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In this paper the turbocharged diesel engine operation is analyzed by means of a second law based method. The instantaneous release and storage of availability inside the several components (cylinders, manifolds, compressor and turbine) are evaluated by following a theoretical-experimental methodology that has been recently proposed by the authors. Examples of availability balances are compared for different values of some parameters which influence the combustion and the exhaust process, or for several arrangements of the engine and turbomachine system. The availability analysis of the engine transient development will show the amounts of mechanical energy employed for both in-cylinder storage and turbocharger acceleration and of those available for conversion into external output. These amounts will be compared with the fuel availability and with those destroyed during the several processes (i.e. combustion, gas exchange, turbocharger operation).

According to a methodology that has been proposed by the authors in previous papers, measurements of instantaneous mass flow rate supplying a turbocharged engine were carried out by means of time-varying pressure data recording and of a numerical flow model: this methodology allows unsteady phenomena upstream of the inlet manifold to be followed, so that it seems particularly suitable also to the analysis of engine transient behaviour. The paper presents improvements in the method, since, until now, it has been tested only in the case of a naturally aspirated engine; hence, particular problems arising in unsteady flow analysis of turbocharged engines had to be overcome, owing to the disturbance induced by compressor motion and intake valves closing on the pressure signals. Particular attention is paid to the analysis of unsteady behaviour of the supercharging compressor that may be performed by employing the experimental-theoretical inlet flow model.