Honeycomb Structure with Porous Collecting Layer for Diesel Particulate Filter
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Solution Overview
Problem
Existing honeycomb structures used in diesel particulate filters face issues with high initial pressure loss and reduced collecting efficiency due to particulate matter penetration into porous partition walls, especially when collecting small particle diameters, and the use of certain materials like inorganic fibers is regulated, making it difficult to form even collecting layers.
Innovation Solution
A honeycomb structure with a porous collecting layer having a higher melting point than the partition wall material, a pore surface area per unit volume 2.0 times that of the partition wall, and a thickness of the collecting layer penetrating into pores of 6% or less, along with a manufacturing method involving a ceramic forming raw material, plugging steps, and a collecting layer forming raw material coating step using an aqueous electrolyte solution, to prevent slurry penetration and ensure even layer formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a collecting layer is formed by immersing the honeycomb structure into collecting layer forming slurry or pouring the slurry into cells, then the collecting layer is formed on the surfaces of partition walls, but the slurry penetrates into the pores of the partition walls, causing high initial pressure loss
Solution Approach 1:
The partition wall surface is subjected to preliminary treatment (coating with pore-clogging substance, firing, and water absorption) before applying the collecting layer forming slurry. This preliminary action modifies the surface properties to prevent slurry penetration during the subsequent coating process, thereby reducing initial pressure loss while maintaining collecting efficiency.
Solution Approach 2:
A pore-clogging substance (such as water, alcohol, or combustible substance) is introduced as an intermediary material. This substance temporarily occupies the pores of the partition wall, preventing the collecting layer forming slurry from penetrating into the pores. After the slurry is applied, the intermediary substance is removed (by evaporation, combustion, or other means), leaving the pores available for their intended function while the collecting layer remains on the surface.
2Manufacturing precision
If the collecting layer forming slurry is applied to coat the partition walls, then the collecting layer is formed, but the slurry penetrates into micro cracks, causing high thermal expansion coefficient
Solution Approach 1:
The partition wall undergoes preliminary treatment (coating with pore-clogging substance, firing, and water absorption) before the collecting layer is applied. This preliminary action seals micro cracks in advance, preventing slurry from penetrating into these defects during the coating process, thereby maintaining the stability of the honeycomb structure's thermal expansion properties.
Solution Approach 2:
The pore-clogging substance serves as an intermediary that temporarily fills micro cracks and pores. This intermediary prevents the collecting layer forming slurry from entering these defects. After the slurry is applied and the intermediary substance is removed, the micro cracks remain sealed or are filled with the collecting layer material, preventing future penetration and maintaining thermal stability.
3Reliability
If smaller ceramic particles are used to form a porous film with smaller pore diameters, then the collecting efficiency for small particle diameters is improved, but the slurry penetration into partition wall pores increases, causing high initial pressure loss
Solution Approach 1:
The partition wall surface is preliminarily treated (coating with pore-clogging substance, firing, and water absorption) before applying the slurry containing smaller ceramic particles. This preliminary treatment creates a barrier that prevents the slurry with fine particles from penetrating into the partition wall pores, allowing the use of smaller particles for improved collecting efficiency without the penalty of high initial pressure loss.
Solution Approach 2:
The pore-clogging substance acts as an intermediary that temporarily blocks the pores of the partition wall during the coating process. This allows smaller ceramic particles to be used in the collecting layer forming slurry, as the intermediary prevents these fine particles from penetrating into the partition wall. After the intermediary is removed, the collecting layer with small particles remains on the surface, providing high collecting efficiency for small PM particles without causing high initial pressure loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively suppresses the increase in initial pressure loss and enhances the initial collecting efficiency of particulate matter, while also complying with material regulations and ensuring energy efficiency in the manufacturing process.
Implementation Method 1
a collecting layer forming raw material coating step of attaching, to the surface of the non-fired partition wall parent material in the remaining cells of the honeycomb formed body, a collecting layer forming raw material containing a ceramic raw material for the collecting layer which has a higher melting point than the ceramic raw material and an aqueous electrolyte solution having a concentration of 50 to 100% of a saturated solubility
Implementation Method 2
an aqueous electrolyte solution having a concentration of 50 to 100% of a saturated solubility
Implementation Method 3
a melting point of a material constituting the collecting layer is higher than that of a material constituting the partition wall parent material
Implementation Method 4
it is necessary to securely collect the PM having small particle diameters. It is known that the PM having the small particle diameters is collected by the surfaces of pores which are present in a filter, mainly by diffusion
Implementation Method 5
a pore surface area per unit volume of the collecting layer is 2.0 times or more a pore surface area per unit volume of the partition wall parent material
Data Source
AI summary
There is provided a honeycomb structure including a honeycomb base material including a porous partition wall parent material; plugged portions; and a porous collecting layer disposed on the surface of the partition wall parent material in the remaining cells. A melting point of a material constituting the collecting layer is higher than that of a material constituting the partition wall parent material, a pore surface area per unit volume of the collecting layer is 2.0 times or more a pore surface area per unit volume of the partition wall parent material, and a thickness of a portion of the collecting layer which penetrates into pores of the partition wall parent material is 6% or smaller of that of each of partition walls including the partition wall parent material and the collecting layer.