What exactly does Diesel Exhaust Fluid (DEF) do?

Diesel Exhaust Fluid (DEF) is an after-treatment technology that is sprayed into the exhaust system to break down the generated NOx into harmless nitrogen and water molecules. This reaction happens in the Selective Catalytic Reduction (SCR) System. SCR technology is designed to permit NOx reduction reactions to take place in an oxidizing atmosphere. It is called “selective” because it reduces NOx levels using ammonia as a reductant within a catalyst system. The chemical reaction is also known as a “reduction,” where DEF is the reducing agent that reacts with NOX to covert the pollutants into nitrogen, water, and a tiny amount of CO2. SCR technology alone can reduce NOx up to 90%.

DEF technology has been used for decades in agriculture, industrial, and large-scale power generation applications but only recently became more widely used to meet the Final Tier 4 emission requirements and EPA standards. DEF is a mixture of urea and de-ionized water. DEF is stored in a separate tank. DEF gets sprayed into the exhaust through special injectors that ensure the correct amount is added when the machine is on. DEF is a vital component in today’s emissions-compliant engine. It’s a non-hazardous, non-toxic, non-flammable material that lowers NOx concentrations.

How can DEF become contaminated?

It doesn’t take much to contaminate Diesel Exhaust Fluid. Maintaining the integrity of your DEF is vital to protect your engine. DEF is an aqueous urea solution made with 32.5% urea and 67.5% de-ionized water, or a 1:2 solution. If that ratio is thrown off at all, the DEF will no longer work as intended. DEF is also highly sensitive to chemical impurities. The concentration of purity of ingredients is critical to the proper functioning and longevity of the SCR system.

Situations that can cause DEF to become contaminated:

• DEF is vulnerable to sunlight and extended periods of temperatures over 86. If left in the heat, some of the water could evaporate from the fluid, throwing off its composition.
• DEF will freeze at cold temperatures. While freezing DEF has no effects on its quality, it can expand up to 7%, cracking the tank, lines, or injectors. These cracks can let in dust and dirt, contaminating the fluid.
• If you use any pumps or containers that have been used with other fluids, even a teaspoon of other metals or fluids will contaminate a 5,000-gallon tanker truck of DEF.
• DEF cannot be stored in containers made of carbon steel, copper, or alloys that contain copper or zinc-coated steels.

What happens if your DEF gets contaminated?

The concentration, purity, and quality of the ingredients in DEF are critical to the proper functioning and longevity of the SCR system. Contaminated DEF can turn gummy or crystalize and leave those deposits on the catalyst. Replacing or repairing the SCR unit can be very costly, and you should take every precaution to avoid contaminated DEF.

DEF is naturally clear, so if the fluid looks cloudy or colored- it’s old or contaminated. If you know that the concentration of urea to water is incorrect, do not use the DEF. Using contaminated DEF doesn’t always immediately show results. You can also experience gradual clogging of the SCR system, resulting in costly replacement parts, reduced efficiency, and lost time. In addition, if your SCR isn’t working correctly, you could be producing NOx emissions beyond legal limits.

How to prevent DEF contamination:

There are a few things you can do to help maintain the quality of your DEF. Hamilton Engine is here as a resource, and you can always contact us and schedule time for one of our service techs to take care of any service needs.

Tips to prevent DEF contamination:

• Keep DEF equipment clean and free from dust or dirt.
• Drain DEF systems on larger machines and rinse out with de-ionized water for winter storage. DEF is corrosive, so rinse spillage off the frame.
• Make sure to purge the DEF out of the lines before winter storage.
• Keep separate equipment for DEF. If you need to clean DEF fueling or storage equipment, do so with de-ionized water; anything else will contaminate it.
• Only handle DEF using DEF-safe containers and hardware.