How much growth potential to jet engines have?

[collimatrix]

Since the invention of practical jet propulsion in the 1940s, jet engines have become enormously better. Great strides in power density, reliability and more modest improvements in fuel economy have allowed enormous improvements in the overall performance of fighter aircraft. Most of these improvements have been facilitated by improvements in the fundamental thermodynamic cycle of the gas turbine; i.e. by increasing the overall pressure ratio and by increasing the turbine inlet temperature. These improvements, in turn, have been facilitated by improvements in materials technology, mostly metallurgy of high-temperature alloys. More modest improvements have occurred due to advances in computer technology, which has allowed for better optimization of compressor and turbine blade shapes as well as on-board control systems like FADEC. There have also been some small architectural improvements, such as the switch from ejector nozzles to petal nozzles, and generally better design of air intakes and other aspects of propulsion/airframe integration.

Just how much better can these things be made? General Electric is already working on silicon carbide composite turbine blades, which suggests that little further growth is possible with even the mono-crystal nickel alloy blades. Pressure ratios have continued to grow, but the improvements in efficiency afforded by greater pressure ratios aren't linear, and they have actually entered a plateau of diminishing returns some decades ago.

So, practically speaking, just how much better can these things get?

[madrat]

The unobtainium answer is that they could double efficiency. The practical answer is very little on today's technology.

[zero-one]

Thats interesting and I think the answer will be dictated by what the demand is.

In the 1950s to 60s, the big thing was speed. We went from fighters that can barely go Mach 1 in a dive to suddenly having interceptors and Recon aircraft that can go Mach 3+. Using this trend, one might think that by 2010, Military aircraft would go Mach 15 or more.

But the demand changed in the 70s and 80s, the new craze was agility, the teen series opened up the envelope, they slightly improved on the average maximum speed of the 60s era fighters, but with far greater maneuverability. Back then a lot of people thought 3D TVC would be on every fighter by the 2000s on wards. I know the JSF program seriously considered it.

But in the 90s and 00s the craze shifted to information, both obtaining it and denying the enemy of it. Stealth and S.A., so they marginally improved on the speed of the 60s, marginally improved on the maneuverability of the 80s but now they added Stealth and S.A.

I'm not saying engine technology will stagnate, it will improve, but if the demand is not there, we will see the same marginal improvements and the focus on where the next demand is.

ADVENT looks like it will combine fighter performance levels with bomber like range performance. But if some studies are to be believed and that Fighter performance will no longer be needed, then future engine makers may just make very efficient albeit non high performance engines. (i.e. airliner type engines)

[mixelflick]

This is a tough question to answer, unless you're on the inside at P and W or GE. Certainly thrust levels will continue to improve, but I think the biggest advance has been in durability/reliability. The F-35 hasn't suffered a single in flight engine failure in how long? 15 years of development? At the Great New England airshow, an F-35 driver described an incident where one of the air intake covers got sucked into the engine. He was talking to a civilian P@W fellow next to me, and said no problem - the engine just ingested it, chewed it up and spit it out and went right back to normal operation. Understandably, the P@W guy was beaming with pride.

Pratt is talking about thrust and fuel savings improvements for the 2020's F-135. GE is doing work on one too. Competition is a great thing, and those two have really upped the bar over the years with their advanced F-100 and F-110 derivatives. GE needs a win soon though in the 5th gen realm, as both the F-22 and 35 are Pratt powered birds. Would be nice to see them get something flying on the F-35, kind of like how some F-16's today fly the F-110 and a lesser number F-100's. I'm sure they're gunning to power PCA too, and one can only imagine what that's going to look like. Like all technology, engines will continue to get better and better. It's the one area where the US has at least a 2 decade lead over the Russians, Chinese and everyone else. Let's hope we can keep it that way...

[jetblast16]

Great question. To make more power holding all things constant, you can either suck more air or burn hotter, possibly both. So either they run the turbine hundreds of degrees hotter than is currently being done today and/or suck much more air into the fan/compressor. Both are difficult to do. You only have so much volume and weight limits in a fighter-constrained power plant placement..run the turbine at 3,000 degrees Fahrenheit? Draw in 500+ LBS of air a second at max power? Maybe the biggest change to jet engines they can do is how to fundamentally alter how they actually burn their fuel (combustion sciences / physics), so that for a given fuel volume, more power can be extracted for longer periods. Lastly, there are pre-cooler concepts to chill the air entering the engine for a larger delta in heat.

[jetblast16]

Maybe the better question to ask is, what will eventually replace the jet engine, or the jet engine as we know it?