A turbo-compound engine uses the exhaust gases through a downstream turbine. This can be installed in addition to a turbocharger.
While the first exhaust gas turbocharger provides more boost pressure in the combustion chamber due to the exhaust gas energy and thus higher engine power, the second turbocharger converts the remaining energy into movement power. The generated energy is passed on to the crankshaft via a mechanical or hydraulic transmission.
The overall complexity of a turbo-compound system and especially for road vehicles quite low saving effect has prevented widespread introduction of the turbo-compound engine.