Importance

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Abstract

A filter unit (10) for removing particulates from exhaust gases for example from a diesel engine, includes several filter elements (24) arranged so the gas flows through them are in parallel and that no individual element carries more than a fifth of the total flow. Each element (24) comprises a tubular heating element (50) of high voidage electrically conducting material, with a secondary filter layer (52) adjacent to its upstream surface, and with means (53-63) to ensure the gas flow and particulate deposition are substantially uniform over the upstream surface. At intervals the heating elements (50) are electrically energized, in turn, to burn off deposited particulates. At any one time only a subset of the elements (24) is energized through which at that time no more than a fifth of the total gas flow passes. The unit (10) might have thirteen such elements (24), energized one at a time. Alternatively it might have fewer such elements (24) along with a valve to reduce the flow of gas through the element or elements which are at that time being energized.

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First Claim