[Rivergoer]

What is the capacity of the DEF tank?

Gen 1 DEF = 4.5 Gal (17.0 L)
Gen 2 DEF = 3.8 Gal (14.4 L)

 

[Rivergoer]

People generally say it's proportional to fuel use.. but knowing the kind of engine parameters that would require it, think excess air in the combustion process, with high pressure and temperature... That is what makes NOx, and DEF is injected into the exhaust to react in the SCR catalyst to scrub NOx from making it out the tail pipe.. so, think of conditions where those parameters might be met.. ironically lower engine loads, higher RPM etc.. so it's a bit more complicated to determine all the parameters that determine actual DEF consumption.

Sent from my Moto G (4) using Tapatalk

So DEF consumption is not limited solely to the regen cycle?

This is my first DEF vehicle so I’m still learning. I always assumed regen was only time DEF is consumed.

 

[Rivergoer]

No, from my research it is injected to react with the SCR catalyst and the reaction reduces NOx (though I don't think at all times, hence the NOx sensor before the SCR). The non-DEF LNT method (on my 2009 Cummins Bluetec) uses an absorption method (Lean NOx Trap). When that "trap" has absorbed all the NOx it can.. the Regen for the LNT (different from DPF regen) burns off the NOx using fuel in the exhaust stream. Since SCR uses no fuel for regen of the SCR, and uses small amounts of DEF.. the SCR technology has won the competition since it yields better MPG, and with less engine oil fuel dilution problems associated with post injection for the Regen events, no no diesels use the LNT emissions system.

https://www.dieselforum.org/about-clean-diesel/what-is-scr

Also, the 2012 Jetta I had was LNT emissions.. and the "cheat" was a big contributor to the better MPG than it would otherwise not get with the proper LNT regens taking place.

So if I’m understanding this correctly, the SCR ‘cleaning’ process uses DEF and the DPF Regen uses diesel fuel. Both processes occur independently of each other.

Correct??

This is my 3rd diesel but never had all this emissions stuff to deal with.

The 09 TDI required no DEF and the 06 Cummins 5.9 (2nd owner) was modified before I bought it so it never had any emissions stuff on it, no Cat, just a Magnaflow muffler and 4” exhaust (no emissions testing in my part of the state).

Never had a CEL in either vehicle with over 400,000 miles combined.