AdBlue (Diesel Exhaust Fluid, DEF) is a key fluid in the Selective Catalytic Reduction (SCR) system of diesel vehicles, which reduces exhaust emissions by converting nitrogen oxides (NOx) into harmless nitrogen and water. Its performance depends directly on strict adherence to global specifications; unqualified AdBlue may damage SCR catalysts, cause vehicle malfunctions, and lead to non-compliance with emission regulations.
This article provides a detailed analysis of the core specifications, international standards, quality testing methods, and compliance requirements for AdBlue urea, serving as a practical reference for fleet managers, automotive industry practitioners, and chemical manufacturers.
AdBlue is a high-purity urea solution used in selective catalytic reduction (SCR) technology to reduce harmful emissions from diesel vehicles. Injecting AdBlue into the exhaust system helps to decompose nitrogen oxides (NOx) into harmless nitrogen and water vapor.
The specifications of AdBlue urea are crucial for ensuring efficient and effective operation of the solution in the SCR system. Any deviation from the correct composition will affect the functionality of the SCR system and, ultimately, the vehicle’s emission level. Therefore, manufacturers and consumers must comply with the prescribed AdBlue urea specifications.
The following are the main specifications for defining high-quality AdBlue:
The urea concentration in AdBlue must be accurate to 32.5%.
This precise concentration is crucial to ensure optimal performance of the solution in the SCR system. If the concentration is too high or too low, the SCR system will not operate as expected, potentially leading to higher emissions and engine performance issues.
The urea used in AdBlue must have high purity (usually greater than 99.9%).
Pollutants such as urea, ammonium carbamate, and other impurities can interfere with the SCR process and damage engine components over time. That’s why AdBlue only uses high-quality urea in its production.
The water used in AdBlue must be deionized to ensure it is free of minerals and impurities. The deionization process can remove harmful salts and metals, thereby improving AdBlue quality and protecting the SCR system.
AdBlue has specific density and viscosity requirements to ensure appropriate flow through the SCR system. The standard density at 20°C is 1.09 kg/L, and the solution must maintain its viscosity within the specified range to prevent clogging or freezing in cold weather conditions.
The freezing point of AdBlue is approximately -11°C (12.2°F). In colder weather, AdBlue storage tanks and pipelines may freeze, affecting system performance. Manufacturers typically design AdBlue systems with heating tanks to prevent freezing.
The ISO 22241 standard (ISO 22241-1, -2, -3, 4) is the most widely used global specification, covering:
+ISO 22241-1: General requirements (composition, impurity limits, physical properties).
ISO 22241-2: Test methods (laboratory analysis of urea content, conductivity, impurities).
ISO 22241-3: Requirements for mixing, storage, and transportation.
ISO 22241-4: Specification for AdBlue storage tanks and delivery systems for vehicles.
North America: ASTM D22241 (equivalent to ISO 22241) and EPA regulations (mandatory for diesel vehicles from 2007 onwards).
Europe: DIN 70070 (German standard, aligned with ISO 22241) and EU emission standards (Euro 6 and above models must comply with AdBlue compliance requirements).
China: GB 29518-2013 (developed in accordance with ISO 22241, mandatory for diesel vehicles that meet National V and VI standards). AUS 32: In Australia and other countries, AdBlue is also known as AUS 32 (32.5% urea solution) and meets specifications similar to those of ISO 22241.
All mainstream standards require a 31.5% urea content, a deionized water matrix, and uniform impurity limits to ensure that AdBlue produced by different manufacturers can be interchangeable worldwide.
These standards ensure the safe use of AdBlue, protect the environment, and help vehicles comply with strict emission regulations.
The following standard testing methods are required to verify compliance with specifications:
Urea content: determined by near-infrared (NIR) spectroscopy or titration method (according to ISO 22241-2).
Conductivity and pH value: Measure with calibrated instruments (to ensure the quality of deionized water).
Impurity analysis: Heavy metals are analyzed by inductively coupled plasma (ICP) spectroscopy; anions (such as phosphorus) are analyzed by ion chromatography.
Density and viscosity: tested using a densitometer and a viscometer to confirm that the concentration and flowability meet the standards.
Freezing point: validated through low-temperature testing to ensure reliability during winter use.
Key points for on-site rapid inspection
Appearance inspection: AdBlue should be a clear, colorless liquid with no precipitation or turbidity.
Packaging verification: Select sealed containers with ISO 22241 certification markings (to prevent contamination during storage).
The AdBlue urea specification is a core prerequisite for the reliable operation of SCR systems, compliance with emission-reduction standards, and legal compliance. Following ISO 22241 and regional standards can ensure that diesel vehicles meet global emission regulations, avoid high maintenance costs, and maintain fuel efficiency.
For users, choosing certified products and following the correct storage method is key; For manufacturers, strict quality control and certification are essential conditions for entering the global market. By adhering to the correct urea concentration, water quality, and purity standards, you can help reduce your environmental impact and ensure optimal engine performance.
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