Emission-Free Flying on the Horizon

https://cryo.memberclicks.net/assets/news/0222-cw-news-Boeing-composite-linerless-cryogenic-fuel-tank1.jpgBoeing’s groundbreaking cryogenic fuel tank and Airbus’s hydrogen-powered jet engine bring promise to the future of aviation. A new type of cryogenic tank, designed and manufactured by Boeing, completed a critical series of tests at NASA’s Marshall Space Flight Center at the end of 2021. The successful test campaign advances the large, fully composite, linerless tank for safe and ready use in aerospace vehicles. The reusable tank shell was originally constructed as flight hardware for the Experimental Spaceplane Program of the Defense Advanced Research Projects Agency (DARPA).

The 4.3-meter-diameter composite tank is built upon composite cryotank technology that NASA developed and proved efficient through their composite cryotank technology development program and other efforts. It is similar in size to the propellant tanks intended for use in the upper stage of NASA’s Space Launch System (SLS) rocket, which is the foundational capability in NASA’s Artemis lunar and deep space human exploration program. If the new composite technology were implemented in evolved versions of SLS’s Exploration Upper Stage, the weight savings technology could increase payload masses by up to 30%.

“Composites are the next major technological advancement for large aerospace cryogenic storage structures,” said Boeing Composite Cryotank Manufacturing Lead Carlos Guzman. “And while they can be challenging to work with, they offer significant advantages over traditional metallic structures.”

During the testing, which was funded by DARPA and Boeing, engineers from Boeing and NASA filled the vessel with cryogenic fluid in multiple test cycles, pressurizing the tank to expected operational loads and beyond. In the final test, which was intended to push the tank to failure, pressures reached 3.75 times the design requirements without any major structural failure.

“NASA’s support through this testing has been invaluable,” said Boeing Test Program Manager Steve Wanthal. “We were able to use their technical expertise and investments made in the testing infrastructure at the Marshall Space Flight Center to continue to advance this technology, which will ultimately benefit the entire industry.”

Applications for the technology expand beyond spaceflight. The test, which amplifies Boeing’s extensive experience with the safe use of hydrogen in aerospace applications, will greatly benefit the company’s ongoing studies of hydrogen as a potential future energy pathway for commercial aviation – a goal the company has already invested in by completing five flight demonstration programs with hydrogen in addition to their space program tests.

“Boeing has the right mix of experience, expertise and resources to continue to advance this technology and bring it to market in a variety of applications across aerospace and aeronautics,” Guzman added.

As growing pressure mounts on the aviation industry to achieve emission-free flying, cryogenic storage tests on commercial airplanes will become more prevalent, as evidenced by European-based aircraft manufacturer Airbus’s announced plans to test a hydrogen-powered jet engine by the middle of the decade as it pushes to meet its 2035 deadline to build a zero-emission aircraft. Airbus’s plan calls for the first flight of an A380, the world’s largest passenger aircraft, to be powered by a modified GE Passport turbofan by the end of 2026. To achieve this, they have teamed up with CFM International, the world's leading supplier of jet engines for commercial airplanes.

As the flying testbed, the prototype will be equipped with four tanks holding 400 kilograms of liquid hydrogen stored near the back of the airplane’s interior. (The four hydrogen tanks will be surrounded by a hermetically sealed container for safety.) On their part, Airbus will define the hydrogen propulsion system requirements, oversee flight testing and provide the A380 platform to test the hydrogen combustion engine in the cruise phase. CFM has agreed to modify the combustor, the fuel system and the control system of the GE Passport turbofan, which will run on hydrogen.

The physical size and light weight of the engine, as well as its turbomachinery and fuel flow capability, made the engine an ideal choice for the partners. Additionally, its size allows flexibility for installing all the various systems and pipes needed for efficient conversion of liquid hydrogen to gas. The engine will be mounted on the upper fuselage of the A380, just ahead of the tail, to allow for monitoring of emissions separately from those of the engines powering the aircraft. But first, CFM will execute an extensive ground test program ahead of the A380 flight test.

“Hydrogen combustion capability is one of the foundational technologies we are developing and maturing as part of the CFM RISE Program,” said CFM chief executive Gael Meheust. “Bringing together the collective capabilities and experience of CFM, our parent companies [GE and Safran] and Airbus, we really do have the dream team in place to successfully demonstrate a hydrogen propulsion system.”

According to Airbus Chief Technical Officer Sabine Klauke, some technical hurdles the project will face center on the fact that hydrogen burns 10 times faster than jet fuel, raising challenges involving the stability of the flame. Subsequently, Michel Brioude, chief technical officer of Safran, explained that additional challenges involve the need for cryogenic fuel pumps and new piping and seals to accommodate the very cold temperatures (as low as -250 °C) at which the hydrogen must be stored in its tanks. Prior to combustion, the hydrogen will be converted from liquid form into gas. As hydrogen gas burns at a higher temperature than kerosene, the plane must be adapted to withstand the extreme heat.

“There are many technical issues, but I can tell you we are committed and confident that we will address them,” said Brioude. “During the flight test program, what we want to characterize are the condensation trails produced by the engine in different atmospheric conditions. Hydrogen does not produce CO2, but it produces three times more water emissions. So those kinds of condensation trails might be a contributor to the greenhouse effect. Today, we don’t know how long it lasts in the atmosphere, so we need to do the tests and collect the data to be able to know the effect on climate change.”

GE Aviation Engineering Division Vice President and General Manager Mohamed Ali spoke of the need for partnerships across the industry, including with regulators, to build a framework to meet safety standards expected by the public. To date, GE has collected more than 8 million hours of experience running ground-based hydrogen gas systems. “So, we know how to put the safety precautions around that, and all of these findings would be taken into the future testing of this program,” Ali explained.

Technical challenges will undoubtedly be the biggest hurdle the project will face, but Brioude is optimistic because the partners have already reached out to the European Union Aviation Safety Agency and the Federal Aviation Administration for better understanding of the regulatory requirements for ensuring the platform can fly safely and to start to define the key points for earning certification.

“We have data and we have experience we can share with them,” Brioude noted. “And they are very open-minded about working with us.”

Energy Evolution LLC President and former CSA President James Fesmire is excited to see liquid hydrogen gaining momentum and application in these industries. “It is great to see this latest accomplishment from Boeing, undoubtedly building on the data and lessons from the last three decades and now providing a foundation for future application for a significant advance in aerospace vehicles. With the plans for liquid hydrogen aircrafts and a path to clean aviation around the Earth, this technology could see application of significant advancement as well.”

Elements of this story are attributed to Josh Barrett, Boeing Global Media Relations, and Gregory Polek, AIN Online.

Image: Boeing’s all-composite cryogenic fuel tank undergoing pressure testing at NASA’s Marshall Space Flight Center. Credit: Boeing



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