Soot filters: how they work
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• Regenerating soot filters are the size and shape of conventional heavy truck exhaust silencers. They contain a particulate filter medium—either a porous ceramic "monolith" or ceramic fibres wound around a number of perforated tubes or "candles"—and a dieselfuelled burner with an output of 5kW-135kW.
As the exhaust gases flow through a monolith soot particles are deposited in the pores and, in time, a coating of so id soot for on the surface of the filter. Depending on the porosity of the ceramic aody and th coating of soot, the efficiency of the filter is generally 70-90%. In the case of filter candles, soot particles form deposits in the felt-I ke cavities 1 the windings. The degree of separation for this type of filter is 60-90% dependin on particle volumes.
To prevent filters becoming clogged and engine back pressure building up, soot particles must be burnt off. Using the diesel-fuelled burner soot is converted at around 700°C into CO2 and water vapour.
EberspCicher produces two types of regenerating filter: static and co tinuous. The static filter traps soot particles which are then burnt off when the vehicle is not working. Typical applications are on warehouse/forklift trucks construction vehicles and service and delivery trucks with engines up to 17 W (240hp). Regeneration is by a small 5kW type burner and takes 5-10 hours.
The con inuous filter uses a igh power (100kW-pl s) burner to burn off s ot while the vehicle is eing driven. Combusti n air is fed into the filter via an air
pump, powered electrically ar direct from the engine.
Burner el (diesel) is supplied by several piston-ty e metering pumps hich are engaged s necessary.
A pr grarnmable electronic control unit identifies he optimum time for r generation and act votes and controls t e burner. A diagnostic +splay warns the driver of any faults.