Are Passenger Jet Engines Hitting Their Technical Limits?

Internal combustion engines in cars have been around longer and we’re still pushing record amounts of power and record amounts of efficiency.

Why would one think that? It seems kind of arbitrary. Guns have been developed and iterated on for half a millennia and there are still technological advancements coming out regularly.

I doubt an engine would undergo the addition of a stage as that's pretty major but there's no reason a mfc couldn't charge you a mil for better compressor blades and give you a thrust rating upgrade for your patronage.

Edit: I'll keep talking as more info is coming to my head. Jet engines have fadec computers that get to decide what your maximum power level is. This maximum is programmed into the engine as a thrust rating. Let's say you engine has 8 possible power levels to configure, when you test the engine when new or after maintenance, you will look up a chart based on parameters that your test cell has logged, ie thrust vs EGT (exhaust temp) is a big one, so too is vibration at the different bands. This chart will tell you what to program the ECU with (forgot the actual acronym, its analogous to an ECU on a car). So to your point, when you get more performance out of an engine, you can set these levels higher, so you wouldn't expect more degradation from you engine for a higher power level as the manual will tell you what power level the engine can be set to which will keep everything within its maintenance limits. (Sorry if that's not super clear)

Edit 2: Funny implementation detail of setting a thrust rating, it's literally a jumper based system similar to old motherboards, except you manually wire a blanking plug to bridge the connections. A blanking plug is an electrical connector that has a cap on it with a little bit of space to run wires from one pin back to another.

Also the correct acronym is EEC.

I hope ICAO can begin studying the affects of pollution on aircraft more heavily because compressing air with an AQI over 1,000 (like India has experienced recently) could have very unknown consequences elsewhere in the engine after the blades, (unless it just pushes all the pollution particulates back into the cabin, which is another issue that needs to be solved)

Now the current CMC method employed by GE uses silicon carbide, which has a melting temperature of about 3000K. If one day they could switch to hafnium carbide, with a melting temperature of more than 4100K, the carnot efficiency could reach more than 89%.

[1] https://www.ornl.gov/news/ceramic-matrix-composites-take-fli...

What are we talking about here, building aircraft or operating them? Factory noise or takeoff/landing/sonic boom noise?

This makes supersonic airliners infeasible for the really long routes that they would truly help with. The Concorde only shaved 3.5 hours off the NY-London time, and cost about 8x as much to operate.

The extremely high costs then mean that you have to sell what are essentially coach seats at greater than business class prices. There aren't many people willing to pay business class prices, so you can't run the planes very often, and you can only run them between very large, rich cities.

Since the whole point of supersonic is speed, you can't effectively sell connecting flights, because if you fly, say, Boston-London through NYC, the direct flight from Boston subsonic will arrive at nearly the same time as the supersonic flight with a connection.

This leads to a very small passenger market. It also means that supersonic planes will operate on an infrequent schedule. Many people in a position to pay for a supersonic flight will prefer a subsonic flight that meets their schedule over a supersonic flight that doesn't.

With the advent of lie-flat beds, in-flight wifi and power, and higher cabin pressurization, being on an airplane an extra 3.5 hours isn't even so bad anymore, so the practical advantage isn't nearly as great.

All of these factors make supersonic a very small niche market. This means that few planes will be produced. High performance aircraft have high development costs, and those need to be amortized over the production run. Concorde was a complete financial disaster because they only produced 14 of them, for all of the reasons above. The only solution is to somehow make the airframe far more efficient.

"The Low-boom Flight Demonstration mission has two goals: 1) design and build a piloted, large-scale supersonic X-plane with technology that reduces the loudness of a sonic boom to that of a gentle thump; and 2) fly the X-plane over select U.S. communities to gather data on human responses to the low-boom flights and deliver that data set to U.S. and international regulators."

https://www.nasa.gov/X59

Seriously, look at an airport. get the number of flights and where they come from and their frequency, now imagine trying to build a sufficient number of rail lines to do the same.

air travel saves time that no rail line could except in short hop scenarios where extra time to process through an airport might tip a balance. let alone you can have nearly an number of planes in flight between two points

It does, however, matter quite a bit for emerging technologies which may be aimed at lowering emissions. Higher efficiency, for example, can overcome a lot of drawbacks that come with new technologies, like power to weight ratios. Electric cars, for example, have nowhere near the amount of energy storage that gas fueled cars do, but they are now getting similar ranges because they convert it to kinetic energy much more efficiently.

And how long does the blade stay together? What happens to the blades if a foreign object is ingested? These blades are being made to run at T that make them very ductile, the centrifugal forces literally bend the blades.

Mitsubishi isn't the only one trying to increase the T.

"Second, it is possible to reduce compression losses in 3 spool designs." And increase the losses due to mechanical coupling and decrease reliability.

"Lastly, it's entirely possible to slap a recuperator, intercooler, and reheater on the engine if things will get too desperate. " At what weight and aerodynamic cost?

Its not my intention to contradict you, but to highlight that it's not obvious that any of these things will ever commercially.

