Page 1 of 1

Future engine improvements

Posted: Sat Feb 09, 2019 4:27 pm
by SEPilot
There seems to be an assumption on this forum that engine efficiency will continue to be improved indefinitely, and that we can just assume that in 10 years we will have engines available that are 10% more efficient than the ones available today. However, as an engineer I know that there are absolute limits to efficiency, and I know from experience that the closer you get to those limits the harder it is to get more improvement. On top of that, ALL of the engine manufacturers, with RR seeming to lead the pack, are having various degrees of difficulty meeting delivery and/or performance and reliability commitments. So my question is are we approaching a plateau where engine improvements are going to be much less dramatic than we have experienced over the last 20 years or so? There was a long period, from around 1980 to about 2000 when engines changed very little, if any, and then suddenly we got on this march of seemingly continual improvements. We now are at the point where the GE90-110/115, which was only introduced in 2004 and was a marvel of efficiency and reliability, is already obsolete and is being replaced. How long before its replacement is obsolete? So what do you think; is there still a lot of room for improved efficiency or are we approaching the limits?

Re: Future engine improvements

Posted: Sat Feb 09, 2019 4:46 pm
by WIederling
https://www.hq.nasa.gov/office/aero/eve ... soaeng.pdf p1
( not reaching into the present, but the first easy find of sfc vs date )

You saw the step changes leveraged by fundamental changes in engine design.
turbojet -> turbojet with lowish bp -> turbofan -> ( GTF?)
( and there is a melee' of new engines around 1980+-3 )
all other improvements are incremental gains on details. Basic setup doesn't change.

all areas are still far enough away from theoretical limits that incremental gains
will show as ~constant ( in % to the last item ) improvements. ( actually an exponential curve.)

Re: Future engine improvements

Posted: Sat Feb 09, 2019 5:46 pm
by SEPilot
WIederling wrote:
https://www.hq.nasa.gov/office/aero/events/encompat/soaeng.pdf p1
( not reaching into the present, but the first easy find of sfc vs date )

You saw the step changes leveraged by fundamental changes in engine design.
turbojet -> turbojet with lowish bp -> turbofan -> ( GTF?)
( and there is a melee' of new engines around 1980+-3 )
all other improvements are incremental gains on details. Basic setup doesn't change.

all areas are still far enough away from theoretical limits that incremental gains
will show as ~constant ( in % to the last item ) improvements. ( actually an exponential curve.)

That chart is pretty old, and it does not show what the theoretical limits are. The practical limits will only be found when we get there, and hence it is very difficult to say before we get there what they will be. But I suspect it will be a gradual thing, as improvements will be harder and harder to achieve, and in smaller increments.

Re: Future engine improvements

Posted: Sat Feb 09, 2019 9:24 pm
by acjbbj
SEPilot wrote:
We now are at the point where the GE90-110/115... is already obsolete


They're still being made, right? UA just ordered four new 77W's.

Re: Future engine improvements

Posted: Sat Feb 09, 2019 10:31 pm
by wildwobby
FWIW, one area efficiency will improve is with material science for high temperatures which currently limits the temperature in the burner.

A higher delta-T in the burner is more efficient, but current material limitations don’t allow for it currently.

https://www.grc.nasa.gov/www/k-12/airplane/burnth.html

Re: Future engine improvements

Posted: Sun Feb 10, 2019 1:33 am
by SEPilot
acjbbj wrote:
SEPilot wrote:
We now are at the point where the GE90-110/115... is already obsolete


They're still being made, right? UA just ordered four new 77W's.

Yes, but the 77X is coming soon, with something like 15% better economics. But UA needs them now.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 8:10 am
by KFLLCFII
The GE9GTF is still a ways out.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 10:26 am
by WIederling
SEPilot wrote:
Yes, but the 77X is coming soon, with something like 15% better economics.

Which is not synonymous with 15% better engine sfc.

wildwobby wrote:
A higher delta-T in the burner is more efficient, but current material limitations don’t allow for it currently.
https://www.grc.nasa.gov/www/k-12/airplane/burnth.html


On the other end higher temps and higher pressure ( OPR ) have real and high impact on NOx creation.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 11:10 am
by SEPilot
WIederling wrote:
SEPilot wrote:
Yes, but the 77X is coming soon, with something like 15% better economics.

Which is not synonymous with 15% better engine sfc.

