AdBlue – what is it and how does it work?

Have you ever wondered what that extra fluid is that needs to be added to modern diesel engines? AdBlue – it sounds a bit like the name of a gadget or an isotonic drink, doesn’t it? But it’s actually an inconspicuous yet crucial component of the exhaust gas treatment system in diesel cars. Without it, you won’t get anywhere. Literally.

In recent years, AdBlue has become a mandatory component of many passenger cars, vans and trucks. This is to meet increasingly stringent emission standards and reduce the amount of harmful nitrogen oxides emitted from exhaust pipes. But… how does it actually work? Do you really need to add it? What happens when it runs out? And how much does it all cost?

In this article, we clear up all your doubts. We will show you what AdBlue fluid is, how it works, where to refill it and how it affects the performance of diesel vehicles. No beating around the bush (although – spoiler alert – there will be a little bit of beating around the bush).

What is AdBlue fluid?

AdBlue is a transparent fluid that looks like water at first glance. And actually… it is a bit like water. It is an aqueous solution of urea – approximately 67.5% of it is demineralised water, and the rest is specially purified urea. It is odourless, non-flammable and, contrary to what its name might suggest, it is not a fuel additive, but works in a separate system.

Its task is to neutralise nitrogen oxides (NOx) produced during the combustion of diesel fuel in diesel engines. And since nitrogen oxides are one of the most harmful components of exhaust gases, AdBlue is not just an ‘additive’ but a real lifesaver in the fight against air pollution.

AdBlue does not pose any threat to humans or the environment, provided it is handled properly. However, it has strong corrosive properties, so it is best not to spill it on car paint or engine parts.

How exactly does AdBlue work?

AdBlue can be compared to an invisible firefighter who jumps into action in the exhaust system before the exhaust gases reach the atmosphere. But it does not extinguish the fire – it only neutralises harmful gases. How exactly does this work?

When a diesel engine is running, various exhaust gases are released into the atmosphere, including nitrogen oxides (NOx), which are particularly harmful to health and the environment. This is where the AdBlue system comes in, using selective catalytic reduction (SCR).

In practice, the fluid is fed into a separate AdBlue tank, from where it is drawn by a pump at the right pressure and sent to a special injector. This sprays it directly into the exhaust system, just before the SCR (Selective Catalytic Reduction) catalytic converter. There, under the influence of high temperature, the urea solution breaks down into ammonia and carbon dioxide. As a result of a chemical reaction, the ammonia combines with the nitrogen oxides present in the exhaust gases, converting them into volatile nitrogen and water vapour – completely harmless components that are released into the atmosphere. Simple? Maybe not quite, but effective – very effective.

Sounds like magic? It’s chemistry in the service of ecology. Thanks to this reaction, nitrogen oxide emissions can be reduced by up to 90%, enabling compliance with the stringent EURO 6 and EURO 7 emission standards.

What happens when AdBlue runs out?

Importantly, the AdBlue system only works when the fluid is present in the tank. Without it, the entire SCR technology simply has nothing to work with, so nitrogen oxide neutralisation stops working. This, in turn, means that the vehicle no longer meets the emission standards on which its roadworthiness is based.

Car manufacturers are well aware of this, which is why vehicles with AdBlue are equipped with safety systems. When the AdBlue fluid level drops, the on-board computer starts sending warnings – subtle at first, then increasingly urgent. And if you ignore them, you may have a problem.

If you ignore all AdBlue refill messages and the tank empties completely, the on-board computer will prevent the engine from restarting after it is switched off. This means that you can still get to where you are going, but once you switch off the engine… the journey is over.

Some cars first limit engine power or torque to give you a final warning: ‘Hello, add AdBlue before it’s too late!’. This is a kind of emergency mode designed to motivate you to take action.

It is also worth remembering that AdBlue is consumed in proportion to fuel consumption – on average, this is about 1-3 litres per 1,000 km, although with larger vehicles (e.g. trucks), AdBlue consumption can be significantly higher – up to 10-15 litres per 1,000 km.

Okay, but where did AdBlue actually come from and when was it introduced?

Although it may seem that AdBlue is a recent invention, its history actually goes back much further, to the 1950s.

However, AdBlue was introduced to the mass market in 2005-2006, when trucks had to start meeting increasingly stringent emission standards under EU EURO regulations. AdBlue began to be used in trucks in response to the EURO 4 and EURO 5 standards.

With the introduction of the EURO 6 standard, which came into force in 2014-2015, AdBlue became a permanent fixture in passenger cars and delivery vehicles with diesel engines. This marked the beginning of the real expansion of the SCR system and AdBlue fluid in the automotive industry. Today, it is almost mandatory equipment for modern diesel engines.

