What is a Turbo Charger?
First developed in 1924, the turbo charger uses the engine's exhaust gases to power a turbine, which drives a compressor, and pushes more air into the engine. This allows the engine to produce more power without any increase in size. Turbochargers have provided such significant improvements in engine efficiency that they are now fitted to almost all new diesel engines.

How does it work?

Operation of a basic turbocharger.

A turbo charger is an exhaust-driven turbine which drives a centrifugal compressor wheel.
The compressor is usually located between the air cleaner and the engine intake manifold, while the turbine is located between the exhaust manifold and the tail pipe of the exhaust system.
The prime job of the turbocharger is, by compressing the air, to force more air into the engine cylinders. This allows the engine to efficiently burn more fuel, thereby producing more horsepower.

Basic parts of a turbocharger

All of the engine exhaust gases pass through the turbine housing. The expansion of these gases, acting on the turbine wheel, causes it to turn. After passing through the turbine, the exhaust gases are routed to the atmosphere. In many cases, the turbine muffles the exhaust sound, so no muffler is needed.
The turbine also functions as a spark arrester. For example, it is recognised by the U.S. Department of Agriculture as providing a spark arrester function adequate for forestry operations.
The compressor is directly connected to the turbine by a shaft. The only power loss from the turbine to the compressor is the slight friction of the journal bearings.

Air Intake comparison

Air is drawn in through a filtered air intake system, compressed by the wheel, and discharged into the engine intake manifold.
The extra air provided by the turbocharger allows more fuel to be burned, which increases horsepower output. Lack of air is one factor limiting the engine horsepower of naturally-aspirated engines.
As engine speed increases, the length of time the intake valves are open decreases, giving the air less time to fill the cylinders. On an engine running at 2500 rpm, the intake valves are open less than 0.017 second. The air drawn into a naturally-aspirated engine cylinder is at less than atmospheric pressure.

A turbocharger packs the air into the cylinder at greater than atmospheric pressure. The flow of exhaust gas from each cylinder occurs intermittently as the exhaust valve opens. This results in fluctuating gas pressures (pulse energy) at the turbine inlet. With a conventional turbine housing, only a small amount of the pulse energy is needed.
To better utilise these impulses, one design has an internal division in the turbine housing and the exhaust manifold which directs these exhaust gases to the turbine wheel. There is a separate passage for each half of the engine cylinder exhaust.
On a six-cylinder engine, there is a separate passage for the front three cylinders and another passage for the rear three cylinders.
By using a fully divided exhaust system combined with a dual scroll turbine housing, the result is a highly effective nozzle velocity. This produces higher turbine speeds and manifold pressures than can be obtained with an undivided exhaust system.
The turbocharger offers a distinct advantage to an engine operating at high altitudes. The turbocharger automatically compensates for the normal loss of air density and power as the altitude increases.

Twin Passage Turbine

With a naturally aspirated engine, horsepower drops off 3 percent per 1000 ft (300m) because of the 3 percent decrease in air density per 1000 ft (300 m). If fuel delivery is not reduced, smoke level and fuel dilution will increase with altitude.
With a turbocharged engine, an increase in altitude also increases the pressure drop across the turbine. Inlet turbine pressure remains the same, but the outlet pressure decreases as the altitude increases. Turbine speed also increases as the pressure differential increases. The compressor wheel turns faster, providing approximately the same inlet manifold pressure as at sea level, even though the incoming air is less dense.
However, there are limitations to the actual amount of altitude compensation a turbocharged engine has. This is primarily determined by the amount of turbocharger boost and the turbocharger-to-engine match.
All turbochargers operate at a very high speed. This can range from 40,000 to 280,000 rpm or more.

 

Altitude compensator

The appearance, construction, and operation of the altitude compensator is the same as that of a turbocharger. However, the purpose is different.
The purpose of a turbocharger is to increase the power output of an engine by supplying compressed air to the engine intake manifold so increased fuel can be utilised for combustion.
The purpose of the altitude compensator is to maintain consistent power output and efficiency of an engine operating at all altitudes. This is done by supplying compressed air to the engine intake manifold at a pressure about equal to that at sea level.
There is no increase of fuel for combustion and consequently no increase in basic horsepower of the engine. However, the extra air provided by the altitude compensator normally increases combustion efficiency, which generally will improve fuel economy and reduce smoke level.