I realize that; I believe the engine improvement is around 10%. The rest is the new wing, which allows less thrust, and hence less fuel, to lift the same weight.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 5:02 pm
by frmrCapCadet
Perhaps the new field for improvements could be making great engines cheaper, more reliable, and easier to maintain.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 6:46 pm
by TWA772LR
I feel we've already reached that at least as far as big twins are concerned. The example is the 777X. A bigger plane that flies farther with more weight than it's predecessor all with a less powerful engine, updated nonetheless and still very efficient, but the vast majority of the performance is the wing. Similar can be said for the 737 Classic -> 737NG, refined (not really an upgrade) engine and brand new wing.

I started college as an aerospace engineering major but changed because I wasn't disciplined enough at age 19 to do calculus. But it was airflow and wing design that really attracted me to the field to make commercial airliners more efficient.

But the jet engine has pretty much been the same for 60 years, and many of its advancements have come from increased knowledge of airflow, computerization, and new materials. It's come a long way but who knows what the next propulsion revolution will be. Hydrogen fuel cell? Solar? Nuclear? Ion? Unicorn farts?

Re: Future engine improvements

Posted: Sun Feb 10, 2019 8:52 pm
by 1989worstyear
WIederling wrote:
https://www.hq.nasa.gov/office/aero/events/encompat/soaeng.pdf p1
( not reaching into the present, but the first easy find of sfc vs date )

You saw the step changes leveraged by fundamental changes in engine design.
turbojet -> turbojet with lowish bp -> turbofan -> ( GTF?)
( and there is a melee' of new engines around 1980+-3 )
all other improvements are incremental gains on details. Basic setup doesn't change.

all areas are still far enough away from theoretical limits that incremental gains
will show as ~constant ( in % to the last item ) improvements. ( actually an exponential curve.)


It's really 1990 +/- 3 due to the A320, but I otherwise agree. The JT8d and 9d were still state-of-the in 1986, but not 1987 or 1988.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 9:13 pm
by JayinKitsap
I came across this very good article about the GE90. Actual data in a number of areas.

http://www.team.aero/images/aviation_da ... de_777.pdf

The efficiency improvements require higher temperatures, higher material strengths, newer ceramic and non-metal items, and other items at the bleeding edge of technology. Clearances are getting quite tight to where differential expansion can be quite tricky, an engine soaked at -40C then landing in the desert at 45C would have the fan temperature rising faster than the casing, in reverse taking off from DXB and reaching altitude at -30C would have the fan shrinking more than the casing. Sitting after landing on a short turn around ends up with the top of the core being hotter than the bottom causing both shaft bow and casing ovalling. With the dimensions of the parts in question and tolerances in the 0.001 level thermal growth plays havoc.

On the Trent 1000's these kind of things have been causing high levels of maintenance, with many planes sitting for weeks. Is that a cost the airlines want to bear for a 2% improvement. Unlikely.

There is a coming period where engines will settle into a lull until the tech matures and the bugs get out of this new level of tech.

Re: Future engine improvements

Posted: Sun Feb 10, 2019 10:45 pm
by WIederling
JayinKitsap wrote:
On the Trent 1000's these kind of things have been causing high levels of maintenance, with many planes sitting for weeks. Is that a cost the airlines want to bear for a 2% improvement. Unlikely.

There is a coming period where engines will settle into a lull until the tech matures and the bugs get out of this new level of tech.


The GE90 was a rather fickle engine at the beginning and an emissions pig and ran on an FAA exemption.
( But all three could be fixed by PR at the time. :-)

IMU the Trent1000 coating problems seem to have not been performance linked but to changes in process ( to get cheaper? no idea )

Re: Future engine improvements

Posted: Mon Feb 11, 2019 6:19 am
by kitplane01
TWA772LR wrote:
I feel we've already reached that at least as far as big twins are concerned. The example is the 777X. A bigger plane that flies farther with more weight than it's predecessor all with a less powerful engine, updated nonetheless and still very efficient, but the vast majority of the performance is the wing. Similar can be said for the 737 Classic -> 737NG, refined (not really an upgrade) engine and brand new wing.

I started college as an aerospace engineering major but changed because I wasn't disciplined enough at age 19 to do calculus. But it was airflow and wing design that really attracted me to the field to make commercial airliners more efficient.

But the jet engine has pretty much been the same for 60 years, and many of its advancements have come from increased knowledge of airflow, computerization, and new materials. It's come a long way but who knows what the next propulsion revolution will be. Hydrogen fuel cell? Solar? Nuclear? Ion? Unicorn farts?


