Diesel Exhaust Fluid Systems Reduce Emissions and Improve Fuel Economy

The 1970 Clean Air Act was amended by Congress in 1990, signed by President George H.W. Bush, directing the U.S. Environmental Protection Agency (EPA) to increase the regulation of air pollutants from diesel vehicles. The amendments mandated that all on-road diesel vehicles from class 1 to class 8 manufactured after January 1, 2010 be equipped with nitrogen oxides (NOx) emissions reduction technology.  The technology developed by the industry to meet the new stringent emissions standards utilizes a pre-exhaust treatment system and a urea-based liquid called Diesel Exhaust Fluid (DEF).

Though the Clean Air Act of 1970 resulted in a significant decrease in the amount of air pollutants, NOx actually increased by 10 percent, calling for additional and specific attention to these particular pollutants as included in the 1990 amendments. NOx result as byproducts of the combustion of fuel when oxygen and nitrogen are combined in a high pressure and high temperature environment to create new compounds including nitric oxide and nitrogen dioxide. NOx have been implicated in a variety of health problems, such as childhood asthma, and make up the largest percentage of ground-level ozone and smog. They also contribute to global climate change.

NOx are emission byproducts of the combustion of all fossil fuels including diesel, gasoline, ethanol, coal, and propane with the EPA estimating that 49 percent of NOx emissions come from vehicles. While diesel fueled vehicles have better fuel economy than gasoline powered engines, the higher density of the fuel increases the NOx emissions. The new clean diesel vehicles blend a liquid urea solution, or DEF, into the hot exhaust gas. This results in the DEF releasing ammonia to allow the catalytic converter in the vehicle to convert NOx into environmentally harmless water and nitrogen. Vehicles with this technology emit up to 80 percent less NOx to enable compliance with the new stringent Clean Air Act requirements.

Diesel exhaust fluid is not an additive that is mixed with diesel fuel. Vehicle equipped with the system have separate on-board tanks to hold the DEF from six to ten gallon capacity in cars to ten to thirty gallons capacity on large trucks. Heavy-duty vehicles will consume about 500 gallons of DEF a year and be filled like fuel, that is from bulk dispensers. Light-duty vehicles such as automobiles will use about ten gallons of DEF a year with owners adding their own DEF or synchronizing DEF service intervals with oil changes. DEF systems also increase fuel economy for added benefit.