Diesel Filter Materials

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Abstract: Diesel filter materials should be characterized by high filtration efficiencies, high maximum operating temperatures, low thermal expansion, resistance to thermal stress, and chemical resistance to metal oxides (ash) present in diesel particulates. A number of materials have been under development, including ceramic wall-flow monoliths, ceramic fibers, or sintered metals.

Material Requirements
Overview of Materials

Material Requirements

The filter substrate is the key component of the diesel filter system, affecting both its performance and durability. Its task is to physically capture solid particulates and hold them until they can be removed in the regeneration process (periodic or continuous). Design targets for diesel particulate filter materials include the following:

High filtration efficiency:
- particle mass
- particle number
High maximum use temperature
High soot holding capacity
Thermal shock resistance
Strength and mechanical integrity
Low pressure drop
- empty
- loaded with particulates and ashes
- low scatter of pressure drop (i.e., repeatable ΔP at a given gas flow rate and soot load)
Chemical stability:
- resistance to exhaust gas components including sulfur
- low reactivity with ash compounds
- oxidation resistance
Compatibility with regeneration methods:
- coatability with a catalyst
- compatibility with fuel additives
- other methods
No generation of secondary emissions (such as fiber loss in fibrous media)
Small size and low weight
Long life and high durability
Low cost

Depending on the regeneration method, diesel filter materials may be exposed to very high temperatures, significantly in excess of 1000°C, as well as rapid temperature changes. These thermal conditions are caused by the release of heat during rapid oxidation of soot accumulated in the filter. Since the distribution of soot is not necessarily uniform throughout the filter, the thermal stress frequently has a local character. Thermal phenomena, both high temperature and thermal stress, are responsible for most instances of filter failure, such as melting or cracking.

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