I think that makes as much sense as saying that automobiles have not changed much in 60 years.

Cars 60 years ago required the insertion of keys, did not have seat belts, and had "tune ups". If you pushed the left-most pedal, the brakes locked up. They didn't have built in maps of the world, nor SiriusXM radio. The power/weight ratio was poor, and they emitted lead vapor. My car tells me when it want's it's oil changed, and I bet yours does too.

Re: Future engine improvements

Posted: Mon Feb 11, 2019 7:32 am
by Faro
There is a wealth of efficiency to gain from rotating CMC components...so far all applications of CMC's have been for static parts...like turbine shrouds and inlet guide vanes...the day you can implement CMC turbine blades you may see 5-10% efficiency gains...but that would still seem to be some time off in the future it seems...


Faro

Re: Future engine improvements

Posted: Mon Feb 11, 2019 9:40 am
by WIederling
kitplane01 wrote:
Cars 60 years ago required the insertion of keys, did not have seat belts, and had "tune ups". If you pushed the left-most pedal, the brakes locked up. They didn't have built in maps of the world, nor SiriusXM radio. The power/weight ratio was poor, and they emitted lead vapor. My car tells me when it want's it's oil changed, and I bet yours does too.


Why would brakes lock up when you push the leftmost pedal? :-)

Interesting that you mostly describe curlicues added to the fringe and not basic improvements
like highly improved roadhandling, specific fuel consumption, passive savety, ...

Re: Future engine improvements

Posted: Tue Feb 12, 2019 4:24 am
by planecane
WIederling wrote:
kitplane01 wrote:
Cars 60 years ago required the insertion of keys, did not have seat belts, and had "tune ups". If you pushed the left-most pedal, the brakes locked up. They didn't have built in maps of the world, nor SiriusXM radio. The power/weight ratio was poor, and they emitted lead vapor. My car tells me when it want's it's oil changed, and I bet yours does too.


Why would brakes lock up when you push the leftmost pedal? :-)

, ...


You beat me to it! I'd imagine 60 years ago the left most pedal wouldn't have caused the brakes to lock up on the vast majority of cars.

Re: Future engine improvements

Posted: Tue Feb 12, 2019 9:04 am
by WIederling
planecane wrote:
You beat me to it! I'd imagine 60 years ago the left most pedal wouldn't have caused the brakes to lock up on the vast majority of cars.


No idea when automatic gearboxes became pervasive in the US. ( Stickshift is still near 70% in Germany )

Quite interesting the <clutch><brake><accelerator> arrangement seems to be rather universal ( over history, LHD, RHD ).
indicator, wiper control, lights are more varied

Re: Future engine improvements

Posted: Tue Feb 12, 2019 1:59 pm
by SEPilot
WIederling wrote:
planecane wrote:
You beat me to it! I'd imagine 60 years ago the left most pedal wouldn't have caused the brakes to lock up on the vast majority of cars.


No idea when automatic gearboxes became pervasive in the US. ( Stickshift is still near 70% in Germany )

Quite interesting the <clutch><brake><accelerator> arrangement seems to be rather universal ( over history, LHD, RHD ).
indicator, wiper control, lights are more varied

Most American cars were automatic by the mid 60s, at least the larger ones. Imported cars, which were becoming rapidly more popular, were still mostly stick shift, as were trucks. Stick shift has been losing ground since then; now it is not offered at all in most vehicles.

Re: Future engine improvements

Posted: Tue Feb 12, 2019 5:04 pm
by stephanwintner
kitplane01 wrote:
I think that makes as much sense as saying that automobiles have not changed much in 60 years.

Cars 60 years ago required the insertion of keys, did not have seat belts, and had "tune ups". If you pushed the left-most pedal, the brakes locked up. They didn't have built in maps of the world, nor SiriusXM radio. The power/weight ratio was poor, and they emitted lead vapor. My car tells me when it want's it's oil changed, and I bet yours does too.


I don't know about you, but whether it was 60 years ago or today, if it is a "car" then the left-most pedal is for the clutch, and won't lock up the brakes. If it is / was equipped with only 2 pedals, it's not a "car" in my eyes. ;)

Re: Future engine improvements

Posted: Tue Feb 12, 2019 5:25 pm
by stephanwintner
As far as the subject - as far as I understand it, within the bounds of the high bypass turbofan architecture, there is a bit or room left (CMCs, better metal materials, better cooling approaches) but the approaching limits are what drove Pratt to the GTF architecture.

