302 Diesel Technology Copyright Goodheart-Willcox Co., Inc. Charge air coolers can reduce the temperature of the compressed air by as much as 90°F (32°C), making the air denser and allowing more air to be packed into the com- bustion chambers. This results in: ❑ More power as the additional air allows the fuel to burn more completely, resulting in higher horsepower. ❑ Because the fuel is burned more completely, more power is produced from a given amount of fuel. ❑ Quieter combustion by controlling warm air for air-fuel mixing. A smoother pressure rise in the engine cylinder is produced. ❑ Reduced particulate emissions as a result of more complete fuel burning. Note: Charge air coolers are commonly referred to as intercoolers or aftercoolers, depending on the manufacturer and appli- cation. Regardless of the application or terminology, these devices perform the same basic function. They are heat exchangers that cool compressed intake air. Types of Charge Air Coolers (CAC) There are two types of CACs currently in use with turbocharged engines: coolant CACs and air-to-air CACs. In coolant CACs, engine coolant flows through the cooler’s core tubes, Figure 13-37. As the hot compressed air from the turbocharger passes around the coolant tubes, it is cooled since the coolant temperature is lower than the air temperature. Air flows through the cooler to the cylinders in the opposite direction of coolant flow. In some coolers, the coolant can actually pass through the core several times. This design usually provides better charge air cooling for improved combustion. Additional cooling fins can also be used to improve cooler efficiency. An air-to-air CAC is attached to the front of the radi- ator, Figure 13-38. This type of cooler is similar to a radi- ator. Outside air that passes through the cooler core cools the engine’s intake air charge. The air charge leaving the turbocharger is approximately 275–375°F (129–190°C). Some CAC systems can reduce this temperature to about 110°F (43°C) before the air charge enters the intake mani- fold. Air-to-air CACs are more popular than coolant-type CACs in modern mobile diesels. CAC Service The servicing of an air-to-air CAC is basically the same as for radiators. Clean the core openings of debris, leaves, and other foreign matter with compressed air or water spray. Always clean the core from the engine side. Never use a wire or a screwdriver. Hose clamps must be kept tight and must be replaced when they deteriorate. Charge air cooler Water filter Cooler vent line Cylinder head vent line Surge tank Petcock Check ball Radiator Coolant flow direction Water pump Oil cooler Thermostat housing Figure 13-37. Coolant is used as a part of the charge air cooler system as can be seen by this coolant flow schematic (turbo not shown). (Cummins Engine Co., Inc.)