Peek Into: Turbochargers and Superchargers
Although turbochargers and superchargers are both designed with the intention to improve engine performance there are differences in how they work. How are they different? Is one inherently better than the other? What considerations do we need to take in before deciding on a system?
First, let’s recap our understanding of forced-induction – the basis of operation for both turbochargers and superchargers.
As the name implies, forced-induction is a system where air is forced into an engine. In the case of turbo/superchargers this is accomplished by an air compressor. This creates a higher fuel/air ratio, in which the primary oxidizer, oxygen from the air (atmospheric oxygen), allows the engine, an internal combustion engine, to burn fuel more efficiently which translates into additional power. The difference between a turbocharger and a supercharger is how their compressor turbines are spun.
Now that we understand how forced-induction and engines work it’s onto the details:
Turbochargers rely on the kinetic energy of an engine’s exhaust gases to spin its centrifugal compressor. The compressed air is then let into intake manifold where it is mixed with fuel, creating a rich fuel/air mixture, before entering the engine. Because turbochargers rely on exhaust gases it doesn’t put any mechanical load/stress on the engine like superchargers do.
A turbocharger’s reliance on exhaust gases makes it efficient, since exhaust gases are otherwise released into the environment. Due to advances in material technology, many car and engine manufacturers have adopted turbochargers because of the efficiency that comes with it.
However, turbochargers are affected by turbo-spool, or a ‘lag’ in the time boosts are experienced at low engine RPMs due to the low gas pressures required to turn the turbocharger’s compressor turbine, with a sudden surge of acceleration happening as the gas flow to the turbine reaches the turbocharger’s designated operating parameters.
Superchargers, on the other hand, are mechanically driven. They rely on power transferred from the engine’s crankshaft over a belt, gear or chain drive to spin the supercharger’s compressor turbine.
A supercharger is capable of producing far greater rotations to its turbine compressor at relatively low engine speeds because it isn’t reliant on gradual gas pressure build up that characterizes a turbocharger. This provides increases in speed directly proportional to the speed of the engine.
While it isn’t affected by the turbo-spool ‘lag’, engine performance gains are minimal at low RPMs. A supercharger also relies on mechanical energy from the engine to spin its turbine and so as power-efficient as a turbocharger.
A system that uses a combination of supercharger and turbocharger is known as a twincharger.
Did you know?
While Nitrous Oxide itself isn’t flammable itself at low temperatures, it is used to super-cool the air entering the engine. Cooler air is denser, which compacts the oxygen molecules creating an oxygen-rich environment that reacts more readily with the fuel. Nitrous oxide itself breaks down at temperatures in excess of 565 degrees Fahrenheit and provides oxygen as per normal.
This can, however, significantly raise temperatures to dangerous levels and cause damage to the engine. If temperatures get too high it could cause the fuel-air mixture to detonate, causing damage to the engine. This also limits its uses on hot days. Nevertheless, superchargers are picked when power and boost response times take precedence over other considerations.