HAMBURG: In a bid for cleaner air and to reduce levels of nitrogen oxide (NOx), carmakers developed a technology for diesel cars that had long been in place for commercial vehicles.
The process - selective catalytic reduction (SCR) - uses a catalytic converter to specifically reduce the nitrogen oxides in the car's exhaust gases.
But for the process to work, you need an additional liquid, a product widely branded as AdBlue and formally known as diesel exhaust fluid.
The substance triggers a chemical reaction that cleans your exhaust emissions.
AdBlue is a mix of 67.5 per cent water and 32.5 per cent synthetic urea, explains technical inspector Erik Pellmann.
The fluid is stored in its own separate tank in the car and is continually injected into the exhaust system, and then chemically broken down by a hydrolysis catalyst, says Pellmann, an expert from European vehicle inspection company Dekra.
In the exhaust system, the fluid responds to the nitrogen oxide that's generated during the engine's combustion, in a chemical reaction that takes place in seconds. It transforms the emissions into hydrogen and nitrogen, both of them harmless.
You have to be careful with AdBlue, however, and make sure it doesn't get in the diesel tank.
"AdBlue is not a fuel additive and must never be mixed with diesel," says Pellmann. It has its own separate tank with its own filler neck in the spare wheel well, next to the diesel nozzle or in the engine compartment.
The size of the tank varies, between 10 and almost 40 litres, depending on your car model.
Your car consumes AdBlue at about 3 to 5 per cent of its fuel consumption rate.
Depending on how your exhaust system is tuned, engine capacity and driving style, your tank will need refilling around every 5,000km to 15,000km. It might last far longer, however.
Your car will generally let you know if you're running out of the substance, and should give you advance warnings before the sensor spots that the tank is empty. At that point, the engine likely won't start anymore.
In most countries the system is monitored by an engine control software. You don't need to head to the garage to refill the tank. But if you do it yourself, you will need a special hose to fill it.