Why diesel engines in particular? Because despite their economy and efficiency, diesel engines generate significantly more nitrogen oxides, which are the pollutants that need to be neutralised. SCR AdBlue technology has proven to be the most effective and economical solution for both vehicle manufacturers and users.

In other words, AdBlue is not a fad, but a ticket to eco-friendly diesel driving, whether you drive a car, a van or a truck.

Where is the AdBlue tank located?

If this is the first time you’ve heard about adding AdBlue, you may be wondering, ‘Okay, but where do you actually put it?’ Don’t worry – the AdBlue tank is not hidden somewhere deep in the engine. On the contrary, its location is usually quite logical and easily accessible, although it varies depending on the type of vehicle.

You will most often find the AdBlue filler:

• next to the fuel filler, under the same flap (often marked with a blue cap),
• in the boot, under the carpet or service flap,
• under the bonnet, less often – but it does happen.

In trucks and vans, the AdBlue tank is usually more visible – typically mounted outside the vehicle frame, with a separate cap and markings so that it cannot be confused with the fuel filler.

And here is an important note: the AdBlue tank is completely separate from the fuel tank. These are two different systems that have no physical connection. So do not, under any circumstances, try to mix AdBlue with diesel fuel – this is a recipe for a serious (and expensive) disaster.

What about the tank capacity? Again, there is no single rule – in passenger cars, it is usually between 10 and 20 litres, which is enough for several thousand kilometres. In larger vehicles, the tanks are proportionally larger – in HGVs, it is usually between 50 and 100 litres.

How does AdBlue refuelling work and how do you top it up?

Adding AdBlue is no big deal – although it can be a little stressful for someone doing it for the first time. Fortunately, topping up AdBlue is as easy as refuelling with regular fuel. All you need to know are a few basics.

Firstly, where can you refuel AdBlue? You have several options to choose from:

• Petrol stations – more and more of them offer special dispensers for refuelling AdBlue. You will usually find them at truck stops, but they are also becoming increasingly common for passenger cars.
• Bottles and canisters – available in supermarkets, automotive wholesalers and online stores. This is a convenient solution for self-refilling, although it requires a little caution when transferring the fluid.
• Authorised service centre or workshop

The process itself is very similar to standard refuelling – you open the cap (usually blue), insert the nozzle or funnel and pour. With a dispenser, it’s a piece of cake: just like refuelling with petrol.

In newer cars, the on-board computer reminds you when it is time to top up. It displays a low level message and sometimes even informs you how many kilometres you have left before the AdBlue is completely depleted. And remember – it is not worth waiting until it reaches zero. It is better to top up the AdBlue fluid in advance than to get stuck with a broken-down car.

Summary

AdBlue is more than just another fluid under the bonnet – it is a silent hero in the fight for cleaner air. Although its role may seem insignificant, without it, modern diesel engines simply cannot operate in accordance with emission standards.

Now you know:

• what AdBlue is and what ingredients it contains,
• how AdBlue works in the exhaust system and why it is so important,
• where the AdBlue tank is located and how to refill it,
• how often you need to top up AdBlue,
• and what happens when the tank runs out (which is better not to find out the hard way).

Fortunately, AdBlue does not require any specialist knowledge – just a little attention and regular refilling.

Frequently asked questions (FAQ)

What is AdBlue and how does it work?

AdBlue is a solution of urea and demineralised water that helps clean exhaust gases in diesel cars. The main task of AdBlue is to reduce nitrogen oxides in exhaust gases. The use of AdBlue allows cars to meet emission standards such as Euro 6.

How much AdBlue is used per 100 km? How often should AdBlue be refilled?

The average AdBlue consumption in diesel passenger cars is approximately 1-3 litres per 1,000 km.

In larger vehicles (e.g. delivery vans, trucks, coaches), consumption may be higher – up to 10-15-20 litres per 1000 km.

Can you drive without AdBlue?

It is better not to. If the AdBlue tank is empty, the engine may go into emergency mode or refuse to start altogether. The on-board computer will warn you in advance, but if you ignore it, you may not be able to start the car until you top up the AdBlue fluid level.

Read also: 6 ways to reduce TIR fuel costs (in road transport) >>>

What happens if I don’t add AdBlue?

At first, warnings will appear on the dashboard – subtle at first, then increasingly urgent. When the AdBlue fluid level drops to zero, the on-board computer will prevent the engine from starting after it has been switched off. In some models, the car may first limit its power before giving up completely.