Turbochargers and superchargers are engineered to force more air mass (and thus more oxygen molecules) into an engine’s intake manifold and combustion chamber. Intercooling is a method used to compensate for heating caused by supercharging, a natural byproduct of the semi-adiabatic compression process. Increased air pressure can result in an excessively hot intake charge, significantly reducing the performance gains of supercharging due to decreased density. Increased intake charge temperature can also increase the cylinder combustion temperature, causing detonation, excessive wear, or heat damage to an engine block or pistons.
Passing a compressed and heated intake charge through an intercooler reduces its temperature (due to heat rejection) and pressure (due to flow restriction of fins). If the device is properly engineered, the relative decrease in temperature is greater than the relative loss in pressure, resulting in a net increase in density. This increases system performance by recovering some losses of the inefficient compression process by rejecting heat to the atmosphere. Additional cooling can be provided by externally spraying a fine mist onto the intercooler surface, or even into the intake air itself, to further reduce intake charge temperature through evaporative cooling.