ZeroAvia is partnering with San Francisco startup Verne to bring a more energy-dense form of hydrogen to clean aviation. Compared with cryogenic liquid hydrogen, cryogenic compressed hydrogen can reduce costs, speed up fueling, and increase flight distance by 40%.
Hydrogen is a rather troublesome fuel. It is difficult to store and transport, requiring ultra-cold temperatures or energy-intensive compression to convert it into useful volumes. Making hydrogen is energy inefficient and there is no distribution network of its own.
But it is currently the only fuel option if the aviation industry is to be completely decarbonized. It may not carry as much energy as jet fuel, but it offers a significant increase in energy density compared to lithium batteries. As a result, companies like ZeroAvia are working around the clock to test and validate its use on commercial aircraft. Test flights of gaseous hydrogen fuel cells are already well underway, even on small passenger aircraft, and last year the first manned flight using liquid hydrogen as fuel was achieved.
Now, ZeroAvia hopes to bring a third form of hydrogen fuel to the forefront, one that can carry more energy.
The concept of cryogenic compressed hydrogen (CcH2) has been around for 25 years. BMW developed a prototype CcH2 system for passenger cars more than a decade ago, and Cryomotive is one of many companies now looking to apply CcH2 technology to long-haul trucking. The company promises CcH2 is a zero-emission fuel that can store more than 3,000 watt hours per kilogram, with the range of diesel and fast refueling times.
So what exactly is it? CcH2 effectively combines cryogenic cooling for liquefied hydrogen with partial compression technology for storing gaseous hydrogen. Liquid hydrogen requires a temperature below 20K (-253°C/-423°F) at ambient pressure, while gaseous hydrogen often needs to be compressed to the range of 700bar at ambient temperature.
Suppose the hydrogen is kept at 20K and then compressed to 240bar. According to research by Langmi et al., the volumetric storage capacity of hydrogen will increase from 70 g/L to 87 g/L. But it also greatly reduces, and potentially even virtually eliminates, the boiling losses that are characteristic of liquid hydrogen storage. Hydrogen can also be filled at the speed of liquid transfer without the need to install millions of dollars worth of compressor equipment at each filling station.
As Composites World explains, it also makes it possible to use lighter tanks, or to build them from cheaper materials, because there is no need to deal with 700 bar pressure levels or provide active cooling within the vehicle. Insulated tanks can keep themselves cold because every time the fuel is used, the remaining fuel expands into the tank, and thermodynamic principles will help reduce the temperature.
ZeroAvia signed a memorandum of understanding with Verne, which last year partnered with Lawrence Livermore National Labs to demonstrate a CcH2 system operating at undisclosed pressure and temperature levels capable of storing 27 percent more hydrogen than a similarly sized liquid hydrogen system.
Verne believes its CcH2 technology has a usable hydrogen density "40% higher than liquid hydrogen" and is working with ZeroAvia to "jointly evaluate" CcH2 application opportunities in aviation and investigate the ground infrastructure required for rapid hydrogenation at airports.
In an interview with Composites World, Cryomotive's Tobias Brunner explained that his company believes its CcH2 storage technology is "very suitable for the aviation industry" - but only for small aircraft, because once you get to large tanks holding hundreds or thousands of kilograms of fuel, liquid hydrogen re-emerges as a lighter weight solution at the system level.