There was time, not long ago, that “exhaust fluid” was a term that technicians used to joke around with unsuspecting car owners. Muffler bearings, blinker fluid, and fuel injector joints are just a few more of the made up parts that keep your local car guy entertained. I guess that the joke is on us. Exhaust fluid is now a real thing. I wouldn’t hold my breath waiting for blinker fluid.
Diesel exhaust fluid, (DEF) is a liquid that is made up of about 32.5% urea (cow urine) and deionized water. DEF is pumped into the catalytic converter for the purpose of lower emissions.
A catalytic converter consists of a combination of the precious metals palladium, platinum, and rhodium. It is located in the exhaust system, and all of the exhaust that leaves the engine goes through the catalytic converter. As exhaust passes through the catalytic converter, a chemical reaction between the exhaust gases and these metals lowers emissions at the tailpipe. In the USA it’s against the law to remove the catalytic converter from a vehicle. Catalytic converters are on all cars and trucks, whether it runs on gasoline or diesel fuel. Only diesel powered vehicles use DEF.
DEF is pumped into the catalytic converter from a storage tank. As it enters the catalytic converter it atomizes, which means that it is converted into very small droplets. The heat from the exhaust causes the urea in the DEF to separate into carbon dioxide and ammonia. This process converts the nitrogen oxide in the exhaust gases and the ammonia into nitrogen and water.
The reason for this is that nitrogen oxide is a pollutant, and it’s the toughest pollutant to curtail in a diesel engine. So due to the chemical reaction with DEF, water and nitrogen shoot from the tailpipe rather than nitrogen oxide.
That’s it. Short and sweet.
This is the reason that exhaust fluid has actually become a real thing. I would suggest to all you diesel guys that you use OEM DEF. Using what the manufacturer recommends guarantees that you’ll get the best results. I’d be worried about what effect aftermarket fluids might have on diesel particulate filters and on the regenerative process. You don’t need to go to the dealer to purchase OEM DEF, you can get it online. Amazon carries most of them.
