Bjorn’s Corner: New aircraft technologies. Part 9. Engine core advances

By Bjorn Fehrm.

April 21, 2023, ©. Leeham News: This is a summary of the article New aircraft technologies. Part 9P. Engine core advances. The article discusses how developments for the next-generation airliner engine cores will increase the thermal efficiency of next-generation engines.

Figure 1. The Pratt & Whitney PW1100G engine with its compact core enabled by a geared high RPM design. Source; Pratt & Whitney.

Engine core advances

In the last Corner article, we looked at the propulsive efficiency improvements we can expect for the next generation heart of the market airliner engines.

Now we looked at what improvements in thermal efficiency we can expect from the cores that drive these engines’ fans/open rotors.

We look at what defines the efficiency of a core and what sets its size relative to the fan/open rotor it shall drive.

The efficiency is set by the Overall Pressure Ratio (OPR) of the core together with the component efficiencies of the compressors and turbines.

We can expect the next-generation engines to come close to the pressure levels of today’s best longhaul engines, with cruise values around 50:1.

Figure 1 shows how this can be achieved with a compact core. The high core RPMs of a geared engine enable high compressor and turbine stage pressure changes, making for a high OPR core with few compressor and turbine stages (at the expense of a gearbox to the fan).

The core’s Turbine Inlet Temperature, TIT, decides the shaft power level it can deliver to the fan/open rotor.

Better high-temperature coatings and materials and more efficient cooling solutions will increase the TIT on these high-cycle engines close to the level of today’s long-haul engines.

Figure 2. The first turbine’s outer wall (the blade shroud) is tiled with CMCs for the CFM LEAP engine. Source; CFM.

If more heat-resistant materials like Ceramic Matrix Composites can be used for turbine components (Figure 2), the cooling air sapped from the compressor can be reduced. It will benefit the efficiency of the core.

Overall we can expect the next generation of high-cycle cores to reach the efficiency and power levels of today’s best long-range engines.

33 Comments on “Bjorn’s Corner: New aircraft technologies. Part 9. Engine core advances

  1. There is a life limit in number of full power cycles the hottest parts of the engine can take, hence a widebody engine run hotter as it sees fewer cycles. RR understood this when designing the RB211-535 using the core engine of the widebody RB211-524. This increases core flow and lower turbine inlet temperature for the same work output. So defining an engine for 20 000 cycles on wing you have to run it cooler than widebody engine designed for 3000 cycles.

    • Yea the wonder of the CFM-56 was the cycles and hours it made and the reports are the new stuff is not coming close to on wing time. In time maybe.

      CFM-56 good enough it was used on the KC-135R (or the re-engine) as efficient, more power and long wing times as the KC type in US service don’t see the cycles. Others with the A330-MRT may as they have a multi role configuration. Though I saw an Aussie A330MRT parked on the ramp for a week waiting for an excersize to start in AK version of Red Flag (Blue Mountains or some such).

  2. How much of the “hotter” stuff from the CFM (Leap1B) line is incompatible with a GTF setup?

    • Mr. Uwe ,
      The material compositions of the compressor-through-turbine sections will be similar , though not identical .
      The primary differences will be in the rpm. parameters , and the morphologies employed to service those .

      • P&W
        The Leap engines have a 10 stage HP compressor while the GTF has 8
        For the LP turbine CFM has 7 stages ( 5 for smaller fan/lower thrust Boeing version) while GTF has just 3 stages.
        Thats a massive reduction in numbers of fan blades required.

        I would say the Leaps are completely incompatible with geared fan blade approach in the hot sections

        • GTF balde reduction is masssive! ( number, size )

          rpm limits are set by the longest blades on a common (ungeared) spool.
          For the LP spool that is the fan blades.
          This requires the turbine section to have largish diameter for acceptable minimum speeds in the section.
          On the GTF this is unlinked ( via gearbox ratio )
          both spools turbine side turn at similar rpm.

          A CFM geared design would move into the same high rpm LP turbine layout.

          My question further up was about LEAP solution details that pander to the low rpm, largish LPT and would make no sense on a GTF.

    • The hot section parts life is a combination of alloy of material used and singel crystal quality, cooling scheme and coatings, especially Thermal barrier coatings and oxidation coatings. The CMC revolution is moving from turbine shouds into Nozzle guide vanes, burner liners and on to rotating blades and seals. The CFM56 core engine was well developped in the F101, F404, F110 fighter engines before getting into the CFM56. Its big cost advantage was one rotating HPT stage only, its early drawback was the intershaft bearing.

  3. This is a report from an older Av week back in 2022. It lays out the basic outline. So yes higher temp materials but the layout is quite a bit different than CFM current Leap, probably exactly what RISE is doing with its core.

