Experimental assessment of engine charge air cooling by a refrigeration unit

Abstract

Following the increasing awareness on the global warming, international governments have set up severe targets on CO2 emission in transportation sector: the overcoming of these limits produces a fine which directly influences the market value of the vehicle. Moreover, concerning the traditional pollutants, they still remain targeted by future EURO6(b-c-d) limits.Charge air cooling, in turbocharged diesel engines, is widely used to increase air density, improve cylinder filling and, definitively, engine volumetric efficiency. This is usually done through a heat exchanger fed by environmental air positioned after the charge air compression: the cooling is strictly related to vehicle speed, dedicated radiator positioning, engine operating point and environmental temperature. All these factors lead to an in-cylinder intake air temperature in the 40-70°C range.A refrigerating unit, featuring an evaporator, suitably placed inside the intake manifold, could provide an additional cooling. Such an option is not so difficult to be implemented considering that a conditioning unit is already present on board for cabin comfort. This unit often is over-designed and frequently under-employed.In this paper an evaporator was placed on the intake line of a turbocharged diesel engine, available on a test bench, and the effects of the under-cooling of the charge air have been experimentally assessed. The evaporator is fed by an air refrigeration unit present on vehicle board for cabin conditioning. Fuel consumption saving has been observed as well as a sensible pollutants reduction, taking obviously into account the mechanical power required by the compressor.