The turbo compound was developed in the 1940's as a way to increase the power output
of large piston
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
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
. 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.