What is Diesel Exhaust Fluid?

  • Diesel Exhaust Fluid (DEF)  is a urea based fluid designed specifically for use in SCR (Selective Catalytic Reduction) systems to reduce NOx emissions. DEF is API certified and meets ISO22241 specifications. Diesel Exhaust Fluid is non-toxic, non-flammable, colorless, non-hazardous, and very easy to use. Beginning with all 2010 cars and trucks.
  • In 2010, cars and trucks with diesel engines sold in the United States must meet new U.S. EPA emissions requirements. To meet these requirements, many diesel engine manufacturers (OEM’s) have decided to use Selective Catalytic Reduction (SCR), an emissions after treatment technology that converts nitrogen oxides (NOx) in the diesel-engine exhaust stream into nitrogen and water vapor, two natural components in the air we breathe.
  • SCR technology is not new—it has been in use for many years in Europe but it is new in North America. SCR converts NOx to nitrogen and water vapor using a catalyst, the heat from the exhaust, and a diesel exhaust fluid (DEF). The fluid is injected into the diesel exhaust stream. The fluid and the chemical catalyst convert the NOx into the harmless gases.

The 2010 Emissions standards in North America have mandated that all on-road diesel vehicles manufactured in 2010 or later must be equipped with technology to reduce NOx emissions. NOx emissions need to be removed from the air because they contribute to global warming, acid rain, atmospheric particles that visual impairment.

Currently, there are two technologies that meet these 2010 EPA guidelines:

  1. Advanced EGR
  2. Selective Catalytic Reduction (SCR). SCR is the most widely used technology and it is the process of removing the NOx from fuel gases during the combustion process. This technology has been in use since the late 1950’s on large commercial boilers and has been shown to reduce Nox emissions by 70-90%. This helps protect the environment by reducing the amount of harmful nitrogen oxides emitted into the atmosphere by converting them to harmless nitrogen and water.

This conversion is done by injecting Diesel Exhaust Fluid, commonly referred to as DEF, into the exhaust stream which converts the NOx to water vapor and harmless gases to be released from the tailpipe.

diesel exhaust fluidDEF is made from 32.5% high purity urea and 67.5% DI water and is considered to be safe, non-toxic and environmentally friendly. When fueling the SCR equipped diesel engine, DEF is added to a separate tank on the vehicle. The DEF is consumed at a rate, approximately equivalent to, 2% of diesel fuel consumption and contributes to approximately 4% fuel economy savings of the vehicle. When the diesel engine is operating, the DEF is injected into the exhaust stream where it reacts with a catalyst to reduce the amount of nitrogen oxide emitted into the atmosphere, thereby protecting our environment.

What does DEF mean for drivers? Vehicles equipped with an SCR system use sensors to determine that, in fact, DEF is in the system and not a liquid such as water. These vehicles also have other instrumentation such as gauges or warning lights as to alert the driver to the level of DEF in the vehicle. If the vehicle were to be run without a supply of DEF, the vehicle would enter into a ‘Limp Mode’ which would allow the vehicle to be safely driven to the nearest location to replenish the DEF. This ‘Limp Mode’ is similar to the familiar ‘Check Engine’ light familiar to most motorists. While in the ‘Limp Mode’, the diesel engine will not produce full-power and by limiting power and the vehicle will be limited to 5mph with inducement notification.