Variable Geometry Turbocharger

Variable Geometry Turbocharger

Variable Geometry Turbocharger Rating  :      

Variable Geometry Turbocharger

A turbocharger, or turbo, is a mechanical device that increases the pressure of a gas by reducing its volume. A turbocharger is used for forced induction of an internal combustion engine. A turbocharger increases the density of air entering the engine which results in creation of more power. Variable geometry turbocharger (VGTs) is a form of turbocharger.

VGT: How does it Work

VGT allows the effective alteration of the aspect ratio (the ratio of longer dimension to the shorter dimension) depending upon the engine conditions. The optimum aspect ratio at low engine speeds is very different from that at high engine speeds. At low speeds if the aspect ratio is too large, turbo will fail to create boost. Similarly at high speeds if the aspect ratio is too small, the turbo will choke the engine leading to high exhaust pressures. The pistons have to work harder to suck in the fuel-air mixture which results in low intake-manifold pressure and ultimately lower power output.

Maximum efficiency can be delivered if the geometry of the turbine is altered considering the aspect ratio. Thus, the VGTs have a minimal amount of lag, have a low boost threshold, and are very efficient at higher engine speeds. This is the reason why some of the configurations of VGTs do not even require a waste gate which is responsible for diverting the exhaust gases away from the turbine wheel. 

In diesel engines, a VGT is responsible for controlling boost at lower speeds. The VGT has a set of movable vanes in the turbine housing, and they control boost by controlling exhaust turbine inlet pressure mainly at high speeds. At low engine speeds when exhaust flow is low, the vanes are partially closed. This increases the pressure of the exhaust pushing against the turbine blades, making the turbine spin faster and generating more boost. They provide big improvements in diesel engine efficiency and emissions.


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