How a turbo engine works?

Hi,

A long time ago I posted something in English here and I noticed that people from all over the world visited this blog, so I will try to translate everything here as soon as possible. Today I’ll talk a little bit of turbo engines and how it works, compare it with a normal engine and talk about some modifications to avoid destroying it.

I don’t know if all of you know how a common aspirated engine works, so let’s start from beginning. In a common aspirated engine, when the intake valve opens the piston goes down and pulls the air from the intake to the cylinder. At something around 800RPM the engine is considered stable and the pistons have sufficient force to go down and aspirate the air, for this reason this kind of engine is called “aspirated”.

Turbo engines are the ones who uses forced induction of air, but how this induction works?

Now is time to go to engine’s exhaust, from where the gases exit and instead of being thrown into the atmosphere, they are diverted to the turbine, where the gases will give sufficient kinetic energy to turn it.

Turbine with compressor

The turbine makes the compressor turn (once they have the same axis and the gases are turning the turbine), the compressor is responsible to send so much more air mass to the intake, generating a significant increase of pressure inside the cylinder, giving us what we want, more power!

After reading it you must be impatient to put a turbo system in your car, but it’s not just put a turbo on it and start pushing to anywhere, some modifications must to come with the turbo installation, in lower pressures it’s not a big problem but is extremely recommended to do it. I’m talking about more resistant parts like: pistons, rods and exhaust made by forged steel. After doing it you may be safe.

After going out the compressor, the air goes through an intercooler which is responsible for cooling it. According the ideal gases equation (PV = NRT), for the same gas volume and pressure but in lower temperatures we can increase N, which means more air mass. Like the pressure, the quantity of air is important because the power is calculated based volumetric efficiency, that relates the air mass the cylinder can have and the real air mass it has, don’t forget that a bigger air mass implies in a greater torque too.

Intercooler

Now I’ll put a figure and a video that shows what I said until now, I’m sorry it’s in Portuguese but I guess it’s not difficult to understand, on other hand, I studied vehicles for a longer time at my university, so this post for sure is better than the original version.


A common turbo works in a RPM range, it happens because the turbine needs the engine to be in a speed which generates the necessary volume of gas to start turning the turbine, this process is called “Turbo lag”. There are some way to solve turbo lag, we can for example use a volumetric compressor, that is 100% mechanic, linked the engine by pulleys and belts, in addiction to stop turbo lag, with this kind of compressor we can use the pulleys to limit the compressor’s rotation, limiting the pressure.

Volumetric Compressor

In a common turbine, there are some ways to limit the pressure, the most used by car’s manufacturers, is the wastegate valve, it opens when the air climbs until a limit  pressure, preventing any damage caused by overpressure, another kind of valve is the priority valve, which does the same thing the wastegate valves but makes that characteristic turbo overpressure sound we know.

Priority Valve

Another solution is the geometry variable turbo, a special kind of turbine who has small “blades” who can change his angles, what will vary the turbine’s area too. With a smaller area, the turbine needs a smaller gas volume, so it can work from the lower RPM’s to the higher ones. Next video explains how it works:

So guys,

I hope you enjoyed this post, and like I said in the beginning of this post I’ll try to translate all the things here as soon as possible.

Thanks for reading,

Rafael Basilio

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