HYDROGEN AIR TRAVEL

D&T RESEARCH

The biggest alternative to traditional aviation being talked about is Hydrogen. It has the highest energy per mass of any fuel and doesn’t release any emissions. It’s about 3-4 times lighter than traditional aviation fuel, on an equivalent energy basis. There’s a reason why its already a fuel for space travel. Hydrogen is more expensive than jet fuel but as fossil fuel supplies deplete, the cost of traditional aviation fuel is only going to keep going up.

Green Hydrogen is something that is possible in making green and relatively inexpensive jet fuel. The exciting thing with this one is that the big players are getting involved, most notably AIRBUS. Their CEO has stated that ultimately hydrogen is the solution, but that it requires a lot of work.

What I find interesting is that this isn’t a new concept, its actually been around for ages. With tests as far back as the 1950s in America. Most notably I found out that the Soviets actually flew a hydrogen powered passenger aircraft in 1988. While a really astounding thing to hear at first, only one of the three engines were powered by hydrogen making the aircraft a hybrid. This is due to the many issues with hydrogen that still exist today.

Tupolev 155, Illustration, 1989

This is mainly due to the form and scale of storing hydrogen in the aircraft. Hydrogen has to be stored in in a gas form in highly pressurised cylindrical or spherical tanks and therefore would not be able to fit in traditional airline wings. In order to store it in smaller volumes it would have to be in liquid form and stored at -253°C which is also not practical. On the Tupolev 155 these tanks were stored inside the cabin at the expense of passenger seats. Obviously, this didn’t matter in this case as it was an experimental aircraft never designed for service.

There was actually a planned Tupolev 156, a production version of this plane. It was designed with space for hydrogen storage in the rear third of the cabin, separated from the cabin using a pressure bulkhead. Ultimately the plans for this aircraft fell through as at the time they were purely from a monetary perspective not sustainability, and it didn’t seem viable at the time.

ZeroAvia Proposed Timeline for Hydrogen Aircraft

What is Airbus planning to do with Hydrogen? They are currently planning to develop a range of hydrogen concepts which they call ZEROe. This includes a Turbofan variant capable of carrying <200 passengers at Mach 0.78 with a range of 2000+ NM. They are also planning to develop a blended wing variant of the turboprop capable of carrying <200 passengers at Mach 0.78 with a range of 2000+ NM. There is a smaller Turboprop variant that can carry <100 passengers at Mach 0.5 with a range of 1000+ NM.

AirBus ZEROe Turbo Prop Concept

AIRBUS ZEROe Turbo Fan Concept

AIRBUS ZEROe Turbo Fan Blended Wing Concept

They believe that they could have concepts like this flying by 2035. They have also decided to try and go down the route of storing the hydrogen as a liquid, in order to save space and allow for the tanks to fit in a variety of spaces around the aircraft. This diagram explains how they propose allowing the Hydrogen to be stored at these cooled temperatures before being used as fuel. This research is being carried out with the help of AIRBUS defence and space engineering division as they have a background in this type of storage that is used in space travel contexts.

“This is why the Airbus Defence and Space’s Engineering Division has stepped in to help. The team will provide support for the development and industrialisation of cryogenic tanks for liquid hydrogen storage in a three-year project collaboration with the ZEROe programme team” - AIRBUS Newsletter

Ultimately, I think this is where the concept of the blended wing comes back into focus. Like the smaller Bombardier offering from my earlier research, this blends the aircraft wings into the fuselage. Not only will this experience the same boost in efficiency it also helps to give more space for these bulkier hydrogen tanks. So, passenger capacity would be less likely to be affected which is a positive.

AIRBUS Proposed Liquid Hydrogen Tank

They plan to begin testing these engines and tanks on their A380 MSN1 Test Aircraft, which is currently being modified to hold these hydrogen tanks. Their promotional information is vague in regard to specific dates and time frames for this testing but it seems development is well underway. They have set up a development centre in Stade, Germany.

AIRBUS A380 MSN1 Proposed Test Aircraft

In June 2023, Airbus announced the successful test campaign of the hydrogen fuel cell system, which reached its full-power level of 1.2 megawatts. There are two ways hydrogen can be used as a power source for aircraft. The first is with hydrogen combustion in a gas turbine. The second is by using fuel cells to convert hydrogen into electricity in order to power a propeller engine. A hydrogen gas turbine can also be coupled with fuel cells instead of batteries in a hybrid-electric architecture. AIRBUS seem to be taking the fuel cell approach initially for their propellor offerings similar to other companies, stacking them together which allows scalable power output. They have even made physical models of this prototype which indicates they could be quite far along in development. They are also looking into using hydrogen combustion engines to allow for quicker and longer-range aircraft but there seems to be less information about this a part from a few promotional images indicating this could be further off in the future. It seems even they are not sure how effectively this will work. Although not quite as sustainable as hydrogen electric it still boasts massive improvements over the current engines we have now.

ZeroAvia Promotional Material on the Impact of Hydrogen compared to the alternatives

I found this bit of promotional material on ZeroAvia’s website which summarises in very simple terms the different output from these two types of hydrogen engine. You can see the hydrogen electric fuel cell engine that will be used for propellor aircraft basically solves all of the issues raised at the start of my research. If we wanted a truly sustainable way to fly this would be it. Unfortunately, it is not that simple. Hydrogen combustion will basically be needed to provide the range, speed and high-capacity aircraft that people and the industry crave. Without viable replacements I don’t see people taking a step back to propellor age entirely. You can see that hydrogen combustion is still great at reducing CO2 but falls short on the other outputs such as NOx and the vapour in the contrails. Maybe there will be ways in the future to further reduce these types of issues with combustion engines, but I believe these are still the answer. They are still far superior to what we have now.

AIRBUS Proposed Fuel Cell Engine

Obviously, this seems like a long way off. You don’t want to rush something as critical as components on an aircraft and passenger safety is ultimately the top priority. It seems that manufacturers are almost a bit too relaxed though with a clear focus of continuing down the path of traditional combustion engines. I think radical government intervention is what is needed to really put the pressure on companies. This might force their hand into pushing for further development that could lead to quicker changes within the industry.

AIRBUS is taking a step in the right direction making plans to help de-carbonise airports in the lead up to 2035. They are clearly interested in this approach, on multiple occasions claiming it is the future. I just hope this runs as scheduled and we could see emissions begin to reduce massively.

“At scale, and if the technology targets were achieved, fuel cell engines may be able to power a one hundred passenger aircraft with a range of approximately 1,000 nautical miles. By continuing to invest in this technology we are giving ourselves additional options that will inform our decisions on the architecture of our future ZEROe aircraft, the development of which we intend to launch in the 2027-2028 timeframe.” - Glenn Llewellyn, AIRBUS VP Zero-Emission Aircraft

AIRBUS de-carbonisation plans leading up to 2035

USEFUL LINKS

INFORMATION ABOUT SOVIET HYDROGEN RESEARCH
http://blog.privatejetfinder.com/tu-155-hydrogen/

ZEROAVIA INFORMATION ON HYDROGEN AIRCRAFT DEVELOPMENT
https://zeroavia.com

AIRBUS INFORMATION ON ZEROE DEVELOPMENT
https://www.airbus.com/en/innovation/low-carbon-aviation/hydrogen/zeroe
https://www.airbus.com/en/newsroom/stories/2020-11-hydrogen-combustion-explained