Urea injection for diesel

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wemay

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Why do some vehicles require this, i.e., Chevy Cruze Diesel and others do not, like the Jetta TDI? What is the main purpose?
 
Originally Posted By: wemay
Why do some vehicles require this, i.e., Chevy Cruze Diesel and others do not, like the Jetta TDI? What is the main purpose?



The main purpose is to get rid of the high NOX emission on diesel. Some cars don't require it because they run rich once in a while to provide enough HC and CO to be burnt and neutralize with the NOX. With urea you do not have to do that (and in theory can run at higher efficiency overall).
 
It is a reagent in the catalytic process to get rid of NOx. In the USA, we're held hostage by California's geography and thus we can call 8 MPG SUVs "partial zero" emissions vehicles, while diesels are "gross polluters" when they return 50 MPG - and are forced to have this claptrap.

Actually Id rather have urea than not, and go another route. I think the processes to prevent NOx in diesels are worse than the aftertreatment...
 
Standard three-way catalytic converter doesn't really work on diesels, since they are stratified-charge engines that run very lean and therefore have too much oxygen in the exhaust.
 
DEF (urea in 32.5% solution with water) runs about $6/gallon in store, or under $3/gallon at truck stops with DEF pumps.
 
I would have much rather the Urea/SCR thing would have been done first instead of the EGR [censored]. I don't care for any of this stuff, but having all emissions stuff handled outside the engine is a far better way to do it than making an engine eat it's own feces. As a side note, it has been shone that they can reduce EGR because of the SCR, and this in turn allows the engine to be more efficient and in turn the DPF doesn't have to do regens as frequently. Now, if they could just do away with the EGR, things might be more tolerable.
 
Originally Posted By: Stephen M.
The Chevy Cruze does in face have a Urea injection system.

Yuck.
smile.gif
 
Chevy advises to fill every 10k mi or so. Out of curiosity, what would happen if you failed to do so?
 
The vehicle would go into a limp home mode until you refilled the urea container. I think if you go past a given number of miles with the urea system empty, it will refuse to start.
 
Originally Posted By: Wesbo
Could you pee in the tank to get enough solution to get home? I'm only partly kidding...


I wondered the same thing myself!
grin.gif
But there are sensors to check urea concentration that ensure the content of the tank is truly DEF.

I'm thinking someone ought to invent a filter that would separate the water and urea out.
 
Originally Posted By: AP9
Originally Posted By: Wesbo
Could you pee in the tank to get enough solution to get home? I'm only partly kidding...


I wondered the same thing myself!
grin.gif
But there are sensors to check urea concentration that ensure the content of the tank is truly DEF.

I'm thinking someone ought to invent a filter that would separate the water and urea out.


I've also been wondering about the same thing. Is there some kind of special diet one could go on to make himself a urea dispenser? Imagine the earnings possibilities for just doing something that comes naturally. I think we may have a solution to the unemployment problem.
 
Mazda avoided using urea injection because they created a diesel with 14:1 compression. That kept peak combustion chamber temperatures down, avoiding the higher temperatures that create NOx.
 
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