Charge Air Cooler (CAC) is the component that cools the hot and pressurized compressed / charged air from the turbocharger prior to the intake manifold. Also it is called as Intercooler. CACs are generally the Air-to-Air cross flow heat exchangers. Usually they are the second-most significant coolers in Automotive Cooling Systems. Compressed charged air temperatures are generally quite high, some times more than 350 deg C. CAC systems are open circuits as opposed to most of the other cooling circuits of Automotive Cooling Systems (ACS) which are closed circuits.
Generally CAC cores are made of Aluminum (Al) and fitted together with inlet and outlet tanks, and inner fluid carrying hoses in series from turbocharger to intake manifold. The CACs are mounted together with other heat exchangers such as Radiator and Condenser with mounting brackets. Mounting structures and CACs must be structurally designed to withstand internal pressures, thermal cycle, and vibration loads.
The basic objective of cooling the charged air is to lower the source temperature of the air-fuel mixture, thus improving its thermodynamic potential. Cooling of charged air increases the engine intake air density and in turn increases the intake air flow rate. Increase in intake airflow rate, higher the IC engines compression ratios and enhances the engine power output. Also higher temperatures of intake air can increase the cylinder combustion temperature causing pre-detonation (knock), excessive wear, or heat damage to an engine block.
Generally cooling goals of charge air coolers are defined in terms of outlet temperatures of charged intake air. The desired outlet temperatures are often expressed as maximum IMTDs (Intake Manifold Temperature Difference = Temp of air supplied to intake manifold – Ambient air temp).
CAC cooling effectiveness depends up on different factors such as core frontal area, number of fins per inch, external cooling airflow rate, and ambient conditions in which it is being used.
Also the loss of internal pressure of charged air should be minimized throughout the circuit (i.e. from the turbo-compressor outlet to intake manifold), since the pressure loses adversely affects the density. Generally for most of the engines the charged air pressure loss, across the CAC system, should be less than 16kPa. Pressure loss occurs through different parts of the CAC circuit can be expressed as total delP = delP entrance + delP core + delP exit + delP through pipes + delP gravity. If cooling systems design and development is properly engineered, relative cooling will be greater than the loss of pressure.
Most popular CAC manufacturers are:
*Modine http://www.modine.com/v2portal/page/portal/modine/modineAboutModine
* Adams Thermal Systems http://www.adamsthermalsystems.com/
* BEHR http://www.behrgroup.com/
*Modine http://www.modine.com/v2portal/page/portal/modine/modineAboutModine
* Adams Thermal Systems http://www.adamsthermalsystems.com/
* BEHR http://www.behrgroup.com/
In Automotive Industry, in recent times, using Water-to-Air Intercoolers (also known as Water -CAC system) became more popular. Water-to-Air Intercoolers are more efficient than Air-to-Air Intercoolers and also can used in extreme cold weather conditions. In case of Air-to-Air Intercoolers using in cold weather conditions, there are chances of ice formation inside the charged air tubes (i.e. due to water vapour precipitation) and ingress the same into IC engines, which affects the engine performance. At the same time Water-to-Air Intercooler is more complex and has more maintenance issues such water pump leakage etc.
ReplyDeleteAir-to-Air Intercoolers are less efficient; depend on ambient conditions and cooling airflow rate flowing through the CAC.