Environmental legislation is becoming more and more stringent and requires a significant reduction in the fuel consumption and pollutant emissions caused by future vehicles. Apart from exhaust treatment or optimised combustion procedures, supercharging internal combustion engines is a major contribution towards achieving this end. It allows for the so-called downsizing which means that a comparable performance can be generated by using engines that have a smaller piston displacement and/or fewer cylinders. This increases engine efficiency as it considerably reduces losses by internal friction.
Supercharging an internal combustion engine always requires a compressor to deliver the fresh air flow under high pressure. Supercharging systems differ by the method used for driving the compressor. This can be done by a separate electric motor (e-compressor), by direct coupling to the crankshaft (supercharging) or by using a turbine to withdraw energy from the exhaust gas which would otherwise escape to the atmosphere without being used (turbocharging).
Turbochargers must be able to function efficiently over a relatively wide operating range of an internal combustion engine. This requires controlling of the turbocharger. Wastegate (WG) turbochargers and variable geometry system (VGS) turbochargers are the two most utilised concepts. In WG turbochargers, a valve is used to release excessive exhaust flow past the turbine wheel. VGS turbochargers, on the contrary, present movable guide vanes upstream of the turbine wheel to help optimize the flow conditions approaching the turbine wheel.