The AdBlue additive has been a common sight on filling station forecourts for quite a few years now, but unless you drive a diesel vehicle with a selective catalytic reduction (SCR) system and an onboard AdBlue tank, the chances are you’ve never touched the stuff.
It’s not surprising then, that many people still don’t really know what AdBlue fluid is used for, or indeed what you have to do if you need to buy AdBlue and use it. So stick around, and we’ll explain…
Selective Catalytic Reduction (SCR)
When diesel combusts in an engine, various pollutants are released into the atmosphere via the exhaust pipe, and two of the most insidious from an environmental point of view are nitrogen Oxide and nitrogen dioxide. They’re the nasties that cause smog and acid rain, and are also linked to inflammation of the lungs and other horrid respiratory problems.
Selective catalytic reduction is a process designed to remove these oxides of nitrogen from a vehicle's exhaust gases. It works via a liquid solution of urea that is injected into the exhaust gas of a diesel vehicle, that soloution is known as Adblue.
When the Adblue is injected into the exhaust by the SCR system the heat of the exhaust gas causes the urea to release ammonia, which acts as a catalyst in a chemical reaction that eliminates the oxides of nitrogen. Water vapour and nitrogen are all that’s left, both of which are naturally occurring and harmless when they pass out of the car's tailpipe.
So where does AdBlue come in?
So the liquid urea solution used in the SCR system is called AdBlue. It consists of 67.5 per cent de-ionised water, and 32.5 per cent urea. Automotive urea, in case you were wondering, is not an animal derived product although we do excrete urea in urine, it's at much lower concentrations. The stuff used in your car is a man-made substance created by exposing synthetic ammonia and carbon dioxide to heat. As well as being used in liquid form, AdBlue suppliers also make dry pellets for farmers to scatter on their fields as a form of fertiliser.
Which vehicles use SCR?
Heavy goods vehicles – trucks, coaches and buses – have been using SCR technology and AdBlue from as long ago as 2004, and some passenger car manufacturers have been using it for nearly as long. Mercedes and Volkswagen, for example.
It’s the latest Euro VI emissions regulations from the European Commission that have really driven an explosion in SCR technology from the passenger car perspective in Europe, though. The Euro VI regs introduced in 2014/15 demanded nitrogen oxides emissions be cut by a whopping 56 per cent compared to Euro V levels. For most diesel engines over 1.6-litres in capacity, AdBlue and SCR technology has been the only means to achieve this – so most new diesels over that size will feature an AdBlue tank from now on.
How to use AdBlue
When AdBlue was first considered for cars it was going to be a dealer service item. There’d be a sealed tank, and drivers wouldn’t worry about the levels because there’d be enough AdBlue onboard to drive the necessary 10,000 miles or so between dealer services. But service intervals have risen, and the weight penalty of carrying up to 60-litres of AdBlue has an effect on C02 emissions and therefore company car tax rates. So if you have AdBlue in your vehicle, the chances are it will be in a much smaller tank, and so you’ll need to top it up yourself.
With tanks varying in size from 5 to 20 litres, and a mid-size family diesel consuming a litre of AdBlue every 600-odd miles, the requirement to top up the AdBlue may be quite frequent for high mileage diesel drivers.
Fortunately, you car will monitor consumption and give you a series of dashboard warnings as the level drops. It’s wise not to ignore them, as once the AdBlue is all gone the car may not start until the tank is topped up again. (This is to ensure cars don't drive illegally with high exhaust emissions.)
Topping up the tank is simplicity itself. Nowadays the AdBlue filler cap is often located next to the diesel filler, and AdBlue is typically sold in handy containers that dispense without drips – important, as although the AdBlue is pretty harmless to people, it can be quite corrosive to vehicle paintwork or other less obvious things like your car’s wiring. It can also smell pretty bad if you spill a container of it on the boat - as we know from experience.
Older cars may have their AdBlue filler caps inside the vehicle or under the bonnet, but your handbook will tell you where to find it.
Where to buy AdBlue
AdBlue is widely available from main dealers and independent garages, as well as accessory shops and chains. It’s also a staple of every filling station these days, but it’s worth shopping around as AdBlue prices can vary widely.
Do you use Adblue in your car or van? Tell us what you think of it in the comments section below...