START Lab expansion aims to make aviation greener

UNIVERSITY PARK, Pa. – A small increase in gas turbine efficiency can make a ton of climate-friendly impacts in aviation, according to Karen Thole, distinguished professor of mechanical engineering at Penn State. Thole, who directs the Steady Thermal Aero Research Turbine (START) Lab, and doctoral student Chad Schaeffer discussed their work on gas turbines and next-generation hybrid electric propulsion at the Penn State Board of Trustees meeting on Nov. 10.

“Flying accounts for about 2% of global carbon dioxide emissions, and 90% of those emissions come from the single- and twin-aisle aircraft,” Thole said. “The problem that we’re working on is trying to increase efficiency, which decreases carbon dioxide emissions. If we can increase the turbine thermal efficiency by 1%, we can reduce the amount of fuel that aircraft use for a two-hour flight by 50 gallons, which means we can reduce carbon dioxide emissions by about one ton. These are really big numbers that we’re working on, and that’s what drives us.”

For an airplane to fly, turbine blades need to spin in an environment that is so hot the gas flow can melt rock and even the blades themselves. The tradeoff that comes with making an engine more fuel efficient by making it hotter is that it leads to reducing the life of the parts, according to Thole.

To address that tradeoff, Thole and the graduate and undergraduate students working in the START Lab focus on turbine cooling methods, which include a number of technologies such as small film-cooling holes drilled into the blades that allow cool air to pass through them to prevent them from melting. They use additive manufacturing – 3D metal printing – to produce blades that result in shorter development times for new cooling technologies relative to the required single crystal cast blades needed for the engine applications. In December 2022, the START Lab was the first university to spin 3D metal printed cooled turbine blades. To evaluate new cooling technologies, the START team developed a unique infrared thermal imaging system capable of spatially resolving the temperatures of blades spinning up to 500 miles per hour. The probe’s resolution is so high that it allows the researchers to detect when a manufacturer drills the cooling holes differently.

A $26 million commitment from Pratt & Whitney, the Federal Aviation Administration’s ASCENT Program, the U.S. Department of Energy-National Technology Lab and Penn State will expand the START Lab. The expansion will allow Thole and her collaborators to evaluate smaller turbines relevant to hybrid electric propulsion.  Thole leads a NASA funded University Leadership Initiative partnering with Howard University, Georgia Tech, Pratt & Whitney and Collins Aerospace to study hybrid electric propulsion. The work illustrates the growth of Penn State’s research enterprise and the University’s commitment to expanding interdisciplinary research excellence, a key priority for Penn State President Neeli Bendapudi.

“Hybrid electric propulsion is a combination of a gas turbine and a battery, like a Toyota Prius flying through the sky,” Thole said.

Adding a battery allows turbine manufacturers to shrink the size of turbines, but shrinking turbines also poses efficiency challenges, Thole added. Much of the START Lab’s future work will focus on redesigning turbines, making them smaller and more efficient.

Schaeffer is part of the next generation of engineers who will lead the way toward more sustainable aviation. He is currently designing a combustor profile simulator for the lab’s experimental test turbine rig.

“I’m thankful for the opportunity that START has given me, especially for the connections with industry and government and the hands-on approach to research,” he said. “I can’t believe that I’m now a first-generation college student and a top candidate in the gas turbine industry.”