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Automotive turbos have been widely used in production cars since more than four decades ago. Find out how turbocharging technologies have evolved.

11 Mar 2015 | Category: Car Technical Advice

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For internal combustion to take place, fuel needs oxygen, the source of which is atmospheric air. During the intake stroke (as the piston descends within the cylinder), the mass of air inducted is strictly at ambient pressure.

Cylinder volume is a physical constant, but the mass of air that fills any space is a function of pressure. Hence, the higher the pressure, the greater the mass of air that can occupy any given volume, simply because air is compressible.

Exhaust-driven turbine wheel spins its 'attached' compressor wheel to turbocharge the engine's output

A device that 'blows' air into the cylinder would enable more air-mass to be squeezed inside said cylinder than by natural aspiration alone. This concept of forcing air into the cylinder to achieve greater than 100 percent volumetric efficiency at a given ambient pressure is termed 'supercharging'.

The device mentioned in the previous paragraph is called a compressor. It can be driven by an electric motor, or mechanically by a belt off the crankshaft.

The turbocharger, however, relies neither on a motor nor a belt. Instead, a turbo compressor is driven by a shaft-connected turbine, which is made to spin by the hot, fast-flowing exhaust gases of combustion.
In theory, then, turbo-supercharging (to use the 'correct' technical term) consumes no energy on its own since exhaust gases are waste products of the internal combustion process.

Hot and bothered

Turbocharging, though highly effective, isn't as simple as it sounds. Heat is turbocharging's biggest complication.

Compressed air, especially if it flows from an exhaust gas-driven
device, experiences a significant rise in temperature. Not only does this mean a drop in the density of said air, it also causes pre-ignition of the air-fuel mixture in the combustion chamber - a phenomenon that frequently leads to stress failure in the cylinder head (and sometimes even the engine block).

Porsche is one of the first automakers to adopt turbocharging in their series production road cars, such as the 930 Turbo

Torque The article first appeared in the October 2013 issue of Torque. Log on to their website to subscribe.
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