AdBlue® and Car care > AdBlue®: What is it? What does it do?

AdBlue®: What is it? What does it do?

What is AdBlue?

If you’re a motorist, you’ve probably already heard of AdBlue®. But do you know what it is (what it’s made of) and what it’s used for? Let’s find out what you need to know about AdBlue®.

What is AdBlue®? What is its composition?

AdBlue® is an aqueous solution designed exclusively for diesel vehicles fitted with a selective catalytic reduction (SCR) system. This technology has enabled diesel vehicle manufacturers to comply with current European anti-pollution standards.

Composed of 67.5% demineralised water and 32.5% very pure urea, this liquid is colourless, biodegradable, water-soluble and classified as a non-hazardous product.

Also known as AUS 32 (Aqueous Urea Solution), AdBlue® is a diesel exhaust fluid (DEF) that complies with ISO 22241 and DIN 70070 standards.

AdBlue® is a trade name belonging to the Association of German Automobile Manufacturers (VDA).

Composition of AdBlue®: what is demineralised water?

As we have already seen, AdBlue® is mainly composed of demineralised water (67.5%). This is water in which the minerals (calcium, magnesium, sodium, potassium, bicarbonates, etc.) have been removed by a demineralisation process. The purified water used in the composition of AdBlue® is usually obtained :

  • either by deionisation: when it is purified on ion exchange resins
  • or by reverse osmosis: when it is filtered using a semi-permeable membrane.

Where does the urea used in AdBlue® come from?

Urea is the second essential element in the composition of AdBlue®. Also known as carbamide, urea is a product made chemically from ammonia and carbon dioxide. Manufactured on an industrial scale since 1922, it is available in solid (granular) or liquid form.

Urea is also a naturally occurring substance in animal and human urine. It is created in the liver from ammonia derived from certain amino acids.

How is AdBlue® made?

AdBlue® is a liquid that is only manufactured industrially. There are currently two manufacturing processes:

  1. dissolving solid urea granules or pellets in demineralised water
  2. mixing synthetic urea (liquid) with demineralised water.

If you thought you could make your own AdBlue®, you should know that this is virtually impossible. In order to be used, AdBlue® must meet stringent quality requirements, both in terms of precise dosage and purity. Today, only industrial processes are capable of meeting these standards. Needless to say, if you use home-made AdBlue®, you run the risk of causing serious damage to the vehicle’s catalytic converter, and no manufacturer’s warranty will cover the cost of repairs.

What is AdBlue® used for?

AdBlue® is used to limit the polluting emissions produced by the combustion of diesel fuel. This liquid enables diesel vehicles fitted with SCR (Selective Catalytic Reduction) technology to reduce nitrogen oxide (NOx) emissions by 80-90%, which are considered extremely harmful to health and the environment.

SCR technology, which uses AdBlue® to reduce toxic emissions, was introduced on HGVs in October 2006 to meet the Euro 4 emissions standards imposed on them.

In September 2015, the Euro 6 standard required manufacturers to drastically limit emissions of polluting gases from light vehicles (cars and vans). The use of AdBlue® liquid and SCR technology was extended to diesel cars and vans to comply with this standard.

How does AdBlue® work?

Using SCR technology, AdBlue® converts most of the nitrogen oxides (NOx) emitted by diesel vehicles into harmless nitrogen and water vapour.

In practical terms, when the engine is running :

  1. AdBlue® is injected into the exhaust pipe upstream of the SCR® catalytic converter.
  2. Thanks to the high heat of the exhaust, the urea and water contained in the AdBlue® are transformed into carbon dioxide and ammonia.
  3. When it reaches the SCR catalyst, the ammonia mixes with the nitrogen oxide molecules to form nitrogen and water.
  4. The majority of the remaining polluting particles will be retained by the particulate filter (DPF) positioned after the catalyst.
  5. Exhaust emissions will therefore consist mainly of nitrogen and water, which are harmless to the environment.
How AdBlue works

How AdBlue and SCR technology work – Source: Peugeot

AdBlue®: which vehicles use it?

AdBlue® is used by all diesel vehicles equipped with SCR technology: cars, commercial vehicles and heavy goods vehicles. The increasingly stringent European anti-pollution standards have prompted most carmakers to choose this technology to bring their diesel vehicles into line.

Here is a non-exhaustive list of car manufacturers whose diesel vehicles use AdBlue® in whole or in part: Audi, BMW, Citroën, Dacia, DS, Fiat, Ford, Hyundai, Infiniti, Jaguar, Jeep, Kia, Land Rover, Mercedes, Mitsubishi, Nissan, Opel, Peugeot, Porsche, Renault, Seat, Skoda, Toyota, Volkswagen, Volvo.

When and how do I fill up with AdBlue®?

You need to fill up with AdBlue® as soon as the AdBlue® warning light comes on on your dashboard. This is generally accompanied by a message asking you to fill up with AdBlue® within a maximum of 2400 km, otherwise your engine will refuse to start.

You then need to find out where the AdBlue® tank is located: in the fuel filler flap (for recent vehicles), or under the bonnet, or in the boot. If in doubt, your vehicle service manual (or your car dealer) will tell you exactly where the tank is located.

All you then need to do is buy a 5 or 10 litre can of AdBlue® (or go to a petrol station that sells AdBlue®) and fill the tank in question.

Characteristics and precautions to be taken

  • AdBlue® should not be added to the diesel tank, but to the dedicated tank (generally recognisable by its blue cap).
  • It can be stored indoors, in a place where the temperature is between -5 and 30°C:
    • below -5°C, the liquid may crystallise
    • above 30°C, the liquid evaporates
  • Given this risk, a can of AdBlue® must not be exposed to sunlight or near a source of heat.
  • The shelf life of a can of AdBlue® is 12 to 18 months from the date of production (in its original, unopened packaging).
  • Although the liquid is not dangerous, it is advisable to handle it with gloves.
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