An intercooler is a device used on turbocharged and supercharged internal combustion engines to improve the volumetric efficiency and increase the amount of charge in the engine, thereby increasing power. The inter in the name refers to its location compared to the compressors; the coolers were typically installed between multiple stages of supercharging in aircraft engines. Modern automobile designs are technically aftercoolers because they appear most often at the very end of the chain, but this name is no longer used.
Turbochargers and superchargers compress incoming air, causing it to become heated. Since hot air is less dense than cooler air at the same pressure, the total charge delivered to the cylinders is higher than non-compressed air, but still less than it could be. By cooling the charge after compression, even more charge can be delivered, increasing power. Additionally, intercoolers help to increase the total amount of boost possible without causing engine knocking.
An intercooler is essentially a radiator tuned for high volume flow rates and the increasing density of the charge as it cools. Most designs use ambient air for cooling, flowing through the radiator core, and often collocated with other radiators for oil or cooling fluid. This approach is also known as Air To Air (ATA).
An alternate design, often referred to as a charge cooler, uses water or a water/antifreeze mix to cool the charge, then cools the water in a separate radiator. While heavier and more complex, charge coolers can often make arranging the rest of the engine much simpler. This approach is also known as Water To Air (WTA). A variation on this type of charge cooler substitutes a reservoir of coolant for the radiator, allowing the use of an icewater mixture that can bring outlet temperatures well below ambient air temperature even under very high boost pressure. Because of the limitations on the volume of icewater that can be stored and circulated, this approach to charge cooling is only practical for short durations, making it most common in drag racing and land speed record attempts.
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