Density measurements for quality assurance of aqueous urea solutions in SCR applications
In SCR systems, accurate density measurement of aqueous urea solutions enables fast and reliable quality control. By correlating density with urea concentration, it ensures catalyst protection, system efficiency, and compliance with emission standards.
Reducing nitrogen oxide (NOₓ) emissions from diesel engines is essential to meet international environmental and emission standards. The Selective Catalytic Reduction (SCR) process has become a key technology in this effort. It uses an aqueous urea solution (AUS) as a reducing agent that is injected into the exhaust stream to convert harmful NOₓ gases into harmless nitrogen and water vapor.
Aqueous urea solutions for SCR systems typically contain 32.5 % w/w urea and 67.5 % w/w pure, demineralized water. They are available under several trade names such as AUS 32, AdBlue®, ARLA 32®, DEF (Diesel Exhaust Fluid), AGU (Automotive Grade Urea), or NOXy®.
To ensure consistent SCR performance and compliance with environmental regulations, the quality of aqueous urea solutions must meet the requirements of ISO 22241. This standard specifies the physical and chemical properties of AUS 32, including the density at 20 °C.
Measuring density, therefore, provides a fast and reliable method to verify urea concentration and to detect impurities or dilution that may compromise system performance or cause crystallization in the injector and catalyst.
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