Cummins Inc. said its heavy-duty diesel engines that comply with the Environmental Protection Agency’s 2010 standards will not require NOx aftertreatment, although its medium-duty engines will use selective catalytic reduction (SCR) technology.
The decision to meet 2010 standards without SCR in heavy-duty engines stands in contrast with announcements from Detroit Diesel and Volvo/Mack that their 2010 truck engine solutions will employ SCR technology in order to bring NOx levels within EPA’s mandated maximum levels. SCR introduces urea into heated exhaust, causing it to break down into ammonia. The ammonia, in turn, reacts with the NOx in a catalytic converter to produce nitrogen and water.
At a news conference in Nashville on Sept. 23, Steve Charlton, Cummins executive director of heavy-duty engineering, announced that the company’s heavy-duty engines instead would meet EPA demands through a combination of the XPI high-pressure common rail (HPCR) fuel system, improved cooled exhaust gas recirculation, advanced electronic controls, variable geometry turbochargers and the Cummins diesel particulate filter.
Cummins also said the 2010 engines in North America will include 11.9-liter and 16-liter diesel engines to complement its 15-liter product. All will share a common architecture that includes the XPI HPCR, said Ed Pence, vice president and general manager of Cummins’ heavy-duty engine business. “This is the first time in nearly 20 years that we’ve had common architecture across our heavy-duty products,” Pence said.
The HPCR fuel system, which was designed and built by a Cummins-Scania joint venture, offers improved performance and cleaner exhaust by maintaining high injection pressures regardless of engine speed, Cummins said. The company will continue to use the Cummins Turbo Technologies-designed VG turbo. And the Cummins Particulate Filter, designed and built by Cummins Emission Solutions and introduced in 2007, will be the only aftertreatment required for the 2010 solution.
Cummins’ approach toward lowering NOx for 2010 is to continue reducing the amount of oxygen introduced into the combustion process. Reducing the airflow not only reduces NOx, but it also produces other benefits, including high power density, minimum heat rejection and optimal fuel economy, Charlton said. And with less oxygen introduced into combustion, less oxygen comes out for use in cooled EGR, further improving performance and emissions control. “It’s a virtuous circle,” Charlton said.
In the heavy-duty segment, Cummins said it chose its solution with an eye to the key drivers of uptime, operational efficiency and low cost of ownership. By using its chosen approach rather than SCR to achieve NOx reduction, Cummins lowered the complexity and eliminated the need to purchase and manage urea, the company said.
By staying away from SCR, Cummins also differentiates its engines more clearly from the captive engines offered by truck makers. Volvo’s powertrain group, which supplies engines to Volvo and Mack, and Freightliner’s Detroit Diesel have announced that SCR will be part of their 2010 solutions. Meanwhile, International plans to introduce a heavy-duty engine in a joint venture with Europe’s MAN. And Paccar is leveraging engine technology developed by its DAF unit in Europe to introduce Paccar engines in North America for Kenworth and Peterbilt.
Many fleets “will take a deep sigh of relief” that they will not have to deal with the complexities introduced by urea and SCR, Pence said.
For midrange engines, there was a different set of priorities, including diverse application and the need for a wide power range. Cummins already uses SCR for midrange engines in Europe. The need for power density made SCR attractive for midrange engines, said Jeff Weikert, executive director of midrange engineering.
In addition to the performance needs, SCR is operationally more attractive than in long-haul heavy-duty applications because the rate of urea consumption is lower and because midrange equipment typically returns to base daily for fueling and maintenance. For many midrange applications, fleets will be able to replenish urea in sync with their oil change intervals, Weikert said.
