Characterization of Different Types of Diesel (EGR Cooler) Soot Samples

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. Besides, some of the carbon samples were also characterized by TEM, XRD and Raman spectroscopy. From the results obtained from all these techniques it can be concluded that there exist marked physical and chemical differences between bench and vehicle soot samples. Vehicle soot samples presented an important quantity of functional groups, both aliphatic species (coming from lube oil and/or unburned fuel) and some oxygenated compounds, probably adsorbed on soot surface. Moreover, regarding internal structure of primary particles, bench soot shown two major parts: an inner core and an outer shell, while vehicle soot exhibited very disordered structure (almost turbostratic, i.e., amorphous).