June 14, 2021, © Leeham News: GE and SAFRAN took to the stage today to announce the extension of their CFM joint venture to 2050 and the CFM technology program RISE.
RISE stands for Revolutionary Innovation for Sustainable Engines, and it elevates previous work to new levels and introduces some news.
RISE (Figure 1) takes the GE/Avio developed single Open Rotor concept from Clean Sky project IRON (Figure 2) and marries it with SAFRAN’s open rotor knowledge. The result is a new start for Open Rotor with the market’s largest engine OEM, CFM, behind it.
We have presented the base concept, the tractor single Open Rotor with second stage de-swirling vanes here. It was then part of the EU’s Clean Sky 2 program. People in Clean Sky tipped us that this was something new and smart, so we visited the IRON program’s headquarter in Turin last year to discuss the concept.
It keeps the advantages of Open Rotor but simplifies the mechanics to a single rotor from previous projects’ two. In its base, it is not more complicated than a turboprop engine with added variable incidence de-swirling vanes.
What’s new is GE and SAFRAN will fully develop this concept in their CFM joint venture. CFM is our largest engine OEM today, both in terms of delivered engines (over 30,000) and engine deliveries (several thousand CFM 56 and LEAP engines per year).
The development will span some 15 years, with engines ready for prime time by the mid-2030s. The RISE engines will be developed in Jet fuel/SAF and hydrogen burning versions. The latter is the real news in the announcement.
Making a gas turbine run on hydrogen is straightforward (read about it here) and is the shortest and most realistic way to lower air transport emissions of greenhouse gases. It eliminates CO2 emissions and reduces NOx emissions by 80%.
Another technology we have written about is the motor-generator that will be integrated into the new engine core. To call this “hybrid technology” is a bit of a stretch. Previously it was called “an integrated starter-generator,” which is what it is.
It’s an elegant way to combine the engine air starter and the engine-driven aircraft generator into one. Its placement on the core’s main axis can help the engine during revving up and down. This allows the engine’s internal aerodynamics to be further tuned towards efficiency. It can also deliver electricity to the aircraft but so can the generators on the engines of today. They are just placed on the engine’s auxiliary gearbox.
The final twist of the engine is an optimization of the rotor towards a smaller diameter. It has two advantages: It eases the installation of the engine on the aircraft. Whereas the large rotor of previous projects prescribed a rear placement, the smaller diameter version now enables more placement alternatives (Figure 3).
The second advantage is the engine is less sensitive to higher speeds. The reduced diameter reduces the engine’s bypass ratio (in technical speak it increases the specific thrust). It puts the RISE engine’s high-speed characteristics closer to high bypass turbofans, which in turn makes the engine suitable for airliners that fly longer routes, up to our typical single-aisle routes.
So is RISE Open Rotor revisited? Yes, but in a positive way.
The RISE Open Rotor is further tuned for simplicity and reliability, and the bypass ratio is moderated to retain thrust at higher speeds. It also comes in a hydrogen-burning version which is the announcement’s real news.
Hydrogen fueled Fuel Cells feeding electric propulsors might be the ultimate future hydrogen propulsion architecture, as this eliminates the NOx emissions in addition to CO2. But their development for airliners will be long and difficult. Hydrogen-fueled gas turbines are a practical and vital step towards our ambitious 2050 goals for lowered emissions for air transport.