innovation

Geared Turbo­fan: How the engine of the future was developed

The first preliminary studies into a geared turbo­fan were begun by Pratt & Whitney, MTU and Fiat Avio in the 1990s. Today, the inno­vative tech­nology sets standards and brings substantial reductions in fuel, CO2 and noise.

05.2019 | Text: Denis Dilba

Text:
Denis Dilba holds a degree in mechatronics, is a graduate of the German School of Journalism, and founded the “Substanz” digital science magazine. He writes articles about a wide variety of technical and business themes.

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For decades, MTU has been work­ing on ways to make air­craft en­gines con­sume less fu­el, pro­duce low­er emis­sions and be­come qui­eter. The gold­en rule has al­ways been that to ful­fill the am­bi­tious goals of to­mor­row, you must push them through the de­ve­lop­ment process the day be­fore yes­ter­day. This re­quires not on­ly far­sight­ed­ness and con­fi­dence in your own ex­per­tise, but al­so ex­cel­lent part­ners and a good mea­sure of courage. When this bal­ance is right, you can achieve the goals of the fu­ture. A per­fect ex­am­ple of this is the Geared Tur­bo­fan™ (GTF), in­to which vir­tu­al­ly all in­no­va­tions of the past decades have gone.

AEROREPORT series: 50 years of innovation at MTU

From ADP to AT­FI to GTF

Back in the 1990s, Amer­i­can man­u­fac­tur­er Pratt & Whit­ney be­gan work­ing with MTU and the for­mer Fi­at Avio on ini­tial pre­lim­i­nary stud­ies for a geared tur­bo­fan en­gine un­der the pro­ject name Ad­vanced Duct­ed Propul­sor (ADP). How­ev­er, the pro­ject was not fur­ther pur­sued for com­mer­cial rea­sons. But over the years that fol­lowed, ris­ing kerosene prices cou­pled with cus­tomer de­mand for qui­eter en­gines that pro­duced low­er emis­sions led to a re-eval­u­a­tion of the geared tur­bo­fan con­cept’s mar­ket po­ten­tial. At the start of the 2000s, the in­ves­ti­ga­tions were re­sumed with the Ad­vanced Tech­nol­o­gy Fan In­te­gra­tor (AT­FI). This demon­stra­tor con­sist­ed of a propul­sion sys­tem with a re­duc­tion gear­box be­tween the fan and the low-pres­sure tur­bine and was test­ed based on a PW6000 core en­gine. In ad­di­tion to the three ADP part­ners, Pratt & Whit­ney Cana­da were now al­so work­ing on the pro­ject. And so en­gine man­u­fac­tur­er Pratt & Whit­ney laid the foun­da­tion for its patent­ed Geared Tur­bo­fan™ pro­gram, which of­fi­cial­ly launched in 2008. At rough­ly the same time as the test phase of the AT­FI, the MTU en­gi­neers de­vel­oped a new high-pres­sure com­pres­sor as part of the En­gine 3E pro­ject. For the lay­out and com­pu­ta­tion of the six-stage HDV12 com­pres­sor, a nu­mer­i­cal 3D Navier-Stokes flow solver was used for the first time. As a re­sult, the com­po­nent achieved a high over­all pres­sure ra­tio of al­most 11.

A predecessor of the later Pratt & Whitney GTF™ engine: the ATFI dem­on­strator. ATFI stands for Advanced Tech­nology Fan Integrator. Hover over the image for a bigger view

A predecessor of the later Pratt & Whitney GTF™ engine: the ATFI dem­on­strator. ATFI stands for Advanced Tech­nology Fan Integrator.

atfi

A predecessor of the later Pratt & Whitney GTF™ engine: the ATFI dem­on­strator. ATFI stands for Advanced Tech­nology Fan Integrator.

