Variable Geometry Turbocharger
By changing the geometry of the turbine inlet, a turbo's effective range can be extended to the lower and upper ends of the engine's range, while eliminating the need for a wastegate.
Taking the adjustment capability a step further, the geometry can also be changed to purposefully increase exhaust backpressure to promote exhaust gas recirculation, reduce emissions, provide additional engine braking, and increase exhaust temperature for the purpose of regenerating a diesel particulate filter. While increased exhaust backpressure does not increase the efficiency or power of the engine, it can still be used beneficially during short periods (like when shifting).
The diesel particulate filter is also interesting: it captures microparticles and soot and regenerates (or cleans) itself via the application of high heat for a short period to burn away the particles. It can be functionally compared to the catalytic converter of a petrol-powered car (they can share the same structural materials) but instead of requiring oxygen to recharge the catalyst, it uses heat to clear the filter.
