Advanced BioFuels USA

by Gregory Polek (AIN Online) Of all the various renewable energy sources under development, hydrogen represents the so-called “holy grail” in the effort to eliminate carbon emissions from future aircraft, say many scientists. But while the technology exists today to build a hydrogen-powered aircraft, prompting several startup enterprises to develop fuel-cell-based vehicles for the burgeoning advanced air mobility industry, for example, scaling the production and distribution of hydrogen for the wider air transport market presents its own set of challenges.

While several companies continue work to advance fuel cell technology using hydrogen gas for generally small aircraft, the application of liquid hydrogen, or LH₂, appears to carry the most promise for larger airliners due to its superior energy density and versatility. The use of liquid hydrogen stored in a cryogenic tank onboard to power turbine engines presents the most feasible means to introducing a passenger-carrying aircraft to the market, according to experts in the field.

NASA Cryogenics Test Laboratory principal investigator Adam Swanger explained to AIN that although researchers continue to study pure hydrogen fuel cell-electric architectures, the use of onboard liquid hydrogen to power a combustion engine remains a comparatively more straightforward and economically practical solution for large commercial aircraft. “These engines [represent] billions and billions of dollars, and decades of investment,” he said. “And they’re super-optimized for their application. They’re fantastic…some of the most amazing technological achievements ever, but you can’t just swap over to another fuel that easily. On the other hand, fuel cells are great because there are very few moving parts and they have high efficiencies. It’s not that pure fuel cell electric can’t be done, and it might be in the future, but for large aircraft that would most likely require a full, ground-up design. So, if you’re trying to get hydrogen into your aircraft as soon as possible, that’s going to be a hard sell I think.”

A recently published report by the UK’s Aerospace Technology Institute named “green” liquid hydrogen as “the most viable zero-carbon emission fuel.” However, it added that generating, transporting, and storing the vast amounts of hydrogen needed for future use will require “unprecedented” renewable energy capacity. Delivering hydrogen to airports will present another challenge, whether through gaseous pipelines or liquid hydrogen tanker deliveries, while the refueling and servicing of hydrogen-powered aircraft will have to take place safely and efficiently alongside conventional aircraft.

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Swanger added that two of the biggest technical challenges presented by liquid hydrogen center on minimizing boil-off losses and safely managing boil-off gas.

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Meanwhile, the process requires a lot of electricity, which, although getting cleaner with more renewable energy sources, still creates a large amount of carbon itself.   READ MORE