Characteristics of Soot Deposits in EGR Coolers

Characteristics of soot deposits in the EGR cooler were studied, on basis of which a comprehensive model for soot particle depositions was developed. It was found that the soot deposit may be divided into three characteristic layers: a quasi-crystal base layer formed by nano-particles, an intermediate layer of denser packing of soot particles with meso pores, and a highly porous top layer formed by mechanical interlocking of soot particles. The cooler performance is affected significantly by the top layer of the deposit. Because of their weak contact energy, particles in the top layer and intermediate layers may be removed by the shear force under high EGR flows. The contact energy for the particles in the base layer is much stronger than that in the surface and intermediate layers. The base layer may be removed only with physicochemical methods. Due to the aforementioned characteristics of the soot deposit, behavior of the EGR cooler fouling at the transient engine operation differs from that at the steady-state engine operation. This characterization on the soot deposits in the EGR cooler agrees with experimental observations.