What is DEF (Diesel Exhaust Fluid)?

All - 11 Min read

March 26, 2024

DEF stands for Diesel Exhaust Fluid. It's a liquid solution used in diesel engines equipped with Selective Catalytic Reduction (SCR) technology, helping to reduce nitrogen oxide emissions, a major air pollutant. DEF is made of 32.5% urea and 67.5% deionized water. It's injected into the exhaust stream and, when heated, turns into ammonia and carbon dioxide. These then react with a catalyst to convert nitrogen oxides into nitrogen and water vapor, significantly reducing harmful emissions.

What is Diesel Exhaust Fluid (DEF) and its purpose?

Diesel Exhaust Fluid (DEF) is a non-toxic solution used in vehicles with diesel engines to reduce nitrogen oxide (NOx) emissions. It's essential for vehicles equipped with Selective Catalytic Reduction (SCR) systems, helping them meet environmental standards by converting NOx into nitrogen, water vapor, and small amounts of CO2.

What is DEF made of?

DEF is composed of 32.5% urea and 67.5% deionized water. This specific mixture is crucial for facilitating the chemical reaction required to reduce harmful emissions in diesel exhaust.

Is DEF made from urine?

No, the urea in DEF is synthetically produced to ensure purity and effectiveness. It is similar to the urea found in urine but is manufactured specifically for use in reducing vehicle emissions.

How does DEF relate to diesel fuel?

While DEF is used in diesel-powered vehicles, it is not a fuel. It's stored in a separate tank and is injected into the exhaust stream to reduce emissions, working alongside diesel fuel to enhance engine efficiency and environmental compliance.

What is the price of DEF fluid?

DEF prices vary by size and brand. Small 2.5-gallon containers can cost from about $7.69 at Tractor Supply Company to $21.70 at Walmart. For larger quantities, 55-gallon drums are available from $249 on BuySinopec.com to $334.95 at Grainger Industrial Supply, while 330-gallon totes range from $1,189 at Bayringer to $1,235 at Keller Heartt. Retailers like Walmart, Tractor Supply Company, and online suppliers such as BuySinopec.com and Grainger offer a wide selection, catering to both individual and bulk purchase needs.

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