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The demanding CO₂ emission targets for passenger cars are fostering the development of downsized, turbocharged and electrified engines. In this context, the need for high boost level at low engine speed requires the exploration of dual stage boosting systems. At the same time, the increased electrification level of the vehicles enables the usage of electrified boosting systems aiming to exploit the opportunities of high levels of electric power and energy available on-board.
The aim of this work is therefore to assess, through numerical simulation, the impact of the combined exploitation of different (48V vs 12 V) electric superchargers (eSC) with different levels of engine downsizing on vehicle performance and fuel consumption over several mission profiles.
The virtual test rig employed for the analysis integrates a 1D CFD fast running engine model representative of state-of-the-art turbocharged and downsized gasoline engines featuring an eSC in series with the main turbocharger, a six-speed manual transmission and a vehicle representative of a B-SUV segment car.
The evaluation tests chosen for the case study were, on the one hand, vehicle elasticity manoeuvers for the performance assessment and, on the other hand, type approval and RDE driving cycles, for the fuel economy assessment. An evaluation of possible engine and vehicle hardware modifications was also carried out. In particular, the effects of a variation of the final drive ratio, of the increase of the turbine size and of the usage of a high efficiency engine concept (featuring an increased compression ratio from 10 to 12 and a late intake valve closing, exploiting the advantages of a Miller cycle) were investigated.
The introduction of an electric supercharger on a turbocharged downsized gasoline passenger car engine was shown in the selected test cases to lead to up to 16% reduction of the elasticity time and up to 9% improvement in fuel consumption when the high efficiency engine concept was considered.