Thrust for the future

For decades, three let­ters in avi­a­tion have stood for in­no­v­a­tive en­gine so­lu­tions: MTU. The en­gine ex­perts in Mu­nich have re­al­ly made a name for them­selves over the years, re­peat­ed­ly com­ing up with valu­able tech­no­log­i­cal in­no­va­tions. With their con­tri­bu­tions to the Geared Tur­bo­fan™ (GTF) en­gine, they are im­pres­sive­ly shap­ing de­vel­op­ments in the in­dus­try of the present while prepar­ing to shape the fu­ture like nev­er be­fore in the com­pa­ny’s his­to­ry: MTU’s unique ex­per­tise means it is ide­al­ly placed to tack­le the key mis­sions of to­day and to­mor­row: mak­ing com­mer­cial en­gines even more ef­fi­cient and en­vi­ron­men­tal­ly friend­ly and mil­i­tary en­gines even more pow­er­ful.

“Nev­er has MTU had such a de­fin­i­tive tech­nol­o­gy roadmap as to­day,” ex­plains COO Lars Wag­n­er. “We’re con­scious of our ­re­spon­si­bil­i­ty for sus­tain­able, emis­sions-free fly­ing. That’s why we’re al­ready in­vest­ing to­day in pi­o­neer­ing tech­nolo­gies for the avi­a­tion of to­mor­row.” Wag­n­er ex­plains that, from 2030 on­ward, the com­mer­cial seg­ment will be clear­ly ori­ent­ed to­ward the next gen­er­a­tion of the Geared Tur­bo­fan™, while in the mil­i­tary ­seg­ment it is the NEFE (Next Eu­ro­pean Fight­er En­gine) that will de­ter­mine the com­pa­ny’s di­rec­tion. He con­tin­ues: “In the com­mer­cial seg­ment, we’re re­search­ing sev­er­al evo­lu­tion­ary ­ap­proach­es that are al­ready pos­si­ble to­day thanks to sus­tain­able e-fu­els. At the same time, we’re look­ing in­to al­ter­na­tive en­gine con­cepts rang­ing from hy­brid-elec­tric flight to fu­el cells.”

Pro­file of com­mer­cial avi­a­tion in 2050

How­ev­er, MTU’s ex­perts are not sat­is­fied to leave it at that; they are cast­ing their gazes fur­ther in­to the fu­ture. Part of a small band of vi­sion­ar­ies world­wide, they are al­ready work­ing with part­ners from in­dus­try and re­search on ideas for the com­mer­cial en­gines that could fly from 2050 on­wards. Wag­n­er ex­plains: “MTU is work­ing out rev­o­lu­tion­ary en­gine con­cepts to achieve the am­bi­tious goals of Flight­path 2050.” These new en­gine so­lu­tions have to go be­yond to­day’s tech­nol­o­gy, with emis­sions-free flight the greater goal.

The MTU ex­perts have sev­er­al spe­cif­ic en­gine con­cepts in view, in­clud­ing the com­pos­ite cy­cle and the steam-injected and water-recovering gas turbine. Such “rev­o­lu­tion­ary” so­lu­tions in­volve en­tire­ly new tech­nol­o­gy. By con­trast, MTU char­ac­ter­izes the fur­ther de­vel­op­ment of the ­ex­ist­ing Geared Tur­bo­fan™ tech­nol­o­gy as “evo­lu­tion­ary”: the sec­ond GTF gen­er­a­tion still of­fers con­sid­er­able po­ten­tial. Once it has been fur­ther op­ti­mized, it will dra­mat­i­cal­ly re­duce emis­sions and is due to be air­borne by the mid-2030s.

Then there will need to be a tech­no­log­i­cal leap for­ward to de­vel­op tech­nolo­gies and con­cepts that will pave the way for large­ly emis­sions-free flight—this is the re­spon­si­bil­i­ty of the Eu­ro­pean avi­a­tion in­dus­try. Re­source­ful MTU de­vel­op­ers have come up with two ap­proach­es and are com­bin­ing the tried-and-test­ed gas tur­bine en­gine with brand new tech­nolo­gies: in the com­pos­ite cy­cle ap­proach, the con­ven­tion­al high-pres­sure com­pres­sor sys­tem is to be sup­ple­mented by a pis­ton com­pres­sor and en­gine. “This will al­low us to sig­nif­i­cant­ly in­crease ther­mal ef­fi­cien­cy,” says Dr. Ste­fan We­ber, Se­nior Vice Pres­i­dent Tech­nol­o­gy & En­gi­neer­ing Ad­vanced Pro­grams in Mu­nich. The steam-injected and water-recovering gas turbine, meanwhile, in­te­grates a steam pow­er process in­to the gas tur­bine process­es. This in­volves us­ing a gas tur­bine with steam in­jec­tion to feed the heat of the ex­haust stream back in­to the process in­side the en­gine. The wet com­bus­tion would sub­stan­tial­ly re­duce both CO₂ and NO_x pol­lu­tant emis­sions. “We’ll have to see which ap­proach ul­ti­mate­ly of­fers greater po­ten­tial and is eco­nom­i­cal­ly fea­si­ble,” We­ber says. If this turns out to be the steam-injected and water-recovering gas turbine, it will not work in the cur­rent air­craft ar­chi­tec­ture, thus call­ing for a new con­fig­u­ra­tion.

