The main objectives of DPF structural design are:

(1) By increasing the filtration volume of the inlet hole, the ash storage capacity of the DPF is increased, while reducing the back pressure under high carbon smoke load; (2) By optimizing the porosity and average pore diameter distribution of DPF to meet the requirements of different catalyst coating amounts (in wall coating), low pressure drop loss can be maintained;

(3) The design of coating a thin layer of catalyst on the wall can improve the initial PM filtration efficiency and regeneration efficiency of DPF, eliminating deep filtration.

The so-called "in wall coating" coating technology is to evenly distribute the slurry containing catalyst on the surface of the pore grains in the DPF filter wall, achieving the effect of increasing the contact area between soot and catalyst; The 'on wall coating' technology is to apply a thin layer of catalyst containing slurry on the surface of the DPF inlet filter wall to eliminate deep filtration of the DPF wall.

1. Evolution of DPF pore structure

The traditional wall flow DPF pore is a square pore structure with intersecting blockages, forcing the airflow to flow through the filtering wall surface. Particles are trapped on the inner pore surface of the wall (deep filtration) and the wall surface, forming a layer of soot filtration. When the soot load is high, surface filtration will be the main factor affecting DPF pressure loss. Therefore, increasing the effective filtration area of DPF will reduce the thickness of soot accumulated on the DPF filtration wall under the same soot load; In addition, increasing the opening rate of the DPF inlet can effectively improve the filtration capacity of the DPF, enhance the ash storage capacity of the DPF, and extend the cleaning mileage. For this reason, different DPF researchers and manufacturers have made many innovative designs for DPF pore structures. As a leader in the global silicon carbide DPF market, Japan's Kai Electric Company has made many innovations in DPF structure design, among which the most representative is the "OS" pore structure DPF, with an octagonal inlet and a square outlet. The cleaning mileage of the "OS" pore structure DPF is 30% longer than that of the traditional symmetrical pore structure DPF.

As major participants in the DPF market, Corning and NGK from Japan have also developed DPF materials with similar pore structures, such as cordierite, aluminum titanate, and composite silicon carbide. Clean Diesel Ceramic GmbH in Germany has developed a triangular hole structure DPF, which can increase the filtration area by 14% compared to a square hole symmetrical structure DPF; But the company's products are mainly 200 mesh, mainly used in the European in use vehicle modification market. Hexagonal silicon carbide DPF developed by TYK Corporation in Japan. The wavy asymmetric structure silicon carbide DPF developed by Saint Gobain in France can effectively shorten the length of DPF. Sumitomo Corporation of Japan has developed an asymmetric hexagonal pore structure aluminum titanate DPF (AT) with an effective filtration area of up to 14cm2/cm3, which has been built in Poland and put into mass production. In order to further consolidate its market share, Yifei Electric Company has made innovations in product differentiation, adopting effective hole plugging technology and launching the so-called "VPL" (Valve used plugging Layout) DPF. Its effective filtration area is as high as 15.5cm2/cm3, and the effective filtration volume has also increased by 15%. This unique structure can reduce the volume of DPF by up to 33%, lower the operating cost of DPF, and maintain excellent performance.

2. DPF porosity and average pore diameter

Recrystallized silicon carbide has almost no shrinkage during sintering at high temperatures, and the formation of pores mainly depends on the combination of silicon carbide powder with bimodal particle size distribution, thus forming a relatively uniform distribution of micropores. However, DPF using composite silicon carbide, cordierite, and aluminum titanate materials has a relatively large shrinkage rate during the firing process due to the use of pore forming agents, resulting in a wider distribution of average pore diameters.

The initial filtration efficiency of DPF for PM mainly depends on the microporous structure, and the narrow average diameter distribution of pores results in higher filtration efficiency for PM. When a certain amount of PM is captured by DPF, the microporous structure of DPF has no significant effect on the filtration efficiency of PM.

Obviously, the initial PM filtration efficiency of the recrystallized silicon carbide DPF is higher than that of the cordierite DPF. When the PM capture reaches 0.5g/L, the PM filtration efficiency of the two is comparable, reaching up to 99%. This is because at this point, DPF transitions from deep filtration to surface filtration.

3. Structural requirements for different DPF technologies

The so-called "Two in One" technology is to apply SCR catalyst onto the DPF carrier, integrating the functions of SCR and DPF, which can effectively reduce costs and reduce the installation space of the system. However, compared to traditional DPF structures based on CDPF regeneration technology and FBC regeneration technology, DPF structures based on "two in one" technology require larger porosity and average pore diameter. Due to the fast heat release rate based on FBC regeneration technology, the thermal shock to DPF is relatively large. For this situation, design measures such as reducing mesh size, increasing wall thickness, and reducing porosity and average pore diameter are generally used to increase the thermal capacity of DPF, thereby reducing its maximum temperature and temperature gradient during "Drop in Idle" operation. CDPF technology can effectively reduce the temperature during DPF regeneration, which helps improve fuel economy; But generally, the amount of catalyst coating is not very large, 5-10g/L. Therefore, DPF applied to CDPF technology requires moderate porosity and average pore diameter. Based on the "two in one" technology, catalyst coating amounts of up to 90-220g/L or even higher are often required. This will inevitably lead to an increase in the pressure difference of the DPF, deteriorating fuel economy. Therefore, designing a high porosity and large average pore diameter DPF to meet the requirements of high coating volume and low back pressure.