An aftercooler removes heat from the compressed air coming from a supercharger before it enters an engine's induction system. This increases efficiency and power by increasing the density of the air, making for more air molecules per cubic foot. Aftercoolers may also be known as intercoolers. The terms were coined according to the placement of the system within an engine, but aftercoolers and intercoolers function similarly.
Although aftercoolers may be used in many applications, such as air compressors, refrigeration systems and air conditioning, they are best known for their use in forced induction internal combustion engines. They enhance the power and torque produced by such engines by increasing the air charge density through cooling.
A decrease in intake air charge temperature allows a more dense intake charge into the engine, which preserves the benefits of fuel/air burn per engine cycle while increasing efficiency and power. Aftercoolers also help avoid the use of extra fuel for lowering the intake air charge temperature, which is a process that also lowers efficiency.
The term "intercooler" was used because of the placement of the system between multiple stages of forced inductions in aircraft engines. However, in modern automobile design, the system is called an "aftercooler" because of its placement at the end of a supercharging chain.