Turbocharger manufacturers use an efficiency definition derived from the thermodynamics of flow machines which aims to describe the behaviour of the turbocharger under controlled conditions and without any disturbing effects. Engine manufacturers need a more practical approach, that is an easily understood definition which does not require reference to thermodynamic tables or functions and contains information about the effectiveness of the turbocharging on the engine.
This Recommendation is addressed to engine and turbocharger manufacturers. In order to obtain a common basis of understanding the definitions must be unambiguous and exact, taking into account all relevant effects. For the daily work numerically simplified formulae can be derived from the definitions given here which allow the efficiencies for a given class of engines to be calculated in a simpler way. Some suggestions for doing this are given in the annexes.