Effects of Flow Velocity and Particle Size on Soot Penetration Depth determined by Competition of Bridge Formation

Abstract

The soot trapping process on a diesel particulate filter (DPF) occurs in three phases: bridge formation, surface pore filtration, and cake filtration. The accumulation of soot in the surface pores, which is initiated by bridge formation at the constricted area inside a DPF porous channel, causes remarkable increase in pressure drop and negatively affects engine efficiency. An accurate prediction of accumulation depth and location of the bridge facilitates accurate estimation of the accumulated soot mass based on the pressure drop. In this study, soot was introduced into a DPF sample, wherein superficial gas flow velocity and soot size were varied in order to observe their effects on the soot penetration depth. The extracted pressure drop and soot accumulated number for the bridge formation and surface pore filtration were investigated, and the soot packing fraction distribution was obtained via post-observation of the wall cross-section. While the location of the bridge formation is a function of the porous configuration, a smaller soot amount is observed to accumulate inside the surface pores under conditions of lower superficial gas flow velocity or smaller soot size. The variation in soot accumulation with respect to the variation in the condition was a result of the timing of bridge formations, which occurred competitively at various bridging sites. Soot accumulation in deeper areas is prevented by high efficiency of the bridge formation, which is a result of the contribution of Brownian motion, which in turn depends on the flow velocity and soot size.