What is SCR? Selective Catalytic Reduction
SCR (Selective Catalytic Reduction) is an emissions control technology used in modern diesel engines to reduce nitrogen oxide (NOx) emissions by up to 90%. The system injects DEF (diesel exhaust fluid) into the exhaust stream, where a chemical reaction converts harmful NOx into harmless nitrogen gas and water vapor.
How It Relates to Fuel Delivery
SCR has been standard on all on-road diesel engines since 2010 and on Tier 4 off-road engines since 2014. The system consists of a DEF injection unit, a catalytic converter containing a special catalyst, sensors to monitor exhaust composition, and an electronic control unit that manages DEF dosing rates.
The chemical reaction is straightforward: DEF (urea solution) is injected into hot exhaust gases, where it decomposes into ammonia. The ammonia then reacts with NOx on the catalyst surface, producing harmless nitrogen (N₂) and water (H₂O). The system is self-regulating and requires no operator intervention beyond keeping the DEF tank filled.
For fleet operators and equipment managers, SCR systems mean one thing: you must maintain a reliable DEF supply. If the DEF tank runs dry, the engine management system will progressively derate power and eventually force the vehicle into 'limp mode' until DEF is refilled.
Why It Matters for BettyJet Customers
SCR systems in your diesel equipment require a steady supply of DEF. BettyJet delivers DEF in bulk — totes and tanker loads — directly to your site, ensuring your SCR-equipped engines keep running at full power without interruption.
Frequently Asked Questions
Does SCR affect engine performance?
SCR actually allows engine manufacturers to tune for better fuel efficiency and power, since the SCR system handles emissions reduction. Engines with SCR typically deliver 3-5% better fuel economy than those without.
How do I know if my equipment has SCR?
If your diesel engine was manufactured after 2010 (on-road) or 2014 (off-road Tier 4), it almost certainly has SCR. Check for a blue-capped DEF fill port near the fuel fill — that's the telltale sign of an SCR-equipped engine.
Related Terms
ULSD stands for Ultra-Low Sulfur Diesel — a cleaner-burning diesel fuel containing no more than 15 parts per million (ppm) of sulfur. Since 2006, the EPA has required all on-road diesel sold in the United States to meet the ULSD standard, replacing Low Sulfur Diesel (LSD) which contained up to 500 ppm of sulfur.
Dyed DieselDyed diesel — also called red diesel or off-road diesel — is standard ULSD fuel that has been dyed red to indicate it is exempt from federal and state road taxes. It is chemically identical to on-road diesel but costs significantly less because the tax (typically $0.40-0.60/gallon) is not applied.
Wet HosingWet hosing is the practice of fueling vehicles or equipment directly from a mobile fuel truck rather than from a stationary storage tank. The fuel truck pulls up to each vehicle and fills it on-site — no bulk tank, no pump, no infrastructure required.
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