A higher bypass ratio improves propulsive efficiency but is heavier, and makes the LPT harder to design (= more stages = cost & weight). The gearbox is itself heavy and expensive, but allows the higher bypass ratio fan, coupled to a small and efficient LPT. On balance, it wins, says Pratt.

As for thermodynamic cycle efficiency, CMCs are expensive to make and not really repairable, and higher temps have NOx issues. Pratt went GTF, while GE went CMCs and higher temps for their latest engines. Philosophical difference. Pratt will eventually go to CMCs (I imagine they already have in their fighter engines), and GE will (probably) eventually admit the GTF makes sense. I imagine our understanding of NOx formation and combustion will continue to improve. Maybe environmental concerns will push to, say, hydrogen fuel despite the cooling issues. Etc.

The propfan (https://en.wikipedia.org/wiki/Propfan) has been on the drawing boards for a while - eventually the high bypass turbofan won't be a practical way to get the desired efficiency goals. There will be lighter approaches. The propfan has issues with noise and containment but ought to be a big jump in propulsive efficiency, as far as I understand. There are other ideas - the blended wing body, for one, or the truss wing (https://www.boeing.com/features/2019/01 ... 01-19.page).

Electric and hybrids are limited by their batteries. In short, batteries are much heavier than jet fuel, for the same amount of energy - and they will close the gap in future, but only partially. And since they don't burn off, they push up average weight. On the other hand, motors are small and simple, and low noise (though they are already at some physical limits on size). Electric aircraft may eventually catch up but outside of very short ranges, air-taxis, etc, I remain skeptical. Every study or article I see says the same.

Re: Future engine improvements

Posted: Tue Feb 12, 2019 5:39 pm
by Zeke2517
Come to think of it, the E-break in some vehicles is engaged by pushing a little tiny pedal that’s situated... all the way to the left, by the door. That’ll lock your wheels up.

Re: Future engine improvements

Posted: Tue Feb 12, 2019 6:19 pm
by WIederling
Zeke2517 wrote:
Come to think of it, the E-break in some vehicles is engaged by pushing a little tiny pedal that’s situated... all the way to the left, by the door. That’ll lock your wheels up.


Parking brake ?
electric or mechanic?
hand lever ( most cars here ), foot lever very far on the left, ratcheting, release puller from the dash ( Mercedes )
pneumatic one in lorries largish toggle in the dash.
no hands on experience with electric operated park brakes.
French cars used to have a pull lever below the dash, ratcheting, turn to release.

Re: Future engine improvements

Posted: Tue Feb 12, 2019 8:03 pm
by Zeke2517
WIederling wrote:
Zeke2517 wrote:
Come to think of it, the E-break in some vehicles is engaged by pushing a little tiny pedal that’s situated... all the way to the left, by the door. That’ll lock your wheels up.


Parking brake ?
electric or mechanic?
hand lever ( most cars here ), foot lever very far on the left, ratcheting, release puller from the dash ( Mercedes )
pneumatic one in lorries largish toggle in the dash.
no hands on experience with electric operated park brakes.
French cars used to have a pull lever below the dash, ratcheting, turn to release.


Mechanical, just like you described.

Re: Future engine improvements

Posted: Wed Feb 13, 2019 1:58 am
by fdxtulmech
You can get a marked improvement in efficiency by going to a single engine, half the engines half the fuel, duh!

BTW its a joke for those of you whom have lost their online sense of humor. Oh, and a manual transmission is driving, automatic is riding.

Re: Future engine improvements

Posted: Wed Feb 13, 2019 7:40 pm
by acjbbj
Zeke2517 wrote:
Come to think of it, the E-break in some vehicles is engaged by pushing a little tiny pedal that’s situated... all the way to the left, by the door. That’ll lock your wheels up.


*brake

Re: Future engine improvements

Posted: Sun Feb 17, 2019 11:11 pm
by Aerospice
WIederling wrote:
JayinKitsap wrote:
On the Trent 1000's these kind of things have been causing high levels of maintenance, with many planes sitting for weeks. Is that a cost the airlines want to bear for a 2% improvement. Unlikely.

There is a coming period where engines will settle into a lull until the tech matures and the bugs get out of this new level of tech.


