Intercooler

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For the Australian rock group, see Intercooler (band).

A front-mounted intercooler on a Mitsubishi Eclipse

An intercooler is a device used on turbocharged and supercharged internal combustion engines to improve the volumetric efficiency, increase the amount of charge in the engine, and lower charge air temperature thereby increasing power and reliability. 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 term is no longer used.

[edit] Turbocharging

Turbochargers and superchargers compress incoming air, causing it to become heated (see the ideal gas law). 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, the stream experiences further compression which is naturally tied with cooling of matter - upon cooling matter shrinks occupying less volume (usually, see Coefficient of Thermal Expansion). With this further compression even more charge can be delivered, increasing power. Additionally, intercoolers help to increase the total amount of boost possible without causing engine knocking. One of the most efficient intercoolers is water injection - it cools the intake charge and cool down the combustion temperature.

Image:Top mount intercooler.jpg

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 co-located with other radiators for oil or cooling fluid. This approach is also known as Air To Air (ATA).

[edit] Charge Cooling

An alternate design, often referred to as a charge cooler, (heat exchanger) 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 or A/W). A variation on this type of charge cooler substitutes a reservoir of coolant for the radiator, allowing the use of an icewater mixture or liquid nitrogen that can bring outlet temperatures well below ambient air temperature even under very high boost pressure. Because of the limitations on the volume of coolant 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.

Air to air intercoolers need to be mounted so as to maximize air flow and promote efficient cooling. Most cars such as the Saab (except the Subaru WRX-based 9-2X Aero), Dodge SRT-4, Mitsubishi Lancer Evolution, Volkswagen and Audi use front mounted intercooler(s) (FMIC) mounted vertically near the front bumper, in line with the car's radiator. Many older turbo-charged cars, such as the Saab 900, Toyota Supra and Turbo Mitsubishi Eclipse use side-mounted intercoolers (SMIC), which are mounted in the front corner of a bumper, in front of one of the wheels. Side-mounted intercoolers are generally smaller and less efficient than front-mounted intercoolers. Cars such as the Subaru Impreza WRX, MINI Cooper S and the MAZDASPEED 6 use top mounted intercoolers (TMIC) which are mounted horizontally on top of the engine (due to a low hood line) and use a hood scoop to force air over the intercooler. Some World Rally Championship cars use a reverse-induction setup, where air from ducts in the front bumper is forced up over a horizontally-mounted intercooler and then vented through ducts in the top of the hood to further maximize aerodynamic benefits.