Cummins Inc. CMI -0.03% - EPA Tier 4 Final emissions regulations go into effect in January 2014 for mobile generator sets with diesel engines rated from 174 to 751 horsepower. These engines will be required to emit no more than 0.4 grams of nitrogen oxides (NOx) and 0.02 grams of particulate matter (PM) in their exhaust, representing a 90 percent reduction in these two pollutants since Tier 3 regulations which were introduced in 2005. Reaching these emissions goals has been a challenge for manufacturers, but Cummins Power Generation is one of the first to offer Tier 4 Final products in this power node, accomplished by optimizing a combination of emissions reduction techniques while increasing performance and reliability.

While all engine manufacturers will need to employ various forms of exhaust aftertreatment techniques, Cummins Power Generation decided early in the design phase to keep the aftertreatment technology as simple as possible. Cummins Tier4 integrated solution meets Tier4 with an advanced engine which minimizes emissions in-cylinder and only a Selective Catalytic Reduction (SCR) and a compact Diesel Oxidation Catalyst as aftertreatment. While several manufacturers need to employ a more complex SCR and DPF package, Cummins meets Tier4 without having to use a DPF.

"The alternative to a DPF was eliminating PM formation in the engine cylinders during combustion. By increasing fuel injection pressure, and other in-cylinder improvements, Cummins was able to significantly reduce the amount of PM produced in the first place," said Eric Fay, technical project leader, Tier4 Final G-drive, Cummins Power Generation. "As is characteristic of diesel engines, combustion conditions that favor a decrease in PM also favor an increase in NOx. However, NOx is more easily controlled using a combination of cooled EGR and an SCR aftertreatment system. Through years of experience with on-highway aftertreatment systems on its diesel engines, Cummins was well positioned to employ advanced SCR technology for power generation in order to meet EPA Tier 4 Final regulations."

The multipronged approach Cummins Power Generation uses to meet Tier 4 Final emissions standards in its 174 to 751 horsepower diesel engines includes a variety of in-cylinder and aftertreatment techniques.