Editing Turbofan (section)

=== Future progress ===
Engine cores are shrinking as they operate at higher [[Overall pressure ratio|pressure ratio]]s and become more efficient and smaller compared to the fan as bypass ratios increase.<!--<ref name=AvWeek26Mar2015/>-->
Blade [[tip clearance]]s are more difficult to maintain at the exit of the high-pressure compressor where blades are {{cvt|0.5|in|mm}} high or less; [[Structural system|backbone]] bending further affects clearance control as the core is proportionately longer and thinner and the fan to low-pressure turbine driveshaft space is constrained within the core.<ref name=AvWeek26Mar2015>{{cite news |url= http://aviationweek.com/technology/reversed-tilted-future-pratt-s-geared-turbofan |title= A Reversed, Tilted Future For Pratt's Geared Turbofan? |date= Mar 26, 2015 |author= Guy Norris and Graham Warwick |work= Aviation Week & Space Technology}}</ref>

[[Pratt & Whitney]] VP technology and environment [[Alan H. Epstein|Alan Epstein]] argued "Over the history of commercial aviation, we have gone from 20% to 40% [cruise efficiency], and there is a consensus among the engine community that we can probably get to 60%".<ref name=AvWeek8Aug2017>{{cite news |url= http://aviationweek.com/technology/turbofans-are-not-finished-yet |title= Turbofans Are Not Finished Yet |date= Aug 8, 2017 |author= Guy Norris |work= Aviation Week & Space Technology}}</ref>

<!-- Advanced low-pressure-ratio fan tested on Pratt & Whitney geared turbofan -->
[[Geared turbofan]]s and further fan [[Overall pressure ratio|pressure ratio]] reductions may continue to improve [[propulsive efficiency]].<!--<ref name=AvWeek8Aug2017/>-->
The second phase of the FAA's Continuous Lower Energy, Emissions and Noise (CLEEN) program is targeting for the late 2020s reductions of 33% fuel burn, 60% emissions and 32&nbsp;dB EPNdb noise compared with the 2000s state-of-the-art.<ref name="faa-cleen">{{cite web |title=Continuous Lower Energy, Emissions, and Noise (CLEEN) Program |url=https://www.faa.gov/about/office_org/headquarters_offices/apl/eee/technology_saf_operations/cleen |website=www.faa.gov |publisher=Federal Aviation Administration |access-date=11 February 2023}}</ref><!--<ref name=AvWeek8Aug2017/>-->
In summer 2017 at [[NASA Glenn Research Center]] in [[Cleveland, Ohio]], Pratt has finished testing a very-low-pressure-ratio fan on a [[PW1000G]], resembling an [[open rotor]] with fewer blades than the PW1000G's 20.<ref name=AvWeek8Aug2017/>

The weight and size of the [[nacelle]] would be reduced by a short duct inlet, imposing higher aerodynamic turning loads on the blades and leaving less space for soundproofing, but a lower-pressure-ratio fan is slower.<!--<ref name=AvWeek8Aug2017/>-->
[[UTC Aerospace Systems]] Aerostructures will have a full-scale ground test in 2019 of its low-drag Integrated Propulsion System with a [[thrust reverser]], improving fuel burn by 1% and with 2.5-3 EPNdB lower noise.<ref name=AvWeek8Aug2017/>

<!-- Safran ground-testing open rotor as potential path forward -->
[[Safran]] expects to deliver another 10–15% in fuel efficiency through the mid-2020s before reaching an [[asymptote]], and next will have to increase the [[bypass ratio]] to 35:1 instead of 11:1 for the [[CFM LEAP]]. It is demonstrating a counterrotating [[open rotor]] unducted fan (propfan) in [[Istres, France]], under the European [[Clean Sky]] technology program.<!--<ref name=AvWeek8Aug2017/>-->
[[Computational fluid dynamics|Modeling]] advances and high [[specific strength]] materials may help it succeed where previous attempts failed.<!--<ref name=AvWeek8Aug2017/>-->
When noise levels are within existing standards and similar to the LEAP engine, 15% lower fuel burn will be available and for that Safran is testing its controls, vibration and operation, while [[airframe]] integration is still challenging.<ref name=AvWeek8Aug2017/>

<!-- GE focusing on thermodynamic boosts through CMC and advanced cycles -->
For [[GE Aviation]], the [[energy density]] of jet fuel still maximises the [[Breguet range equation]] and higher pressure ratio cores; lower pressure ratio fans, low-loss inlets and lighter structures can further improve thermal, transfer and propulsive efficiency.<!--<ref name=AvWeek8Aug2017/>-->
Under the [[U.S. Air Force]]'s [[Adaptive Engine Transition Program]], adaptive [[thermodynamic cycle]]s will be used for the [[sixth-generation jet fighter]], based on a modified [[Brayton cycle]] and [[Constant volume]] combustion.<!--<ref name=AvWeek8Aug2017/>-->
[[Additive manufacturing]] in the [[General Electric Advanced Turboprop|advanced turboprop]] will reduce weight by 5% and fuel burn by 20%.<ref name=AvWeek8Aug2017/>

