[MRO1791]

Is DEF usage linear with respect to miles driven, or is it based on engine speeds and miles driven?

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.

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[MRO1791]

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.

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, now 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.

 

[MRO1791]

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.

Your 09 Jetta had the LNT system.. that was an NOx Absorber, and it would absorb NOx (until tested!, it was not doing many regens, due to the cheat) then it would regenerate using fuel in the exhaust stream to react with the NOx to produce N2 and water... making the NOx "trap" ready for more action.

The SCR is totally different.. it is a catalyst bed, where the DEF can react with NOx in the exhaust stream. It never absorbs NOx, so it is never needing a "clean". The reason why the EPA mandates the warnings and reduced power if the DEF runs out, is because without the DEF, there is no absorption of the NOx, and hence no controls of NOx emissions, or very little, the EGR is another way to limit NOx production in the combustion chamber, and the new Diesels are running lower compression ratios which also helps limit NOx in the combustion process. EGR has been very problematic in other ways, and they are looking to not use EGR in the future, but I thing SCR will be around for the long haul.

Your 06 Cummins would not have been made with any of this stuff, the requirements came in force in 07.5, and the first trucks had many, many issues.

The DPF Regen uses fuel primarily to attain the very high temperatures needed to complete the burn on the accumulated soot, the fuel use in that case is to get the temperatures up to burn the soot.. where with the LNT trap temperature was only part of the action, the other was the need for the un-burned hydrocarbons to react with the absorber to chemically combine to produce N2, CO2, and water.. and with that clear out the accumulated NOx in the trap.

The LNT on my Cummins ('09) requires more than 30 minutes to complete a regen, on the Gen 1 Cruze its at most 20 minutes, and that difference is largely due to not having the LNT, the SCR is much better technology, but more complex, more expensive, and hence the VW cheat which literally saved $330 per car.. had they done SCR back in 2009, and not cheated they would have been much better off.. but they also saved $600 per car to use a very crappy HPFP that had epic failures... so I'm glad I got rid of that car fast once the data started adding up.

 

[MRO1791]

bad def isnt a thing.

its company policy to fill the def in our trucks daily

we carry jerry cans of def for when fuelling in the bush (no def available) that def could be in that jerry can for months

ive still yet to see a truck or meet a mechanic that has worked on a truck that has been down due to bad def.

As cold as it is in Canada might be why. DEF does have a shelf life, but when cold, or frozen it can last indefinitely, at high temperature it does break down, perhaps Canada doesn't have high temperature long enough for it to ever become a problem.. but a low miles Florida car could be a totally different thing altogether.

https://www.google.com/url?sa=t&sou...UDKkQFggwMAM&usg=AOvVaw2colFaMdas_6wZwiX2-1Wl


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[MRO1791]

ive still yet to seen proof of this or heard of it.

youd need 100f for 6mos 24hrs a day for it to degrade

the vehicle would simply dose more def to get the job done.

There have been issues..http://www.thedieselstop.com/forums/showthread.php?t=299707

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[MRO1791]

because its never bad def.

Just because you haven't seen it, nor does it seem to be a frequent occurrence, that does not mean "its never bad". That is objectively false. If you say it is unlikely, and you have never seen it, or that is seems it has never been proven in your experience.. that is OK, but you are incorrect and just factually WRONG to say it is "never" bad. It does degrade over time, and it degrades based upon storage temperature and exposure to light.. so some DEF sitting on a shelf in a warm, bright place for a couple of years, then put in a car, is quite likely to be be an issue.. Certainly it would be ill-advised to tell someone to not worry about old DEF that was kept in a warm bright place. That is the point. You tell people here is is "never" bad and you are leading some to eventually find out the hard way that it can be, in perhaps rare, even unlikely circumstances.. but it's just not true to say "never". Words matter.

https://www.cumminsfiltration.com/sites/default/files/MB10033.pdf

From this document, and it can be found in many other places:

Q. What is the shelf life of DEF?
A. The shelf life of DEF is a function of ambient storage temperature. DEF will degrade over timedepending on temperature and exposure to sun light. Expectations for shelf life as defined by ISO Spec22241-3 are the minimum expectations for shelf life when stored at constant temperatures. If storedbetween 10 and 90 deg F, shelf life will easily be one year. If the maximum temperature does not exceedapproximately 75 deg F for an extended period of time, the shelf life will be two years.

Q. What impact will exposure to high temperatures for an extended periodof time have on DEF?
A. While DEF exposure to constant, high storage temperature may have some impact on shelf life, thisshould not concern operators. Extensive testing in very hot climates has been conducted confirming thatDEF stored at a constant temperature of 95 deg F had a shelf life of over 6 months.

Q. What happens if a non-DEF substance is accidentally entered into theDEF tank?
A. The SCR system will recognize solutions other than DEF, and the DEF indicator light will appearnotifying the driver. Depending on the level of contamination in the tank, the vehicle may requireservicing.

 

[MRO1791]

I've been going >5000 miles to a DEF tank refill, so I am curious ax to how the OP could be using so much DEF? one round trip to FL, approx 3000 miles total did not require a DEF top off, but when I did, it only took about 2 gallons, not even the whole 2.5 of Ad Blue I had.

I also use very little DEF..but the general rule is 2-3% of fuel use, and a big variance for driving patterns. I think it uses more DEF on coasting and idle than highway under load also. Conditions where there is excess oxygen in Combustion, thus light throttle.. ironically that would imply better MPG, but it also implies speeding up and slowing down.. hence more likely city where the overall MPG is less. Many factors affect DEF usage.

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[MRO1791]

If you guys were smart. You'd be hitting the truck stops for def. They have them at the pumps. Which means a nozzle instead of a jug. AND, it's 50% cheaper at least.

You don't see or hear of semi's buying the expensive box crap and trying to fill their 20 gallon tanks. That would cost twice as much and take 10 time longer to fill.



And that BAD DEF light. Is the same thing as the check engine light. Doesn't mean the def is bad. It means there's a trouble code.

I could see def going bad though. Specially in hotter climates. As the liquid content would evaporate and you're left with residue. For as many miles as you all get on 1 tank. I don't see any reason to actually be storing a box of the stuff though. Just fill the darn thing up every other fuel fillup.

The Cruze DEF tank is only about 4 gallons (slightly less Gen 2, slightly more Gen 1), and in most cases it will get about 5000 miles, or even much more on that small tank.. so it's not that often that it needs a fill, and even then not very much. Walmart sells a 2.5 Gal jug for about $8.. that's pretty cheap, and for many much easier to find a Walmart than a truckstop, depending on where you live of course. I only ever add a 2.5 Gal jug when it starts counting down, as it's not empty and will then take that much, but not much more. It's not worth the hassle to top it off and spill it all over the place.