Letting the PM-KAT out of the bag

摘要

Selective catalytic reduction (SCR) or exhaust gas recirculation (EGR)? This is perhaps the most fundamental question faced by engineers preparing truck and bus engines for the Euro-4 exhaust emission legislation that comes fully into force (for all new vehicle registrations) in October 2006. Most European truck-makers have plumped for SCR. But top engineers at MAN'S Munich headquarters remain quietly confident that cooled exhaust gas recirculation is preferable. They explained exactly why last month at the unveiling of Euro-4 engines which will go on public display for the first time at this month's big IAA show in Hanover. Compared with SCR systems like those adopted by Daf, Mercedes, Volvo and lveco, MAN'S EGR is claimed to be lighter, cheaper and simpler. It is expected to prove more reliable too. On the thorny question of fuel consumption, MAN engineers concede that SCR has at least a theoretical advantage but only on trucks covering high annual distances. And by October 2006 MAN expects its engines to have returned to Euro-3 fuel-economy levels.