New turbo transfers power direct to the crank

[ConnClark]

Turbo compounds work best in applications with constant loads. The key draw back however is expense. Also on smaller engines smaller turbines must be used which in turn means they have to spin faster. The faster they spin the associated gearing to reduce the rpm to a usable speed gets more complex and parasitics take their toll.

[gone-ot]

...it's also a question of "...diminishing returns..." as 150 hp out of 3,000 hp (aircraft engine) would lineraly 'scale' downward as only 15hp out of 300 hp (automotive engine), etc.

[mechman600]

Detroit Diesel currently uses a compound turbo on their DD15 diesel truck engine. The turbine uses spent exhaust gasses exiting the primary turbo to mechanically help turn the rear gear train, gaining 50 "free" horsepower, according to the propaganda. Turbo-Compound engines have been around forever. Go to the library and read all about WW2 bombers engines. Quite fascinating and terribly complicated. AKA: Cool.

Call me silly, but if you want to add an turbo to an engine for economy sake, a compound turbo is the only way to go, unless you start with an extremely undersized engine to begin with and add a turbo to get the power up to "normal" levels. And this (the latter option) is exactly what the auto companies are finally realizing.

[Frank Lee]

They didn't "finally realize" it; they've known practically forever. Before, that last mpg wasn't worth the expense.

[NiHaoMike]

Originally Posted by ConnClark

Turbo compounds work best in applications with constant loads. The key draw back however is expense. Also on smaller engines smaller turbines must be used which in turn means they have to spin faster. The faster they spin the associated gearing to reduce the rpm to a usable speed gets more complex and parasitics take their toll.

What about integrate a high speed alternator into the turbine and have it supply power to the hybrid system?

[Frank Lee]

Since the crank and turbine are geared together, might as well take loads from the cranks since they are at more favorable rpms.

[NiHaoMike]

Integrating an alternator into the turbine means that no gearing is needed. The design of electric motors and generators actually favor higher operating speeds.

[Frank Lee]

How high?

[ConnClark]

Originally Posted by NiHaoMike

What about integrate a high speed alternator into the turbine and have it supply power to the hybrid system?

If you think a alternator or generator working above 100,000 rpm is going to be efficient you better think again. Hysteresis losses will be quite large.

[NiHaoMike]

Originally Posted by ConnClark

If you think a alternator or generator working above 100,000 rpm is going to be efficient you better think again. Hysteresis losses will be quite large.

A 120kRPM, 8 pole alternator is only 8kHz. Common silicon steel would be quite lossy at those frequencies, but it can easily be handled with powdered iron or ferrite. Switching power supplies, the most common application of those magnetic materials, operate at tens to hundreds of kHz.

A friend of mine has built a hybrid A/C that uses a centrifugal compressor operating at 75kRPMs, driven by a switched reluctance motor. I don't know about the compressor efficiency but the overall system efficiency is about 40 SEER equivalent. (It started in the low 30s, but optimization brought it up, with no changes to the compressor.)