11 September 2000
Mack Trucks, Inc. has announced further steps in its ongoing evaluation of Selective Catalytic Reduction (SCR) technology as a possible solution to the future emission reduction targets that are facing the heavy-duty diesel engine industry in the US In doing so, Mack has introduced a Vision by Mack™ tractor equipped with an SCR system into its intra-company parts distribution fleet, based in Hagerstown, MD.
According to Stephen F. Homcha, Mack executive vice president - Class 8 programs, putting the concept vehicle into regular over-the-road duty represents the next major milestone in development. “We have been extremely pleased with the results that have been generated so far with our SCR-equipped unit”, he said. “Our joint evaluation team—composed of individuals from Mack and Siemens Westinghouse Power Corp.—has been able to cut transient emissions of nitrogen oxides (NOx) by up to 70% and particulate matter by up to 25%. Steady-state emissions of NOx have dropped by up to 85% - all with no sacrifice to fuel economy”.
The SCR technology has been originally developed for NOx control from stationary sources, such as power plants. Siemens, among other developers, has been adapting the SCR technique for mobile diesel engines. The Siemens system is known under the name SINOx. Mack and Siemens have worked jointly to apply the SINOx system to a mobile heavy-duty truck engine - specifically the Mack E-Tech™ engine. The process involves metering a liquid urea solution into the exhaust stream prior to its entering a catalyst. The urea then decomposes to ammonia, which reacts with NOx over the SCR catalyst to produce harmless nitrogen and water. The urea solution, carried in an on-vehicle tank, has to be periodically replenished.
“In March, we published an SAE paper highlighting our results to promote accelerated development of this technology in the United States”, said Homcha. “While much field-testing has been completed by European truck manufacturers, we believe this is the first American made truck to test SCR in an active vehicle on a daily basis”. Over the next year Mack also plans to build 10 more SCR-equipped trucks that will be tested by various fleets across the Northeast.
“SCR technology could become a key component for our emission reduction strategy for the 2007 requirements”, added Homcha.
In Europe, the SCR technology is being considered and actively developed as an emission control option for meeting the Euro IV/V emission standards for heavy-duty diesel engines. In the United States, the EPA expressed reservations about SCR, based primarily on the urea distribution and replenishment issues. SCR-equipped vehicle operators have generally no incentive to replenish the urea solution, what is perceived by the EPA as a potential serious regulatory compliance problem.