AdBlue®: what it is and how it works

AdBlue® is a diesel exhaust fluid (DEF) mixture used in all heavy-duty diesel engines produced after January 1st, 2010 and most commercial vehicle and car diesel engines made after September 2015 – primarily Euro 6-compliant models. AdBlue® is not a fuel additive as it’s added to the exhaust gas after combustion has taken place.  

AdBlue® reduces Nitrogen Oxide (NOx) emissions. Nitrogen oxide is a harmful gas that can damage the human respiratory system, reducing lung function, increasing allergen exposure and the risk of respiratory illnesses. It promotes the formation of fine particulate pollution and ground ozone – harmful to both health and vegetation. 

It’s for these reasons that governments set limits on vehicular NOx emissions and promote the use of AdBlue®. This improves air quality and reduces the danger of diesel pollution-related illness and death. 

The term AdBlue® is a worldwide trademark of the German Association of the Automotive Industry (VDA) relating to DEF produced in accordance with the ISO 22241 specifications. 

AdBlue® is made of a colourless mixture of high-purity urea (32.5%) and deionised water (67.5%), as set out in the ISO 22242 standard. Urea contains ammonia; the active ingredient in AdBlue® that reacts with NOx and neutralises it before it enters the atmosphere. 

AdBlue® works alongside vehicle engine selective catalytic reduction (SCR) systems to reduce nitrogen oxide (NOx) exhaust emissions. Vehicles that use the active emissions control technology can usually be identified by the use of ‘SCR’ or ‘Blue’ in their model names.  

After exhaust gas passes through the diesel particulate filter, AdBlue® DEF is sprayed and mixed into it via a dosing control system as it enters the SCR catalytic converter. Here, the ammonia within the urea reacts with NOx in the exhaust stream, neutralising it to form harmless nitrogen (N2) and water vapour (H2O), while additionally reducing total fuel consumption by 2-6%.  

AdBlue and SCR systems are highly effective, reducing NOx emissions by up to 90%, hydrocarbon and carbon monoxide emissions by 50-90%, and particulate emissions by 30-50%. 

If your car is a diesel, there is a high chance it will require AdBlue®. If you’re unsure, consult your vehicle’s handbook, or search for the filler cap located next to the fuel filler, under the bonnet or in the boot of the vehicle.

If your diesel vehicle was registered after September 2015, it likely uses AdBlue®. Often, the model name will feature the words ‘SCR’ or ‘Blue’, and if the vehicle is produced by a European manufacturer, the use of AdBlue® technology is more likely.

If you’re wondering how long AdBlue® lasts and how much you should use in your vehicle, the rate at which your AdBlue® depletes is around 1 litre for every 350 to 600 miles. The exact rate at which you should top up your AdBlue® depends on your vehicle’s engine size, your driving style, and the size of the vehicle’s AdBlue® tank, which varies between 5 and 20 litres in size.  

For more information on your specific usage rates, consult your vehicle’s handbook or a qualified mechanic, but bear in mind that your dashboard should indicate when you need a top-up. 

While there are different names for AdBlue®, such as Bluedef, BlueTec and so forth, all mixes should contain the same solution of 32.5% urea and 67.5% de-ionised water. The German Association of the Automotive Industry’s AdBlue® marque can be confidently relied upon to meet these requirements, while others may not. 

You should never use water instead of AdBlue®, and the VDA notes that vehicles should not use urea solutions not denoted by the ‘AdBlue’ trademark. While inexpensive, these can harm the SCR catalytic converter, so it’s always best to stick with legitimate, branded AdBlue®. 

It’s impossible to drive without AdBlue® – your engine will not start, and you’ll see a notification noting ‘AdBlue® is empty’. A notification will also appear when your AdBlue® tank is running low. 

Most diesel vehicles require an AdBlue® top-up every 3,000-4,000 miles, depending on the engine. Check your vehicle manual for a figure specific to your make and model. 

AdBlue® is generally considered to reduce NOx emissions by over 90%, making it a crucial tool for improving air quality and combatting environmental issues.

AdBlue® can freeze at temperatures below -11°C, however it will usually thaw due to the heat of the engine in cold winter conditions, without any change in concentration or effectiveness.

If driving in exceptionally cold conditions, it can be a good idea to keep a bottle of liquid AdBlue® in your vehicle to top up the tank in case of freezing – automatic warming systems can take up to 20 minutes to thaw frozen AdBlue® tanks.

AdBlue® DEF is water soluble, biodegradable and non-hazardous, however you should rinse thoroughly in case of contact, avoid AdBlue® vapours, and clean surfaces that come into contact, as it is slightly corrosive to certain materials. 

TotalEnergies offer AdBlue® in bulk, barrel and small commercial vehicle packs, and offer all the benefits of fully compliant AdBlue® to drivers and fleet operators. 

As well as reducing NOx without harming engines, TotalEnergies AdBlue® also features TotalEnergies ClearNOx, an additive within the solution that cleans SCR systems, improving their cold and stop-start performance. Reducing clogging in exhaust, ClearNOx has been shown to remove the risk of clogging for up to 50,000km and reduce maintenance costs.