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Tier IV looms
Proper technology selection will become even more crucial as Tier IV approaches. Starting in 2008, engines under 75 hp will begin to fall under Tier IV emissions limits. Even more restrictive limits for larger engines will be phased in through 2014.

"The off-highway regulations known as Tier IV/Stage III establish extremely low levels of oxides of nitrogen (NOx) and particulate matter (PM)," says Farrar. "These standards will ultimately drive the use of aftertreatment technologies for a large portion of off-highway engines. There are several combustion and aftertreatment technologies aimed at NOx reduction - cooled EGR, selective catalytic reduction (SCR), NOx adsorbers and lean-NOx catalysts."

The variety of off-road equipment makes meeting Tier IV/Stage IIIB more of a challenge due to the lower volumes sold. "What might be cost effective for Class 8 trucks, sold in units of tens or hundreds of thousands a year, is not as easily done or as cost effective when you talk about the variety of off-highway equipment that any manufacturer of equipment would make," Farrar points out.

"The harsh working environments in which the non-road equipment is used can make Tier IV/Stage IIIB an even greater challenge - not insurmountable, but a challenge," he continues. "As we look to Tier IV, the differences from on-highway become somewhat more pronounced - from the availability of ram air to packaging constraints. Tier IV Final/Stage IIIB will require very close design integration between turbo/engine and aftertreatment."

Tier III solutions did not require aftertreatment. "To date, Cummins emission reduction efforts for off-highway engines have been achieved in-cylinder through improving combustion technology," says Farrar. "To reach Tier IV Final/Stage IIIB PM reductions, it's assumed that all manufacturers will be forced to develop forms of aftertreatment technology. Cummins A Series engines in the 31- to 48-hp range already meet Tier IV Interim requirements today, and will require no changes to the engines until Tier IV Final begins in 2013, at which time some form of aftertreatment technology will be applied."