The Environmental Protection Agency (EPA) has been involved in the regulation of emissions from off-highway mobile machines since 1994, following the 1990 amendment of the Clean Air Act and has a mandate to issue pollution regulations. Off-highway machinery is divided into different power bands, each with different emission standards and implementation dates.
We have highlighted the powerbands and some examples below:
In May 2004, the U.S. EPA issued its final programme to reduce emissions from off-highway diesel engines, to be phased in from 2008 to 2015. The Tier 4 Final rule requires emissions of particulate matter (PM) and NOx to be further reduced by 90% from Tier 3 standards. The implementation timetable of Interim Tier 4 standard depended on the rated power of the engine. Tier 4 Final will apply to all off-highway vehicles from 2014 and therefore is now in effect. The EPA indicated in its final rule that it will continue to consider a long-term NOx standard for mobile machinery.
In addition, the EPA has mandated that diesel fuel for off-highway applications must meet a 500ppm sulphur cap from June 2007 and 15ppm (Ultra-Low Sulphur Diesel, ULSD) from June 2010 (June 2012 for locomotive and marine fuels).
Each of the major off-road engine manufacturers has confirmed the use of SCR for engines above 75 hp in their product range for Tier 4 Final.