Honeycomb Filter Surface Layer Design for DPF Pressure Loss
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Solution Overview
Problem
Diesel particulate filters (DPFs) with honeycomb filters face issues such as rapid pressure loss increase during initial PM trapping, hysteresis in pressure loss vs. PM deposition, high initial pressure loss due to small pore diameters, surface layer peeling, and inefficient PM trapping efficiency.
Innovation Solution
A honeycomb filter design with a surface layer having a peak pore diameter of 0.3-20 µm, porosity of 60-95%, thickness of 0.5-30% of the partition wall thickness, and composed of ceramic or metal fibers, along with a catalyst layer containing platinum and palladium, to minimize pressure loss and maintain PM trapping efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pore diameters of the partition walls are decreased and the partition walls are thickened to efficiently trap PM, then the PM trapping efficiency is improved, but the pressure loss of the partition walls themselves increases before PM deposition
Solution Approach 1:
The partition wall is segmented into two distinct layers: a base material layer providing structural support and a surface layer with optimized pore structure for filtration. This segmentation allows each layer to have different pore diameter and thickness characteristics, resolving the contradiction between trapping efficiency and pressure loss.
Solution Approach 2:
Different regions of the partition wall are given different properties: the base material layer has larger pores for low resistance, while the surface layer has smaller pores for high trapping efficiency. This local differentiation allows the filter to achieve both low initial pressure loss and high PM trapping efficiency.
2Reliability
If a surface layer is provided on the partition wall to prevent PM entry into pores, then the PM trapping efficiency is improved, but the surface layer peels off reducing filtering precision
Solution Approach 1:
The partition wall is constructed as a composite material system with a base material layer and a surface layer made of different materials optimized for their respective functions. The surface layer material is specifically selected and bonded to prevent peeling while maintaining filtration precision.
3Reliability
If the PM is trapped in the pores of the partition walls during initial deep layer filtering, then the PM trapping efficiency is improved, but the substantial porosity decreases causing rapid pressure loss increase
Solution Approach 1:
The filtration process is segmented into two stages: initial deep layer filtering in the base material layer, and subsequent surface filtering in the surface layer. This segmentation prevents rapid porosity depletion and pressure loss increase by distributing the trapping function across different layers.
Solution Approach 2:
The surface layer is pre-configured with optimized pore structure to handle the majority of PM trapping from the beginning, preventing rapid clogging of the base material layer pores and avoiding sudden pressure loss increases.
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 design achieves stable PM trapping efficiency with minimal pressure loss, prevents rapid pressure loss increase, and reduces hysteresis, while ensuring the surface layer does not peel easily, thus maintaining engine performance and filtration precision.
Implementation Method 1
the surface layer has a peak pore diameter of 0.3 µm or more and less than 20 µm and a porosity of 60% or more and less than 95%
Implementation Method 2
a catalyst layer containing platinum and palladium
Implementation Method 3
the PM needs to be combusted and removed to regenerate the filter
Data Source
Figure 1~2
Figure 3~5
Figure 6~7
AI summary
A honeycomb filter including partition walls having a porous partition wall base material and a surface layer provided on only an inflow side or both the inflow side and an outflow side of the partition wall base material, and satisfying the following conditions (1) to (5) is applied as a DPF. (1) The peak pore diameter of the surface layer is equal to or smaller than the average pore diameter of the partition wall base material, and the porosity of the surface layer is larger than that of the partition wall base material. (2) The surface layer has a peak pore diameter of 0.3 µm or more and less than 20 µm and a porosity of 60% or more and less than 95% (the measurement method is mercury porosimetry). (3) The thickness L1 of the surface layer is 0.5% or more and less than 30% of the thickness L2 of the partition walls. (4) The mass of the surface layer per filtration area is 0.01 mg/cm2 or more and less than 6 mg/cm2. (5) The partition wall base material has an average pore diameter of 10 µm or more and less than 60 µm and a porosity of 40% or more and less than 65%. According to such a DPF, there is not any rapid pressure loss increase immediately after PM trapping start, a relation between the amount of deposited PM and pressure loss does not have any hysteresis characteristics, and pressure loss in an initial state in which any PM is not deposited can be minimized.