Pratt & Whitney, a subsidiary of RTX, has provided an update on its Hydrogen Steam Injected, Inter-cooled Turbine Engine (HySIITE) program. The program, launched in 2022, received $3.8 million in funding from the US Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E).
The engine manufacturer emphasized the promising potential of the HySIITE architecture in improving efficiency while significantly reducing nitrogen oxide (NOx) emissions. In a media briefing attended by AeroTime, Pratt & Whitney stated the HySIITE system could improve energy efficiency by 35% compared to current single-aisle aircraft powerplants.
Turning challenges of hydrogen power into an opportunity
Neil Terwilliger, a technical fellow for advanced concepts at Pratt & Whitney, highlighted that while hydrogen-powered aircraft emit over twice the amount of water vapor compared to conventional engines, this can increase condensation trails in certain atmospheric conditions. Additionally, hydrogen combustion produces higher levels of NOx, which contribute to global warming.
Pratt & Whitney addressed these challenges by integrating a condenser near the exhaust to capture water vapor and reinject it into the combustion chamber. Michael Winter, Chief Scientist at RTX, noted that water injection is a well-established technique in stationary power generation and has been used in aviation since the early days of the B-52 strategic bomber.
As part of the HySIITE program, three critical components were designed and tested separately at the RTX Technology Research Center. These included a combustor that achieved a 99.3% reduction in NOx emissions, a condenser capable of recovering 1.26 liters of water per second, and an evaporator designed to support steam injection.
While standard hydrogen combustion offers only an 8% energy gain over power-to-liquid synthetic sustainable aviation fuel, a hydrogen-powered engine incorporating water recovery and steam injection could potentially triple net energy savings.
Long road ahead
Despite these advancements, industry experts acknowledged the long development timeline for hydrogen-powered engines, with commercialization not expected to occur before 2050.
Addressing concerns over hydrogen storage and its impact on aircraft design, Terwilliger highlighted a 15% weight penalty. However, Winter proposed that alternative configurations, like blended-wing designs, could help alleviate these challenges. Notably, the HySIITE architecture was proven to fit within a conventional turbofan nacelle.
Regarding maintenance, Terwilliger stated, “Our target would certainly be that maintenance intervals are at least as long as they are today, and I don’t see a particular reason why that couldn’t be true in the future.”
While the HySIITE project has officially concluded, the company affirmed its commitment to advancing hydrogen propulsion through other ongoing initiatives like NASA’s Advanced Aircraft Concepts for Environmental Sustainability program and Canada’s HyADES project, which is testing hydrogen combustion on a PW127XT engine.
