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Driven by a demand for better fuel economy and increasingly stringent emissions regulations over a wide range of customers and applications, engine manufacturers have turned towards engine downsizing as the most potent enabler to meet with these requirements.
With boosting systems featuring a variety of technologies ranging from single to multistage turbines and compressors to electrified turbocompound systems, alternative compressor and turbine technologies, the difficulty in the selection of the appropriate system becomes obvious; overall boost performance, thermal efficiency and packaging criteria are of paramount importance.
These boosting trends include variable geometry, a shift from single to two (or more) stages, extensive actuation for bypassing exhaust flows, exhaust flow regulation and pulsating exhaust energy recovery, severe electrification and an extensive effort downstream from the turbine to capture waste heat after the principal turbocharger/supercharger (the last effort is spearheaded by the resurrection of turbocompounding, both in mechanical and electrified forms). | 
