Diesel Exhaust Fluid

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  • 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 urea solution
  • 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)
  • May be irrelevant if (near)Stoiceometric Diesel Combustion Can Be Reached (and thus standard Catalytic Converters can be used


  • 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

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