Experimental Investigation On Soot Deposition Process In DRF

In order to understand the working process of filter,based on a visualized filtration testing system for diesel particulate filter?DPF?,which was built by the lab condition,the deposition process of particles deposited on DPF substrate piece and the influence of filtration velocity,the characteristics of carbon black and ash deposition have been investigated by experiment.The experimental results showed that:The filtration process of diesel soot on filtration surface can be divided into four stages,namely:the deep bed filtration stage,the particle‘tree'growth stage,the particle‘tree'connection stage and the particle layer filtration stage.In the deep bed filtration stage,the particle deposited in the filter microspores,thus the soot layer thickness measured by laser displacement sensors on filter surface is 0?m;in the particle‘tree'growth stage,the particle accumulated in the pores area,deposited to form a‘tree',the highest point of‘particle tree'can be measured by laser displacement sensors and the soot layer thickness increased rapidly and linearly;in the particle‘tree'connection stage,the particle‘tree'connected to each other,particle deposited on the skeleton area of filter surface,and the soot layer thickness increased slowly,even to appear a"platform"phenomenon;in the particle layer filtration stage,the particle‘tree'connection was completed,and the particle deposited on the whole surface of the soot layer.The particle‘tree'growth stage and the particle‘tree'connection stage were actually correspond the transitional stage of the typical three stage.With the increase of soot layer thickness,the curve of the pressure drop over time and the pressure drop over the soot layer thickness presented to be typical three stages.The pressure drops of carbon black Printex-U is smaller than the diesel particulate matter from DK4A engine.In addition,the soot layer thicknesses of the end of the transition stage were approximately 20?m both for the diesel particulate matter and carbon black Printex-U.When the filtration velocity was less than 0.15 m/s,the bulk density of carbon black Printex-U was presented to be about 90 kg/m³,while the bulk density of diesel particulate matter from DK4A engine is larger than that of carbon black Printex-U,presented to be about100 kg/m³.With the increase of filtration velocity and the decrease of particle size and the increase of SOF content,the bulk density of particle increased rapidly at first,then gradually up to a steady value.In the particle layer filtration stage,the pressure drop did not increase quadratically with the filtration velocity.Instead,the ratio of the pressure drop to velocity was larger than 2.With the increase of filtration velocity and Pe,the permeability and the porosity of particle layer decreased rapidly at first,then gradually down to a steady value.The descending order of the bulk density of four kinds of carbon black is that SB 250,SB4A,CB FW200,P-U.With the increase of specific surface area,the bulk density increased with the same particle size of particle;the bulk density,permeability and porosity of soot layer affected by the specific surface area and particle size at the same time.In addition,in each of the soot layer conditions,the soot layer thickness of the end of the transition stage was also approximately 20?m.With the increase of ash loading,the initial pressure drop increased,and the total pressure drop increased linearly with ash loading.Under the same filtration condition,when the ash loading of hollow bead with 5000 mesh was less than 4 g/L,the total pressure drop was less than that of no ash in particle layer filtration stage.The ash loading with 1 g/L showed the lowest pressure drop,and the possibility of ash loading leading to lower pressure is validated by this experimental results.When the ash loading was larger than 4 g/L,the pressure drop was always larger than that of no ash.The ash loading has both the positive and negative effect on the pressure drop.As to 1250 mesh ash of hollow bead and Al₂O₃,when the ash loading were larger than 5 g/L,3 g/L separately,the total pressure drop were higher than that of no ash.In the same amount of ash deposition,if the particle size of ash was larger,the initial pressure drop was smaller,because of the porosity of the larger size of the ash was higher than that of smaller size;In the same amount of ash deposition and the same particle size of ash,the initial pressure drop of pure Al₂O₃ is larger than the 5000 mesh hollow bead ash,because the 5000 mesh hollow bead ash was a mixture of Al₂O₃ and SiO₂,which was compared with the pure Al2O3 ash..