EGR vs SCR - The Main Event
07/09/2009
CCJ, July 2009 by Jack Roberts
With less than six months to go before Jan. 1, 2010, few rounds remain in the bout between the two approaches for meeting the U.S. Environmental Protection Agency’s diesel emissions mandate. Selective catalytic reduction (SCR) introduces a urea solution known as diesel exhaust fluid (DEF) to neutralize nitrogen oxides (NOx) in the exhaust stream. Advanced exhaust gas recirculation (EGR) combines today’s approach with high-pressure common-rail fuel injection and electronically controlled air and fuel management. While differences between the two paths sound like a matter for engineers and gearheads, there’s much at stake for fleet owners and for the truck and engine makers that supply them.
Most heavy-duty diesel engine makers – Cummins, Detroit Diesel, Mack, Paccar and Volvo – have chosen SCR, leaving Navistar standing alone with advanced EGR. The fight between the two camps has been public and often quite pointed. Navistar was the early aggressor, attacking SCR on the grounds of added cost, maintenance and weight due to the aftertreatment hardware and the need to carry and replenish DEF. The basic message is that advanced EGR places the burden of emissions compliance on the truck maker, not the fleet owner. Navistar also has attacked DEF itself and most recently has taken its fight to court, arguing that EPA illegally adopted lax ground rules for operation of SCR-equipped trucks when the aftertreatment system isn’t working. (See “Seeking the judges’ ruling,” page 50.)
The other truck and engine makers respond that SCR has been used successfully in industrial applications in the United States for decades and in European heavy-duty trucks for several years. But while Navistar often has put its competitors in a defensive posture, SCR proponents aren’t exactly adopting a “rope-a-dope” strategy; they are getting in a few jabs of their own.
Because an aftertreatment allows for less aggressive EGR than today’s engines, SCR-equipped engines will have greater fuel economy than their 2007-technology counterparts and, probably, Navistar’s 2010 engines, the engine makers say. Some competitors further question whether Navistar truly has a high-displacement option for 2010. And for fleets that might be concerned with actual emissions performance, some SCR proponents point out that Navistar’s engines will emit more NOx than others, achieving regulatory compliance by cashing in emissions credits. On the other hand, EPA condones the use of credits as a reward for early emissions reductions.
The protracted fight has been tedious at times and mildly entertaining at others, but the stakes for fleet owners are increasingly high. With neither time nor economic conditions allowing for a significant pre-buy of today’s engines, truck buyers may need to become comfortable with 2010 engines fairly quickly once freight demand returns.
For the full article visit: http://www.etrucker.com/apps/news/article.asp?id=79717
Technorati Tags: SCR, EGR, diesel emissions, fuel economy, EPA 2010