Experimental Evaluation of Steady State Performance of an Automotive Electric Supercharger

Nowadays, the electric supercharger for turbocharged downsized automotive engines is mainly used to improve torque at low engine speeds in order to obtain an improvement of the time to boost. These components are usually designed to fill the gap in terms of torque in transient operation caused by the main turbocharger with reference to the typical turbo lag issues. An advanced solution of the engine boosting system was taken into account, considering the adoption of an e-booster system coupled to a waste-gated turbocharger, typically adopted alone in order to provide a reduced turbo-lag, i.e. an optimized transient response of the system. In the experimental activity described in this work, the maximum speed of the e-booster used is about 70000 rpm, the maximum pressure ratio is 1.5 and the maximum power required on the shaft is less than 4 kW. The compressor unit have to be maintained in the idle condition in order to avoid excessive electric consumption and overheating problem when the boost given by this component is not required. In order to highlight the behavior of the electric supercharger coupled to the turbocharger, the first experimental investigation regarded the steady flow characterization of the compressor. Due to problems related to the over temperature, the working time of the e-booster is limited, avoiding an accurate evaluation of compressor efficiency, which is related to upstream and downstream temperature measurements. A driving system (instead of the electric machine) was designed and made up by the Authors to provide a more accurate evaluation of the compressor map. For this application a turbocharger turbine have been selected according to the requested power levels. The experimental investigation was developed at the turbocharger test facility of the University of Genoa using different sensors for the measurements of the average levels of thermodynamic quantities. Besides, accelerometers and microphones were adopted to measure noise and vibrations operative levels in order to check the correct operative functionality of the system.