A turbocharger, (or turbo), is a turbine-driven forced induction
device that increases an internal combustion engine’s efficiency and power
output by forcing extra air into the combustion chamber.
The objective of a turbocharger is to
improve an engine’s efficiency by increasing the density of the intake gas
(usually air), thereby allowing more power per engine cycle.
How does it work?
A turbo is made
up of two halves joined together by a shaft. On one side, hot exhaust gasses
spin the turbine that is connected to another turbine which sucks air in and
compresses it into the engine. This compression is what gives the engine the
extra power and efficiency because as more air can go in the combustion
chamber, more fuel can be added for more power.
The turbocharger’s compressor draws in ambient air and
compresses it before it enters into the intake manifold at increased pressure.
This results in a greater mass of air entering the cylinders on each intake
stroke. The power needed to spin the centrifugal compressor is derived from the
kinetic energy of the engine’s exhaust gases.
Advantages
In addition to
the extra power, turbochargers are sometimes referred to as devices that offer
“free power” because unlike a supercharger, it does not require the engine’s
power to drive it. The hot and expanding gasses coming out of the engine are
what power a turbocharger so there is no drain of the engine’s net power.
Turbocharged engines are also not affected in the same way as naturally
aspirated engines are when they go at higher altitudes. The higher in altitude
a naturally aspirated engine climbs, the harder it becomes for it to get oxygen
due to the thinning atmosphere. A turbocharger gets around this problem because
it forces the oxygen into the engine’s combustion chamber, sometimes at 2 times
the pressure of the atmosphere.
Turbochargers
also improve the fuel efficiency of a vehicle however there is a misconception
when it comes to turbocharged vehicles and fuel efficiency. Taking a naturally
aspirated engine and slapping on a turbocharger on it will not improve fuel
efficiency. The way that manufacturers improve fuel efficiency though
turbocharging is by down-sizing an engine and then turbocharging it. For
example, take a 2.5L inline-4 cylinder naturally aspirated engine and decrease
the displacement to 1.4L and then turbocharger it. The smaller, turbocharged
engine would still have the same performance figures (or slightly better) but
because of the smaller displacement, it would also use less fuel.
Disadvantages
Turbochargers
have 2 main disadvantages when compared to a naturally aspirated or
supercharged engine. Firstly is heat. Because a turbo is powered by hot exhaust
gasses, it gets very hot. Sometimes under certain engine conditions, the
turbocharger itself could start glowing red but of course this doesn’t happen
in everyday driving conditions; it happens when the engine is pushed to its
limits for a continuous amount of time. This is why you see some turbocharged
sports cars with vents in the hood or down the side, it’s to try to get air
moving through the engine bay and keep things cool.
The other big
disadvantage of a turbocharger is something called turbo lag. Under certain
conditions, whenever you put your foot down on the throttle, there is a delay
between the time you demand power from the engine and the moment you actually
start to feel it. That is turbo lag. When the engine’s speed is low, there
isn’t a lot of exhaust gasses passing through the turbocharger so when you do
demand power from the engine, the turbocharger turbine needs time to start
spinning at an optimal speed. The effects of this can be reduced by
downshifting to a lower gear but keen drivers can still sometimes notice the
split delay in response.
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