The turbo compound was developed in the 1940's as a way to increase the
power output of large
piston engines.
The only production engine to eventually use turbo compounding was the
Wright R-3350-32W. These engines were installed on
Lockheed L-1049 Super Constellations and
Douglas DC-7C's. They were
finicky and hard to maintain properly but when well maintained they were good engines.
The "turbo" part of turbo compounding works just like a turbocharger in that there is a turbine in the flow of the engine's exhaust, Wright called these "PRT's" or "
Power Recovery Turbines." The pressure from the expansion of the
exhaust gas turned the turbine which was connected by a
torque converter and
transmission back to the engine
crankshaft. Each R-3350 had three PRT's. R-3350 turbo compound engines were able to convert 20 to 30 percent of otherwise wasted
heat energy into
horsepower. Where a normal
turbosupercharged R-3350 could produce 2,800 horsepower, the R-3350-32W turbo compound engine produced 3,500 horsepower.
Today some European truck manufacturers are claiming this as a revolutionary advance... but like most piston engine technologies it's been around the block a few times.