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I saw a meme this morning that purported to illustrate the difference between commercial aircraft emissions of yesteryear and today, with the former depicted by heavy black smoke and the latter by nothing at all.
What is the real difference?
If you were to create a visual representation of the difference in emissions, how do you think they should really be depicted? Were, say, the 1970s so bad that the smoke should be thick and black? Are modern planes so virtuous that the smoke should be non-existent?
How bad are modern planes as pollutants, and how bad were they back in the day?
What is the real difference?
Between science and memes?
On an individual aircraft level, emissions are falling.
Current production airliner efficiency is approx 8 times that of one from 1970.
On an industry level, so many more people are flying so much further, that emissions are rising.
Also they've improved the stuff they put in the chemtrails so it's not visible in the emissions, unless you know how to look...
Does it factor in Chemtrails?
Does it factor in Chemtrails?
They've become much more stealthy about their chemtrail program.
1960s chemtrails
Modern chemtrails
In a number of cases that black smoke was the result of water injection. Although it increased power for takeoff in turbojet or low bypass engines the water lowers the temperature and the engine burns "dirty". Modern high bypass engines are a different story and much cleaner (although still very polluting in the grand scheme of things).
@thols
B-1, first flight 1974, might need a better example for 'modern', although 'modern' jet bombers are a bit thin on the ground (air?)
Lots more aviation around these days (well, pre Covid anyway). And although modern engines are much cleaner burning, the sheer quantity of aircraft makes the overall pollution greater (or at least on par) with the 70’s. Purely my opinion btw.
Aircraft/Engines these days are designed to fly at optimum flight levels. Not uncommon for a Boeing 787 to cruise above 41000ft for the most efficient flight profile, and flying huge distances with only 2 engines.
Efficiency drops massively on the ground/departure phase of flight. So a busy US airport for example with congested skies would have greater local pollution than where something could climb immediately to their requested optimum cruise level.
Of course most commercial 70’s aircraft would struggle to reach anything like 35000ft. Thicker air=more fuel burn.
Of course most commercial 70’s aircraft would struggle to reach anything like 35000ft. Thicker air=more fuel burn.
Rubbish! 747-200, VC-10 even the 707 have ceilings of over FL400.
It’s modern jet engines, that make the most difference in pollution, high bypass, more efficient, less NOx, quieter.
That’s why BA got rid of the 747-400, inefficient, two more engines to maintain and a much higher fuel cost per passenger than a 787/A350.
The reason why the black soot came out of the jet pipes was that the engines where far less efficient in burning all the jet A1 that went into the engine.
Bit like the old Diesel engines, you never see a euro 6 diesel chucking out soot now (unless you remap it and remove the dpf)
@SaxonRider glad you see you are still alive, I messaged you and you didn't reply!
Thicker air=more fuel burn.
Yes but more oxygen = more cleanly burned fuel because there are more oxygen molecules near your fuel droplets. Hence turbo diesels.
Also re the OP - it is generally the case that engines of most kinds burn cleaner and more efficiently than they did, however there are so many more of them that the remaining pollutants stack up more - often with different results. It's often been said that cleaner burning technologies result in less smoke and soot - which is great for local air quality, but all the smoke actually reduced the sunlight hitting the earth and cooled it a bit. Removing it all might make the earth warmer, paradoxically.
B-1, first flight 1974, might need a better example for ‘modern’,
The chem trails from a Stealth Bomber will be invisible.
