A charge air cooler (abbreviation LLK, English intercooler ) is a heat exchanger that reduces the temperature of the combustion air supplied to the engine in the intake tract of a supercharged internal combustion engine. It is installed in the intake tract between the compressor (compressor wheel of a turbocharger or compressor ) and the inlet valve and dissipates part of the heat that is generated by the compression of the air in the turbocharger.
The aim is to increase the performance and efficiency of the engine. By reducing the temperature of the supplied air, the same volume contains a larger air mass, which means that proportionally more fuel can be burned. The intercooler thus increases the possible output power and increases the efficiency by lowering the initial temperature in the Carnot process .
Charge air cooling is already mentioned in the German Reich patent 95 680 with priority from March 6, 1896, which was granted to Rudolf Diesel.
Charge air coolers play a role not only in powerful engines and in racing, but also when downsizing engines, as charge air cooling enables more power and lower consumption. Today, charge air coolers are practically indispensable, as the consumption and exhaust gas values required today would otherwise hardly be achieved without them.
Mode of action
The relationship for the approximately steady flow process can be derived from the intensive form of the general gas equation
This means that the mass of air required for combustion can be increased in two ways:
- The density of the air sucked in at the intake valve of the engine is increased by the polytropic compression of the supercharger, but at the same time the temperature of the air also rises because the mechanical work of the compressor increases the internal energy of the compressed air and thus its temperature .
- After compression, the increased air temperature in the charge air cooler is reduced by dissipating heat to the environment, thereby increasing the mass flow ( ) of the combustion air further, because the compressor can deliver more air with the same charge pressure.
The increasing air density causes the following in the combustion chamber:
- The most important effect is that more oxygen gets into the combustion chambers. This means that more fuel can be burned and the engine's output and efficiency increase.
- Because of the lower air temperature, there is less thermal stress on the engine (cylinder head and walls, valves, spark plugs (only Otto engine ), pistons, but also the turbocharger itself, which can rotate more slowly with the same delivery rate) and avoidance of combustion problems ( knocking (only Otto engine ), Deterioration in exhaust gas values, uneven combustion, etc.).
Disadvantages of the intercooler are:
- Costs due to additional components, greater effort in calculating the flow through the engine compartment (cooling air routing for the intercooler) and in the arrangement (packaging) of the components in the engine compartment.
- Larger gas volume between the compressor and the inlet valve, which may result in poor engine response when the load changes.
- Increased flow resistance for the sucked in air, increased over the service life by deposited oil from the crankcase ventilation and possibly particles from the exhaust gas recirculation .
Charge air coolers themselves are either air or water cooled. With the latter, the heat is transferred to its own cooling circuit. There are also other variants, for example the cooling effect of an air-cooled intercooler can be increased by spraying it with water, but this is only possible with engines for racing (e.g. in the WRC ) due to the additional construction and maintenance effort . However, since local vehicles have to be derived from road vehicles and homologated , this technology is already found in normal cars, such as the Subaru Impreza WRX STi .
Vehicle / commercial vehicle installation locations
- FMIC (FrontMountedInterCooler), mostly in the center of the front
- SMIC (SideMountedInterCooler), on the side, sometimes also two pieces, left and right
- TMIC (TopMountedInterCooler), mounted above the motor (the air flow is then mostly through an air scoop )
- Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Kraftfahrtechnisches Taschenbuch , 25th edition. Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3
- Peter A. Wellers, Hermann Strobel, Erich Auch-Schwelk: Expertise in vehicle technology , 5th edition. Holland + Josenhans Verlag, Stuttgart, 1997, ISBN 3-7782-3520-6
- Kurt-Jürgen Berger, Michael Braunheim, Eckhard Brennecke: Technology automotive technology , 1st edition. Verlag Gehlen, Bad Homburg vor der Höhe, 2000, ISBN 3-441-92250-6
- Karl Zinner: Supercharging of Internal Combustion Engines - Basics · Calculations · Explanations , 3rd edition, Springer, Berlin / Heidelberg 1985, ISBN 978-3-540-15902-5 , p. 12