Application 101: Charge-Air Coolers

Application 101: Charge-Air Coolers

Charge Air Coolers - An Overview 

The rather interesting story of Charge Air Coolers goes all the way back to the end of the 19th century, starting with the advent of the diesel combustion engine.  In the early 1890s, German inventor Rudolf Diesel produced a working model of his reciprocating engine design that could derive its power from compressing air so high that it would cause fuel to self-ignite.  Today, we find diesel engines in nearly every industrial and commercial sector, providing mechanical power that can be used for countless applications.  

The more air mass that can be delivered to a diesel engine, the more oxygen molecules will be present to feed combustion.  Ever since the early days of diesel engines, a component known as a turbocharger has been used to compress intake air in order to increase intake air pressure and density.  Turbos also add unwanted heat, presenting the question: how do we get turbocharged air at non-turbo temperatures?  We use a charge air cooler.  

A charge air cooler (or CAC) is a heat exchanger that sits between the turbocharger and the diesel engine's intake manifold.  As intake air is brought into the engine compartment and compressed by the turbocharger, that higher pressure and temperature air is then routed through the charge air cooler where it is cooled back down closer to ambient temperature.  This cooled air then flows into the engine's cylinders where it can now efficiently be further compressed by the engine's stroke to proper ignition temperature.  The result here is that we get the benefit of higher intake air pressure and thus higher density of oxygen molecules from the turbo, at the lower air temperature that the engine wants for combustion, thanks to the charge air cooler.  

To give readers an idea of the benefits we're talking about, a common truck CAC will lower the turbo's discharge air from 450*F down to about 110*F, which can increase engine performance by up to 120% at a fuel savings of about 10%, all thanks to cooling the turbocharged intake air.  

Charge Air Cooler Applications

Where are charge air coolers most commonly used?  The short answer is anywhere that you find a turbocharged diesel engine (or turbodiesel) that has access to external cooling air or liquid media (such that a CAC can be utilized).  Common applications by industry include:

  • Transportation – engines in everyday passenger trucks and SUVs.
  • Logistics – engines in nearly all freight-moving trucks and vans.
  • Rail – engines and generators in most freight rail and some passenger trains.
  • Industrial - high-torque mechanical system engines (such as aggregate conveyors in mining) and generators (such as standby fire pumps at manufacturing plants).  
  • Commercial - emergency power and support system generators.    
  • Marine – engines and generators in sea-faring ships.
  • Telecommunications – emergency power and support system generators in critical communication infrastructure, from cell tower stations to data centers. 
  • Emergency Response – packaged mechanical engine and power generators from disaster response field fleets to local first responder equipment.
  • Agriculture – engines in tractors, farm vehicles, and infield farm equipment.
  • Defense – engines and generators found in military vehicles, field operating bases, and tactical engineering equipment.

Across all of the above examples, you'll generally see that turbodiesel engines either perform mechanical work or provide electrical power.  Both areas share very important requirements of their engines, which need to be very fuel-efficient, provide high power output, and be extremely dependable overall.  Charge air coolers make all of these goals possible in the below ways:

  1. Reducing the charge air temperature increases air density, which reduces the amount of fuel needed to generate the expected combustion force.
  2. Higher air density allows for more combustion force to be produced from the same combustion chamber volume.
  3. Lower charge air temperatures reduce the total combustion temperature experienced, which results in lower temperatures in the engine block, together reducing heat-related wear and tear.

Key Considerations in Selecting a Charge Air Cooler 

When specifying a Charge Air Cooler, buyers can select from multiple styles and options to best fit their application.  CACs are available on the market in both liquid-to-air and air-to-air designs.  

  • Liquid-Air Charge Air Coolers
  • Liquid-to-Air CACs are most common in stationary turbodiesel engine applications, where an external cooling media is provided to the CAC heat exchanger to cool the charged intake air.  Hot discharge water is sent to drain or recirculated through a separate refrigeration system to remove the excess heat.     
  • Air-Air Charge Air Coolers
  • Air-to-Air CACs are most common in vehicles, using ambient air to flow through a finned heat exchanger that looks very similar to the vehicle's coolant radiator.  This CAC sits in front of the radiator and uses airflow while the vehicle is in motion to remove the excess heat.

Focusing on the more common air-to-air design, buyers should look for key features in their next charge air cooler purchase to ensure that they receive the integrity and performance that they expect.  The below features are found on all Cincinnati Radiator Charge Air Coolers as standard options, which will exceed the requirements of most vehicular applications.  

  • Technical Design:  any CAC purchase discussion should begin with full engineering specifications on the engine, turbocharger, and operating conditions that make up the application, which will drive the selection of the correct unit to begin with.
  • Construction:  bar and plate construction is the most preferred style, selected for its very simple assembly and easy repair should there ever be a problem.
  • Materials:  all-aluminum materials offer the best combination of low weight, high thermal transfer, and economical cost.
  • Cleaning:  both pre-and post-brazing, CACs should receive a thorough cleaning pass inside and outside of the unit to ensure proper fabrication and in-vehicle performance.
  • Assembly:  CACs are engineered for a specific heat transfer target based on airflow, surface area, and temperature delta, which means that each CAC should be assembled to very exact dimensions and tolerances in order to achieve the expected design point.
  • Brazing:  brazing connections using high-alloy aluminum with additional sheet cladding achieve deeper penetration, which helps combat leaks even under aggressive conditions across many years. 
  • QC:  to assure that the assembly process was a complete success, every unit should be fully checked prior to shipment for dimensional accuracy, brazing penetration, joint integrity, and zero leakage.  
  • Packaging: the fins on a CAC are made of very thin aluminum sheet, often down to 0.2mm thick, and must be fully protected for shipment by carefully packaging the assembly.  
  • Warranty: Our welds have a 5 year leak free warranty as they are pressure tested to 100% guarantee our coolers are leak free. If you upgrade to Bar & Plate design Charge Air Coolers we offer a limited lifetime warranty. Upgrading to a Bar & Plate CAC design, means increased power performance and fuel savings, as well as eliminating tube to header failures which is a common issue in Header Style CAC’s.For Standard Header Style Charge Air Coolers we offer a 2 year warranty.
  • Customer Support: after the purchase, buyers should expect full and readily available support should they have any questions around installation, operation, and troubleshooting concerns, at any time during the long life of the charge air cooler.  

Mission-critical vehicles and equipment in over a dozen infrastructure sectors rely on heat transfer components manufactured by Cincinnati Radiator.  CR works directly with Original Equipment Manufacturers and Aftermarket service channels to supply premium-grade, long life radiators, coolers, and full cooling packages into extreme applications all over the world.  With our expanding inventory and fabrication space at our Fairfield, Ohio facility, we pride ourselves on having a personal touch, ultra-fast lead times, and one-off custom design capabilities.  For your next vehicle or heavy equipment heat transfer project, call us at (513) 874-5555, email us at, or visit our website at 

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