While the original Clean Air Act was passed in 1963 and the most recent amendments to the measure won approval 20 years ago, implementation of one of the legislation’s most important provisions affecting agriculture starts in 2011.
That’s when the latest and most stringent regulations for off-road diesel engines rated at 174 horsepower and above go into effect. The new rules call for a 90 percent cut in particulate matter (smoke) and a 50 percent reduction in oxides of nitrogen emissions, often referred to as "smog" because they contribute to the formation of atmospheric pollution.
Referred to as Interim Tier 4/Stage III B, the new requirements replace the current Tier 3 emissions rules which mandated a 40 percent reduction in oxides of nitrogen compared with standards earlier in effect.
But the story doesn’t end there. Final Tier 4/Stage IV regulations will take emissions of particulate matter and oxides of nitrogen to near-zero levels by 2014.
In addition to larger tractors and harvesting machinery, the off-road diesel emissions rules apply to bulldozers, graders and other heavy construction and logging equipment, portable generators and airport tugs. Marine engines and locomotives are affected by somewhat different regulations and engines used in underground mining equipment are regulated by the Mine Safety and Health Administration.
To meet the standards, engine manufacturers will be required to produce new engines with advanced emission control technologies. Also, refiners will be supplying more ultra-low sulfur diesel (ULSD) fuels. Sulfur content in the ULSD product already being used in diesel-powered highway vehicles is limited to 15 parts per million (ppm), compared to 500 ppm in low sulfur diesel fuel.
According to Environmental Protection Agency (EPA) estimates, the costs associated with complying with the final emissions rules will be one to three percent of the purchase price for most categories of off-road diesel equipment, depending on the size and complexity of the machine. Rumors abound but some industry experts say the EPA estimate is low and compliance costs could add 10 percent or more to prices.
The necessary use of ULSD to meet tighter emissions standards has other consequences as well. Brad Nobbe (pronounced NO-bee), a principal in the Wm. Nobbe & Co., Inc., John Deere dealership based in southwestern Illinois, noted in a recent review that biodiesel no longer will be an option for farmers and other users of diesel fuel. In addition, EPA cost estimates for producing and distributing ULSD have ranged from four to seven cents more per gallon, an amount that, in part, could be offset by lower maintenance expenses.
The new diesel emission regulations do not require retrofitting older engines already in service. However, the agency has estimated, when all older off-road engines have been replaced, the tougher emissions rules annually will prevent up to 12,000 premature deaths, one million lost work days, 15,000 heart attacks and 6,000 children’s asthma-related emergency room visits.
Not everyone agrees on what constitutes the best engine design technology for meeting the Interim and Final Tier 4 emission requirements.
One method uses cooled exhaust gas recirculation (EGR) along with an exhaust filter that reduces particulate matter. In this system, measured amounts of exhaust gas are cooled and mixed with incoming fresh air to lower the engine’s peak combustion temperature, thereby reducing oxides of nitrogen to an acceptable level. However, the lower combustion temperatures increase the amount of particulate matter, requiring the exhaust gases be routed through an exhaust filter containing a diesel oxidation catalyst and a diesel particulate filter. Particulate matter trapped in the filter is oxidized into nitrogen gas and carbon dioxide, and expelled through the exhaust pipe.
The second method for reducing emissions is with selective catalytic reduction (SCR) and a diesel oxidation catalyst. Unlike EGR technology, SCR raises the peak combustion temperature so the engine runs like a hot, cleaner-burning fire. Such conditions mean less particulate matter but more oxides of nitrogen. The remaining particulate matter is handled by a chemical reaction in the diesel oxidation catalyst. Reducing oxides of nitrogen is accomplished by injecting a diesel exhaust fluid (urea and purified water) into the exhaust stream. When the exhaust gases combine with the urea in the SCR catalyst, the oxides of nitrogen break down into nitrogen gas and water vapor and are expelled from the exhaust pipe.
There are pros and cons for both emission control methods.
EGR proponents, among them John Deere, say the technology is more operator-friendly and less complex to maintain. Deere explained it used cooled EGR technology to meet Tier 3 diesel engine requirements and it simply makes sense to build on a system with a proven record of reliability by adding the exhaust filter to meet the Interim Tier 4 emissions standards.
Further, Deere noted urea is not widely available today and some farmers may have to drive a distance to find a retailer handling the product. Urea’s price and storage issues, especially in colder areas where urea can freeze, pose other questions, the company said.
SCR advocates, including Case IH, claim the technology is the best approach for high horsepower agricultural equipment because it means longer service intervals, lower fuel consumption and wider fuel compatibility. The company also stated leading engineers believe all manufacturers will need to use SCR to meet the more stringent Final Tier 4 standards beginning in 2014. In addition, Case IH maintains its dealers will help ensure customers have the infrastructure needed for the transition to SCR systems.
While Case IH will be using SCR technology for medium and heavy-duty diesel engines, it will use the cooled EGR system in engines less than 100 horsepower.