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Fouling phenomenon is a key issue for EGR cooler operation. In spite of the fact that soot deposition is imposed by the characteristics of the exhaust gases flow, the design of the EGR cooler has a significant impact for effect on the engine. New combustion modes corresponding to new engine developments and combination of EGR system with other post-treatment devices make that fouling conditions for future generations of EGR coolers can be significantly different from previous applications from Euro 3 to Euro 5. An investigation has been performed in order to characterize the response of different EGR coolers designs for different conditions of the exhaust gases. As for the design, the technology selected has been tube-and-fin heat exchanger, which is a high performance technology that fits Euro 6 customer specifications. The variations in design have been made through modifications in fin characteristics, both in configuration and geometric dimensions.

The paper analyses a procedure, based on thermodynamics concepts, to calculate the isentropic outlet temperature taking into account the changes in specific heat during the thermodynamic process; the results obtained were compared whit those given by the traditional methods. Besides, using data from tests, performed in a specific turbochargers test bench, the differences in isentropic efficiency have been evaluated and compared too. Moreover, another factor related with the influence of the gas specific heat on turbocharger performance is the effect that the humidity contents on gas has on the efficiency calculations. Normally, ambient conditions are taken into account just to obtain the corrected values of the main variables in compressor calculations, however the humidity ratio is not included and its effect is neglected. This study presents also a theoretical- experimental analysis about the effect of taking into account this factor.