Extra emission controls, but with a difference.
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In efforts to keep diesel-fuelled engines on the right side of emissions laws, manufacturers are turning to more and more aggressive means of reducing the kind of bad stuff coming out of the tailpipe.

And when things like exhaust gas recirculation and diesel particulate filters aren’t cutting the mustard, something called selective catalytic reduction (SCR) is employed.

Such technology is particularly prevalent in European vehicles, where ever-tightening emissions laws are forcing the hand of manufacturers.

So, what is it? And how does it work?

AdBlue is a trading name that has gone into common vernacular, like Hoover and Kleenex. A more common name is diesel exhaust fluid (DEF), which enables that process called selective catalytic reduction. In particular, it targets your exhaust's nitrogen oxide (NOx) content and looks to reduce it.

Essentially, a bunch of sensors in your exhaust system monitor the contents of your exhaust gasses. When required, a spray of DEF is injected into the exhaust system.

This fluid, which is a solution of urea and distilled water, causes a reaction. Urea contains ammonia, which reacts with the nitrogen oxide inside a catalyst and breaks it down. So, instead of nitrogen oxide leaving the tailpipe, it’s nitrogen and water.

DEF consumption is typically very low, around 2–5 per cent of your fuel consumption. For example, a Ford Everest’s 18-litre tank will cover 2400km of driving. Other vehicles will have enough range to only require top-ups at service time.

However, it’s worth knowing that under law, a vehicle with an empty DEF fluid tank will not start. And under hard working conditions (like four-wheel driving and towing), consumption will increase along with your fuel consumption. Don’t get caught out; it’s just as bad as having no fuel.

This technology has allowed diesel-powered vehicles to remain on sale in some markets, but has also allowed manufacturers to turn up the wick, so to speak, with efficient and high-performance diesel-powered vehicles. Here’s looking at you, Audi SQ5.

Other things to know

While most vehicles have a filler point next to the fuel tank, they are sometimes tucked away in the boot. It’s worth knowing where your filler point is, and knowing how to check on the level. Often, it’s hidden somewhere within your multifunction display.

Not all diesel-powered vehicles require this system, and it depends mostly upon emissions laws for particular vehicles in different markets.

For example, Volkswagen’s early and higher-specification Amaroks with 580Nm made in Hannover Germany have selective catalytic reduction. As production has been taken over by the Argentine factory at Pacheco, the additional emission controls were removed.

As time rolls on, the availability of diesel exhaust fluid (or AdBlue) is becoming greater and greater. While some of your country and outback servos might be a bit hit-and-miss, the fact that many trucks have SCR means you should be able to find it in most places these days.

Some service stations will have AdBlue available through a bowser, which often works out to be the cheapest way to top up. Other service stations (and auto stores) will have bottles in various sizes. This is handy if you want some spare in the boot for that long road trip you are planning.

For example, Caltex has 130 locations around Australia with AdBlue available at the pump, along with 330 additional locations with bottles.

Diesel exhaust fluid has a shelf life of 12 months. We aren’t sure how bad out-of-date stuff is, but if you’ve got an ageing bottle sitting around, you might as well dump it in your tank and buy a fresh one.

Diesel exhaust fluid is another complication that serious 4WDers will need to accommodate. Along with calculating your fuel range on big trips, know how long you can comfortably go between DEF refills, and carry some extra with you.

Additionally, depending on how your four-wheel drive is designed, the DEF tank might be in an unprotected location underneath. Consider some additional protection if you're planning on dragging yourself over plenty of rocks, especially if it’s a plastic tank.

While human urine also contains urea, it’s only a few per cent (depending on your diet). The concentration isn’t strong enough to act as a substitute, and it contains all manner of other things (once again, depending on your diet) that could damage your AdBlue system. Repairs and replacement will cost well in the thousands, not the hundreds.