Silicon Carbide Honeycomb Filter with Rare Earth Oxide Coating
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Solution Overview
Problem
Conventional honeycomb filters face challenges in maintaining low pressure loss and high soot mass limit during regeneration, as they suffer from increased thermal stress and reduced thermal conductivity due to silica coatings, leading to potential cracking and inefficient heat release.
Innovation Solution
A honeycomb filter design featuring silicon carbide grains with a 0.1 to 2 µm thick silicon-containing oxide layer and an aperture ratio of at least 20% at the exhaust gas emission side, with plugged portions arranged in vertical and horizontal lines to enhance heat release and reduce thermal stress, combined with exhaust gas introduction and emission cells having uniform cross-sectional shapes to optimize flow resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a silica coat is applied to reinforce the honeycomb filter, then strength is improved, but thermal conductivity is reduced leading to increased thermal stress
Solution Approach 1:
The patent changes the chemical composition parameters of the coating material from conventional silica-based coatings to rare earth metal oxide coatings (such as cerium oxide, neodymium oxide, or praseodymium oxide). This parameter change maintains the protective function while improving thermal conductivity and reducing thermal stress during regeneration processes.
Solution Approach 2:
The patent uses composite material structures by combining rare earth metal oxides with silicon carbide substrate to create a coating layer that provides both mechanical strength and thermal management properties. The composite nature of the rare earth metal oxide coating allows it to bridge the thermal conductivity gap between the ceramic substrate and the exhaust gas environment.
2Strength
If a silica coat is applied to reinforce the honeycomb filter, then strength is improved, but cracking resistance is reduced due to thermal stress
Solution Approach 1:
The patent changes the coating material parameters from silica-based to rare earth metal oxides, which have superior thermal shock resistance properties. This parameter change directly addresses the cracking resistance issue by reducing thermal stress accumulation during repeated heating and cooling cycles in regeneration processes.
Solution Approach 2:
The patent converts the potentially harmful effect of thermal stress into a beneficial outcome by using rare earth metal oxide coatings that not only resist thermal stress but also actively manage heat distribution. The coating transforms thermal energy management from a problem into a functional advantage, preventing crack formation while maintaining structural integrity.
3Stress or pressure
If the aperture ratio is increased to reduce pressure loss, then flow resistance is reduced, but filter strength is reduced
Solution Approach 1:
The patent uses the composite material properties of rare earth metal oxide coatings to strengthen the cell walls, enabling them to maintain higher strength even when aperture ratios are increased. The coating reinforces the structural integrity of thinner cell walls, allowing for larger openings that reduce pressure loss without compromising overall filter strength.
4Duration of action of stationary object
If conventional coatings are used to protect the honeycomb structure, then durability is improved, but heat release performance is reduced during regeneration
Solution Approach 1:
The patent changes the thermal and chemical parameters of the coating material to rare earth metal oxides, which have higher thermal conductivity and catalytic activity compared to conventional silica coatings. This parameter change enables the coating to facilitate heat release during regeneration while maintaining long-term durability through resistance to thermal degradation and chemical corrosion.
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 effectively increases the soot mass limit, reduces pressure loss, and improves heat release performance, making the filter more resistant to cracking and maintaining low pressure loss even after significant PM accumulation.
Implementation Method 1
the silica coat hinders heat transfer in highly thermally conductive silicon carbide, and thus reduces the thermal conductivity (K in the formula)
Implementation Method 2
the plugged portions of the exhaust gas introduction cells being arranged in vertical and horizontal lines with the cell walls residing therebetween in the end face at the exhaust gas emission side
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(a)~3(b)
AI summary
The present invention provides a honeycomb filter capable of effectively dispersing heat generated upon regeneration, and having an increased soot mass limit (also referred to as maximum amount of PM accumulation). The honeycomb filter of the present invention includes a silicon carbide honeycomb fired body including porous cell walls and exhaust gas introduction cells and exhaust gas emission cells each having a plugged end. The honeycomb fired body includes silicon carbide grains having a thick silicon-containing oxide layer with a thickness of 0.1 to 2 µm on the surface thereof, the exhaust gas introduction cells and the exhaust gas emission cells each have a uniform cross sectional shape except for the plugged portion in a direction perpendicular to the longitudinal direction of the cells thoroughly from the end at the exhaust gas introduction side to the end at the exhaust gas emission side, the honeycomb filter having an end face with an aperture ratio of not less than 20% at the exhaust gas emission side, and the plugged potions of the exhaust gas introduction cells are arranged in vertical and horizontal direction across the cell walls residing therebetween.