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In 1917, French Prof. Rateau built and operated the first turbocharger. He used an axial turbine because of existing experience from the steam turbine to drive a centrifugal compressor. From then on the axial turbine was improved regarding temperature capability and performance and is still the first choice for larger turbochargers today. From the beginning, multi-entry turbines, as discussed in the patent of Büchi in 1925, were applied to make use of the pulse effect and, thus, to improve the engine performance at low speed and during transient operation. Between 1936 and 1945, the radial turbine for gaseous substances was proposed and finally implemented for smaller units, mainly because of lower complexity and cost. From the beginning, variable nozzle turbines were designed and built but without entering mass production. Up until 1963, multi entry turbine housings for radial turbines, like the axial turbine variants, were solely segment controlled.

In recent years sales of diesel-powered cars and trucks have increased dramatically worldwide. The efforts to raise specific power of diesel engines to allow for smaller and more efficient powertrains should include variable valvetrain technology. Some benefits that might become available with application of camshaft-based variable-valve mechanisms have been studied in [1]. Significant progress has also been reported in the development of camless actuation mechanisms [2, 3]. To fully evaluate the torque improvement opportunities for light duty diesel, the authors have assumed that a camless valvetrain will become available in the future. This will provide the ultimate flexibility to choose timing and duration of valve events to maximize full load torque. Simulation results revealed potential for a substantial increase in engine torque by optimizing the intake and exhaust valve timing together with turbocharger operation.