NASHVILLE, Tenn. - In defiance of the widely-held belief that NOx aftertreatment systems such as SCR would be required to meet EPA2010 emissions standards, Cummins has announced its heavy-duty engines...
NASHVILLE, Tenn. – In defiance of the widely-held belief that NOx aftertreatment systems such as SCR would be required to meet EPA2010 emissions standards, Cummins has announced its heavy-duty engines will meet 2010 requirements with no NOx aftertreatment.
The surprising announcement came during the Technology and Maintenance Council’s fall meetings in Nashville.
“We feel we have the key technology to deliver a product in 2010 that will satisfy customer requirements and will not need NOx aftertreatment,” Steve Charlton, executive director of heavy-duty engineering with Cummins announced. “What you’ll get in 2010 is exactly the same as what you have today, with cooled EGR, a variable geometry turbocharger, a crankcase ventilation system and a particulate filter. There will be very little change in terms of the architecture.”
Cummins officials said they will adopt Selective Catalytic Reduction (SCR) for the company’s mid-range engines. The company said it chose different paths based not on emissions requirements, but on customer preferences. Mid-range customer requirements revolve around diversity of applications, power range and best overall value whereas heavy-duty operators are more concerned about uptime, reliability, operational efficiency, resale value and low cost of ownership, Charlton explained.
“We believe we’ve chosen the right technology for our respective markets,” he said.
So how exactly does the company plan to meet EPA2010 standards for heavy-duty engines without NOx aftertreatment? Simply put, by doing much the same as in 2002 and 2007, while boosting EGR levels and reducing airflow.
More EGR, less airflow
Central to Cummins 2010 emissions strategy is a new XPI high-pressure common rail fuel system, which the company said generates better performance and cleaner exhaust by maintaining high injection pressures.
The new fuel system will be used across the company’s entire 2010 heavy-duty engine lineup. Dubbed the X-Family, the current 15-litre ISX will be complemented by a new 11.9-litre and 16-litre offering. The ISM will be retired from the North American on-highway market.
The new fuel system will enable Cummins to increase EGR levels to further reduce NOx. EGR levels of about 15% were introduced to meet EPA02/04 emissions levels and that drove NOx emissions down about 50%.
A further 50% reduction in NOx was achieved in 2007 by ramping up EGR levels to just 25%. Cummins said it will repeat the process in 2010, once again increasing EGR levels to reduce NOx tailpipe emissions.
Along the way, the company has also been reducing airflow through the engine, from a 28:1 air-to-fuel ratio in 1998 to a 21:1 ratio in 2007. Charlton explained the company’s ability to reduce the air-to-fuel ratio has allowed it to make significant NOx reductions with comparatively small increases in EGR levels.
“You need proportionately less EGR with each step because the quality of the gas being recycled is higher and higher,” Charlton explained.
“In 2010 we’re going to take more air out of the engine, and that will allow us to preserve power density. We’ll have a minimum heat rejection increase and it will give us optimized fuel economy.”
The company said it expects to be able to maintain its current fuel economy performance in 2010. Power, torque and maintenance intervals should also be unaffected, the company said.
The diesel particulate filter (DPF) will remain largely unchanged in 2010, but will feature a new close-coupled catalyst which will help ensure maximum oxidation temperatures. Cummins’ variable geometry turbocharger (VGT) will remain as-is for 2010.
The company plans to roll out its first EPA2010-compliant field test units in early 2008, and some prototype vehicles will be cold weather-tested in Canada this winter.
SCR for mid-range engines
While Cummins rejected SCR for its heavy-duty engine lineup, it has decided to embrace the technology for its mid-range products.
Jeff Weikert, executive director of mid-range engineering with Cummins, said when opting for SCR the company considered “the overall best value of the product…not just initial cost, but total cost while delivering reliability, low maintenance and hitting the power density for all the different markets our mid-range engines play in.”
Cummins’ 2010 mid-range engines will feature the same technology employed to meet existing EPA emissions standards, most notably EGR, a DPF and a crankcase breather and coalescent filter.
The company will tack on an SCR system which consists of a urea tank, dosing system and the necessary plumbing.
A small amount of urea will be injected into the hot exhaust stream, where it will become ammonia, explained Weikert.
The ammonia then travels into the SCR catalyst, reacts with NOx in the catalyst forming harmless water and nitrogen which is then expelled into the air.
Any ammonia that slips through uncatalyzed will be captured by an ammonia slip catalyst, Weikert added.
SCR is already widely used in Europe and several engine manufacturers have already committed to the technology as their 2010 heavy-duty engine solution.
Cummins is targeting a 1% urea usage ratio, meaning one gallon of urea will be consumed for every 100 gallons of diesel. (For more on SCR, see pg. 85).