How dual SCR differs from today\u2019s catalytic reduction<\/h3>\n
First let\u2019s talk SCR. Current SCR is itself a quite advanced active emission control technology system that injects a liquid-reductant agent\u2014automotive-grade urea in the form of diesel exhaust fluid (DEF)\u2014into the exhaust stream of a diesel-burning engine. SCR technology is designed to permit NOx reduction to take place in an oxidizing atmosphere. It\u2019s called \u201cselective\u201d because it reduces NOx levels using ammonia (the urea after it is exposed to heat) as a reductant within a catalyst system.<\/p>\n
When operating optimally, this aftertreatment technology cuts NOx by up to 90% and meets current U.S. Environmental Protection Agency (EPA) and California Air Resources Board (CARB) standards.<\/p>\n
Dual SCR promises perhaps more than 90% reduction, where government rules are almost certain to land in a few years. The question for fleets is how to keep current systems working well enough to perform up to today\u2019s NOx rules? But it\u2019s also critical for them to anticipate what might arrive in their shops to fix in the next five to 10 years.<\/p>\n
Think of dual SCR as SCR with an extra urea injector, with designs in R&D that place one injector closer to the engine and one farther away from it. The difference between the two is NOx emissions get processed by the DEF at two locations rather than one.<\/p>\n
No heavy-duty truck in production today uses dual SCR. OEMs such as\u00a0Volvo Trucks<\/a>\u00a0and\u00a0Daimler Trucks North America<\/a>, and aftermarket manufacturers such as Bosch and Eaton, are all in R&D with dual systems or their likely components. And they all anticipate a tightening of government standards in the U.S. by the EPA and CARB, which is usually even stricter than EPA.<\/p>\n Volvo\u2019s director of product marketing, Johan Agebrand, said regulators might also restrict the warmup periods for on-highway diesel engines, which is quite long with SCR, called the \u201cemissions slippage\u201d time. \u201cThey won\u2019t be allowed to have a warmup period anymore, no more emissions slippage,\u201d Agebrand said.<\/p>\n Volvo, which is pioneering electric trucks coming into the heavy-duty market, also is a leader in sustainability solutions for trucks that still burn diesel\u2014and dual SCR is no exception, Agebrand said.<\/p>\n Daimler also helped lead the way with SCR in 2007 with the development of its BlueTec emissions technology, said Len Copeland, product marketing manager for Detroit Diesel Corp., a Daimler subsidiary and the OEM\u2019s engine manufacturer.<\/p>\n Copeland touted the existing SCR in Detroit Diesel power plants, its DD13 and DD15 Gen 5 engines, as already-efficient reducers of NOx with their advanced communication among various components. The two engines use asymmetric fuel injection, which \u201cbiases\u201d fuel towards different cylinders based on engine load or through a thermal control valve, modulating exhaust flow at low load, high idle, or extended PTO operation to increase exhaust temperatures.<\/p>\n \u201cWhile dual SCR is newer to the industry, it functions on the same principle and with the same efficiency as existing systems,\u201d Copeland added. Dual SCR \u201cincreases NOx conversion due to the two catalysts can also be achieved by increasing the size of a single Diesel Oxidation Catalyst (DOC), where packaging permits. Newer aftertreatment systems, such as the new ATS paired with the heavy-duty Detroit Gen 5 engines, are smaller and lighter (60-plus lb. in this case) than previous generations without increased complexity or cost.\u201d<\/p>\n Any R&D that produces a system that cuts NOx above 90% might be a prescient investment, whichever OEM pioneers it first.<\/p>\n In August, the EPA announced plans to lower greenhouse gas (GHG) emissions and other air pollutants from heavy-duty trucking via several rules over the next three years. All part of the Cleaner Trucks Initiative, the first will be finalized next year and will apply starting with 2027 model year heavy-duty trucks.<\/p>\n The EPA said \u201cfrom 2007 to 2017, NOx emissions in the U.S. dropped by more than 40%. But there is more work to be done. Heavy-duty vehicles are the largest contributor to mobile-source NOx emissions and will be one of the largest contributors to ozone in 2025. The EPA last revised NOx standards for on-highway trucks and engines in 2001.\u201d<\/p>\n The EPA is also developing ways to strengthen and streamline existing technologies to further reduce emissions. SCR and dual SCR would fall under this category.<\/p>\n
![\"Scr](\"https:\/\/img.fleetowner.com\/files\/base\/ebm\/fleetowner\/image\/2022\/01\/SCR_infographic_Diesel_Tech.61dc9e740c577.png?auto=format&w=1500&h=843&fit=max\" "\\"Scr")
<\/div>\n<\/figure>\n<\/div>\n<\/div>\n<\/div>\n![\"\"](\"https:\/\/advancedfleetmanagementconsulting.com\/eng\/wp-content\/uploads\/sites\/3\/2021\/07\/AFMC4000-300x150.jpg\")
<\/a><\/p>\n