How the system works. Click to enlarge.

The SCR system, which converts the NO_x in the exhaust gases into nitrogen and water vapor, is integrated with the particulate filter (DPF) in a compact unit that takes up the minimum possible space. The particulate filter is automatically regenerated during operation.

The exhaust flow first encounters the DPF then moves through the AdBlue mixing box, where the urea solution is injected into the exhaust stream. The exhaust and AdBlue mixture goes through two parallel SCR catalysts for the conversion of NO_x to nitrogen and water. At the end a slip cat takes care of any remaning ammonia form the AdBlue.

EGR is used primarily to raise the exhaust gas temperature when the engine is not sufficiently hot to heat up the exhaust gases—as an example, during city driving—which must reach at least 250 °C for the SCR system to operate optimally. Unlike conventional EGR systems that cool down the recirculated exhaust gases in order to lower engine temperature and thus reduce nitrogen oxide emissions, the Euro 6 engine’s EGR system is virtually inactive during highway cruising, so it does not impact fuel consumption during such operations.

Another way to increase temperature is to create back pressure by means of the exhaust engine brake.

In situations where the exhaust heat is not sufficient for DPF regeneration, diesel is sprayed into the exhaust stream by means of a 7^th injector. When the diesel hits the oxidation catalyst, it burns, and creates hear for the filter regeneration.

Customer demand for Euro 6 trucks is still at a modest level, Volvo notes, with two years remaining before the requirements become compulsory for all new trucks. Meeting the tougher emission standards involves advanced engine solutions, including many new components, which in turn mean higher cost for customers. However, the increased cost can be partially offset by various financial inducements and incentive packages, above all in regional traffic and long-haul operations in Europe.