Diesel is in the news lately, and for the wrong reasons. At least from VW’s viewpoint. What seems to be the main reason for this unhappy situation is the fact that most VWs don’t use urea injection, whereas other diesel manufacturers (like Mercedes) do.
What IS urea injection anyway? Well, it all comes down to chemistry and molecular hookups in a hot and noisy place, much like your average downtown bar scene.
The problem with diesel engines is that besides the ba dah boom in the cylinders that make the wheels go round and round, the whole combustion thing creates nitrous oxides; combinations of nitrogen and oxygen. These are the guys that when set free in our lovely towns and countryside help create the thick brown smog that nobody but nobody appreciates. Yuck.
So the question is, what to do about them? And the clever answer is to counsel those N’s and O’s to break up and start associating with more socially conscious atoms. How? Through the matchmaker known as catalysis. Once injected in to the exhaust stream, the urea vaporizes and produces ammonia (four cute hydrogens plus a single nitrogen atom). The ammonia and nitrous oxides are then persuaded to reassemble into … plain old nitrogen and water! Most of what we breathe is plain old nitrogen so that’s an easy win. And water is water, nothing wrong there.
And that’s roughly the size of it. Mix urea into the exhaust and produce emissions goodness. Of course, that means your car needs a tank for the urea and it needs to be refilled occasionally. Kind of like you have to refill your gas tank, just way less often. The extra plumbing and hardware costs money, takes up space and weighs the car down. That’s not necessarily a deal killer but when you’re trying for lightweight, lots of space and cheap, it doesn’t help your cause. And that’s the reason VW decided they’d try and avoid that whole urea scene in the first place and solve the problem with good old fashioned ingenuity.
Which apparently is a synonym for cheating.