civil engines are orders of magnitude cleaner than they used to be. There have been about 4 or 5 generations of engine technology progression since the engines of the '70's and each at least 10% more fuel efficient as the last...no point in developing a new engine unless it is at least 10% more fuel efficient than the previous generation because the business case doesn't work and it wouldn't sell. And that is 10% just on engine efficiency. You'll typically get another 3 - 10% fuel burn efficiency improvement from airframe improvements depending if the airframe is all new or a derivative airframe. Fuel efficiency is by far the most powerful factor regarding environmental impact....the best way to get cleaner is to simply burn less fuel in the first place. Emissions is all about the move to lean burn and more efficient thermal cycles...so regarding engine design basically driving the increase the bypass ratio. Engines of the 70's were either pure turbojet engines (zero percent bypass ratio) or very low bypass ratio's - 2% - 3%. The latest gen engines are 10% bypass ratio which is why you've seen the fan diameter get so much larger in the latest generation of engines and next gen engines will upto 15% and towards 20% bypass ratio's. The fan is a super efficient propeller and generates about 90% of the thrust. The actual gas turbine bit is tiny compared to the size of the fan and has got alot smaller relative to the size of the fan as bypass ratio's have increased, so energy density of the machine has increased significantly - so the equivalent of about 90,000 HP from a machine that is about the size of a Ford Focus in the larger more powerful engines.
And the improvements are set to continue with more technologies being developed now that will deliver similar 10%+ efficiency improvements in the next generation of engines as well as cleaner synthetic fuels generating less particulates, less contrails and overall emissions. Also covid has actually helped as it will hasten the retirement of older generation and less fuel efficient aircraft that would have provably lumbered on for another 10 years or so. The traffic levels are not set to get to pre covid 2019 levels until about 2024 at the earliest so the growth has been set back a good 4 or 5 years.
Old engines used to chuck out alot of black smoke, which is unburned fuel, to manage combustion and turbine temperatures meaning engines ran with a very rich mixture. As materials technology has improved over the last 40 years the combustion and turbine temperatures have bene able to increase significantly meaning engines can burn much leaner, not quite lean burn but not far off, so actual emissions have cleaned up and the challenge now is to continue increasing turbine temperatures well into the lean burn region without generating too much NOX.
So to try to put that into context...just comparing new gen aircraft introduced in the early '90's compared to the latest B787/A350 generation aircraft you're looking at a saving of at least 600,000 gallons of fuel per aircraft per year for the large wide body jets, so significantly more savings than that compared to aircraft of the 70's.
Much more efficient to cruise at altitude.. air is thinner and drag is significantly reduced at altitude. Thin air is not a problem. A gas turbine engine is basically a self propelled turbo charger. They spend 99% of their time at altitude so are designed and optimised to fly up there.
Great post wobbli, thanks.
Don't forget though that the biggest problem we face is still coming out of jet engines in large quantities, it's just invisible.
Aye, they use a shit load of A1, so any efficiency saving is massive over the life of an engine. Just performance testing an engine post overhaul will use between 5000-10000 litres of fuel, get one of the bigger bypass engines like a GEnx or GE90 and it'll burn a gallon a second at take off/max continuous power.
Bizarrely, I miss that smell. 🙂
The latest gen engines are 10% bypass ratio
90%, surely?
90% is about right. Boeing 777x has a bypass ratio of 10:1
Yeah wobbliscott has mixed up bypass ratio to percentage, but it's otherwise a decent post.
Well aside from the fact that in the 70s, the bypass ratio was still about 4:1 in the latest engines and is now around 10:1. We were on the right track back then, but you needed a lighter fan to have a decent bypass ratio whilst still having low mass. The difficulty now is that bypass ration has driven fan diameters to such a large diameter that the nacelle and cowling weight are now troublesome.
Its also worth pointing out that commercial aviation accounts for around 2% of global emissions.
That includes moving people, freight, everything. It's not nothing, but it's not as high as people think. For Air transport there is no viable alternative to a kerosene powered aircraft as yet as the energy density for almost anything else is around 40>100x less by the time you take into acount how the fuel is used in an aircraft.
Would you stop all tourism and a significant proportion of trade to save that 2% or would you target other areas first whilst we work on the technology (hydrogen, batteries, etc) ?
