Intercooling and aftercooling in engines

"Charge-Air Cooler", is an air-to-air or air-to-liquid heat exchange device used to improve the volumetric efficiency of internal combustion engines by increasing intake air-charge density through isochoric cooling. A fall in air intake temperature offers a denser intake charge to the engine and offers more air and fuel to be combusted per engine cycle, which increases the performance of the engine.

In the past, turbochargers were run in stages. The first stage compressor fed the inlet of the second stage compressor which, in turn, would further compress the air before it enters the engine. Extremely high pressure is developed in such arrangements and a charge-air cooler is placed between the first and second stage compressors. That cooler is called the "Intercooler".

Another charge-air cooler is often positioned after the second stage, which is the final compressor stage, and that is called the "aftercooler". An aftercooler is a type of cooler whose outlet fed the engine.