To resolve these contradictions, let turbocharged engine at low speed can be guaranteed a good booster effect, VGT (Variable Geometry Turbocharger) or called variable geometry VNT turbo technology will come into being. In the field of diesel engines, VGT variable geometry turbocharging technology has been very widely used. Because the gasoline engine exhaust temperature is much higher than the diesel engine, reaching about 1000 ° C (400 ° C for diesel engines around), and hardware materials used VGT difficult to bear such a high temperature environment, so this technology is also the delay in the application on gasoline. In recent years, BorgWarner and Porsche jointly overcome this problem, BMW Cartridge the use of high-temperature aerospace materials technology, which successfully developed the first equipped with a variable geometry turbocharger for gasoline engines, Porsche will this technique is called VTG (Variable Turbine Geometry) variable turbine blade technology.
VGT variable geometry turbine technology is a core part of the adjustable guide vane vortex section, we can see from the chart, the outer part of the turbine has increased by an electronic system to control the angle of the guide vanes, the relative position of the guide vanes is fixed, but the blade angle can be adjusted, during system operation, the exhaust gas will be fed along the guide vanes on the turbine blades,bmw turbo by adjusting the blade angle, the control flow through the turbine blades and the flow rate of gas, thereby controlling the rotational speed of the turbine . When the low exhaust pressure at low engine speeds, when the angle of the guide vanes open small. According to principles of fluid mechanics, then import the turbine at the air flow will accelerate, increasing the exhaust gas pressure at the turbine blades, which can more easily drive a turbine to rotate, effectively reducing turbo lag phenomenon,http://www.maxspeedingrods.co.uk/turbocharger/bmw-turbocharger.html but also to improve the response of the engine at low speeds time and acceleration. With the increase in lifting speed and exhaust pressure, the blade also increases the opening angle at full load condition, the blades remain fully open state, exhaust back pressure is reduced, so as to achieve as large turbo booster effect. As a simple example, in windy weather, we feel the wind in the open at significantly than (for example between two closely spaced buildings) in a non-enclosed narrow channel at the small lot. In addition, due to changes in rotational speed of the turbine blade angle can be effectively controlled, which also achieve the overload of the turbine, and therefore the use of a VGT turbocharger technology it is unnecessary to provide the wastegate.
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