If you use diesel exhaust fluid (DEF), you’ve probably heard of refractometers. These tools are an essential part of making sure that the DEF you’re using is of quality so you can get the appropriate amount of NOx (Nitrogen Oxide) reduction to meet the requirements set by the Environmental Protection Agency (EPA). Since all diesel engines manufactured post 2010 requires a Selective Catalytic Reduction (SCR) system, the refractometer has been a mainstay for anyone who services diesel engines and needs to measure the quality of DEF before usage.
Why It Matters
DEF is a mixture of environmental grade urea and deionized water, and when injected into the exhaust system of a diesel-powered vehicle it services to reduce NOx emissions, which have been shown to be harmful to the environment. The key, though, is that you need to use DEF that meets spec or it won’t provide the emissions reduction that’s required by the EPA and quite possibly shut down your system.
Verifying DEF Purity
Refractometers are not a new tool—they’ve long been used as a way to measure a number of things in a variety of industries—but now they come specially designed to measure and test diesel exhaust fluid.
A basic refractometer consists of a prism, cover plate, correction screw, mirror tube, and an eyepiece. These portable tools allow a user to determine the precise level of DEF and its purity by taking a liquid sample and placing it on the prism. Light that passes through the sample bends (refracts) according to how concentrated the liquid is—more concentrated means more refraction. Peering through the magnified eyepiece, you can determine if the refraction levels meet the requirements for DEF.
In order to work properly, a refractometer must be focused and calibrated, a process you can achieve by putting a couple drops of pure water on the tool. After it’s calibrated, you can place a couple of drops of DEF on the prism and determine, based on where the bottom of the shadow line intersects with the scale, whether you have the correct amount of urea, more is needed, or the concentration is too high and it must be diluted.
A digital refractometer, which Certified DEF offers, consists of a handheld device that offers a number of different scales for a specific fluid. By placing a sample of the fluid with a pipette on the measuring surface and closing the evaporation cover and pressing the “Go” button a test result will appear in the window within a few seconds. It’s recommended to take an average of five tests to verify the most accurate reading.
Just make sure to always treat it like a precision tool and use and store it as directed in a clean and dry place until its next use to ensure accurate readings moving forward.
Since most DEF comes in premixed containers, a problematic sample with the refractometer would likely indicate that either the DEF is low quality, or it has become contaminated during storage or transport. Contaminated or low quality DEF must be drained entirely and the container washed out by a professional before being refilled with only high quality fluid from a place like Certified DEF.