TURBOCHARGERS AND SUPERCHARGERS

 When talking about high performance cars, we often hear the terms turbochargers and superchargers. These are forced induction systems that force compressed  air at a high pressure into the cylinders of the engine. This means that fuel is burnt in the cylinders with an high amount of pressurized air which gives a higher power output. The typical boost obtained from either a turbocharger or a supercharger is 6-8 psi. Since normal atmospheric pressure is 14.7 psi.
at sea level, you are getting about 50-percent more air into the engine. Therefore, you would expect to get 50-percent more power. It’s not perfectly efficient, though, so you might get a 30-percent to 40-percent improvement instead.

TURBOCHARGERS

Turbochargers get their power from the exhaust gases from the engine. The exhaust gases enter the turbine housing where they rotate a ceramic turbine at around 150,000 rpm and are then expelled out . A shaft connects the turbine wheel to a compression wheel in the compression housing. Here the air is sucked in through the center and is directed outwards due to centrifugal force.

Due to the high rotational speed of the blades and the hot exhaust gases the system gets heated. This heats the incoming air which has to be sent to the engine. Thus there is an inter-cooling system which cools the air before it reaches the engine.   In order to handle speeds of up to 150,000 rpm, the turbine shaft has to be supported very carefully. Most bearings would explode at speeds like this, so most turbochargers use a fluid bearing. This type of bearing supports the shaft on a thin layer of oil that is constantly pumped around the shaft. This serves two purposes: It cools the shaft and some of the other turbocharger parts, and it allows the shaft to spin without much friction.

One of the main problems with turbochargers is that they don’t give an immediate boost when you step on the gas. It takes a couple of seconds for the turbine to achieve the required speed and then only does it provide the boost. To eliminate this problem we have to reduce the inertia of the rotating parts by reducing its weight or by using a smaller turbocharger.

But a smaller turbocharger gives boost only at the initial stages. At higher speeds more exhaust is produced which may cause unwanted pressure buildup in the turbine housing. Thus there is a wastegate which senses the pressure buildup and bypasses the exhaust thus relieving the pressure.Some cars have two turbochargers, one small one which is used at lower speeds and a bigger one that takes over at higher speeds.

Some turbochargers use ball bearings instead of fluid bearings to support the turbine shaft. But these are not your regular ball bearings – they are super-precise bearings made of advanced materials to handle the speeds and temperatures of the turbocharger. They allow the turbine shaft to spin with less friction than the fluid bearings used in most turbochargers. They also allow a slightly smaller, lighter shaft to be used. This helps the turbocharger accelerate more quickly, further reducing turbo lag.

SUPERCHARGERS

A supercharger works exactly the same way as a turbocharger, but the only difference is that it gets its power to suck the air from belt mechanism connected to the engine.

 
A supercharger places a mechanical load on the engine to drive.For example, on the single-stage single-speed supercharged Rolls Royce Merlin engine, the supercharger uses up about 150 horsepower (110 kW). Yet the benefits outweigh the costs: For that 150 hp (110 kW), the engine generates an additional 400 horsepower, a net gain of 250 hp (190 kW). This is where the principal disadvantage of a supercharger becomes apparent: the internal hardware of the engine must withstand the net power output of the engine, plus the 150 horsepower to drive the supercharger.

     Turbocharging has been more popular than superchargers among auto manufacturers owing to better power and efficiency. For instance Mercedes-Benz and Mercedes-AMG previously had supercharged “Kompressor” offerings in the early 2000s such as the C230K, C32 AMG, and S55 AMG, but they have abandoned that technology in favor of turbocharged engines released around 2010 such as the C250 and S63 AMG biturbo. However, Audi did introduce its 3.0 TFSI supercharged V6 in 2009 for its A6, S4, and Q7, while Jaguar has its supercharged V8 engine available as a performance option in the XJ, XF and XKR.