We keep hearing words like “turbocharged” and “supercharged” engines all the time. How are they different from naturally aspirated engines?
Firstly let us understand what a naturally aspirated engine means.
When an engine has no form of forced induction (turbocharger or supercharger), it is called a naturally aspirated engine. The air-fuel mixture goes into the engine (cylinder), it then combusts and the generated exhaust gases are vented out through the exhaust pipe. This is the most basic form that any engine has. But when more power output is desired, forced induction is added i.e. either a turbocharger or a supercharger. Both, turbochargers and superchargers have their own advantages and disadvantages.
Working of a turbocharger.
To increase performance output of an engine, it needs to run faster. Which means that it requires faster and higher amounts of air-intake. A turbocharger works on the basis of Exhaust Gas Recirculation (EGR).
After combustion, when the resultant exhaust gases are sent from the engine to the exhaust pipe, they have some amount of force and pressure. This force and pressure is used to rotate a turbine. This turbine rotates another turbine that sucks and compresses air from the outside and sends it back to the engine via an intercooler. This mechanism enables more air intake via ‘forced induction’. Hence the engine is able to operate faster using the inertia of the exhaust gases.
Working of a supercharger.
A supercharger is very similar to a turbocharger except for its method of activation. Instead of using the inertia of exhaust gases released from the engine, it operates using the mechanical power from the engine itself. In other words, the turbine that sucks air rotates using a belt that is connected to the crankshaft.
More about Forced Induction:
Since turbochargers use exhaust gases for operation, they need a minimum force to be activated. Every turbocharger has a different activation force requirement depending on its size. Let’s say that a specific car has a turbocharger that spools up or activates at 2000RPM. This means that this turbocharger will not give any usable output or boost below the 2000RPM count. This dead zone on the RPM band is what we call turbo-lag. Turbo-lag causes uneven acceleration in the vehicle. Different techniques are being used to eliminate turbo-lag. Due to uneven/instantaneous acceleration, traction and stability may get compromised.
Ever heard the hissing sound in a high performance car just after it accelerates or just before it changes gears? Remember how a pressure cooker whistles to let steam out and reduce pressure? Both are very similar. The turbocharger compresses air creating a lot of pressure in the system during accelerating. When the accelerator pedal is released, the pressure is let out via a Blow Off Valve (BOV) which acts like a pressure nozzle in a pressure cooker. A turbocharger can operate upto 150,000RPM.
Superchargers are usable almost throughout the entire RPM band and have no lag. They are easier to install. But since they feed directly on the engine to run themselves, fuel economy of the car suffers. Because of this reason we see a lot of car manufacturers turning towards turbochargers compared to superchargers. In fact, turbochargers are known to improve efficiency because they make use of their exhaust gases.
As the name suggests, “forced induction” exposes the engine to a lot of forces (high pressures and temperatures) and for this reason it is important to have all the information required before selecting a forced-induction system by yourself.
Why Forced Induction systems are trending:
With emissions reaching skies, we need to be very serious when it comes to producing powerful vehicles. Every manufacturer is moving towards down-sizing to reduce emissions. Because, bigger the engine-more the amount of fuel it needs. Forced induction is today’s solution to acquiring higher performance with lower emissions. As already mentioned, turbochargers are being preferred over superchargers for efficiency. Many manufacturers are installing 2 turbochargers in their engines to acquire boost throughout the RPM band. Examples include the Twin-Turbo engines by BMW, the Biturbo engines by Mercedes, and so on.
In fighting turbo-lag, hybrid systems have already been introduced to electrically fill in the gaps of lag to acquire linear performance throughout the RPM band(Mclaren P1, Porsche 918 Spyder and Ferrari LaFerrari). Before the world goes completely electric, we are going to see a lot of amazing hybrid systems in the near future.