Clifford Kim
ENG 202C
March 25, 2015
The Process of Turbo Charging an Engine
In today’s environmentally conscious mindset, many automotive companies are focusing
on improving the fuel efficiency of their vehicles. One approach to this problem is to use a
smaller engine that would burn less fuel; however this takes away from the horsepower available
to driver. To compensate for this power loss, vehicles with smaller engines can use an engine
modification known as a turbocharger to match or even exceed power output of larger engines
while still maintaining fuel efficiency.
A four-stroke engine has four cycles which it goes through while in operation: intake,
compression, power, and exhaust. The process of turbo charging an engine modifies each of
these stages by using the pressure of engine exhaust, which would have otherwise been
wastefully blown out of the exhaust pipe, to suck more fresh air into the engine. Because the air
is being forced into the engine, the engine does not need to waste energy during the intake phase
to draw it in and also allows for more oxygen to be present during the compression phase. The
higher concentration of air inside the engine’s cylinders means that a higher percentage of the
fuel that is injected when the driver steps on the pedal is burned during the power phase. In
general, a turbocharger design consists of four main components: the center housing, the turbine,
the compressor and the charge air cooler.
Center Housing
The process of turbo charging an engine begins with the
forcing of engine exhaust gases into the turbocharger’s
center housing, which contains the compressor and the
turbine. The center housing’s spiral shaped structure
directs the exhaust gases entering it to rotate around the
turbine in such a way that it is forced to spin. The
center housing allows the whole assembly to spin at
over 250,000 revolutions per minute and lubricates the
moving components of the turbocharger so that it will
not overheat during use. This image shows how the
turbine is enclosed within the center housing. The
turbine’s square downward facing aperture is where the engine’s exhaust is connected. On the
backside of this housing, there is an identical fan facing the opposite direction which is referred
to as the compressor. The compressor’s circular aperture can be seen facing outward.
Turbine
The metal fan circled in red is known as the
turbine and it is the fan that is exposed to the
engine exhaust. Exhaust gases are redirected
from the engine and into the square connector
of the center housing, where the pressure from
the gas forces the turbine fan to spin. After
passing through the turbine, the hot exhaust
gases are then released from the turbocharger
out of the turbine side exhaust port. The
rotating turbine fan spins an opposite facing
metal fan called the compressor via a steel rod
connection inside the turbocharger’s center
housing.
Compressor
While energy from the exhaust gases spin the
turbine, the compressor circled in blue here
accomplishes the job of using that harnessed
energy to force fresh air back into the engine. The
compressor’s opposite orientation pulls outside air
into the center housing through the large circular
turbocharger intake. Because of the high
revolution speed of the turbine-compressor
assembly, the air that is sucked in is pressurized,
and heated to high temperatures. The charged air is
then forced out of the center housing through the
lower circular aperture. In order for this high temperature air to be usable by the engine, it must
first be directed to the cooling system.
Charge Air Cooler
The charge air cooler is a
special radiator designed
to cool gases that flow
through it. The high
pressure air from the
compressor is pushed
through the charge air
cooler where its
temperature is reduced.
Cooling the turbocharged
air before it is forced into
the engine serves two
purposes, one being that the cooled air increases efficiency because it creates a greater
temperature difference between engine air intake and engine exhaust gas. The second purpose of
cooling the air is to increase its density, which in turn means that more oxygen is able to be
squeezed into the engine. After being forced through the charge air cooler, the pressurized air is
then directed into the engine’s air intake through a hose located at the opposite end of the cooler.
The air forces its way into the engine where it is mixed with fuel and burned. The exhaust
created powers the turbine further and the continuous cycle increases the power of output of the
engine.
Power Increase and Efficiency
The process of using the power of exhaust gases to “push” more air into the engine and increase
its performance is known as turbo charging. By utilizing otherwise wasted exhaust gases that are
created when an engine is running, a turbo charging system saves the engine from the work of
drawing in air during the intake phase. A higher concentration of air allows the fuel inside the
engine to burn more completely. Exhaust gases are forced into the turbine side of the central
housing unit where the turbine harnesses its energy. The turbine fan is connected to an opposing
compressor fan which draws fresh air into its half of the central housing unit and forces it out
into the charge air cooler at high pressure. After passing through the charge air cooler, the lower
temperature air is burned inside the engine and the exhaust further turns the turbine. Because the
turbocharger is powered by the exhaust gas of the vehicle, the amount of boost power it
generates depends on how hard the engine is working at any given time. In other words, the
turbocharger responds to how far the driver depresses the gas pedal on the vehicle. A smaller
engine using a turbocharger will give the driver a power boost that can meet or surpass the power
of larger engine on command while also keeping the benefit of its fuel efficiency.