DEF Diesel additive?

I know its not a fuel additive and is used to keep the cat convertor clean but is it used only in large 18 wheeler type trucks or are there some late model cars and trucks that have a DEF tank?

All new diesel pickups have it and a few cars do as well. I don't know which cars, but a few diesel cars do require DEF.

Mercedes diesels use it. Maybe VW also. It is basically a solution of urea (fertilizer) and water.

It's actually an 11% ammonia and distilled water mix, if I recall.

Problem is commercial (neat) ammonia sometimes isn't pure enough to use without building crystal deposits on the injector and substrate.

We used to mix our own in the lab. Cost $0.11/gallon to make.

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It's actually an 11% ammonia and distilled water mix, if I recall.

Problem is commercial (neat) ammonia sometimes isn't pure enough to use without building crystal deposits on the injector and substrate.

We used to mix our own in the lab. Cost $0.11/gallon to make.

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Kinda sorta. Diesel Exhaust Fluid is really 1/3 urea (a nitrogen compound that TURNS to ammonia when heated) and 2/3 distilled/deionized water. When injected into the exhaust stream (think "after treatment") into a catalytic converter-type burner it very effectively consumes harmful oxides of nitrogen from the exhaust.

The beauty of this system, while cumbersome, is that it's an AFTERTREATMENT approach. Why do I stress this? Simple--the engine doesn't know it's there. Period.
What does that mean? Simple--the engine can be tuned for max mpg and power without regard to oxides of nitrogen.
That's a beautiful thing.