The initiative to lower diesel engine emissions started with on-highway engines in 1973 and now extends to non-road mobile equipment, marine and locomotive engines, and stationary engines. These lower standards present significant technical and operational challenges for both engine users and manufacturers. While stringent diesel engine emission standards generally result in cleaner air, the challenges will continue in the United States as the Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) phase in even more stringent diesel engine emission limits.

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"EPA Tier 4 and the Electric Power Industry"

by Greg Harness

Senior Product Consultant, Electric Power Group, Caterpillar Inc.

1. Understanding Diesel Engine Emission Rules:
Today’s drive toward improved air quality originates from the Clean Air Act of 1970, passed a few months after the first Earth Day. Since then, internal combustion engines have been a high priority for emissions reduction.

2. Standards Affecting Stationary Diesel Engines:
Beginning January 1, 2007, new stationary diesel engines had to meet the EPA’s Compression Ignition (CI) New Source Performance Standards (NSPS) which include diesel powered generator sets. The CI NSPS, for most engine horsepower ranges, incorporated the EPA non-road mobile standards with regard to regulated exhaust pollutants and associated Tier levels.

3. Tier 4 and Electric Power. A Special Case:
The U.S. EPA Tier 4 emissions regulation came into effect for engines below 37 bkw (approximately 30 ekw or electrical kilowatts) in 2008, and will come into effect in 2011 for diesel powered generator sets rated 130 bkw (approximately 120-125 ekw)
and higher.

4. Special Local Regulations:
Along with California, some regions and localities have stationary emission limits far more stringent than EPA diesel engine tier levels. These include non-attainment areas in the United States such as Southern California; the New England states; Atlanta, Georgia; and Houston, Texas.

5. Approaches to Reducing Diesel Engine Emissions for the Electric Power Industry:
Depending on the site and the specific pollutant of concern, the following aftertreatment may be used on diesel engines in an effort to meet specific local codes:

• Selective Catalytic Reduction (SCR) for NO_x.
• Diesel Oxidation Catalyst (DOC) for carbon monoxide, non-methane hydrocarbons, and particulate matter.
• Diesel Particulate Filters (DPF) for particulate matter.

6. The Future:
To meet Electric Power product requirements for 2011 and beyond, Caterpillar is working on cost effective solutions to meet both Tier 4 Interim and Tier 4 Final emissions. Specific technical solutions will involve the latest in diesel engine technology and innovation and will use Caterpillar ACERT® Technology as the foundation.

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