When is urea injected?
Laughing Gas
Joined: Oct 2013
Posts: 861
Likes: 7
From: AZ
All the time, upstream of the catalytic converter, it helps convert NOx to nitrogen and water. The amount it injects follows engine load, more fuel = more urea injection.
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https://www.google.com/search?ei=oZmPW--vHPPy9APvx4CYBw&q=what+is+nox&oq=what+is+nox&gs_l= psy-ab.3..0l10.93527.102041..102514...0.0..0.105.893.1 0j1......0....1..gws-wiz.......0i71j0i67j0i131j0i3.FMa6NSw_f0I
Laughing Gas
Joined: Apr 2012
Posts: 902
Likes: 51
From: Clark, WY
The DEF and DPF are two different animals for two different purposes. Diesel Exhaust Fluid is injected in the exhaust gas stream when Nox emission is to high. It is a chemical reaction.
The Diesel Particulate Filter filters out the soot (black smoke, i.e. rolling coal) from the exhaust gas. When the DPF is full the engine injects raw diesel into the exhaust stroke of the cylinder to fuel a burn-out of the filter. It cremates the particulates from the filter media with fire. This is called a regeneration or regen for short. Yes, we are still cavemen using fire.
The Diesel Particulate Filter filters out the soot (black smoke, i.e. rolling coal) from the exhaust gas. When the DPF is full the engine injects raw diesel into the exhaust stroke of the cylinder to fuel a burn-out of the filter. It cremates the particulates from the filter media with fire. This is called a regeneration or regen for short. Yes, we are still cavemen using fire.
Lead Driver
Joined: Nov 2005
Posts: 5,239
Likes: 4,257
From: Kaysville Utah
Pretty well discussed above.
NOx is created by High Combustion Temps. So when you are idling at 300°F you are not injecting DEF because there is little NOx
When your turbo is at 15 psi boost and you are climbing a 5% grade your EGTs jump to 900°F and you probably are injecting DEF to reduce the NOx created by the higher combustion temps,
The amount of DEF injected is totally dependant on how much NOx is being produced. And that is dependant on the combustion temps in the cylinders
NOx is created by High Combustion Temps. So when you are idling at 300°F you are not injecting DEF because there is little NOx
When your turbo is at 15 psi boost and you are climbing a 5% grade your EGTs jump to 900°F and you probably are injecting DEF to reduce the NOx created by the higher combustion temps,
The amount of DEF injected is totally dependant on how much NOx is being produced. And that is dependant on the combustion temps in the cylinders
Hotshot
Joined: Apr 2013
Posts: 10,123
Likes: 657
From: NH
When your DEF is frozen (truck sits overnight with temps less than 12F) you definitely aren't injecting any for a little while!
EGR is used to lower cylinder temps and balance the need for DEF. But essentially, DEF is used all the time to varying "dosing" amounts. I believe the DEF injector is turned off during a regen because it would serve the purpose of lowering exhaust gas temp before it hits the DPF.
EGR is used to lower cylinder temps and balance the need for DEF. But essentially, DEF is used all the time to varying "dosing" amounts. I believe the DEF injector is turned off during a regen because it would serve the purpose of lowering exhaust gas temp before it hits the DPF.
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Lead Driver
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From: Kaysville Utah
Hotshot
Joined: Apr 2013
Posts: 10,123
Likes: 657
From: NH
That is only true for cab and chassis models. Pickup versions have the order as DOC-SCR-DPF.
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