Sorry, didn't mean to express bypass ratio's in terms of percentage. back in the 70's you were looking at 737's coming with the old P&W JT8-D's which were pure turbojets before they were replaced wi the CFM 56 in the '80's. But the larger engines on the 747 were around 4:1. Conways and engines for 707 were around the 3:1 BPR if memory serves me. So we've more than doubled BPR in 40/50 years, but in order to increase BPR you have to shrink the core and increase turbine temperatures and that is the pacing item in development terms. We're already knocking on the door of 2000 degrees C in the turbine on full chat. Even hotter in the centre of the combustor, so well beyond the melting point of the materials the combustion and turbine is made from, so very clever cooling technology is employed.
The challenge with large diameter fans is indeed drag but as the fan size increases the rotational speed decreses as the tip speeds are limited to not go supersonic as you then get a significant reduction in efficiency not to mention all the complications of the induced mechanical stress and vibration from the pressure wave. So the weight of the fan, though important is not the most challenging issue. The main issue with the fan weight is containment energy in the case of a fan blade failure situation, but that is a combination of the fan speed and blade weight, so if you slow down the fan you have some scope to increase weight, though not desirable. The bigger problem is the turbine that is driving the fan because turbines want to spin fast for efficiency but is being slowed down as you increase fan diameter. The turbine driving the fan has to also increase in size to increase the speed of the turbine blades, so the turbine at the back end of the engine gets very large and very heavy and that introduces all sorts of packaging issues and trying to fit all this under the wing. Thats why we're now starting to see geared fan architectures coming with P&G's Geared Turbofan, so you can de-couple the fan turbine from the fan with a reduction gearbox and really optimise the turbine design. We can go a bit bigger on fan size...maybe upto 135 inch diameter vs current 118 inch diameter (though think GE's new 9x engine is getting on for 130inches), but not much.
A big step change could be achieved if we went to and electric hybrid...so not battery electric power plant, but a gas turbine that drives an electric generator, which then powers electric motors. This way you can shrink the size of your gas turbine and bury it inside the airframe and have several electric motors with smaller diameter fans some of which turn on and off through the flight depending on the power needs. This will then mean Boeing and Airbus can completely change the way aircraft are designed and move away from the current winged tube design which is driven purely to fit big engines under wings, and to something very different and significantly more efficint, like a blended wing body or something else. This would be a significant step change in overall efficiency and something all of us in the industry are working towards. Still some time off, maybe 20 -50 year time frame, new generation aircraft only really come along every 30 years or more (767 is 80's aircraft and superseded by 787 which entered into service in 2009).
Working in the aviation industry I'm very conscious of our impact on the environment and it is no good to sit back on the amazing achievements made so far, we need to keep striving to do our part to minimise global CO2 emissions, and that is just what the industry is doing. The good bit about that is whatever improves efficiency results in a product that is cheaper to operate so that is good for the airlines and passengers. So efficiency improvements benefit everyone in the entire industry so everyone is pulling in the same direction.
edit: sorry for the long post...I get carried away. I love this shit.
Hybrid turbine/elec will be the next step change. Early days though.
Great thread very interesting.
It's not just about the aircraft performance. Airspace design and most efficient routing combined with maximised flow play a huge part.
The detail is in the link.
Rubbish! 747-200, VC-10 even the 707 have ceilings of over FL400.
Not when they're heavy! The VC-10 might have been cleared for FL430, but got stuck at mid-20s when at max weight.
The other difference is that engines are rarely run at full thrust for take-off.
Instead a calculation is run to determine the maximum temperature at which the plane can get airborne without clipping anything expensive, and then the engines are told to assume that this is the temperature outside and to reduce their thrust appropriately.
Ultimately though the big difference is down to engine improvements as others have stated. You can tell when something antique is getting airborne from the cloud of black shit that's pouring out of the engines.
Bit like the old Diesel engines, you never see a euro 6 diesel chucking out soot now (unless you remap it and remove the dpf)
Not to derail the interesting thread, but I believe most diesel "maps" override the manufacturers smoke map calibration (easiest way to trick it to inject more fuel) hence the horrible black clouds
Not when they’re heavy! The VC-10 might have been cleared for FL430, but got stuck at mid-20s when at max weight.
Hmmm, are you talking about military VC-10’s full of fuel ?