone wants to accelerate environmentally sustainable solutions. When they do get to be in-service, they will be there for decades. Thus, an investment, now, in study of maintenance systems will pay dividends in the longer term. Remember, early fatal accidents and incidents can kill otherwise sound projects or at least put them back on the drawing board for a long time.

NOTE 1: I didn’t mention Liquefied Petroleum Gas (LPG). It’s in the mix. Another CO2 contributor. LPG containers have pressure relief valves. LH2 containers will likely have pressure relief valves too. That said, venting LPG is a lot more environmentally damaging than LH2. From a safety perspective they can both create explosive conditions in confined spaces. Maintenance staff may not need to carry a canary in a cage, but they will certainly need to carry gas detectors when working on LH2 powered aircraft. Our noses will not do the job.

NOTE 2: Events on the subject: https://www.iata.org/en/events/all/iata-aviation-energy-forum/

https://events.farnboroughinternational.org/aerospace/sustainable-skies-world-summit-2024

2024 ICAO Symposium on Non-CO₂ Aviation Emissions