Turbocompounding is an engine technology whereby a turbocharger is coupled with a power turbine to recover otherwise lost energy from the exhaust system, and feeding it back into the engine crankcase. The result is increased engine efficiency and lower fuel consumption. The technology has been around a while, and employed in a growing number of truck engines, but is still somewhat of a mystery to many diesel owners. Here’s how it works:
Turbocompounding was originally used in aircraft engines back in the 40’s and 50’s to improve fuel consumption for transport aircraft. In a turbocompounding engine, a power turbine is installed, downstream of the turbocharger. Its function is to re-use exhaust gases from the turbocharger, and redirect the energy produced back into the engine camshaft by means of a specialized gear transmission which mechanically connects the turbine to the crankshaft. This in essence places two turbines in series, which combine to provide several significant benefits.
Due to the fact that the power turbine gathers exhaust gases during the blowdown portion of the piston travel – while it is still on the expansion stroke of travel – it doesn’t generate any back pressure which would rob the engine of some of the energy collected by the turbine. The benefit of this design is greater boost pressure, and more low speed torque. Turbochargers and power turbines in turbocompounding engines are specially matched for maximum efficiency across the engine speed spectrum and airflow range, working in tandem to optimize energy use in the diesel engine.
Recovering otherwise lost energy and converting it into an energy boost for the diesel engine results in improved fuel economy, better thermal efficiency, and increased engine power. Additionally, turbocompound technology has made it possible to reduce the overall size of diesel engines while retaining horsepower output equivalent to larger engines.