Diesel Exhaust Fluid (DEF), a solution of 32% automotive-grade urea and purified water, is essential for the proper functioning of a Cat Scr (Selective Catalytic Reduction) system. This system plays a crucial role in reducing harmful NOx emissions from diesel engines, helping heavy-duty trucks and equipment meet stringent environmental regulations. Understanding DEF and its role in the Cat SCR system is vital for maintaining optimal performance and compliance.
DEF: Availability and Storage
DEF, sometimes referred to as AdBlue, is widely available across the US through a robust distribution network. You can find it in bulk, at retail stores, online, and at most diesel fueling stations. Storage options vary from bulk containers to totes, bottles, and jugs. The American Petroleum Institute (API) rigorously tests DEF to guarantee it meets industry quality standards.
Onboard DEF tanks, typically ranging from 5 to 22 gallons, are easily identifiable by their blue caps and “DEF ONLY” labeling. In pickup trucks and SUVs, the DEF filler port is usually located near the fuel filler nozzle. The image below illustrates a typical DEF filler location next to a diesel fuel cap.
In heavy-duty tractor-trailers, the DEF tank is often positioned beside the diesel fuel tank near the driver’s side. However, in off-road equipment, the location of the DEF tank and filler port can vary significantly due to the diverse nature of these machines.
Preventing Misfuelling
The DEF tank fill opening is specifically designed to accept only a DEF fill nozzle, preventing accidental contamination with diesel fuel. Diesel fuel nozzles are physically incompatible with the DEF tank opening. Additionally, the blue DEF tank lid provides a clear visual distinction from the yellow or green diesel fuel cap. This design helps ensure that only DEF is introduced into the SCR system.
DEF Consumption and Refill Intervals
For light-duty vehicles, DEF refills are generally needed around the same time as an oil change. For heavy-duty vehicles and off-road machinery, the refill frequency depends on several factors like operating conditions, hours of use, miles traveled, and load factors. DEF consumption is typically around 3% of fuel consumption. For example, if a vehicle consumes 100 gallons of diesel fuel, it will likely use about 3 gallons of DEF.
Importance of DEF for Cat SCR Systems
DEF is crucial for the continuous operation of the Cat SCR system. Low DEF levels trigger a sequence of visual and audible warnings to alert the operator. Ignoring these warnings can lead to engine derating, reduced vehicle speed, and eventually, a complete engine lockout, preventing the vehicle from starting.
DEF Storage and Cold Weather Considerations
Proper DEF storage is essential, especially in temperatures below 12 degrees Fahrenheit, where DEF can freeze. Most vehicle DEF tanks and dispensing systems incorporate heating mechanisms to prevent freezing and ensure proper functionality in cold weather. This ensures the SCR system remains operational even in challenging climates.
Future of Cat SCR and DEF
The EPA’s Clean Trucks Initiative aims to implement even stricter emission standards for commercial vehicles, pushing towards near-zero tailpipe emissions. This initiative will likely lead to further advancements in SCR technology, including improved dosing strategies, catalyst design, and placement within the exhaust system. The ongoing development of SCR technology underscores the long-term importance of DEF in meeting increasingly stringent emissions regulations.
