Diesel Exhaust Fluid (DEF) is a crucial component in the emission control systems of modern diesel engines, particularly those equipped with Selective Catalytic Reduction (SCR) technology. DEF is a non-toxic, colorless liquid composed of 32.5% urea and 67.5% deionized water. Its primary function is to reduce harmful nitrogen oxide (NOx) emissions, a major pollutant produced by diesel engines, making it an essential part of meeting stringent environmental regulations, such as the U.S. EPA's Tier 4 and Euro VI standards.

DEF works by being injected into the exhaust stream, where it reacts with NOx gases in the SCR catalyst to form harmless nitrogen and water vapor. This process helps diesel vehicles and equipment achieve compliance with emissions standards, improving air quality and reducing environmental impact. DEF is used in a wide range of vehicles, including trucks, buses, and construction machinery, as well as stationary engines in industries such as agriculture and power generation.

DEF is stored in a separate tank on the vehicle and is consumed during operation, requiring regular refills. It is important for operators to use high-quality DEF that meets ISO 22241 standards, as impurities or improper handling can damage the SCR system or affect vehicle performance. DEF is available at many fueling stations and in bulk, making it convenient for fleet operators to maintain their vehicles' emission systems and ensure regulatory compliance.