This month, three farm machinery manufacturers announced how they will meet EPA’s stringent Interim Tier 4 (IT4) emission regulations for off-road diesel engines such as those in tractors and combines. The regulations, which go into effect next year for engines rated 174 hp and above, call for a 90% reduction in particulate matter (smoke) and a 50% reduction in oxides of nitrogen (also called smog).

Case IH and New Holland plan to use Selective Catalytic Reduction (SCR) in engines rated 174 hp and above to achieve the required reductions. With this method, engine exhaust passes through the catalytic chamber, where it is sprayed with a nontoxic mixture of chemical urea and purified water. When the mixture combines with hot exhaust in the catalytic chamber, it is broken down into water vapor and nitrogen. The companies say advantages to this system include longer service intervals, lower fuel consumption, and wider fuel compatibility. AGCO is also using this approach for IT4.

John Deere plans to use a different approach, called cooled Exhaust Gas Recirculation (EGR), to meet IT4 regulations. This system cools and mixes measured amounts of exhaust gas with incoming fresh air to lower the engine’s peak combustion temperature, thereby reducing oxides of nitrogen to an acceptable level. To reduce particulate matter, exhaust gases are routed through an exhaust filter containing a diesel oxidation catalyst and a diesel particulate filter. Particulate matter is trapped in the filter and — through a process called regeneration — oxidized into nitrogen gas and carbon dioxide, then expelled through the exhaust pipe. John Deere says it is a more operator-friendly technology and is less complex to maintain when compared to SCR systems.

Industry engineers say both approaches will likely be needed to meet the even more stringent final Tier 4 emission regulations that take effect in 2014.