AdBlue is the key to SCR (Selective Catalytic Reduction) systems, which rely on a precise 32.5% urea and 67.5% deionized water mixture to reduce nitrogen oxide emissions.
The use of unqualified or contaminated liquids can result in emission testing failures, vehicle performance issues, and high maintenance costs for SCR systems. Fortunately, there is a fast, simple, and highly accurate method to verify its quality: using an AdBlue refractometer to test urea concentration.
This guide will explain why this test is crucial, what the correct concentration is, and how to conduct it step by step.
The only function of AdBlue urea is to decompose harmful nitrogen oxides produced by diesel engines into harmless nitrogen and water. Its performance depends entirely on the precise urea concentration:
Traditional laboratory methods, such as titration, are accurate but slow and require complex equipment. The refractometer solves this gap by implementing real-time on-site testing.
The refractometer uses Snell’s law of refraction. When light passes through the AdBlue urea solution:
The refractive index of the solution will vary proportionally to the urea concentration.
32.5% urea solution has a specific refractive index (usually around 1.3840 at 20°C).
The AdBlue refractometer has a pre-calibrated reference value, allowing direct reading of concentration without manual calculation.
Temperature compensation: Most models are equipped with automatic temperature compensation (ATC) to adjust the critical value of 10-30 ° C (due to the refractive index changing with temperature).
Portable design: Handheld, lightweight, and battery-free – perfect for on-site testing (garages, truck stops, fleet yards).
Easy to read: Clear scale or digital display screen showing urea concentration percentage (0-40%) and freezing point.
Before your first use or if the refractometer has been subject to temperature changes, you must calibrate it.
Place a few drops of distilled water onto the clean prism.
Close the daylight plate.
Look through the eyepiece and turn the calibration screw until the boundary line between the blue and white fields sits exactly on the “WATERLINE” or 0% mark.
Wipe the prism and daylight plate with distilled water using a soft, lint-free cloth. The surface must be completely clean and dry to ensure an accurate reading.
Using a pipette or dropper, place 2-3 drops of the AdBlue you wish to test onto the prism. Ensure you have enough fluid to cover the entire surface.
Gently close the clear plastic daylight plate over the sample. This will spread the liquid into a thin, even layer. Try to avoid creating air bubbles.
Hold the refractometer up to a natural light source and look through the eyepiece. You will see a scale. The reading is the point where the boundary line between the lower blue field and the upper white field crosses the scale.
The scale on an AdBlue urea refractometer is clearly marked with urea concentration percentages.
The boundary line should fall exactly on the 32.5% mark.
If the reading is significantly lower (e.g., below 31%), the AdBlue has likely been diluted with water. Do not use it.
If the reading is significantly higher (e.g., above 34%), water has likely evaporated from the solution, or it is not a genuine AdBlue® product. Do not use it.
Immediately after taking your reading, thoroughly clean the prism and daylight plate with a soft, damp cloth, then wipe them dry. Storing the refractometer with AdBlue residue on it can, over time, damage the prism’s coating.
Without ATC, a 1°C temperature change will shift the reading by 0.1% of the urea concentration.
Always test the sample at room temperature (reference standard is 20 ° C), or use a refractometer equipped with ATC.
Oil, dirt, or diesel pollution can distort the refractive index, leading to incorrect readings.
If the sample appears turbid or contains particles, filter it using a syringe filter.
Calibrate the refractometer before each use (especially during critical testing).
The refractometer is stored in a protective case to prevent scratches or damage to the prism.
Clean the prism after each use to prevent cross-contamination between samples.
Fleet management: Regularly test AdBlue tanks to ensure compliance with emission standards and avoid SCR system failures on the road.
AdBlue supplier: Verify concentration before delivery to customers – this is crucial for quality control and product certification.
Car repair shop: Diagnose SCR system problems by detecting AdBlue concentration (a common cause of emission faults).
By ensuring that AdBlue remains at the optimal concentration of 32.5%, you can protect engine performance, comply with emission regulations, and avoid expensive maintenance costs.
Using a refractometer to detect AdBlue Urea concentration is a fast, economical, and essential diagnostic step for any diesel car owner or technician. It allows you to immediately verify the quality of the liquid added to the vehicle, protecting your investment and ensuring that your SCR system operates as expected.
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