    At some point materials get so costly that it negates a percentage of improved fuel saving as you have to do all that replacement on overhaul and its the overall life costs that are relevant (unless you sell the aircraft before then and the buyer will account for that cost in what they pay).

  4. Bjorn, I’ve enjoyed this series so far, good work.

    CMC technology is a huge leap (how do ya think GE came up with that name 😉) in jet engine efficiency and reliability. The other factor as you stated is the bleedoff required for internal cooling.

    In ECM (engine condition monitoring) the key factor, besides oil consumption, that drives engines off wing more than anything is EGT margin. EGT margin is worse in dusty/sanding environments. Sometimes doing turbine washes does slight improvements.
    The LEAP engine looks promising with increased on wing time and the ~15% decreased fuel burn! But the EGT margins will still be a carefully watched.

    The reliability of the CFM 56 is astounding. GE and Safran engineering should be applauded.

  5. “The reliability of the CFM 56 is astounding. GE and Safran engineering should be applauded.”

    50+ years since inception.
    Half a century to improve the product.
    Any jet engine with higher numbers produced?
    ( and it didn’t fragment into too many distinct products either.)

    • Didnt come fully formed as it is now out of the box. Major upgrades in late 90s and again decade later
      CFM56-2 was the first model
      The CFM56-3 was the lower thrust version for 737 classic
      CFM56-4 was a higher thrust version of -3 for the A320 but the new IAEv2500 was superior so they had to do a major upgrade for CFM56-5 series

      The king of the variants with highest thrust , BPR and pressure ratio was the -5C series for the A340

      Some major accidents caused by engine failures too, more recently the front fan of Southwest having a series of similar failures. So the last decades or so reliability have wiped the earlier problems away.

  6. The meltdown at P&W continues, with no end in sight:

    “Air New Zealand grounds two Airbus A321neos over global engine shortages”

    “Executives at US-based Raytheon Technologies, the parent company of Pratt & Whitney, warned during the firm’s earnings call in January 2023 that material shortages related to engine castings would continue throughout the year.”

    • This is not an unique P&W experience, they went thru similar with JT9D, PW2000, PW4000 and have lots of ex. PWA engineers that can come back and sort out the problems. So P&W and its launch customers has been thru this a couple of times before. Having UAL, DAL, LHT, SQ as early customers helps solving its problems together with their engine shop engineering teams. Still it should settle down by now.

      • “Still it should settle down by now”

        Yes, it should have been solved at this stage — these engines have now been giving multiple problems for years.
        No wonder that Tim Clark said last year that he would refuse delivery of the his 777Xs unless he was absolutely satisfied that GEnx engines were going to perform to spec from day one.

        • @Bryce: the 777X has GE9X engines; the GEnx is on the 787.

          • Is that a serious question?
            You can’t see reliability as the common denominator?

          • One engine (PW) is in the service having reliability problems. The GE engine is not in service yet. Hence, my confusion.

            Think its safe to say the GE/SAFRAN LEAP is having better reliability at present versus the PW GTF.

            Good to see PW back in the commercial market. Hope they figure it out soon and upscale the tech to larger aircraft.

          • The “one engine” experiencing problems at PW happens to be a component of several major NB programs — and the problems are now into their 4th year.

            Then there’s the recent/ongoing Trent problems at RR.

            The CFM LEAPs are experiencing ongoing durability issues.

            And the GE9x testbed had its own recent bout of issues.

            Tim Clark evidently isn’t interested in being a guinea pig for GE.

      • This supply chain issue is in almost all industries. I’m in Automation and we are seeing up to 2 years lead time to obtain components that once took 6-8 weeks. It’s probably more like a 6 month delay now but there are often a critical 5% of components that suffer severe delays that determine delivery. It’s the same in automotive as well as aviation. Thanks, COVID-19 and the response.

        • Strange that it’s affecting PW more than other engine makers, don’t you think?

    • Strange that essentially a brand new plane is taken out of service as the story says the engines will be used on other planes whose engines are due for scheduled overhaul.
      It seems to me they got caught out by mistiming their overhauls, staffing and the required parts on hand.

      • This: “.. the required parts on hand.”

        Did GE work some insidious magic to entangle the competition ( like on the TP400 gearboxes ) ?

    • So true this was discussed some weeks back on Anet.

      Indigo was swayed by the fancy PW brochures too.

      “Earlier this month, Tata Group-owned Air India placed an order for 470 planes with Airbus and Boeing. However, P&W has not been chosen to supply engines for any of these aircraft and the engines are to be supplied by GE Aerospace, CFM and Rolls Royce.”


      • Can’t blame them, can you?
        At least there’s another engine choice for the A320/A321 — that’s not a luxury that the A220 and E2 enjoy.

        One could be forgiven for asking if this is a “state-sponsered” ploy to thwart competition…

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