Types of Turbos that exist

DO YOU KNOW HOW MANY TYPES OF TURBES THERE ARE?

Do you know how many types of turbos there are? The world of turbocharging has as much variety as engine designs. And do you know what its advantages and disadvantages are? In turbo3 we explain it to you.

There are 6 different types of Turbochargers:

1. Simple turbo
2. Twin-Turbo
3. Dual scroll turbo
4. Variable geometry turbo
5. Variable Twin Scroll Turbo
6. Electric turbo

1. Simple turbo

Individual turbochargers alone have unlimited variability. Differentiating the size of the compressor wheel and the turbine will lead to completely different torque characteristics. Large turbos will bring high-end power, but smaller turbos will provide a better low-end growl as they roll up faster. There are also individual turbos with ball bearings and trunnion bearings. Ball bearings provide less friction for the compressor and turbine to turn, making them faster to wind (while increasing costs).

Advantage

• Cost-effective way to increase the power and efficiency of an engine.
• Simple, generally the easiest to install of the turbocharger options.
• It allows the use of smaller engines to produce the same power as larger naturally aspirated engines, which can often reduce weight.

Disadvantages

• Individual turbos tend to have a fairly narrow effective RPM range. This makes size an issue as you’ll have to choose between good low-end torque or better high-end power.
• Turbo response may not be as fast as alternate turbo settings.

2. Twin-Turbo

As with individual turbochargers, there are many options when using two turbochargers. You could have a single turbocharger for each bank of cylinders (V6, V8, etc.). Alternatively, a single turbocharger could be used for low RPM and diverted to a larger turbocharger for high RPM (I4, I6, etc.). You could even have two similar sized turbos where one is used at low RPM and both are used at higher RPM. In the BMW X5 M and X6 M, dual-displacement turbos are used, one on each side of the V8.

Advantage

• For twin parallel turbos on ‘V’ shaped engines, the benefits (and drawbacks) are very similar to single turbo setups.
• For sequential turbos or using a turbo at low RPM and both at high RPM, this allows for a much wider and flatter torque curve. Better torque at low revs, but power won’t drop at high RPM like with a small turbo.

Disadvantages

• Cost and complexity, since it almost doubles the turbo components.
• There are lighter and more efficient ways to achieve similar results (as explained below).

3. Dual scroll turbo

Twin-scroll turbochargers are better in almost every way than single-scroll turbochargers. By using two scrolls, the escape pulses are split. For example, in four-cylinder engines (firing order 1-3-4-2), cylinders 1 and 4 can be fed to a turbo scroll, while cylinders 2 and 3 are fed to a separate scroll. Why is this beneficial? Let’s say cylinder 1 is ending its power stroke when the piston approaches bottom dead center and the exhaust valve begins to open. While this is happening, cylinder 2 ends the exhaust stroke, closes the exhaust valve, and opens the intake valve, but there is some overlap. In a traditional single-displacement turbo manifold, the exhaust pressure from cylinder 1 will interfere with cylinder 2 sucking in fresh air, as both exhaust valves are temporarily open, reducing how much pressure reaches the turbo and interfering with the amount of air. pulling cylinder 2. By dividing the scrolls, this problem is eliminated.

Advantage

• More energy is sent to the exhaust turbine, which means more power.
• A wider effective boost RPM range is possible based on different displacement designs.
• Greater valve overlap is possible without hampering exhaust cleanliness, which means greater adjustment flexibility.

Disadvantages

• It requires a specific engine layout and exhaust design (for example: I4 and V8 where 2 cylinders can be fed at each turbo displacement, at uniform intervals).
• Cost and complexity compared to traditional individual turbos.

4. Variable Geometry Turbocharger (VGT

Perhaps one of the rarest forms of turbocharger, VGTs have limited production (though quite common in diesel engines) as a result of cost and exotic material requirements. The internal vanes within the turbocharger alter the area-to-radius (A / R) ratio to match RPM. At low rpm, a low A / R ratio is used to increase the speed of the exhaust gases and rapidly accelerate the turbocharger. As revs increase, the A / R ratio increases to allow more airflow. The result is low turbo lag, low boost threshold, and a wide, smooth torque band.

Advantage

• Wide, flat torque curve. The turbocharger is effective over a very wide RPM range.
• It requires a single turbo, which simplifies a sequential turbo setup into something more compact.

Disadvantages

• It is usually only used in diesel applications where the exhaust gases are lower so that the vanes are not damaged by heat.
• For gasoline applications, cost generally keeps them out, as exotic metals must be used to maintain reliability. The technology has been used in the Porsche 997, although very few VGT gasoline engines exist as a result of the associated cost.

5. Variable double scroll turbocharger

Could this be the solution we were waiting for? While attending SEMA 2015, I stopped by the BorgWarner booth to see the latest in turbochargers, among the concepts is the variable twin-scroll turbo as described in the video above.

Advantage

• Significantly cheaper (in theory) than VGTs, making it an acceptable case for gasoline turbocharging.
• Allows for a wide and flat torque curve.
• More robust in design than a VGT, depending on material selection.

Disadvantages

• Cost and complexity compared to using a traditional single turbo or dual scroll.
• The technology has been played around with before (ex: fast spool valve) but it doesn’t seem to be succeeding in the production world. There are likely to be additional challenges with technology.

6. Electric turbochargers

Aeristech’s patented all-electric turbocharger technology is a new enabling technology that will help vehicle manufacturers comply with future stricter emissions legislation, while providing excellent response throughout the engine’s operating range, even at low engine revolutions and vehicle speed. FETT is the ultimate solution for extreme engine downshifting and improved engine efficiency using a single stage turbocharger.

Throwing a powerful electric motor into the mix eliminates almost all the downsides of a turbocharger. Turbo lag? Gone. Not enough exhaust fumes? No problem. Turbo can’t produce low-end torque? You can now! Perhaps the next phase of modern turbocharging, to be sure, there are also downsides to the electric route.

Advantage

• By connecting an electric motor directly to the compressor wheel, insufficient turbo lag and exhaust gases can be virtually eliminated by rotating the compressor with electric power when needed.
• By connecting an electric motor to the exhaust turbine, wasted energy can be recovered (as is done in Formula 1).
• A very wide effective RPM range with uniform torque throughout.

Disadvantages

• Cost and complexity as you now have to factor in the electric motor and make sure it stays cool to avoid reliability issues. That also applies to additional drivers.
• Packaging and weight become an issue, especially with the addition of an on-board battery, which will be required to supply enough power to the turbo when needed.
• VGTs or twin rolls can offer very similar benefits (though not to the same level) for significantly less cost.