There are several different systems already available or
under development to reduce the levels of the more harmful
constituents of exhaust gas. These include:
Selective Catalytic Reduction (SCR), which uses an ammonia solution injected into
the exhaust to react with the NOx to produce harmless nitrogen and water vapour.
DeNox catalysts which remove NOx by adsorption and then break it down in the
presence of a small quantity of diesel fuel particulate traps, which filter out
the micron sized particulates from the exhaust. Regenerative traps burn the collected
particulates during periods of higher exhaust temperatures, aided by the presence
of an oxidising catalyst.
Any treatment system in the exhaust pipe reduces the apparent turbo efficiency
by adding back pressure so turbocharger design and application will need to offset
this. The other problems with these are their extra cost and the extra space
taken up by the additions to the exhaust system.