Nothing left to do but live a good life and to try to make sure everyone is fed, happy, and treats the earth and everything else in it as well as they can.

The only truly depressing future to me is if interstellar travel really is as hard as it seems to us now. There kind of needs to be a physics/propulsion discovery on the order of magnitude of electricity or the journey can only be feasibly made by the immortal AI robot race that replaces us.

NASA is building a low-boom civil supersonic demonstrator (also crewed) that will demonstrate sonic-boom-lowering techniques to enable passenger supersonic flight over the continental US.

There's lots of room to improve these things still. And I'm excited still about lithium battery tech. It's the internal combustion engine of our century and its consequences are perhaps even more far-reaching. The theoretical useful energy of the most advanced versions of this, the lithium-air battery, are on par with that of hydrocarbon fuels, so by the middle of the century it's likely we'll have completely clean civil supersonic transport with low acoustic emissions as well.

I think we still have a very long ways to go to advance technology. Vacuum tunnel maglev trains allow higher efficiency than even conventional rail but without an ultimate speed limit. They could operate at hypersonic speeds in 100 or 200 years from now, with the energy recouped regeneratively at the end. That makes efficiency orders of magnitude better than today's passenger air travel with speed increased by an order of magnitude.

I think ultimately in the further future, if you want something exciting it'll be: Further urbanization of everything, so humanity concentrates in opulent metropolises well-connected by ultra-efficient transport. Food production increasingly goes to single celled organisms, freeing up space for rewilding of the Earth and healing of the ravages of industrialization while individual well-being is far greater. Human economic expansion in space is technically unbounded. The solar system allows access to many, many orders of magnitude greater energy supplies without an impact on the Earth's ecosystems. Things that can tolerate latency, like high performance computing will leave the planet to access unlimited energy in space (Moore's Law coming to a slow end will actually enhance this transition as you can afford to amortize the hardware over long enough periods of time for this to make sense).

Musk's spaceship is just a taste of what's possible. Improvements in efficiency in even chemical rockets (by reducing structural weight, fine-tuning Isp over the mission cycle, using hydrolox near stoichiometric to enhance performance) can reduce cost of space travel to about what long-haul passenger travel currently is.

I think things will continue to improve. And these are only the foreseeable things. The actual future will contain many unforeseeable discoveries.

None of this is guaranteed, but it can be ours if we so decide to make it thus.

A vision of the future beyond the Earth in the timeframes you mention: https://vimeo.com/108650530

This is very, very unlikely. Take a look at all open questions in physics, and you'll see that our understanding of the universe has severe gaps. Usually, whenever such a gap is filled, there's a technological boom. For instance, Einstein got us some: not only relativity (allowing for things like GPS), but also the photoelectric effect, allowing for (eventually) solar panels. Greater understanding of semiconductors (in no small part due to the above) brought us transistors, cheap lasers, which were refined (and still are) by quantum physics. We are dabbling into quantum computers now.

Mind you, both lasers and radio waves were considered curiosities with no practical applications.

Fusion research is still ongoing. Progress is slow, but steady. Once we have mastered, we'll have access to cheap and plentiful power, which will open up applications previously not even considered before. If it is possible to shrink the technology to less then building sized, then you'll also see vehicles (ships or spacecraft).

Bio technology is still in its infancy. I cannot predict what the results will be, it's far too early.

Some of the rapid progress from the last century might have been an anomaly. But we are not even close to running out of things to learn.

These produce electricity, so I don't see how they are an alternative.

> Hydrogen + Oxygen (or even Hydrogen + Air?)

Hydrogen is highly reactive, and not likely a safe fuel for commercial air travel.

An electric motor is >90% efficient. Sure you're added an extra stage converting to electricity, but so what?

Electric drives are so efficient, diesel ICE locomotives have had electric drives (in lieu of transmissions) since the 1950s. That is, they have massive diesel engines that generate electricity instead of moving the train directly.

Anyway, it bothers me one people refer to the constraint being "large aircraft" when the real difficulty on electric flight is range, not how big the aircraft is. Electric flight scales up just fine. It's the range issue that's hardest. Currently can do 1000km, maybe up to 2000km with lithium ion and lithium sulfur chemistries with optimized structure and aerodynamics. Could scale up to larger sizes if desired.

There is a lot of space to improve in

When Nokia's retail division went up it a ball of flames, the engineers didn't just disappear and become janitors or something. They formed HMD, who is the one of the very few mobile phone makers seeing ear on year growth in shipments.

Raw human talent is the major driver of innovation. Companies are just one way they organise themselves. Open source is another. Different organisations suit different circumstances, but you always need the raw human talent.

[1] https://www.quora.com/How-much-fuel-is-burned-during-take-of...

Maintenance?

Catapults are notoriously finicky and expensive to operate. Also the additional stresses on the airframe couldn't possibly reduce maintenance. If anything (assuming they could withstand them), they would require more inspections.

Catapults only solve the problem of not having enough runway. And you'll notice that fighter jets taking off from carries will be on full thrust and full reheat.