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Degradation of anti-pollutant devices must be taken into account in design so durability of the function is guaranteed over the vehicle lifetime. As for NOx reduction of diesel engines, Exhaust Gas Recirculation (EGR) systems are a well-known and robust solution. However, exposure of the EGR cooler inside this system to the exhaust gas conditions leads to a degradation of its function, affecting to the EGR rate and therefore to potential for NOx reduction. So, sizing and technology of these heat exchangers must be selected to avoid malfunction during vehicle operation. Current scenario in Europe with new homologation cycles and focus on NOx emissions of diesel vehicles under real driving conditions is challenging for the design of EGR systems. This leads to the increase of the areas of the engine map using EGR. Moreover new homologation includes also the use of low ambient temperature.

Soot and NOx, may react in situ with each other and reduce, thus, their emissions. Therefore, this reaction can be considered as a strategy of elimination of both air pollutants at the same time. In general, it is well established that heterogeneous reactions between soot and the different gases, generally existent in combustion environments, are affected by soot properties. Detailed characterization of soot samples coupled to reactivity studies towards O2 and NO have been carried out in order to identify the differences and similarities among the kinds of soot studied for understanding in what extent the origin of soot samples is a key parameter on their structure and reactivity. The combined analysis and interpretation of the soot chemical-physical features are essential to correctly interpret and to predict its behavior in the combustion chamber when soot is in contact with the combustion gases at high temperature.

Soot fouling on exhaust gas recirculation coolers (EGRc) decreases thermal efficiency, implying the unfulfillment of NOx standards, and increases the pressure drop producing the malfunctioning of this device. The characterization of soot is of great interest since soot physico-chemical properties may have a direct influence on the degree of malfunctioning of EGRc. Thus, the combined analysis and interpretation of all the soot physico-chemical features are essential to correctly interpret its behavior when soot is deposited on the EGRc walls. In this context, the aim of this study is the characterization of five different types of diesel soot which were collected from several high pressure EGRc, working at different conditions (engine bench and vehicle). Each soot sample was characterized by means of elemental analysis, specific surface area (BET method), FESEM, FTIR, TGA, GC-MS and UV-visible spectroscopy.