Variable Turbine Geometry technology is commonly used in turbo diesel engines in recent years. It is primarily used to reduce turbo lag at low engine speed, but it is also used to introduce EGR (Exhaust Gas Recirulation) to reduce emission in diesel engines.
Here, we concentrate on the former advantage.Ordinary turbochargers cannot escape from turbo lag because at low engine rpm the exhaust gas flow is not strong enough to push the turbine quickly.
This problem is especially serious to modern diesel engines, because they tend to use big turbo to compensate for their lack of efficiency. A Variable Geometry Turbocharger is capable to alter the direction of exhaust flow to optimize turbine response. It incorporates many movable vanes in the turbine housing to guide the exhaust flow towards the turbine. An actuator can adjust the angle of these vanes, in turn vary the angle of exhaust flow.
Look at the following illustration:
At low rpm :The vanes are partially closed, reducing the area hence accelerating the exhaust gas towards the turbine. Moreover, the exhaust flow hits the turbine blades at right angle. Both makes the turbine spin faster.
This problem is especially serious to modern diesel engines, because they tend to use big turbo to compensate for their lack of efficiency. A Variable Geometry Turbocharger is capable to alter the direction of exhaust flow to optimize turbine response. It incorporates many movable vanes in the turbine housing to guide the exhaust flow towards the turbine. An actuator can adjust the angle of these vanes, in turn vary the angle of exhaust flow.
Look at the following illustration:
At low rpm :The vanes are partially closed, reducing the area hence accelerating the exhaust gas towards the turbine. Moreover, the exhaust flow hits the turbine blades at right angle. Both makes the turbine spin faster.
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