Silicon Carbide Honeycomb Filter Pore Distribution Control
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Solution Overview
Problem
Conventional honeycomb structures for diesel engine exhaust gas filtration face challenges in balancing filtration efficiency and pressure loss, with either low initial pressure loss but high pressure increase during PM trapping, or high filtration efficiency but increased pressure loss and catalyst deposition issues.
Innovation Solution
A honeycomb structure with silicon carbide porous ceramics, where the average pore diameter is 1 µm to 15 µm, standard deviation is 0.20 or less, and less than 5vol% of pores have diameters under 2 µm, combined with catalysts like platinum, palladium, and rhodium or alkali metals, to maintain low initial pressure loss and high filtration efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pore diameters are made small to improve filtration efficiency, then PM trapping performance is improved, but pressure loss increases due to resistance to gas passage
Solution Approach 1:
The patent applies parameter changes by precisely controlling the pore diameter distribution of porous ceramics. It sets the average pore diameter to 1-15 μm and limits the standard deviation to 0.20 or less (when pore diameter is represented by common logarithm), thereby optimizing the balance between filtration efficiency and pressure loss through quantitative parameter specification.
2Loss of energy
If pore diameters are made large to reduce pressure loss, then gas passage resistance is reduced, but filtration efficiency decreases as PMs pass through without being trapped
Solution Approach 1:
The patent resolves this contradiction by establishing specific parameter ranges for pore diameter distribution. By setting the average pore diameter to 1-15 μm and controlling the standard deviation to 0.20 or less, it creates an optimized pore structure that maintains low pressure loss while ensuring sufficient filtration efficiency.
3Reliability
If a catalyst is filled in the filter to enhance PM trapping, then filtration efficiency is improved, but pressure loss increases due to catalyst deposition blocking pores
Solution Approach 1:
The patent addresses this issue by controlling the pore diameter distribution parameters. By setting the average pore diameter to 1-15 μm and standard deviation to 0.20 or less, it creates a pore structure that is less susceptible to catalyst deposition blocking, thereby maintaining lower pressure loss even when catalyst is present.
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 structure effectively traps particulate matters with high filtration efficiency while keeping initial pressure loss low and suppressing pressure loss increase, even after PM deposition, and reduces the need for expensive noble metals by minimizing pores less than 2 µm.
Implementation Method 1
PMs in the gas are trapped and removed through surfaces and pores of the porous partition walls
Implementation Method 2
The gas flows in from the cells opened in one direction, passes through the porous partition walls, and flows out from the cells opened in the other direction
Data Source
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AI summary
There is provided a honeycomb structure in which filtration efficiency of particulate matters (PM) in the exhaust gas is high, initial pressure loss is low and increase in pressure loss in accompanied with the trapping of PMs is suppressed. The honeycomb structure includes a plurality of cells partitioned by a plurality of partition walls which are made of silicon carbide porous ceramics and are lined up in a single direction, an average pore diameter of the partition walls measured by mercury porosimetry is 1 µm to 15 µm, a standard deviation in a pore diameter distribution is 0.20 or less when the pore diameter is represented by common logarithm, and percentage of the pores having the pore diameter of less than 2 µm relative to the entire pores is 5vol% or less.