Rotating and static [[ceramic matrix composite]] (CMC) parts operates {{cvt|500|°F}} hotter than metal and are one-third its weight.<!--<ref name=AvWeek8Aug2017/>-->
With $21.9 million from the [[Air Force Research Laboratory]], GE is investing $200 million in a CMC facility in [[Huntsville, Alabama]], in addition to its [[Asheville, North Carolina]] site, mass-producing [[silicon carbide]] matrix with silicon-carbide fibers in 2018.<!--<ref name=AvWeek8Aug2017/>-->
CMCs will be used ten times more by the mid-2020s: the CFM LEAP requires 18 CMC turbine shrouds per engine and the [[GE9X]] will use it in the combustor and for 42 HP turbine nozzles.<ref name=AvWeek8Aug2017/>

<!-- Rolls-Royce targeting 60:1 pressure ratios and geared architectures -->
[[Rolls-Royce Plc]] aim for a 60:1 pressure ratio core for the 2020s [[Ultrafan]] and began ground tests of its {{cvt|100,000|hp}} gear for {{cvt|100,000|lbf|kN}} and 15:1 bypass ratios.<!--<ref name=AvWeek8Aug2017/>-->
Nearly [[stoichiometric]] turbine entry temperature approaches the theoretical limit and its impact on emissions has to be balanced with environmental performance goals.<!--<ref name=AvWeek8Aug2017/>-->
Open rotors, lower pressure ratio fans and potentially [[distributed propulsion]] offer more room for better propulsive efficiency.<!--<ref name=AvWeek8Aug2017/>-->
Exotic cycles, [[heat exchanger]]s and pressure gain/constant volume combustion may improve [[thermodynamic efficiency]].<!--<ref name=AvWeek8Aug2017/>-->
Additive manufacturing could be an enabler for [[intercooler]] and [[recuperator]]s.<!--<ref name=AvWeek8Aug2017/>-->
Closer airframe integration and [[Hybrid electric vehicle#Aircraft|hybrid]] or [[electric aircraft]] can be combined with gas turbines.<ref name=AvWeek8Aug2017/>

Rolls-Royce engines have a 72–82% propulsive efficiency and 42–49% thermal efficiency for a {{cvt|0.63|-|0.49|lb/lbf/h|g/kN/h}} [[Thrust specific fuel consumption|TSFC]] at Mach 0.8, and aim for theoretical limits of 95% for open rotor propulsive efficiency and 60% for thermal efficiency with stoichiometric [[turbine]] entry temperature and 80:1 [[overall pressure ratio]] for a {{cvt|0.35|lb/lbf/h|g/kN/h}} TSFC<ref>{{citation |url= http://www.fzt.haw-hamburg.de/pers/Scholz/dglr/hh/text_2014_03_20_EnginesTechnology.pdf |title= Rolls-Royce technology for future aircraft engines |date= March 20, 2014 |author= Ulrich Wenger |publisher= Rolls-Royce Deutschland}}</ref>

As teething troubles may not show up until several thousand hours, the latest turbofans' technical problems disrupt [[airline]]s operations and [[aerospace manufacturer|manufacturer]]s deliveries while production rates rise sharply.<!--<ref name=SeattleTimes15jun2018>-->
[[Trent 1000]] cracked blades [[aircraft on ground|grounded]] almost 50 [[Boeing 787]]s and reduced [[ETOPS]] to 2.3 hours down from 5.5, costing [[Rolls-Royce plc]] almost $950 million.<!--<ref name=SeattleTimes15jun2018>-->
[[PW1000G]] knife-edge seal fractures have caused [[Pratt & Whitney]] to fall behind in deliveries, leaving about 100 engineless [[A320neo]]s waiting for their powerplants.<!--<ref name=SeattleTimes15jun2018>-->
The [[CFM LEAP]] introduction had been smoother but a [[ceramic composite]] {{abbr|HP|High-Pressure}} Turbine coating was prematurely lost, necessitating a new design, causing 60 A320neo engine removals for modification and delaying deliveries by up to six weeks late.<ref name=SeattleTimes15jun2018>{{cite news |url= https://www.seattletimes.com/business/boeing-aerospace/troublesome-advanced-engines-for-boeing-and-airbus-jets-disrupt-airlines-and-production-lines/ |title= Troublesome advanced engines for Boeing, Airbus jets have disrupted airlines and shaken travelers |date= June 15, 2018 |author= Dominic Gates |author-link=Dominic Gates |newspaper= The Seattle Times}}</ref>

On a widebody, [[Safran]] estimates 5–10% of fuel could be saved by reducing power intake for hydraulic systems, while swapping to electrical power could save 30% of weight, as initiated on the [[Boeing 787]], while [[Rolls-Royce plc]] hopes for up to 5%.<ref>{{cite news |url= https://www.flightglobal.com/news/articles/how-the-future-of-electric-aircraft-lies-beyond-the-460492/ |title= How the future of electric aircraft lies beyond the engines |date= 6 Sep 2019 |author= Kerry Reals |work= Flightglobal}}</ref>