Cummins has full confidence in its SCR
Feb 5, 2009 12:56 PM
Despite Environmental Protection Agency (EPA) concerns that the copper zeolite it intends to use in its 2010 engines could produce carcinogenic dioxins, Cummins said it has complete confidence that EPA will see after further testing that copper zeolite is a safe and effective solution for meeting 2010 emissions regulations.
Cummins first announced it would use copper zeolite to meet the EPA regulations in August, saying that it was an efficient way of reducing oxides of nitrogen (NOx). However, EPA sent a letter to US engine manufacturers last month questioning its use, noting "copper has the potential to catalyze dioxin formation in conditions experienced in incinerators and in diesel exhaust," which could lead the agency to withhold certification for engines that utilize copper zeolite.
However, Tina Vujovich, vice-president of marketing and environmental policy for Cummins, told FleetOwner that the company plans to sit down with EPA to talk about the agency’s findings in subsequent testing of copper zeolite.
"Based on what we’ve seen so far, we don’t have any concern about dioxins,” Vujovich said. “What EPA is doing [with SCR] is no different from what they did when EGR [exhaust gas recirculation] came about. It’s a long process."
The main reason Cummins is confident that its selective catalytic reduction (SCR) system won’t produce dioxins stems from the molecular structure of its copper zeolite catalyst, explained Steve Charlton, Cummins vice-president of heavy duty engineering.
"For dioxin to form in the exhaust stream, you need the presence of a number of materials: a large hydrocarbon molecule, chlorine, and access to the catalyst," he told FleetOwner. "So, first of all, there is very little chlorine produced in diesel combustion. More important, however, is the molecular nature of our copper zeolite catalyst."
He noted that molecular structure of the zeolite ‘cages’ the copper in very small tunnels that allow the passage of ammonia from the urea and NOx but not of large hydrocarbons. "Those hydrocarbon molecules are simply too big to fit into those tunnels, meaning the chances they can come into contact with the copper to produce a reaction are extremely small," Charlton said.
Cummins is also adamantly sticking by copper zeolite as the catalytic material for its SCR package because the company feels it offers several advantages over the iron zeolite used by most of the other engine makers that chose SCR technology to meet the 2010 regulations.
"Copper zeolite is simply a higher performing material than iron zeolite – it offers better low temperature performance at engine idle and better NOx control at highway cruising speeds," stressed Charlton. "In effect, we can begin controlling NOx sooner in the engine operating cycle – down to 200 to 300 degrees Celsius (approximately 392 to 572 degrees Fahrenheit) and then manage it better over the entire engine operating range."
Cummins research also indicates copper zeolite may have a slight advantage over iron zeolite in terms of longevity, offering better thermal stability and reduced degradation over time, noted Charlton.
Because of copper zeolite’s benefits, Vujovich feels it should have no problem passing EPA’s inspections. "EPA is not in the business of shutting down manufacturers," she said. "If they thought [copper zeolite] was a showstopper, they would have already told us. We feel very confident in the work we’ve done, and it’s in their best interest and our best interest to get this approved."
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