Overview
ISO 22241-1:2019 specifies the quality requirements for AUS 32, the aqueous urea solution (commonly known as DEF, AdBlue®, ARLA 32®) used as the NOx reduction agent in selective catalytic reduction (SCR) systems on diesel engines. The standard defines composition, purity limits, physical characteristics and testing requirements needed to ensure reliable and stable SCR operation and to reduce engine NOx emissions without damaging catalysts.
Key topics and technical requirements
- Urea content: Target value 32.5% (mass fraction); permissible range 31.8% – 33.2%.
- Refractive index (nD20): Specified range ≈ 1.3814 – 1.3843 (used as a quality control correlate to urea content, adjusted for biuret).
- Impurities and limits:
- Alkalinity (as NH3): ≤ 0.2% (mass fraction)
- Biuret: ≤ 0.3% (mass fraction)
- Aldehydes: ≤ 5 mg/kg
- Insoluble matter: ≤ 20 mg/kg
- Phosphate (PO4): ≤ 0.5 mg/kg (referee method indicated)
- Trace metals: typical maximums (e.g., Al, Ca, Fe, K, Mg, Na ≤ 0.5 mg/kg; Cr, Cu, Ni, Zn ≤ 0.2 mg/kg)
- Physical properties (informative): density at 20 °C ≈ 1087–1093 kg/m3, incipient crystallization −11.5 °C, viscosity ~1.4 mPa·s at 25 °C.
- Testing and precision: Test methods and precision values are referenced in ISO 22241-2:2019 (test methods) and precision data are given in Annex B. Specified referee methods apply in case of dispute.
- Production control and marking: Manufacturers must implement production control plans and mark containers/pumps with the designation (e.g., “AUS 32 ISO 22241-1”).
Applications and who uses it
- Vehicle and engine manufacturers: to specify compatible DEF quality for SCR systems and warranty considerations.
- SCR converter and catalyst suppliers: to prevent catalyst poisoning or deposits and ensure expected NOx reduction performance.
- Producers, distributors and logistics providers of AUS 32: to guide production, handling, storage and quality control across the supply chain.
- Fleet operators and maintenance facilities: to verify purchased DEF quality, avoid SCR system faults and maintain emissions compliance.
- Testing laboratories: to perform referee testing per ISO 22241-2 and report against ISO 22241-1 limits.
Related standards
- ISO 22241-2:2019 - Test methods for AUS 32 (referee methods and precision).
- ISO 22241-3 - Handling, transportation and storage of AUS 32.
- Other referenced standards include ISO 3696 (water quality) and ISO 4259 (precision of measurement methods).
Keywords: ISO 22241-1, AUS 32, DEF, aqueous urea solution, SCR converter, NOx reduction, urea content, refractive index, biuret, aldehydes, trace metals, diesel emissions.
