Diesel Particulate Filters – Different types
The EHC diesel particulate filter (or DPF) is a device designed to remove diesel particulate matter or soot from the exhaust gas of a diesel engine.
Cordierite wall flow filters
Cordierite is a ceramic material that is also used in catalytic converters. It provides excellent filtration efficiency and has thermal properties that make it easy to package filter systems for installation in vehicles. The main drawback is that cordierite has a relatively low melting point (about 1200 °C) and cordierite substrates have been known to melt during filter regeneration. This is mostly an issue if the filter has become more heavily loaded than normal. It is also more of an issue with passive systems than with active systems, unless there is a system break down.
A cordierite filter core looks like a catalytic converter core that has had alternate channels plugged. The plugs force the exhaust gas to flow through the wall. Then the particulates are collected on the inlet face.
Silicon carbide wall flow filters
In the EHC PF we have chosen to use the popular filter material silicon carbide (SiC). SiC filters provide excellent filtration efficiency and the material has a high melting point (2700 °C).
Small SiC filters are made of single pieces, while larger filters are made in segments, which are separated by a special kind of cement. This way the heat expansion of the core will be taken on by the cement, rather than the package.
SiC filters are usually more expensive than cordierite variants. However they are manufactured in similar sizes, and one can often be used to replace the other. Silicon carbide filters (much like cordierite filters) look like catalytic converters that have had alternate channels plugged.
The characteristics of the wall flow diesel particulate filter substrate are:
- Broad band filtration (the diameters of the filtered particles are 0.2-150 μm)
- High filtration efficiency (up to 95%)
- Highly refractory
- Notable mechanical properties
- High boiling point
Disposable micro glass fiber
EHC HT, EHC L20 and EHC P15 are made of a micro glass fibre material. Disposable micro glass fibre paper is used in certain specialty applications, where there is no regeneration strategy. Paper filters are also used when a diesel machine must be used indoors. For example on forklifts used inside an industrial building or store. A micro glass fibre filter must be used at low temperatures, at most 250-300°C. The particle reduction is very high, up to 99% of the 0,4 micron particle.