Numerical analysis of the transient operation of a turbocharged diesel engine including the compressor surge

The paper deals with the simulation of a multi-cylinder turbocharged diesel engine for automotive applications, employing a one-dimensional approach with the aim of refining the turbocharger modelling during transient manoeuvres. The proposed methodology is able to handle stable compressor behaviour and also compressor surge. In addition, a wastegate model is introduced to account for the instantaneous variation in the valve section as a result of the control signal, which is provided by the engine control unit, and the engine state. Preliminarily, the engine model is tuned against experimental data in terms of both the global performance parameters and the in-cylinder pressure cycles. The compressor performance is described through an ‘extended’ map obtained using a one-dimensional turbocharger model; in this way, a refined surge analysis can be performed, accounting for both direct flow compressor operations and reverse flow compressor operations. The one-dimensional model is applied to analyse different transient manoeuvres. First, the vehicle’s maximum speed is predicted and compared with the manufacturer’s data, during an acceleration manoeuvre. Then, a sudden part-to-full-load step is described with the aim of analysing in detail the turbo-lag. Finally, a full-to-part-transient manoeuvre is also analysed to verify the capability of the model to represent the compressor surge phenomenon. The numerical results provided in this work qualitatively reproduce the experimental observations available in the literature for transient operation of engines. Thus, the developed computational tool can be successfully used to support the design process and the transient analysis of turbocharged internal-combustion engines. The paper presents a numerical model aiming to refine the simulation of a turbocharger during transient manoeuvres. In particular, a 1D compressor model is employed to extend the manufacturer’s map in the unstable and reversal flow regions in order to allow the description of the compressor surge phenomenon. In addition, a physical model of the waste-gate actuation system is proposed with the aim of better analysing the turbocharger regulation strategies during transient manoeuvres. The proposed methodology is applied to a sixcylinder turbocharged diesel engine. After the engine model was tuned to different steady-state points, three transient cases are simulated: two acceleration manoeuvres and a transient test during which the compressor surge is induced. The obtained results qualitatively correspond to the experimental findings available in the technical literature. The developed model allows to predict the instantaneous engine–turbocharger matching and the surge conditions during transient operations. The considered methodology, showing the capability to describe the inception and development of the deep surge, represents a useful tool for identifying the tuning and management of the engine in order to avoid the occurrence of this unsafe issue in the turbocharging application. A validation of the proposed methodology is currently under development on a dynamic test bench.