It is well known that the downsizing philosophy allows the improvement of Brake Specific Fuel Consumption (BSFC) at part load operation for spark ignition engines. On the other hand, the BSFC is penalized at high/full load operation because of the knock occurrence and of further limitations on the Turbine Inlet Temperature (TIT). Knock control forces the adoption of a late combustion phasing, causing a deterioration of the thermodynamic efficiency, while TIT control requires enrichment of the Air-to-Fuel (A/F) ratio, with additional BSFC drawbacks.In this work, a promising technique, consisting of the introduction of a low-pressure cooled exhaust gas recirculation (EGR) system, is analyzed by means of a 1D numerical approach with reference to a downsized turbocharged SI engine. Proper “in-house developed” sub-models are used to describe the combustion process, turbulence phenomenon and the knock occurrence.The effects of cooled gas recirculation are studied for various EGR and A/F levels. The presented results highlight that the proposed solution involves significant BSFC improvements. In particular, it is able to reduce the engine knock tendency, resulting in the possibility to advance the combustion phasing. Moreover, it involves a TIT reduction that allows to limit the over-fuelling.The developed numerical procedure is able to take into account the complex interactions among different driving parameters affecting the fuel consumption. It can be hence very useful to define a numerical engine pre-calibration and to realistically predict the EGR-related BSFC advantages which can be gained at different speed and load conditions.

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 waste-gate 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.