Air-to-air intercooled diesel
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• Mack and AiResearch, two members of the American conglomerate Signal Oil, have together produced a new turbocharged, intercooled diesel known as the Maxidyne 300 series. This, it is claimed, is the first truck diesel in the world to use integral airto-air intercooling.
More commonly truck engines have waterto-air intercoolers which use the relatively high temperature water jacket for cooling. Conventional air-to-air intercoolers, which are usually positioned in front of the main radiator with the engine fan producing the cooling air flow, have the disadvantage of needing to be relatively large to achieve the required heat transfer without causing a large pressure drop between turbocharger and engine.
In the AiResearch intercooler, air from a conventional turbocharger is used to drive a tip turbine which then drives a fan which draws ambient air over the intercooler matrix. Advantages of the air-to-air intercooler system are that the components can be designed for minimum size and weight by employing the most efficient shape and heat transfer technology, and be located to suit the installation and to fit where space is available.
A further significant benefit is that the charged air is not over-cooled during lightload operation in cold weather. As the engine • load drops, the turbocharger boost also drops and less bleed pressure is available to drive the turbine fan. As there is less supply of cooling air from the fan, the intercooler becomes less effective. The engine can be up-rated without requiring modification of the cooling system including the fan and radiator.