Diesel engine vehicles can be damaged by using low quality diesel exhaust fluid (DEF). This includes catalyst poisoning, deposits which can restrict equipment from operating, and DEF injector and filter clogging. Repairs can be very expensive with long downtime possible, and damage could void the manufacturer’s warranty.  

These potential dangers demonstrate why education about using high quality DEF is crucial. 

Diesel engines in trucks and other applications sold in the United States must meet stringent U.S. Environmental Protection Agency (EPA) emissions requirements. Many of those engines use Selective Catalytic Reduction (SCR) to meet the requirements. SCR is an emissions aftertreatment 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. 

Diesel exhaust fluid (DEF) is an essential part of the process. It is injected into the diesel exhaust stream, and the heat from the exhaust, the fluid, and a catalyst convert the NOx into the harmless gases. 

DEF is made from a 32.5% solution of “technically pure” urea with the rest of the mixture consisting of purified water. For the SCR unit to operate properly, the DEF must meet an exacting purity standard established by the International Organization for Standardization (ISO). This ensures that the DEF provides the purity required by diesel engine manufacturers and the quality to preserve the emissions control system and the environment.

Purchasing DEF on the Road 

On the road, one of the main challenges for drivers is knowing the brand of DEF they are being sold as many fill-up locations don’t identify the manufacturer and brand name on the receipts to their customers.  

Regulations in many states require this information be provided when bulk DEF is delivered to the location. Without it, fill up locations cannot provide the information on dispenser receipts. It is then difficult for drivers to confirm they are buying DEF that is licensed by API’s Diesel Exhaust Fluid Certification Program unless it is marked, or the information is otherwise conveyed. 

Many diesel engine manufacturers recommend that drivers use API-licensed DEF. 

Drivers accustomed to purchasing DEF in containers should look at the expiration date on the bottle and be sure to use it before this date as the product has a limited shelf life. If a date is not present, ask for the most recently delivered DEF products. 

Storage conditions also have an impact on its quality. DEF can be expected to have a minimum shelf life of 12 months or even longer in optimum conditions. Check the label for recommended storage temperatures. API recommends that you don’t store if for too long in your truck once you purchase it, especially if the storage area in the vehicle is routinely hotter than the recommended storage temperatures displayed on the label. Be sure to look for the API certification mark on the bottle as well. 

Purchasing DEF for Shop Use 

API has found that the biggest misconception by fleet managers is the belief that if the urea concentration of their DEF is on spec, then the DEF meets the required quality. While it is absolutely true that the concentration is very important, there are many other important quality characteristics built into the ISO 22241 specification. 

Refresher: What is Selective Catalytic Reduction (SCR)?  

According to the Diesel Technology Forum, SCR aftertreatment systems are part of a complex emissions reduction system that has reduced NOx emissions by up to 90%, hydrocarbon and carbon dioxide emissions by 50%-90%, and particulate matter emissions by 30%-50%, compared to pre-2010 diesel engines. 

According to the Diesel Technology Forum, "SCR technology is designed to permit nitrogen oxide (NOx) reduction reactions to take place in an oxidizing atmosphere. It is called 'selective' because it reduces levels of NOx using ammonia as a reductant within a catalyst system.  

The chemical reaction is known as ‘reduction’ where urea-based diesel exhaust fluid (DEF) is the reducing agent that reacts with NOx to convert the pollutants into nitrogen, water and tiny amounts of CO2. The DEF can be rapidly broken down to produce the oxidizing ammonia in the exhaust stream. SCR technology alone can achieve NOx reductions up to 90%." 

Use of sub-standard urea (such as agricultural-grade urea commonly used as fertilizer) or use of water derived directly from the public water system without proper treatment can introduce contaminants and metals that are not only detrimental to the life of the Selective Catalytic Reduction (SCR) system but can also affect the SCR system’s ability to reduce harmful NOx emissions. 

Fleet managers responsible for procuring DEF should confirm that their suppliers are providing DEF that meets the ISO quality standard. One way to do this is to ensure that their supplier is providing a Certificate of Analysis with every shipment that addresses all of the quality characteristics that the specification requires.  

Fleets and drivers can check to see if the DEF they are buying is licensed through API’s real-time directory of licensees on the API website. 

Managing DEF in Shops 

For shops, the handling, storage, and dispensing of DEF is very important so that off-spec DEF doesn’t reach the marketplace. Temperature during transport or at the point of storage or sale can harm the shelf life of DEF sold in containers.  

Make sure the stock is rotated to use the oldest product first. Proper storage temperatures in a shop is also vital. Storing in temperatures above 86 degrees Fahrenheit will limit the shelf life of the DEF over time.  

Some additional things to consider in storing and handing DEF include: 

  • Bulk storage tanks should be dedicated for DEF. Don’t switch products in the bulk tank without thoroughly rinsing the tank with distilled or de-ionized water or on-spec DEF. 
  • A closed loop system for transferring DEF from a drum or bulk tank is recommended, so contaminants don’t get into the DEF. This is particularly important in a shop or construction site that has dust or dirt in the air. 
  • Use dedicated equipment for dispensing DEF. Don’t use funnels, pitchers, hoses, etc. that are used for other fluids when putting DEF in a tank. 
  • Anything used for dispensing DEF should be cleaned with distilled or de-ionized water and followed by a DEF rinse. Don’t use tap water for cleaning. 

For shops and drivers, it’s important to know what you are putting into your DEF tank. The quality of the DEF going into your vehicle is as important as the quality of the engine oils or fuels used in your vehicles. Use of API-licensed Diesel Exhaust Fluid will ensure that the DEF meets the high standards required by engine and vehicle manufacturers. 

Jeffrey Harmening is the team lead, diesel exhaust fluid, for the American Petroleum Institute.

Originally posted on Business Fleet