The idea of using hydrogen as fuel in aviation has been around for 75 years. The hydrogen-related research activities repeat themselves in what could be looked upon as cycles. Today we are part of the third hydrogen aviation cycle.
Airbus, NASA, and ZeroAvia – three very different aerospace companies are now implementing the use of hydrogen as an alternative fuel. Each company is aiming at a different market sector and each company has taken a different approach on how to exploit hydrogen.
There is one thing they all have in common – they believe hydrogen will become an important part of future aviation despite its downfalls in the past. The question is – can we learn from the past to succeed this time?
THE EARLY BEGINNINGS
The first truly hydrogen-dedicated research in aerospace began in the 1950s. At that time, it only had one goal – to investigate if hydrogen fuel would be a better choice than jet fuel for very high-altitude military aircraft (up to 90 000 ft.).
The implementation of hydrogen was partially successful but resulted in only a few LH2 modified Martin B-57B test flights. After the test flights, the program was abandoned due to its enormous complexity. The associated costs and constraints we’re not in line with the potential benefits.
This was in 1957 and it showed two key insights. First, it is not economically feasible to create a hydrogen supply chain only for a very limited aircraft fleet. And secondly, this hype cycle was funded by the US defense budget, not the private sector.
THE OIL SHOCK
The second hype cycle was triggered by the global oil crisis in the 1970s. The prices of conventional jet fuel surged substantially and aerospace engineers started to look for the use of alternative fuels. This time the R&D activities were focused mainly on Soviet Russia.
Two alternative fuels were selected as feasible – liquid hydrogen (LH2) and liquified natural gas (LNG). It took more than a decade to put together a flying testbed which was a trijet Tu-155 with one modified engine to run on hydrogen. This was in 1988. The flights were successful and the “cryoplane” made several flights also to Western Europe.
The technology was looked at as “promising” and in 1990 German-Russian Cooperation (DASA, Tupolev) was established with one goal – to transfer the technology to the Western world. The proposed conceptual study was called Cryoplane. Its task was to modify an Airbus A310 to run on LH2.
At the beginning of the 1990’s the oil crisis was over and the hydrogen fuel research was given no more interest from both Western and Russian OEMs and governments minor efforts continued in Germany (e.g., to convert Do-328 to a cryoplane).
The key findings of the second hype cycle are that it was initiated by the search for cheaper fuel for civil aviation and that the efforts to establish a viable hydrogen supply chain were unsuccessful because by the time the technology implementation was starting to look feasible, the need of alternative fuel was over (due to significant oil prices drop).
Modern Tupolev Tu-155
THE NEW AGE
The hype cycle we are living in right now is different from the previous two. Technology has come forward and hydrogen is not only looked at as fuel for aircraft gas turbine engines (which was the case in the first and second one) but also as fuel for fuel cells and power generation.
The reason for the extensive ongoing hydrogen research in the 2020s is also different. Rising CO2 emissions and climate change are the key drivers today, as aviation is under pressure to introduce zero-carbon technology.
Today more than 2 % of global CO2 emissions are created by air travel (and the percentage might increase as the volume of air travel is projected to double in the next 20 years).
But aviation is not the only industry that needs to drastically cut CO2 emissions. This means establishing a hydrogen supply chain is now more feasible as the need for green hydrogen production, distribution, and usage is needed throughout numerous sectors.
The third hype cycle is a response to climate change issues and the need for CO2 emission levels reduction not only in aviation. Hydrogen supply chain creation is now strongly supported by billions of euros from EU initiatives with European countries establishing national hydrogen strategies reaching as far as 2050. This suggests that the ongoing cycle is very probably going to exist up until a feasible solution is introduced.
STORAGE & DISTRIBUTION – THE KEY BARRIERS
Currently, there are still barriers in each part of the hydrogen supply chain (from production to utilization). To evaluate and explain the key technology constraints associated with hydrogen economy creation, we need to look at hydrogen chemical properties.
Hydrogen`s gravimetric energy density is 3 times higher than that of jet fuel and 100 times higher than that of current electric batteries. The downside is the volume/energy density ratio which makes hydrogen difficult to store.
To reach the highest volumetric energy density hydrogen needs to be liquified and cryogenically stored at -253°C. In the DASA-Tupolev Cooperation in the 1990s cryogenic storage was one of the key barriers. But since then, technology has come forward.
According to the engineers from a leading cryogenic and aerospace manufacturer PBS Velka Bites “Hydrogen compression and liquefaction technology are now more advanced than 30 years ago as we can now for example use more efficient aerodynamic bearings which decrease the level of contamination and leakage”.
Also, since the 1990’s there is a considerably higher hydrogen industry competition as the number of companies stepping into the business is rapidly increasing.
This phenomenon drives down the prices and product development times as the demand is increasing and the companies are naturally competing. These are fundamental principles of a free-market economy – yet they are critical in establishing and maintaining a viable self-sufficient hydrogen ecosystem.
Hydrogen economy establishment efforts in the past were not taken gradually – this is what has to be taken into account in today´s cycle.
As the first step hydrogen will most likely be used in fuel cells for electric or hybrid electric smaller commuter aircraft for approximately 20 passengers (this can be technologically achieved by the year 2025).
Another gradual step is then expected from the airport infrastructure to fundamentally include hydrogen in their future developments. We have seen this in Paris CDG airport modernization which will include hydrogen infrastructure.
Wide-body aircraft (such as the proposed Airbus ZEROe turbofan concept) cannot be fitted with fuel cells or batteries (based on current weight/power generation ratio). This is where we might see hydrogen-fueled modified super-efficient turbofan engines in around 2035.
Much is also anticipated to be done by other industries (e.g., power generation, energy, transportation) as aerospace is not the only business that is under pressure to come up with a solution to reduce its carbon footprint. This multi-industry connection is very important as more sectors can share the costs in future development.
The third hydrogen hype cycle will probably be the last one. Either if proven successful or unsuccessful. The aviation change is inevitable and will very probably include hydrogen in various forms and uses.
RADIM JANSA, Product and Business Development, PBS GROUP