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Emissions from diesel engines are a significant air-quality issue, accounting for about one-third of the nation's emissions and one-quarter of the PM emissions from mobile sources. The U.S. EPA has responded with new, tougher emissions standards, the first tier of which took effect in 2004 (October of 2002 for engine builders affected by the consent decree). Even more stringent rules will take effect in 2007 and 2010, along with new diesel fuel standards requiring lower sulfur levels.

With these changes, a review of technology options available to OEMs, fleet owners and operators is in order.

First, let's take a brief look at the standards themselves. The EPA's standards introduce a lower limit of 0.2 g/bhp-hr that must be fully phased in by 2010. Between 2007 and 2009 at least 50% of this emissions limit must be achieved. Manufacturers can satisfy this requirement by bubbling the emissions and certifying that the limit for all their 2007-2009 model engines is approximately 1.1 g/bhp-hr. In other words, the phase-in will be on a percent-of-sales basis, i.e., a 50% reduction from 2007 to 2009 and 100% by 2010.

The EPA has also introduced a new emission standard of 0.01 g/bhp-hr for PM (down from the current 0.1 g/bhp-hr) that must be met by 2007. These standards thus include flexibility provisions to facilitate the transition to the new standards, and encourage early introduction of clean technologies for both new and existing sources.

Major manufacturers such as Caterpillar, Cummins, Detroit Diesel and International Truck and Engine have adopted diesel particulate filters as the preferred strategy/technology for PM reduction, but there is no consensus on control technologies. The two most practical and cost-effective approaches to lower emissions from diesel trucks are in-cylinder techniques such as a high rate of EGR and exhaust system technologies such as urea-SCR, which is being adopted in the European Union started in 2005.

These new standards will also indirectly affect existing diesel trucks and fleet operators in several non-attainment regions of the nation. There are approximately 11.3 million diesel trucks operating in the United States, and an estimated four million trucks operate in various non-attainment areas. Such fleet owners will be subject to a voluntary retrofit program accompanied by financial incentives to encourage compliance.

Source:[allbusiness.com]