Car Care: Demystifying Diesel Exhaust Fluids
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With vehicle emissions very much in the New Zealand spotlight currently, there’s likely to be more diesel vehicles arriving using Diesel Exhaust Fluid (DEF), which is used to reduce the amount of air pollution created by the engine.
Most of these vehicles will arrive from European countries, due to the strict emissions regulations already in place there. We’ve put together a guide to help you with some of the jargon surrounding DEF.
Selective Catalytic Reduction (SCR)
Due to the Environmental Protection Agency (EPA), American rules for diesel vehicles are some of the most stringent emission standards in the world.
The majority of light and heavy-duty diesel vehicle manufacturers have found that the only way to meet these rules without compromising engine performance and efficiency is through Selective Catalytic Reduction (SCR). SCR systems are currently used on some Mercedes-Benz BlueTEC models, as well as diesel vehicles from Volkswagen, Peugeot and Citroen.
SCR is an after treatment technology, where fluid is sprayed into the exhaust stream to cause a chemical reaction that breaks down NOx emissions into harmless nitrogen and water.
SCR systems were patented in 1957 by Engelhard Corporation using ammonia as the reducing agent. Development continued in Japan and the US in the early 1960s, with research focusing on less expensive and more durable catalyst agents. This was originally only found on large ships and gas turbines, but is now used in automobiles. Nowadays, urea is used as the reducing agent.
Diesel Exhaust Fluid (DEF)
Diesel engines with SCR systems use a special Diesel Exhaust Fluid (DEF), known by various brands such as Z Dec, AlliedBLue, GoClear, or AdBLue: a non-toxic solution of 32.5 per cent urea in deionized water. This fluid is stored in a separate container and sprayed into the exhaust stream of diesel vehicles to cause a chemical reaction that breaks down NOx into nitrogen and water. This is how
modern diesel engines are able to meet the latest worldwide emission standards (including Euro 5 and 6, EPA10 and JLT05).
DEF is not toxic or harmful, but needs to be stored and used correctly. The fluid is corrosive for some metals such as carbon steel, aluminium, copper and zinc. If you spill a small amount of DEF, it can be washed away with water or wiped up. If you leave it to dry it will turn into white crystals. These can be washed away with water.
DEF must only be poured into the vehicle’s separate tank, and must not be put into the fuel tank and is not to be mixed with any additives or diluted with water. The filler nozzle is usually coloured blue and designed to have a smaller filler tube, as to not confuse it with the diesel fuel filler nozzle at filling stations.
Due to the corrosive properties on steel, it’s a very big deal if exhaust fluid is put into a fuel tank (petrol or diesel) by mistake. To minimise contact damage, don’t start the engine or, better still, don’t turn the ignition on to the start position, as this will only send the fluid through the pumps toward the engine and the potential for serious damage is accelerated.
The fluid will need to be drained and disposed of correctly, and any contaminated components will need flushing or may even need replacement to avoid long-term corrosion issues. If this does happen, it’s best to consult your insurance company for advice before undertaking repairs.
The electrics of a DEF diesel will not allow the engine to be started if the fluid runs out. The size of the tank has been designed so that a vehicle owner should not have to refill in between standard service intervals.
On average, one litre of DEF should last around 1000km, but usage can be higher depending on driving conditions.
Before a vehicle’s DEF tank runs empty, the driver is given a series of alerts or the remaining distance counter on the dashboard displays. As an example, when the DEF tank level drops below 10 per cent an amber warning lamp may come on, at five per cent this lamp starts flashing, and below 2.5 per cent a solid amber warning light is displayed.
DEF fluid doesn’t last forever, and has a two-year lifespan from date of production. It is essential that the fluid containers are stored between -5 degrees and 20 degrees Celsius. DEF can decompose if it is stored at 30 degrees or more for extended periods of time.
If you’re in the market for a diesel vehicle, check on what its emissions reduction method is to avoid surprises. And if you do get caught short between your service interval, DEFs can be found at most truck stops.