It is very similar to road salt you’d see in winter time—and urea is even used as a non-corroding alternative to rock salt for road de-icing in some instances (although it performs rather poorly in single digit or lower temperatures).
Here are some Frequently Asked Questions I had that Cummins Filtration answered for me today:
Question: What exactly is Diesel Exhaust Fluid (DEF)?
Answer: “DEF is the reactant necessary for the functionality of the SCR system. It is a carefully blended aqueous urea solution of 32.5% high purity urea and 67.5% deionized water.”
Q: What is urea (in layman terms)?
A: “Urea is a compound of nitrogen that turns to ammonia when heated. It is used in a variety of industries, including as a fertilizer in agriculture.”
Q: How will I know that the DEF product I purchase will work as advertised?
A: “The DEF you purchase should state and display the certification of the American Petroleum Institute (API), German Institute of Standardization DIN70700, the International Organization for Standardization ISO 22241-1, and meet AUS – 32 specifications. This will ensure the proper purity and concentration (32.5%) of urea.”
Q: Can I make DEF myself? (We know it’s possible)
A: “Cummins Filtration does not recommend customers make DEF themselves. DEF has strict requirements for maintaining concentration and purity of ingredients that is critical to the proper functioning and longevity of the SCR system. Cummins and other OEMs require that DEF used with their SCR systems meet all ISO22241 specifications as well as API certification requirements. It is recommended that end users purchase certified DEF and avoid blending it themselves.”
Q: Is the 32.5% urea solution really that critical?
A: “Yes, The 32.5% urea concentration is the ideal solution as it provides the lowest freeze point. Also, SCR systems will be calibrated to the 32.5%, so that optimum NOx will be reduced during operation.”
Q: What is the freeze point of DEF?
A: “A 32.5% solution of DEF will begin to crystallize and freeze at 12 deg F (-11 deg C). At 32.5%, both the urea and water will freeze at the same rate, ensuring that as it thaws, the fluid does not become diluted, or over concentrated. The freezing and unthawing of DEF will not cause degradation of the product.”
Q: Does DEF expand when frozen?
A: “Yes, DEF expands by approximately 7% when frozen. DEF packaging and tanks are designed to allow for expansion.”
-this is why you can top off a new Ford or GM’s urea tank well beyond their published tank capacity.
Q: How much does DEF weigh?
A: “DEF weighs approximately 9 pounds per gallon.”