Forced Induction: The Turbocharger
Being created more than 100 years ago, some time after the supercharger, the turbocharger has continuously evolved along the internal combustion engine and by now there are millions of cars equipped with this technology on the road.
Now, before getting into the whole oomph and whoosh of the turbines, we need to comprehend at least the basic functioning of an internal combustion engine. Like most devices that include internal explosions in order to work, the internal combustion engines have to “breath. In other words, they have to draw in air and fuel for their energy. This energy transforms into power the second the air and fuel mixture is ignited.
After all this happens, the exhaust gasses created by the explosion are being expelled from the engine. This usually exemplifies the four strokes of a regular Otto-cycle engine. In order to create a better combustion, and hence more power, engineers have a a number of choices, from which we are evidently only choosing the turbocharger as our point of discussion.
Basically, the turbocharger makes the air and fuel mixture in the cylinders of an engine more combustible by forcing more air in. The surplus air is directed into the engine's combustion chamber, thus creating more power when the pistons are forced downward (or sideways if we're talking about a Boxer engine) by the resulting explosion inside.
The turbocharger accomplishes this work by compressing the air molecules coming into the engine, thus making the air the engine “breaths” more dense. Basically an air pump, the turbine works in a very similar way to the supercharger, the only major difference residing in the way the pump is powered.
Since the basic laws of Physics tell us that compressing air makes it not only dense but also hotter, thanks to both the compression and the friction involved, this came as somewhat of a disadvantage. One of the few disadvantages this supercharging system has.
Enter the intercooler, charge-air cooler or heat exchanger, whatever you want to call it. This acts as a normal radiator and can use either air or water to cool down the air coming out of the turbocharger and entering the engine.The basic principle of a turbocharging system is rather simple but we're talking about a fairly complex device on the whole.
The most obvious advantage is the “free” power added to the engine. Practically, instead of wasting the thermal energy coming out of the engine through a normal exhaust system, those expelled gasses can be redirected to rotate a turbine which in turn rotates another one that is used to pump fresh air into the combustion chamber at much higher pressure than normal atmosphere, hence the term “forced induction”.
Better weight/power ratio
Since instead of using more cylinders or a bigger displacement to achieve higher power output, the overall weight of a turbocharged engine is much less than a bigger natural aspirated engine. This can lead indirectly to better handling, acceleration and braking, since there's less weight to carry.
The main downside of a turbocharger, especially compared to its supercharger counterpart is the lag in engine response at low rpm. Since the turbine has to spin at a given speed before actually becoming efficient enough to make a difference in the power output of the engine, this is experienced in what is called “turbo lag”. There are different ways to counteract this, but the lag is still present, though much lower, even in modern engines.
Another disadvantage comes from the actual compression of the air, which increases its temperature, therefore minimizing its volumetric efficiency. This in turn goes exactly against the effort of the turbocharger itself, but the problem can be greatly minimized by the addition of an intercooler. This problem can be found in any forced induction engine, no matter by which method.