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EGR vs. SCR * USA - Navistar Urges Recall of 2010 SCR Engines
Wareensville,ILL,USA -Transport Topics, by Eric Miller -Aug. 30 2010: -- Navistar Inc. has urged U.S. and California environmental regulators to recall 2010-compliant heavy-duty truck engines using selective catalytic reduction emissions technology that the company claims can be defeated by drivers... Navistar said all 2010 SCR engines are “programmed to run without diesel emissions fluid, with the wrong fluid, with slush or frozen DEF or with the system disconnected” ... Navistar, the only manufacturer using exhaust gas recirculation rather than SCR to meet 2010 emissions standards, said the agencies must refuse to certify additional engines until a full review is conducted... EPA in the past defended its SCR engine-certification process and said the technology is effective. CARB’s Hebert said that for a recall to take place, regulators first would need to show that the engine being sold is not the same one that was certified for the marketplace, and they would have to show the engine was actually having a negative effect on emissions... An attorney representing sister firms Mack Trucks and Volvo Trucks North America said the manufacturers did not object to the EPA-Navistar legal settlement, but they are concerned with “the potential example EPA may be setting through this settlement” ... EPA and CARB also have been criticized by 11 members of Congress from California, who demanded in a letter that the agencies fix the “loophole” in the nitrogen oxides standard...
* SCR and EGR: Pros and cons
New York,NY,USA -Fleet Owner, by Wendy Leavitt -(originally published) Jul 1, 2008: ... While EGR and SCR are both proven paths to reducing NOx emissions, there are trade-offs associated with each approach.
SCR advantages:
* Permits more optimized combustion
* Can enable better fuel efficiency/power
* No concerns about engine durability/oil degradation
* End product is nitrogen, water and carbon dioxide
* Urea not classified as hazardous to health
SCR trade-offs:
* System adds weight
* Adequate urea supply infrastructure not yet in place
* Purchasing urea is additional cost
* System, including sensors and other compliance-related devices, must be maintained
* Urea freezes at 12 deg. F., so may require heated storage
* Most effective at constant speeds and high loads; least in stop/start
* Urea (also in some fertilizers) is a water pollutant/harmful to fish
Cooled EGR advantages:
* Does not require additional onboard hardware
* Does not require the use of an additional fluid
* No loss of payload
* No impact on service intervals
* No driver intervention necessary for compliance
Cooled EGR trade-offs:
* Increases heat rejection, creating need for greater cooling capacity
* Decreases power density, fuel efficiency
* Potential engine durability and oil degradation issues
* Less combustion efficiency produces increased particulate matter, hydrocarbon, carbon monoxide
Sources: Chevron Oronite Co. LLC; Scania; VDI, Germany, “Market Overview of Exhaust Gas Treatment Solutions for Diesel Engines in Commercial Vehicles for Meeting Current and Upcoming Emission Legislation in the EU”; Volvo Trucks NA, “SCR: For EPA ‘10”; Environmental Protection Agency Heavy-Duty On-Highway Center, Argonne National Laboratory
Labels: EGR vs SCR
posted by Unknown @ 7:37 AM
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