The instrumentation of the high-pres­sure com­pres­sor rotor calls for dex­ter­ous, sensitive fingers. Hover over the image for a bigger view

The instrumentation of the high-pres­sure com­pres­sor rotor calls for dex­ter­ous, sensitive fingers.

hochdruckverdichter

The instrumentation of the high-pres­sure com­pres­sor rotor calls for dex­ter­ous, sensitive fingers.

Computer animation of sections from the high-speed low-pres­sure turbine (LPT) to be integrated into the Pratt & Whitney GTF™ engine. Hover over the image for a bigger view

Computer animation of sections from the high-speed low-pres­sure turbine (LPT) to be integrated into the Pratt & Whitney GTF™ engine.

niederdruckturbine

Computer animation of sections from the high-speed low-pres­sure turbine (LPT) to be integrated into the Pratt & Whitney GTF™ engine.

Preparing to run a stress test on the PW6000, which also helped. Hover over the image for a bigger view

Preparing to run a stress test on the PW6000, which also helped.

pw6000

Preparing to run a stress test on the PW6000, which also helped.

The HDV12 was to form the ba­sis for the high-pres­sure com­pres­sor of the PW6000 en­gine for the Air­bus A318—and sub­se­quent­ly, like the ADP and AT­FI demon­stra­tors, to pave the way fur­ther for the Geared Tur­bo­fan™. Its core de­vel­op­ment start­ed in 2005, when the part­ners de­cid­ed to de­vel­op and test a demon­stra­tion en­gine. The ini­tial tests of the over­all sys­tem in 2007 im­me­di­ate­ly yield­ed very pos­i­tive re­sults with re­gard to the func­tion­al­i­ty of the crit­i­cal com­po­nents. How­ev­er, it was al­so clear that the new en­gine over­all had one big area of im­prove­ment left: fur­ther de­vel­op­ment would pay off on­ly if it cre­at­ed a whole Geared Tur­bo­fan™ en­gine fam­i­ly. Con­vinced by the con­cept, Pratt & Whit­ney and MTU sys­tem­at­i­cal­ly in­vest­ed fur­ther in the en­tire process chain so as to per­mit the cre­ation of geared tur­bo­fans of dif­fer­ent thrust class­es. Just one year lat­er, the Geared Tur­bo­fan™ took off for the first time on flight tests.

En­gi­neer­ing courage pays off

With the two ma­jor MTU work­shares, the high-speed low-pres­sure tur­bine and the first four stages of the eight-stage high-pres­sure com­pres­sor en­gi­neered in blisk de­sign, the en­gine of the fu­ture al­ready achieves a very high de­gree of ef­fi­cien­cy to­day. The im­pres­sive re­sult: fu­el con­sump­tion and car­bon diox­ide emis­sions are re­duced by 16 per­cent each, and the noise foot­print by 75 per­cent. And as few­er com­pres­sor and tur­bine stages are need­ed, not on­ly are the en­gines lighter, but main­te­nance costs de­cline as well, be­cause few­er com­po­nents are ex­posed to the hot gas. For the key GTF com­po­nent, the high-speed low-pres­sure tur­bine, MTU won two Ger­man in­no­va­tion awards. Ger­many’s lead­ing en­gine man­u­fac­tur­er is the on­ly com­pa­ny in the world to have mas­tered this tech­nol­o­gy. The pa­tience and per­se­ver­ance was worth it: as well as rep­re­sent­ing a tech­no­log­i­cal quan­tum leap, the Geared Tur­bo­fan™ con­cept has al­so been a ma­jor com­mer­cial suc­cess.