Sus­tain­able, re­new­able fu­els

Work on these two MTU pi­lot con­cepts is be­ing ac­com­pa­nied by oth­er ac­tiv­i­ties. “These mea­sures alone won’t be enough for us to reach the am­bi­tious goals for 2050,” says We­ber. “They will get us a good part of the way there, but by no means will they let us achieve them com­plete­ly. We need to close the re­main­ing gap through the de­vel­op­ment of sus­tain­able fu­els.” The idea is to shift away from con­sum­ing fos­sil fu­els to­ward sus­tain­able, re­new­able fu­els. “We want to en­cour­age their use,” We­ber says. Promis­ing ap­proach­es for pro­duc­ing syn­thet­ic fu­els are of­fered by so­lar en­er­gy and by elec­tric­i­ty—pro­vid­ed it is gen­er­at­ed sus­tain­ably. The lat­ter tech­nol­o­gy is al­ready avail­able to­day. One of the ma­jor ad­van­tages of syn­thet­ic fu­els is that they don’t re­quire any new in­fra­struc­ture; they can sim­ply be “dropped in” to ex­ist­ing pe­tro­le­um-based in­fra­struc­ture. To com­plete­ly cut out NO_x emis­sions as well, there’s no get­ting away from fu­el cells—mean­ing fly­ing with hy­dro­gen. MTU has this tech­nol­o­gy in its sights, too.

E-fly­ing

One top­ic has been gain­ing more and more pub­lic at­ten­tion re­cent­ly: elec­tric fly­ing. This is be­cause pure­ly bat­tery-dri­ven air­craft fly com­plete­ly emis­sions-free—pro­vid­ed the elec­tric­i­ty they use has been gen­er­at­ed sus­tain­ably. “Emis­sions-free” does not in­clude noise, as this sim­ply can­not be ful­ly avoid­ed when it comes to flight. Re­al­is­ti­cal­ly, how­ev­er, from to­day’s per­spec­tive there are large ob­sta­cles to over­come be­fore we will see pure­ly bat­tery-pow­ered pas­sen­ger air­craft. We­ber elab­o­rates: “Elec­tric propul­sion sys­tems and bat­ter­ies reach per­for­mance lev­els to­day that per­mit their use in pow­er glid­ers, sport­ing air­planes and oth­er air­craft in that class.” But at present, trans­fer­ring this tech­nol­o­gy in­to air­craft in the Air­bus A320 class is im­pos­si­ble, as the bat­tery ca­pac­i­ty falls far short of what’s need­ed. “And we cur­rent­ly see no promis­ing tech­no­log­i­cal ap­proach­es open­ing up in the fu­ture.”

What does seem tech­ni­cal­ly fea­si­ble from to­day’s per­spec­tive are tur­bo-elec­tric or hy­brid-elec­tric sys­tems that in­te­grate the tur­bo­ma­chin­ery and gen­er­a­tor in­to the air­craft fuse­lage. The cur­rent for the elec­tric mo­tors could be gen­er­at­ed by a gas tur­bine; in turn, the elec­tric mo­tors would pow­er dis­trib­uted fans on the wing. Whether there is tru­ly po­ten­tial to be tapped with this ap­proach re­mains to be seen. Suc­cess ul­ti­mate­ly hinges on tech­ni­cal progress in the field of bat­ter­ies and elec­tric mo­tors. MTU has its fin­ger on the pulse here, too, and is in­volved in var­i­ous stud­ies and ini­tia­tives: for ex­am­ple, it is col­lab­o­rat­ing with part­ners to in­ves­ti­gate hy­brid-elec­tric or all-elec­tric pow­er­trains for air taxis or even 19-seater air­craft.

We­ber is cer­tain about one thing: “As a con­cept, the gas tur­bine en­gine will con­tin­ue to hold sway. It’s fit for the fu­ture and holds po­ten­tial for fur­ther op­ti­miza­tion.” Us­ing sus­tain­able drop-in fu­els with the ex­ist­ing in­fra­struc­ture would make it pos­si­ble to quick­ly put a sig­nif­i­cant dent in pol­lu­tion emis­sions. There are two con­ceiv­able ap­pli­ca­tions for the gas tur­bine in air­craft: ei­ther as an im­proved, green­er main en­gine or else as the ba­sis for low-emis­sions hy­brid sys­tems, in­so­far as their in­tro­duc­tion is proven to be ben­e­fi­cial over­all.

MTU has po­si­tioned it­self clear­ly: it re­mains true to it­self and its tra­di­tion, and is eye­ing all pos­si­bil­i­ties for en­sur­ing fur­ther progress in the skies. Af­ter all, as the ex­perts know, the fu­ture of avi­a­tion be­gins to­day.