Selective Membrane Coating for Wall Flow Filters
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Solution Overview
Problem
Current diesel particulate filters are inefficient for capturing fine particulates and impose fuel consumption penalties due to high exhaust backpressures, while existing methods for manufacturing membrane filters face challenges such as high processing costs, uneven membrane thickness, and durability issues.
Innovation Solution
The method involves processing unplugged porous honeycomb bodies by masking channels, applying a membrane-forming composition to unmasked channels, curing it to form a thin, uniform, and permeable membrane, and then converting the filter to a wall flow configuration with controlled plugging, using refractory materials suitable for high-temperature environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional diesel particulate filters with large pore size and thick walls are used, then backpressure is reduced, but filtration efficiency for fine particulates deteriorates
Solution Approach 1:
The filter wall is segmented into two distinct functional layers: a thick porous support layer that provides mechanical strength and low backpressure, and a thin dense membrane layer that delivers high filtration efficiency. This segmentation allows each layer to optimize its specific function without compromising the other.
Solution Approach 2:
Different regions of the filter wall have different properties: the support layer has large pores and high porosity for low resistance to flow, while the membrane layer has small pores and low porosity for high particle capture efficiency. This local differentiation of properties resolves the contradiction between backpressure and filtration efficiency.
2Ease of manufacture
If slurry coating method is used to apply membrane to all channel walls, then manufacturing cost is reduced, but materials cost and filtration performance deteriorate
Solution Approach 1:
The membrane layer is extracted from being applied to all channel walls and is instead selectively applied only to specific channels based on flow direction. This extraction of the membrane application to only where needed reduces membrane material consumption while maintaining filtration performance.
Solution Approach 2:
Instead of applying membrane to all walls and then plugging channels (conventional approach), the invention inverts the sequence by first determining which channels need membranes based on flow direction, then selectively applying membrane only to those channels, reducing overall membrane material usage.
3Strength
If high firing temperature is used to consolidate membrane coating, then membrane bonding is improved, but plug integrity and channel bond durability deteriorate
Solution Approach 1:
The firing temperature parameter is changed from high temperature (conventional) to low temperature (below 900°C), which is sufficient to consolidate the membrane coating while preserving the integrity of the plug materials and channel bonds that would be damaged at higher temperatures.
Solution Approach 2:
The membrane coating is applied and consolidated at low temperature before the final plug setting operation. This preliminary consolidation of the membrane at a temperature safe for subsequent plug materials ensures membrane bonding without compromising future plug integrity.
Data Source
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Figure 4~6
AI summary
Wall flow membrane filters, fabricated by masking a first subset of the channels at one or both ends of a honeycomb body comprising an array of open-ended through-channels separated by porous channel walls, applying a membrane-forming composition to the porous channel walls of a second subset of the channels, curing the membrane-forming composition to provide a wall-adhering fluid-permeable membrane; and then plugging the first subset of channels at a first end of the body and the second subset of channels at a second end of the body, are useful in exhaust systems of improved particulate filtration efficiency for gasoline direct injection or diesel engines.