Diesel engine manufacturers are using two methods to meet the tighter emission control standards. Some manufacturers are using exhaust gas recirculation (EGR) to control nitrous oxides, plus a filter in the exhaust system to capture and later burn the particulate matter. Other manufacturers use selective catalytic reduction (SCR) technology or a combination of EGR and SCR technologies. Both methods are effective and are proven technology.

The EGR technology diverts 20 to 30 percent of the exhaust gas into a cooler on the side of the engine. Cooling the exhaust lowers its oxygen content. The cooled exhaust gas is routed to the intake manifold. This lowers the oxygen content of the intake air, which reduces the combustion temperature. The lower combustion temperature results in lower nitrous oxide content in the exhaust. This method reduces nitrous oxides, but the lower combustion temperature results in more soot (particulate matter).

Generally, these manufacturers use a filtering system that oxidizes the particulate matter by burning diesel fuel injected into the hot exhaust. When the particulate levels cannot be burned by hot exhaust gases, such as during prolonged engine idling, fuel is injected into the catalytic chamber to assure burning. Caterpillar, Cummins, Deutz, John Deere, Komatsu and Perkins are using EGR technology to comply with Tier 4 regulations.

The SCR technology used by other manufacturers uses higher combustion temperatures that effectively control the particulate matter levels in the exhaust. However, this method produces unacceptable levels of nitrous oxides. These manufacturers use a post-combustion catalytic chamber outside the engine to catalyze the nitrous oxides. A mixture of urea and deionized water called diesel exhaust fluid (DEF) is injected into the post-combustion catalytic chamber. The chamber converts the nitrous oxide into nitrogen, carbon dioxide and water before exhausting it into the atmosphere. AGCO, Case IH and New Holland are using SCR technology.

In addition to the catalytic chamber, SCR technology includes a DEF storage tank and an electronic control unit on the engine. SCR technology uses approximately 1 gallon of DEF for every 25 gallons of diesel fuel. The cost of DEF is similar to diesel fuel and is available at many fuel stations.

DEF is 68 percent water, freezes at 12 degrees F, gels at minus 25 degrees and can degrade if stored above 90 degrees. Heat from the engine warms the DEF in its storage tank, which allows the engine to perform properly within the EPA regulated time of 30 minutes after the engine starts. The system also is designed to remove all DEF from the fuel lines after stopping the engine to prevent freezing when the outside temperature is cold.

“Engines that run out of DEF are computer programmed to lose some power, which makes the equipment unusable for field work, but still allows the operator to drive the tractor to a refueling location at reasonable road speeds,” Nowatzki says. “The electronic control system on the engines is programmed to gradually reduce engine power, which allows operators to continue normal equipment operation at least to the edge of a field.”