Mechanisms Study On Filtration And Microwave Regeneration Of Wall-flow Diesel Particulate Filter

As the diesel emission standards become stricter and stricter, wall-flow diesel particulate filters (WFDPF) are being the indispensable device for reducing particulate emissions. The mechanisms of steady and transient filtration, particle motion and deposition, and regeneration are the difficulties of WFDPF. The mechanisms of steady and transient filtration relate with the filtration efficiency and the flow resistance of WFDPF, the mechanisms of particle motion and deposition determine the deposition distribution in WFDPF, and the mechanism of microwave regeneration restricts the life-span of WFDPF. Accordingly, it has the important theory signification and engineering value to study the mechanisms of the steady and transient filtration, particle motion and deposition, and microwave regeneration.This paper is supported by National"863"Program ( 2008AA11A116 )"Manufacture of High Efficiency & Low Emission Diesel", National Natural Science Foundation of China(50876027)"Research on Mixed Regeneration Mechanics of Diesel Particulate Trapped Porous Medium Based on Microwave and Ce-Mn Fuel Additive"and Hunan Natural Science Funding Key Program of China(06JJ20018)"Numerical Simulation of Gas-Particle Two-Phase Flow and Combustion During Complex Regeneration in Vehicle Diesel Particulate Filter". The mechanisms of steady & transient filtration, particle motion and deposition, and microwave regeneration have been studied using numerical simulation and experiment. The main obtained results are expressed as follows:1,Based on the theories of packed bed filtration and fiber filtration, two different steady filtration models have been developed. The calculated results from the two models have been compared with the experimental results and literature's calculated results. The compared results demonstrate that the steady filtration model based on the theory of packed bed filtration can describe the steady filtration process of WFDPF exactly. By solving these models, the effect laws of exhaust parameters and geometry parameters on steady filtration process are obtained.2,Based on deeply analyzing the characteristics of the transient-state filtration process of WFPM, a numerical model describing the transient-state filtration process of WFPM has been developed. This model can distinguish between the deep-bed filtration and the cake filtration by defining concept of saturation degree, and it can quantitatively estimate the amounts of particles deposited inside and on porous wall. And this model is validated by experiment. Based on this model, the evolution of the transient filtration and transient flow resistance, the transient-state deposition and the transient variation of WFPM's geometry parameters are investigated in detail. Furthermore, the effect laws of exhaust parameters and geometry parameters on transient filtration process are obtained.3,A two-dimensional gas-particle two-phase flow model of WFDPF has been developed. The particle motion trajectories for various particle source locations and various particle sizes are presented. The effects of partial slip, Brownian motion, particle size, wall permeability and upstream velocity on the particle deposition are investigated. The three dominant mechanisms, which are drag force, Brownian motion and particle inertia, are analyzed deeply. These results demonstrate that the drag force always plays the most primary role in determining the particle motion and deposition. On the other hand, the effects of Brownian motion and particle inertia vary with Pe number and Rep* number, respectively. As Pe number and Rep* number increase, the effect of particle inertia enhances, while the effect of Brownian motion lowers.4,Based on deeply analyzing the effect of the particle deposited inside the porous wall, the non-uniformly of particle layer and the reflection of microwave on microwave regeneration, a mathematical model describing the microwave regeneration process of WFDPF has been developed. The model is reasonable by validating the predict results. Based on this model, the evolutions of the energy stream density of microwave, the wall temperature, the temperature gradient, the distribution of particle layer, the wall porosity, the wall velocity, the regeneration efficiency and the pressure loss in the filters of cordierite and SiC are investigated. Lastly, the effects of the position of microwave source, the parameters of exhaust, particle loading and geometry on the behavior of microwave regeneration are analyzed.These works not only can provide an important theory basis for exactly predicting the filtration behavior and the flow resistance behavior of WFDPF, but also can provide the significant reference for optimizing the design of the structural parameters of WFDPF and the regeneration process. On the other hand, these works have the reference value on the design of other DPFs and the other regenerations.