The GE90 was a rather fickle engine at the beginning and an emissions pig and ran on an FAA exemption.
( But all three could be fixed by PR at the time. :-)

IMU the Trent1000 coating problems seem to have not been performance linked but to changes in process ( to get cheaper? no idea )


My understanding of the Trent1000 problem was that the original Trent 1000 blades were manufactured using a new higher strength material which was more susceptible than expected to corrosion fatigue cracking when operating in certain environments. The fix was to change the blade alloy and a different coating system with improved corrosion resistance.

Re: Future engine improvements

Posted: Wed Feb 20, 2019 4:33 pm
by Carmitage
Couple of points that, I believe, need clarification - CMCs do help with temperature, but really we are approaching the upper bounds of benefit due to:
1) NOx formation - the black art of combustion is to have the highest average temperature in the combustion chamber, with no hot spots to form NOx
2) the benefits are getting lower - the thermal efficiency boundary is (Thot - Tcold)/Thot - so if running at 1,700k and outside temperature of 200k, the thermal efficiency is (1700-200)/1700 = 88.2%. Going up 50k (which normally any jet engine engineer would sell their grandmother for) would take that to (1750-200)/1750 = 88.6%, or about 0.5% gain.

HOWEVER, the two areas where CMCs really help are:
1) no (or much less) cooling air - given 10% of the compressor's air is used for cooling the turbine, eliminating cooling air offers a big advantage (I'm not too sure how much - comments gratefully received - I read somewhere that it is about 60% of the overall power, which sounds a lot - however, eliminating 10% of that is clearly lots.)
2) weight - CMCs are a third of the weight of nickel alloys. This is nice for the static parts (which is where GE has so far gone), but really offers benefits on the rotating parts (which is where P&W is focussing its CMC effort) as the centripetal forces are much less, so the disks can be made much lighter etc....

Re: Future engine improvements

Posted: Wed Feb 20, 2019 4:56 pm
by Carmitage
Couple of points that, I believe, need clarification - CMCs do help with temperature, but really we are approaching the upper bounds of benefit due to:
1) NOx formation - the black art of combustion is to have the highest average temperature in the combustion chamber, with no hot spots to form NOx
2) the benefits are getting lower - the thermal efficiency boundary is (Thot - Tcold)/Thot - so if running at 1,700k and outside temperature of 200k, the thermal efficiency is (1700-200)/1700 = 88.2%. Going up 50k (which normally any jet engine engineer would sell their grandmother for) would take that to (1750-200)/1750 = 88.6%, or about 0.5% gain.

HOWEVER, the two areas where CMCs really help are:
1) no (or much less) cooling air - given 10% of the compressor's air is used for cooling the turbine, eliminating cooling air offers a big advantage (I'm not too sure how much - comments gratefully received - I read somewhere that it is about 60% of the overall power, which sounds a lot - however, eliminating 10% of that is clearly lots.)
2) weight - CMCs are a third of the weight of nickel alloys. This is nice for the static parts (which is where GE has so far gone), but really offers benefits on the rotating parts (which is where P&W is focussing its CMC effort) as the centripetal forces are much less, so the disks can be made much lighter etc....

Re: Future engine improvements

Posted: Wed Feb 20, 2019 10:01 pm
by WIederling
2) the benefits are getting lower - the thermal efficiency boundary is (Thot - Tcold)/Thot - so if running at 1,700k and outside temperature of 200k, the thermal efficiency is (1700-200)/1700 = 88.2%.

do you actually get 200K ( air temp ~= -70°C ) as Tcold?
Tcold is the exit temp of the working fluid. Core exhaust should still be 2..300K more : i.e. 4..500K ?

Re: Future engine improvements

Posted: Thu Feb 21, 2019 7:00 am
by Carmitage
My thermodynamics was a long time ago (and I wasn't very good at it then), so a) I was illustrating the point, but b) it should be the exit temperature of all the gas (as the LPC has converted some of the core gas temperature into energy in the bypass air), shouldn't it? I guess it should be somewhere around 80% x 230 (at -40C) + 20% x 500k = 284K? Happy to be corrected

Re: Future engine improvements

Posted: Thu Feb 21, 2019 10:02 am
by WIederling
As a Carnot process you look at turbine inlet vs turbine outlet temps over all turbine stages
.. theoretically done in adiabatic expansion. i.e. for Tlow you look at exhaust gas temps from the core.
together with the theoretically done in adiabatic compression work of the compressor sections ...