Video: Floor-based assembly system Article with video

Floor-based assembly system

MTU Aero Engines’ final assembly line for the PW1100G-JM engine powering the A320neo is the only one of its kind in the world. To the video

To­day, Air­bus of­fers the GTF for the A320neo and the A220 (for­mer­ly Bom­bardier C Se­ries), Mit­subishi has it in their MRJ, and Em­braer has it in the new E-Jets of the E-170 and E-190 fam­i­lies. More­over, Irkut wants the GTF for the MC-21. At present, a to­tal of 80 air­lines world­wide have or­dered more than 8,000 of the GTF en­gines. More new MTU in­no­va­tions have gone in­to the cur­rent ver­sion, such as the first ad­di­tive­ly man­u­fac­tured com­po­nents and brush seals. In ad­di­tion, MTU has looked af­ter a third of the en­tire fi­nal as­sem­bly for the A320neo PW1100G-JM en­gine since the end of 2016. To this end, MTU in­vest­ed some 20 mil­lion eu­ros in a track-guid­ed as­sem­bly line sys­tem, which was de­vel­oped in-house and is unique world­wide. “What we’ve achieved of course makes us proud, but no­body at MTU should rest on these lau­rels,” em­pha­sizes Dr. Jörg-Michael Henne, Se­nior Vice Pres­i­dent En­gi­neer­ing and Tech­nol­o­gy at MTU. Over­all, the GTF has the po­ten­tial to re­duce fu­el con­sump­tion and CO2 emis­sions by up to 40 per­cent.

Interaction: Geared turbofan™ compared to everyday noises

Geared turbofan™ compared to everyday noises

A jackhammer? A freight train? Or perhaps just a car going by at 60 kph? It's surprising how quiet a GTF engine is compared to everyday noises. To the interaction ...

Fur­ther de­vel­op­ment al­ready be­ing pre­pared

For in­stance, it would be pos­si­ble to achieve even low­er fan pres­sure ra­tios step by step over the com­ing years, which would fur­ther in­crease the by­pass ra­tio—from the cur­rent 12:1 to as much as 20:1 by 2035. More­over, MTU’s en­gi­neers are work­ing on fur­ther im­prov­ing the core en­gine’s ther­mal ef­fi­cien­cy by in­creas­ing the pres­sure and tem­per­a­ture ra­tios. This will in­volve in­creas­ing the over­all pres­sure ra­tio well be­yond its cur­rent val­ue of about 50:1, while dra­mat­i­cal­ly re­duc­ing the amount of cool­ing air need­ed.

And for 2050 and be­yond, MTU is al­ready de­vis­ing ini­tial stud­ies, con­cepts and ideas in col­lab­o­ra­tion with uni­ver­si­ties and oth­er re­search in­sti­tutes: “We need rev­o­lu­tion­ary ap­proach­es that must go be­yond to­day’s tech­nolo­gies, and above all else, we need new air­craft ar­chi­tec­tures,” says Dr. Ste­fan We­ber, Se­nior Vice Pres­i­dent Tech­nol­o­gy & En­gi­neer­ing Ad­vanced Pro­grams at MTU. Among the op­tions un­der re­view for the en­gine are the use of high­ly ef­fi­cient heat en­gines with ex­treme­ly high pres­sures or the in­te­gra­tion of re­cu­per­a­tive el­e­ments to im­prove the ther­mo­dy­nam­ic cy­cle. Shield­ed pro­pellers or fans dis­trib­uted around the fuse­lage are al­so pos­si­bil­i­ties. In ad­di­tion, there are tech­no­log­i­cal so­lu­tions such as al­ter­na­tive fu­els and steps to­ward tur­bo-elec­tric flight, with­out which fu­ture tar­gets can­not be met.

All im­prove­ments al­ways have the same goal: im­prove ef­fi­cien­cy and there­by min­i­mize fu­el con­sump­tion, emis­sions and noise. The en­gine of the day af­ter to­mor­row has long been in the start­ing blocks—and MTU is al­ready tak­ing re­spon­si­bil­i­ty to­day for mov­ing avi­a­tion to­ward emis­sions-free flight.

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AEROREPORT is an aviation magazine published by MTU Aero Engines, Germany's leading engine manufacturer. Neatly summed up, AEROREPORT offers an MTU perspective on the world of aviation. The word “REPORT” in the title stands for the high-tech and outstanding service “made by MTU”. “AERO” represents broader horizons and general aviation topics.

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