After years of studying the possibilities of liquid hydrogen becoming the next generation of aviation fuel, Phil Ansell decided it was time to take research from conceptual designing on paper to physical production. With funding from The Grainger College of Engineering and the Department of Aerospace Engineering at the University of Illinois Urbana-Champaign, and partnering with GenH2, liquid hydrogen production will be, not just possible, but palpable.

Ansell is an aerospace engineer and the director of the Center for Sustainable Aviation at U. of I. After eight years, he believed it was time to move from design concepts to experimentation.

“There are a lot of near-term ideas for sustainable aviation that are good and useful but it’s time to double down on the things that are working. One research concept that is working is cryogenic fuels for aviation,” he said. “Though, such a change to cryogenic fuels introduces a wealth of very practical challenges that can only be addressed by turning to hardware. There comes a point when it is necessary to progress beyond theoretical studies and into experiments, and I decided to raise my hand and invest in the novel capabilities that allow us to take a leading role in these efforts.”

The new hydrogen liquefier system fits in a 20-foot shipping container so it will be mobile, but large enough that it can produce more fuel than current Illinois research requires. Ansell said the new equipment can be used for academic and industry partners who want to test with liquid hydrogen but don’t have a resource. Additional capabilities to provide on-site liquefaction and zero-boiloff storage of renewable methane are also currently in development, which will allow both cryogenic fuels to be studied in experiments.

“We’ll be one of just a few universities to have the capability to produce liquid hydrogen,” he said. “We have aspirations to utilize liquid hydrogen and other cryogenic fuels in flight test research,” he said. “The beauty of this system is that, if we have the opportunity to flight test at NASA Armstrong in the desert of Southern California, for example, we can transport the entire system and reconfigure it to support fuel production on-site.”

Ansell is eager to use the new equipment to help address five open questions that need to be answered concerning system operational resiliency, technological readiness, safety, regulatory preparedness, and overall energy efficiency.

For system operational resiliency he said proving cryogenic liquid fuels can work at a small scale will allow them to adapt incrementally up to the large-scale demands of an airplane.

Much like our current system that uses jet fuel, “We need a system you don't have to treat delicately,” he said. “When an aircraft arrives, there will be fuel and it will be reliable. We do this component by component and then build that into the working system.”

Ansell said there are numerous aspects to consider in technological readiness.

“We are proposing to build prototype fuel tanks. That’s just one example. We need to understand how to build these systems more effectively before they can enter service or be integrated into an aircraft product.”

The tanks need to be designed with insulations strategies to maintain the cold state of the fuel but also withstand increasing pressure from fuel boiling and becoming vapor. And material degradation is also an issue.

Hydrogen is the first element on the periodic table. It’s so small that it can wedge itself into the intermolecular structure of steel. As time goes on and more hydrogen gets itself buried into the material, it does what's called embrittlement, making the materials weaker.

“The only way we can know if the fuel system can stand a 30-year duration of an aircraft lifetime is by doing accelerated lifetime testing. We load it up and then purge it repeatedly, cycle by cycle, to see observe how the integrity of the structure changes.”

Safety is a concern when working around jet fuel, but even more so with cryogenic hydrogen and methane. Both boil at a very low temperature and can easily ignite. In fact, hydrogen flames are quite difficult to visually perceive.

“If we want to operate with this fuel at an airport, we need to have in place a very robust fire prevention plan and fire management plan.”
Although federal regulations already exist for transporting liquid hydrogen and liquefied natural gas via trucks on the highway, the certification rules to use cryogenic fuels for a commercial aircraft product don’t exist yet.

“Federal airworthiness regulations must be in place, but we don’t have the requisite knowledge to make a reasonable regulatory framework yet. We to envision the practical elements of a day in the life of a cryo-fuel airplane to know the risk factors and what regulation we need to ensure these systems can be implemented safely and reliably.”
In the case of liquid hydrogen, the specific energy, which is the energy per unit mass of the fuel, is 2.8 times denser than conventional jet fuel. But, using hydrogen as a means for storing energy typically requires large amounts of volume, with the energy density, which is the energy per unit volume, being one quarter of that of conventional jet fuel. “Hydrogen, being cryogenic, has its own inherent chemical energy, but it also has all of this energy that is imbued within it to bring it to 20 Kelvin,” Ansell said. “There’s no shortage of heat production on airplanes from avionics, batteries, wiring, the environmental control system, etc. so we’re looking for ways to leverage the latent heat that’s baked into the cryogen itself – to use the heat absorption capability of the 20 Kelvin liquid hydrogen to manage a thermal load somewhere else on the airplane.”

Ansell is looking forward to using this new equipment to find answers to these and other questions.

“We’ve been working in the paper design land for eight years, looking at hydrogen as an energy carrier for aviation. I'm quite confident that we know enough and are now ready to move beyond just these paper design studies. Now we need to make it possible. Looking holistically at all sorts of varieties of cryogenic fuels for aviation will allow us to understand what key technology elements and safety protocols are compatible with which specific method of energy storage.”

Ansell expects the GenH2 hydrogen liquefier system will be installed and commissioned early next year.