May 9, 2022, © Leeham News: Pratt & Whitney thinks a hybrid-electric propulsion system might be ready for installation on the next new airplane from Boeing or Airbus by 2031. But more likely is that the new airplane, whatever design it is, will more likely be powered by a conventional engine that is capable of running on 100% Sustainable Aviation Fuel (SAF).
Graham Webb, the chief sustainability officer at Pratt & Whitney, said PW is “obviously investing in our Geared TurboFan. That’s our bread and butter. We are working to infuse a large number of technologies, including ceramic matrix composites, and aerodynamic improvements to the turbines and the compressor. We’re working on improving the cooling optimization and sealing, and the traditional core efficiency suite of technologies to enable us to get to the higher overall temperatures we need for the next generation cycles.
“We’ve already completed a suite of work with the FAA and our clean aviation program that enabled us to expand the bypass ratio of our Geared TurboFan engine further from where we are till now. We’re going to use that technology to grow the engine. We’ll put a different fan-drive gear system technology as a result of that expansion. That’s kind of like the traditional engine efficiency piece,” Webb said at the Aviation Week’s MRO Americas event in Dallas. LNA spoke with Webb on the sidelines of the huge event, attended by more than 13,000 people.
Under the FAA CLEEN Phase I program, PW developed ultra-high bypass ratio technologies beyond the current 12:1 present in today’s GTF engines. These technologies are ready for deployment for a future new aircraft. The specific bypass ratio of this new engine will be optimized to each installation on the new airframe configurations being developed by the airframers, a spokesperson added.
PW is working on what Webb calls disruptive technologies with Collins Aerospace, a PW sister company, with funding from the Canadian and Quebec governments. He’s referring to hybrid electric propulsion with Pratt & Whitey Canada. De Havilland Canada is a partner. PW is marrying a one-megawatt electric motor generator from Collins to a thermal one-megawatt engine. These work in parallel to generate a two-megawatt power system, about the same power as the PW120 turboprop engine.
“The electric motor will only operate in a complementary mode to the thermal engine and generate power in such phases as take-off and climb. It will phase back the electrical power in the cruise range, where the thermal engines are quite efficient, and charge those batteries back up for the next flight,” Webb said. It’s a 1,000 volt system, which is nearly four times what’s currently permitted by regulations. The plans include marrying this technology with not just a turboprop but also the GTF. Installed, the net fuel gain would be about 10% better than today’s engines.
A hybrid power system requires “robust” modeling and engineering to integrate it into the aircraft. “To be able to effectively do the trades and understand how benefits of the thermal efficiency and the thermal engine augmenting it with the electrical motor system. Webb said technology must reach a point where the fuel benefit outweighs the weight of the battery, the robust containment to protect against fires. We’ve done that work. It is a net benefit.
“In the case of our regional turboprop demonstrator, our forecast is a 30% efficiency, installed, all-in, over the regional turboprops, the PW121 engine,” Webb said. The improvement over today’s GTF is far less, under 10%. The PW121 is an old technology engine while the GTF is the most recent technology.
PW also is now considering ceramic composites, a technology it eschewed in developing the GTF. CFM, on the other hand, favored ceramic composites over a geared turbofan. Now, CFM plans to employ a geared turbofan in its RISE Open Fan developmental engine and PW contemplates adding ceramic composites.
Webb said the composites technology has matured to an acceptable risk level to get the temperatures needed in the engine for the next step in fuel and emissions efficiencies.
The prevailing conventional wisdom is that Boeing “must” launch a new airplane in the 2023-24 period for an entry into service around 2031. Although Airbus appears focused on hydrogen power and hybrid technology is under study, in all likelihood, an airplane in the A320-737 category will be with a conventional engine that is 100% SAF capable.
CFM, with partners GE and Safran, is developing the RISE Open Fan engine. GE says that the engine will be ready for EIS in 2035. GE and PW have long studied open rotor engines, dating to the Boeing 727 and McDonnell Douglas MD-80 days. PW isn’t a supporter.
“From our perspective, it comes down to the risk of installation and how it affects aircraft aerodynamics and fuel burn. It’s noise, certification challenges, and safety,” Webb said.
GE believes the noise and safety issues have been overcome. As for installation, the company says close coordination with the airframe designer will be required to install and certify the airplane/engine combination. The goal is to achieve 20% lower fuel burn, with corresponding emissions reduction, after the installation.