Intercooler

Multiple stages of compression

In automotive engines where multiple stages of forced-induction are used (e.g. a sequential twin-turbo or twin-charged engine), the intercooling usually takes place after the last turbocharger/supercharger. However it is also possible to use separate intercoolers for each stage of the turbocharging/supercharging, such as in the JCB Dieselmax land speed record racing car. Some aircraft engines also use an intercooler for each stage of the forced induction.^{[citation needed]} In engines with two-stage turbocharging, the term intercooler can specifically refer to the cooler between the two turbochargers and the term aftercooler is used for the cooler located between the second-stage turbo and the engine. However, the terms intercooler and charge-air cooler are also often used regardless of the location in the intake system.^[2]

Method of heat transfer

Air-to-air intercoolers are heat exchangers that transfer heat from the intake air directly to the atmosphere. Alternatively, air-to-liquid intercoolers transfer the heat from the intake air to intermediate liquid (usually water), which in turn transfers the heat to the atmosphere. The heat exchanger that transfers the heat from the fluid to the atmosphere operates in a similar fashion to the main radiator in a water-cooled engine's cooling system, or in some cases the engine's cooling system is also used for the intercooling system. Air-to-liquid intercoolers are usually heavier than their air-to-air counterparts, due to additional components making up the system (e.g. water circulation pump, radiator, fluid, and plumbing).

The majority of marine engines use air-to-liquid intercoolers, since the water of the lake, river or sea can easily be accessed for cooling purposes. In addition, most marine engines are located in closed compartments where obtaining a good flow of cooling air for an air-to-air unit would be difficult. Marine intercoolers take the form of a tubular heat exchanger with the air passing around a series of tubes within the cooler casing, and sea water circulating inside the tubes. The main materials used for this kind of application are meant to resist sea water corrosion: Copper-Nickel for the tubes and bronze for the sea water covers.

Alternatives

An alternative to using intercoolers - which is rarely used these days - was to inject excess fuel into the combustion chamber, so that the vaporization process would cool the cylinders in order to prevent knocking. However the downsides to this method were increased fuel consumption and exhaust gas emissions.^[3]