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Introduction to Diesel Exhaust Fluid (DEF) Posted on Categories Diesel Exhaust Fluid

In January 2010, the U.S. Environmental Protection Agency to meet requirement set by the Clean Air Act brought in new emissions standards requiring medium and heavy-duty vehicles to significantly reduce engine emissions, particularly NOx and particulate matter. Vehicle manufacturers decided to use a technology called selective catalytic reduction or SCR to meet these standards. 

SCR technology uses ammonia to break down dangerous NOx emissions produced by diesel engines into nitrogen and water. In automotive applications SCR delivers ammonia through a urea solution called Diesel Exhaust Fluid (DEF) which is sprayed into the exhaust stream by an advanced injection system and then converted into ammonia on a platinum catalyst. When the NOx from the engine exhaust react inside the catalyst with the ammonia, the harmful NOx molecules in the exhaust are converted to harmless nitrogen and water, which are released from the tail pipe as steam.

DEF is a synthetically made urea solution which is a mixture of high-purity, automotive-grade urea and de-ionized water. This liquid is clear, nontoxic, nonflammable, non-explosive, and generally nonhazardous. Additionally, DEF is classified as a minimum risk for transportation. The fluid is mixed at a ratio of 32.5 percent formaldehyde-free urea and 67.5 percent de-ionized water. DEF weighs 9.1 pounds per gallon, and while it starts to freeze at 12 degrees, its composition and quality are not affected by freeze or thaw. In fact all truck DEF tanks are designed to freeze. When the engine is on hot coolant is then used to thaw the DEF in tank.

The most important quality of DEF is its purity. For example, one teaspoon of salt would contaminate 5,000 gallons of DEF. SCR systems are very sensitive to potential impurities, so it is essential that DEF remains uncontaminated, and that consumers only purchase fluids that adhere to the ISO 22241 quality standard and never try to mix their own.

This is why it’s very important you use a credible DEF supplier that meets or exceeds API, ISO and PEI transport, storage and handling guidelines and has a dedicated and closely managed closed supply chain. Your DEF supplier should provide you with valuable assurance that an investment in diesel powered equipment with selective catalyst reduction is protected from tainted, off-spec DEF, or non-conforming product, which can void SCR system warranties, or worse – render the SCR system inoperable by fouling the on-board catalyst.

DEF may be a less significant product line for non-dedicated distributors, but its importance to you and your clean diesel operations means support and service should be a priority with focus on quality, availability and expertise.