Variable Geometry Turbocharger (VGT)

A variable-geometry turbocharger uses movable nozzle vanes ahead of the turbine to change the effective flow area, raising boost at low load and easing it at high load. This widens the usable engine map, improves part-load and transient response, and helps hold the air-fuel ratio for low NOx and smoke during slow steaming. On marine two-strokes the same end is often met by exhaust-bypass or sequential turbocharging rather than fully variable vanes.