The turbocharger (turbo) is a device that when attached to an engine correctly it creates more horsepower and torque. This is done through forced induction, where air is forced into an engine at pressures greater than the surrounding air. The increase in pressure of the air creates a denser gas, and means more oxygen is in the engine. More oxygen allows more fuel to burn, and this allows greater power.
To understand how a turbocharger works one must understand the basic principle of increasing engine power. More burning fuel equals more engine power. The turbo increases the amount of fuel burned per cylinder.
The turbocharger itself is actually two turbines in separate housings that are connected by either a direct linkage or belts and pulleys. One of the turbines is dedicated to powering the device, while the other turbine is used to pressurize the air into the engine.
The power turbine is connected to the exhaust pipes of an engine. The hot exhaust runs through the turbine and spins it at thousands of revolutions per minute (RPMs.) If the power turbine were the only piece attached to the engine, the overall power of the engine would be less as energy would have to be spent by the engine to push the exhaust through the power turbine, but no work would be done to help the engine gain power.
The energy collected from the exhaust gases is transferred to the intake turbine. This turbine pulls air from outside the vehicle and compresses it into the cylinders of the engine. The average pressure of air is a little more than 14 pounds per square inch (PSI). A turbo can increase this pressure by another 7 to 14 PSI depending on turbo and the engine being used. By increasing the pressure 1.5 times above normal, the engine will have 1.5 times more fuel burning at any given time.
Using the equation P*V = n*R*T where: P = pressure ,V = volume, n = number of moles (amount of substance), R = gas constant, T = temperature, one can see the effect of increasing pressure in numbers. Assume the pressure is 14 PSI and the volume is 1 gallon. R will remain constant (value of 1) and T will remain constant (value of 1). n will equal the amount of oxygen in the cylinder at ignition (value before compression is 14). Assume the equation becomes:
14*1 = 14*1*1
This represents the engine when there is no compression of the air the cylinders. Now the pressure of the air is increased to 7 PSI above normal for a total of 21 PSI. The equation becomes:
21*1 = 14*1*1
The equation must remain equal, so one of the variables on the right side must change. We are assuming that the temperature is constant, along with the gas law constant, so the amount of air must increase to keep the equation balanced. The equation becomes:
21*1 = 1.5*14*1*1 OR 21=21
By increasing the pressure the amount of air is increased allowing more burning to take place.
If the energy to compress the air was free
, the engine would experience an increase in power of 1.5 times its original before the turbo. However, because the engine must force the exhaust through the turbine, the turbines must fight friction
to move, and that the turbines are not one hundred percent efficient
in compressing the air, the actual power experience is dropped by up to 50%.
A common addition to a turbo is an intercooler. This device cools air that has been through the turbo, increasing the density of the air further. When air is compressed, it heats up slightly. Also, the turbo spinning through the air creates friction between the turbo parts and air increasing temperature and the friction of the turbo parts gainst themselves increase the temperature of the air.
The reason that many turbo-equipped vehicles do not come equipped with an intercooler is that the change in temperature does not have as drastic an effect on the density of the air as does compressing it. The amount of extra power obtained through and intercooler is not worth the expense of the part for most engines. Racing engines, where a horsepower or foot pound of torque equals miles for long distance courses, are generally the only engines equipped with intercoolers and turbochargers.
The supercharger is the same in operation and effect as a turbocharger. The only difference between the two is that a supercharger is mechanically connected to the engine though belts for power to compress that air instead of using the exhaust gases as a turbocharger does.