AT A GLANCE Specifications
Page 28
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The truck manufacturers that developed EGR for Euro-4/5 have already endured the majority of pain to meet Euro-6. With EGR already established, adding SCR is less of a challenge, both technologically and financially.
Scania’s 12.7-litre Euro-6 offering is achieved by adding a diesel oxidising catalyst (DOC) unit and a diesel particulate filter (DPF) ahead of the SCR part of the exhaust system.
This requires a new Scania engine management system to control the engine parameters, borrowed from the 16.4-litre V8, and the introduction of an intake air throttle. This uses a butterfly valve that serves to both cool the engine on prolonged trips and allows heat to build within the driveline to burn any particulate matter that builds up over less intensive journeys.
Scania has designed a compact silencer unit with dual SCR and ammonium slip catalysts (ASC) as the final stage of its emission system. Scania says half of nitrogen oxide (NOx) emissions are eliminated at source by EGR, 95% of the remaining NOx during the SCR stage, with ceramic diesel particulate filter eliminating 99% of the lingering particulate matters before emission into the atmosphere.
To stop the build up of particulate matter residue, Scania has developed a regeneration process for the particulate filter, which informs the driver of its condition and what action is required. Rising soot levels will harm fuel economy.
‘Normal situation’ means regeneration while driving; ‘regeneration needed’ means drive with more engine revs or stop and press the regeneration switch; ‘forced regeneration needed’ means stop and press the switch; and ‘workshop attention needed’ means exactly that.
Emission levels and engine response are electronically controlled, but two NOx sensors, one at the beginning of the exhaust process and another at the end, act as back-up.
Replacing the particulate filter is a 30-minute job, increasing downtime for a Euro-6 truck, and it will need changing at 240,000km on long-haul trucks.
AdBlue use on Scania’s Euro-5 engines runs at about 5% to 6%, but for Euro-6 this is expected to drop to 3% to 4%. “AdBlue injection is more accurate,” says Per-Erik Nordstrom, product affairs. “It is about two-thirds of that required for Euro-5 SCR systems. There is more precise injection and control of AdBlue.” However, he warns a high sulphur fuel will have a harmful affect on the system.