Although the use of turbocompounding is relatively new for diesel truck applications, the concept actually goes back quite a long way. The concept was originally used back in the late 1940s and '50s on two notable aircraft engines, the Wright Cyclone and the Napier Nomad, although its promise of low fuel consumption for transport aircraft was soon overtaken by the rapid development of the gas turbine and the turboprop engines.

What is turbocompound? In the case of automotive diesel engines, it means the introduction of a power turbine downstream of the turbocharger. The power turbine generates more work re-using the exhaust gasses from the original turbocharger. The work generated by the power turbine is then fed back into the engine crankshaft via a sophisticated transmission. It differs from a standard turbocharger as it does not have a compressor cover or compressor wheel. Instead it uses a gear connected to the turbine shaft.

What are its advantages? In extracting work from waste energy, the overall thermal efficiency of the engine is increased (46% instead of 42%). In simple terms more is extracted from the fuel consumed. This creates a more powerful engine and provides better efficiency.