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When it arrived on the scene in 2006, the Euro 4 standard was a huge change. This change was not only in terms of the benefits to the air we all breathe, but also in terms of the technology required to achieve the standard.
For the first time on trucks we saw effectively chemical treatment plants bolted onto the chassis and engines to clean up the exhaust.
If a truck had EGR (Exhaust Gas Recirculation) only (favoured mainly by MAN) then it needed no additional liquids, unlike SCR. EGR takes the hot exhaust gases and recirculates them back into the engine. The technology involved is quite complicated and not as robust as the SCR alternative.
SCR (Selective Catalyst Reduction) uses Adblue (the commercially manufactured version of Urea – or pigs wee) and it sprays it in a treatment facility bolted to the side of the chassis to help clean the particulates from the exhaust. The downside to this is the truck operator has to buy Adblue – the truck cannot work effectively without it.
Nearly all truck manufacturers opted for the SCR route, as it was viewed as the more straightforward option and involved less engineering. MAN Trucks were the exception and opted for RGR only, subsequently majoring massively on their ‘Diesel Only’ campaign at the time. MAN’s idea was to dissuade operators from having to invest in the Adblue infrastructure by only buying MAN trucks that didn’t require Adblue thanks to their EGR only system.
Both of these technologies are in use for the current standard at Euro 6