engine requirements?

[rtry9a]

I think the problem arguing efficiency involving electrical equipment is that most take a narrow view and assume electricity originates at the wall plug... There are huge energy losses that involve generation, transmission, and storage in the grid. Storage weight is the killer for aircraft use.

I do wonder about one possibility however- linking a generator to a turbocharger as a way to compound waste heat energy, to add power to the primary power source and possibly increase overall efficiency.

[RVbySDI]

Originally Posted by rtry9a

I think the problem arguing efficiency involving electrical equipment is that most take a narrow view and assume electricity originates at the wall plug... There are huge energy losses that involve generation, transmission, and storage in the grid. Storage weight is the killer for aircraft use.

I agree that there is some losses from production through transmission to final delivery of electricity. This is another one of those ways to measure "efficiency" that I referred to earlier. Looking at efficiency one can take on many perspectives to define it.

Originally Posted by rtry9a

I do wonder about one possibility however- linking a generator to a turbocharger as a way to compound waste heat energy, to add power to the primary power source and possibly increase overall efficiency.

Seems to be there would be a weight penalty that would be hard to overcome. Perhaps if one designed the aircraft to be able to carry the extra weight there could be enough energy recovery to make it worthwhile. I think the aircraft would have to be designed around the power plant and not the other way around though.

[SvingenB]

Originally Posted by rtry9a

I do wonder about one possibility however- linking a generator to a turbocharger as a way to compound waste heat energy, to add power to the primary power source and possibly increase overall efficiency.

That is exactly what the turbo+intercooler in a diesel engine do, increases both HP and efficiency. A gasoline engine will allways hit the wall efficiency vise due to limited max compression rate, turbo or not.

[rv6ejguy]

Originally Posted by rtry9a

rcraft use.

I do wonder about one possibility however- linking a generator to a turbocharger as a way to compound waste heat energy, to add power to the primary power source and possibly increase overall efficiency.

Turbocompounding has been in use for 60 years where turbines are linked back into the crankshaft through gearsets and fluid couplings. Wright and Allison had engines with this technology. This was recently rediscovered and employed on some new heavy diesel truck engines. BMW and others are now experimenting with it also. Something like 10% is recoverable from the exhaust stream. Neat but complicated.

[airguy]

Originally Posted by rv6ejguy

Turbocompounding has been in use for 60 years where turbines are linked back into the crankshaft through gearsets and fluid couplings. Wright and Allison had engines with this technology. This was recently rediscovered and employed on some new heavy diesel truck engines. BMW and others are now experimenting with it also. Something like 10% is recoverable from the exhaust stream. Neat but complicated.

Ah yes, that would be the infamous "Parts Recovery Turbine" on the Wrights. Good workable technology once the bugs were found and corrected.

[Rivethead]

Originally Posted by speed

I know this is going to be an open ended question. What attributes/specifications make an engine good for aviation ?

IMHO and in order are a long front bearing as found in Lycoming and Continental engines, Low weight, few moving parts and full power development at fairly low RPM.

[gmcjetpilot]

I recall that the max reliability of piston engines, even at their Zenith in the 50's was always measure in a few 1000 hours. Engine failures where not unheard of. Where turbines (jets) go 10,000's of thousand hours with great reliability, less maintence and fewer parts. Engine failure or shut downs are rare, new making events. Turbo compound engines where and are still very complicated. I would dispute they worked the bugs out, they simply became irrelevant when jet power took over.

http://en.wikipedia.org/wiki/Turbo-compound_engine.

The idea of back driving a turbine through a piston engine requiring a gear box or two, is heavy and complicated. Somewhat like jets you have to get large scale enough to justify it. For small HP engines this makes no sense, IMHO.

[rv6ejguy]

I think the sheer complexity of the Wright R3350 had more to do with failures and shutdowns rather than the 3 PRTs. When you have thousands of parts whirring around, something will have to give.

Detroit Diesel and Daimler Benz are introducing new turbocompounded models and one other one I can't remember the name of has been in production for over 5 years. They are saying fuel savings of 5-8% on a diesel- probably bigger gains on a gasoline engine which has lower thermal efficiency to start. I think the Allison V12 TC model was seeing something over 10% lower fuel flows for the same shaft hp. Viable technology you will probably see more of on bigger engines in the future.

[SvingenB]

Scania has been using turbocompounding for some years in their mid sized inline 6 truck engines. A rather complicated thing with reduction gearing and a clutch. The turbine rotates at 55000 rpm.