Yes it was. Sarcasm.
I was interested in all this so I did do a bit of further looking into it.
There are a few very small turboprops (UAV) in development with recuperators. They were part of the original design which makes them simpler. But the science gets more complicated. The small engines are not much more than a turbocharger plus combustion changer and gearbox. Single stage centrifugal compressor, single stage turbine. The temperature of the compressor outlet will not be that high, so transfering heat into it is easier (Delta T, or difference in temperature).
The bigger the engine, usually the compressor and turbine have many more stages, and higher pressure ratios, usually above 10. Same as the compression ratio of an ICE. The compressor outlet temperature is really high. Many hundreds of degrees. I can't remember how many degrees, and I don't think I ever flew a plane with a compressor outlet temp gauge. I want to say 500 or 600C, but that is a guess from memory.
So a single stage engine recuperator is transferring heat from an exhaust of 800 C to a compressor inlet temp of 100C or so. A comparatively smaller recuperator works, and aids a lot in efficiency. Their claim was up to 100%
An 8 stage engine might have the same 800 C EGT, but the compressor outlet temp is much hotter. Again, the 500C was a guess, from an old memory. It would take a much bigger recuperator to transfer heat, because the Delta T is much closer. The bigger recuperator is going to have more pumping losses, etc. And a lot more weight.
The single stage 50 hp UAV engine was said to weigh a bit more than the ICE wankel engine it replaced, but burned very slightly less fuel.
Big aircraft use "bleed air" for a bunch of things, including pressurization and deicing. The last engine I flew had low pressure from the 4th stage, and high pressure from the 9th stage of the compressor. The air is so hot, if you get a "duct leak" caution, or on other aircraft a "bleed air leak", It is considered a fire. It will melt aluminum. It did on airplanes I was flying. Twice.
The larger, multi stage engines are much more efficient to start with than the single stage centrifugal designs. Extracting extra efficiency gets heavier and more expensive.
It appears to be technology that works already in power plants, where weight is not an issue. Turbine power plant engines are basically the same as large transport jets, minus the fan. Companies that make airplane jets, sell power turbines as well.. If they thought they could adapt it to aircraft, they already have the expertise to do it.
I did not see any large recuperated engines being advertised as in development.
I was interested in all this so I did do a bit of further looking into it.
There are a few very small turboprops (UAV) in development with recuperators. They were part of the original design which makes them simpler. But the science gets more complicated. The small engines are not much more than a turbocharger plus combustion changer and gearbox. Single stage centrifugal compressor, single stage turbine. The temperature of the compressor outlet will not be that high, so transfering heat into it is easier (Delta T, or difference in temperature).
The bigger the engine, usually the compressor and turbine have many more stages, and higher pressure ratios, usually above 10. Same as the compression ratio of an ICE. The compressor outlet temperature is really high. Many hundreds of degrees. I can't remember how many degrees, and I don't think I ever flew a plane with a compressor outlet temp gauge. I want to say 500 or 600C, but that is a guess from memory.
So a single stage engine recuperator is transferring heat from an exhaust of 800 C to a compressor inlet temp of 100C or so. A comparatively smaller recuperator works, and aids a lot in efficiency. Their claim was up to 100%
An 8 stage engine might have the same 800 C EGT, but the compressor outlet temp is much hotter. Again, the 500C was a guess, from an old memory. It would take a much bigger recuperator to transfer heat, because the Delta T is much closer. The bigger recuperator is going to have more pumping losses, etc. And a lot more weight.
The single stage 50 hp UAV engine was said to weigh a bit more than the ICE wankel engine it replaced, but burned very slightly less fuel.
Big aircraft use "bleed air" for a bunch of things, including pressurization and deicing. The last engine I flew had low pressure from the 4th stage, and high pressure from the 9th stage of the compressor. The air is so hot, if you get a "duct leak" caution, or on other aircraft a "bleed air leak", It is considered a fire. It will melt aluminum. It did on airplanes I was flying. Twice.
The larger, multi stage engines are much more efficient to start with than the single stage centrifugal designs. Extracting extra efficiency gets heavier and more expensive.
It appears to be technology that works already in power plants, where weight is not an issue. Turbine power plant engines are basically the same as large transport jets, minus the fan. Companies that make airplane jets, sell power turbines as well.. If they thought they could adapt it to aircraft, they already have the expertise to do it.
I did not see any large recuperated engines being advertised as in development.
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