Bench Experiment And Simulation Research On Flow Uniformity Of Diesel Particulate Filter

Nowadays the extensive use of diesel engines is the main trends, but the shortcoming is that the emission from diesel engines contains large quantities of particulate matters, which are up to about 60 times than gasoline. The particulate matters not only pollute our living environment but also constitute a great threat to our health. To solve this disadvantage, the aftertreatment equipment diesel particulate filter (DPF) which has high efficiency to remove particles has been widely used in diesel engines. The DPF can clean particles up to 90% or more. The main working focus of DPF is the former soot loading process and the latter regeneration. The DPF continuously traps particulate matters from engine exhaust, once meeting the conditions, the regeneration starts. If the distribution of the trapped particulate matter in the substrate is not uniform, the temperature in different regions will be different when generation happens, there will come thermal stress and damage the catalytic substrate. So ensure there is a uniform flow field when loading the particulate matter can keep the uniformity of the particulate matter in the substrate, and decrease the temperature grads when generation, extending the using life of DPF.The premise of loading particulate matter uniformly is that there is a uniformity flow field at the inlet cone. The difference of the structure of DPF encapsulation shell will cause different flow field. We can set up a diffuser which can lead the gas flow at the inlet cone to make the gas distribution more uniform. In addition,The catalyst coat of the substrate is also one of the factors which affect the flow uniformity. The degree of catalyst coat uniformity will affect the gas distribution directly.There are two main contents on the research of the flow uniformity of DPF in this paper. First study the influence of the catalytic coat to the uniformity by the cold bench experiment. We can't measure the velocity at the inlet of the substrate expediently because of the DPF encapsulation shell. So we study the outlet flow field of the substrate to reflect the inlet flow distribution. The experiment uses three DPFs with different catalytic coat respectively, the results shows that as the catalytic coat increases, the back pressure increases obviously. Compared to the one with no catalytic coat, the other two DPFs take 2.6 times and 3.1 times on the resistance. The catalyst coat also affects flow distribution in the substrate. The two DPFs with catalyst coat take 1.016 times and 1.057 times on the uniformity respectively. By comprehensive consideration, we accept the DPF with no catalytic coat is the best test sample.Take the DPF with no catalytic coat as the simulation model, making mesh model by AVL FIRE directly and define the boundary conditions by the CAE pre-processing ANSA. Do the simulation by the commercial CFD software FLUENT. The flow medium is pure air. From the simulation results we can see the flow distribution in the DPF model is accord to theory analyze. The flow field is like parabola and the data from simulation anastomoses the bench experiment results.Secondly, set up diffuser models by CAD software Pro/e. The main purpose is to decrease the high speed region at center and increase boundary gas flux, making the flow field more uniform. We establish pore plate mode, guide tube mode and spiral mode diffusers with different configuration sizes to analyze. From the simulation results after integrate with the diffusers, we can see that the pore plate mode diffusers don't improve the uniformity and they bring extra back pressure to the system. The guide tube diffusers have the best effect on the uniformity. They change the flow field distribution effectively. As the expanding angle of the guide tube gets larger, the uniformity gets better; moreover, there is little effect on the back pressure of the system. The spiral diffusers lead the gas to the boundary to decrease the center high speed region. The four kinds of diffusers all have well effect on the uniformity, but the spiral angle effects back pressure of the system severely. The diffusers with larger spiral angle have better effect on the uniformity, but they increase the system back pressure. So they are unbefitting spiral diffusers. If we want to get a good spiral diffuser for DPF, the most important is to design an excellent spiral angle. From the results of the simulation in this paper, we can say that the guide tube diffuser II is the best diffuser model.