Basics

Often abbreviated as DEF
A Consumable Fluid Used for Selective Catalytic Reduction (SCR) systems (essentially wet scrubbers/gas-liquid contactors, but scaled down) mainly on portable diesel engines to reduce NOx emmissions
Is essentially an aqueous solution of Urea
According to wikipedia:
- an aqueous urea solution made with 32.5% urea and 67.5% deionized water
There are some issues with amonia venting off over time and it thus getting "weaker"
The injection rate of DEF into the exhaust depends on the specific after-treatment system, but is typically 2–6% of diesel consumption volume
Commercial Truck Stops Have it "On tap" ie from a pump in most cases
Most consumers get it in small disposable tanks
- Can often be "expired" with this sales model
Supposedly small issue with excess amonia out of the exhaust if dosage ratio is off (simple control issue)
This product and SCR based systems may be be irrelevant if (near)

Stoiceometric Compression Ignition (Diesel) Combustion Engines Can Be Developed+Produced (and thus standard Catalytic Converters can be used)

To-Do

Any way to sense offgassing? Also what sensors are needed, outside of standard oxy-fuel ratio sensors (ie ammonia gas sensor, liquid sensor...)
DIY Via pelletized/powderized urea? (aggricultural supply, may store better)
See how far off Stoic Diesel is, if it even is possible

Buying DEF in Bulk for a tank in your Vehicle Maintenance Bay /Parking Lot / Fuel Farm etc
- Then between having a high quality supplier + Traceability , having a Storage Tank Monitoring System + Routine Samples/Tests, you SHOULD be good
  - Granted investment vs debatable savings is probably what would kill this idea
Is this regulated akin to Fuel storage/dispensing is the other question?

In aviation, fuel tanks are tested with either a Fuel Sampler (essentially a modified Syringe ) or a Aviation Fuel Tester which is a somewhat specialized Sample Jar essentially (some of which also preform some tests themselves such as Debris Separation and Water Contamination of Fuel etc
To an extent a portable tester such as this could be used with a sample volume of DEF first before pumping it into the tank
- The main question is it as simple as an Aviation Fuel Tester (ie “no debris, no water, it’s good!”) or Ethanol-Gasoline Blends test where a Phase Separation “Crash Test” with Water works, or would it be more akin to testing Fuel Stabilizer where a proper Titration setup is needed, as well as reagents etc
- The SWAP-C of these testing kits becomes a concern too if it is intended to become a part of a driver’s VEDC etc
  - For self storage, most of that equipment could be stored in the onsite lab/in a cabinet somewhere until it is needed etc

Every so often go and fill 10x (or more if needed) Containers (potentially even reused OTS Packaged DEF Containers), after first testing the source
- These then are used in the same manner as the packaged ones (negating the need for a bulk tank), yet also the need for testing before using is not put on the drivers either
Only limitation is if there are any rules on filling non-standard containers (as some places have for Motor Fuels etc, or on how much can be transported without a Manifest (such as Propane etc)
- Especially if you use approved containers/reused DEF containers (inspected to be sure they are in “good working order/condition” etc) though it shouldn’t be TOO MUCH of an issue

The Wikipedia Page on DEF
A Duramax Forum Post Titled “DEF production / expiration explained and simplified”
- Also mentions GM Engines DO NOT work with the “Platinum” version of def
  - Uncertain if this is akin to Marine DEF where it’s more concentrated of a solution, or what?
- Also goes into detail on how to read the date codes