How does a turbine with variable geometry work?

High competition in the automotive industry is a driving force for the development of new technologies in the field of engine topping. One of the most interesting is the turbocharger with variable geometry. What is its effect and why is it more effective?

Turbine and its impact on performance

The use of a turbocharger-based turbocharger is an effective solution so that the power and, above all, the torque generated by the propulsion unit can be significantly increased in a technologically easy way. Importantly, better performance does not translate into a dramatic increase in combustion, as is the case with increased displacement and number of cylinders. In addition, the turbocharger is relatively small and lightweight, so it has no impact on the vehicle’s mass. For this reason, it is quite common to install two turbochargers in a more powerful engine.

Principle of turbocharger operation

In order to understand the effect of variable geometry, it is necessary to know the principle of operation of the engine boost. The turbine rotor is driven by exhaust gases emanating from the cylinder, but on one axis it is connected to the compressor rotor. Flue gas, while driving the turbine, also makes the compressor move. Thanks to its rotary motion, this component absorbs air from the intake system while increasing the system pressure. As a result of the compression process, the volume of gas in the unit is simply filled up, which results in more potential energy reaching the cylinder where it is released by the combustion process of the fuel-air mixture.

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The problem of “turbo”

The biggest problem with turbochargers is low efficiency at low engine speeds. Under such circumstances, the exhaust gas velocity is also low and can not accelerate the turbine rotor to a maximum rotational speed of up to 200,000 rpm. Since the turbine does not operate at full power, the compressor is unable to pump a sufficiently large amount of air into the cylinder. The time elapsed since the accelerator pedal is applied to the high-speed turbine, resulting in a significant increase in torque, is commonly referred to as a “turbine”.

Variable geometry is an effective solution

The problem of “turbo”, in particular, concerns diesel engines which generate relatively low power without turbochargers. At low revs, the reaction of the car to the pressure of the gas is poor and aggravates the feeling of driving. This is not the case for mechanical compressors (compressors) because they generate linear momentum and the constant and constant speed of the turbine rotor ensures the crankshaft driven v-belt.

Engineers had to find a way to speed up the exhaust gases at the lowest engine rotational speeds. The solution proved to be very simple, and in practice, it was called the variable geometry of the turbocharger steering. These handlebars are blade-shaped elements that act as a guide to the turbine impeller. There is a clearance between the steering wheels, which, in the case of a variable geometry turbine, can be adjusted by changing the angle of inclination. If the engine is running at low speed, then the clearance is reduced to the minimum. In this way, the flow velocity of the exhaust gas increases and the impeller rapidly reaches the required speed. In practice, the negative effect of the “turbo” is then limited.

A simple experiment, based on the analogy of operation, can be carried out using a vacuum cleaner. Just plug it in and cover the end of the tube with your hand. We will soon see in our own skin that the velocity of the vacuum cleaner air will noticeably increase as a result of the laws of physics.

Caring for a turbine is essential

Advanced variable geometry turbines are many times more expensive to buy, and their regeneration is not recommended, although many services offer such services. It is therefore important to place particular emphasis on the quality of the oil being poured, which lubricates the turbocharger bearings. It is not advisable to switch to semi-synthetic lubrication technologies, even at high mileage.

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