In 2010, EPA regulations will require an 83 percent reduction in NOx emissions from EPA 2007 emissions levels. The only way to meet 2010 emissions standards at the tailpipe is running an engine with selective catalytic reduction (SCR) technology.
How does DEF work within an SCR system?
The goal of an SCR system is to reduce levels of NOx (oxides of nitrogen emitted from engines) that are harmful to our health and the environment. SCR is an after-treatment technology that treats exhaust gas downstream of the engine. Small quantities of DEF (automotive grade urea solution) are injected into the exhaust stream and when mixed with NOx, change into harmless nitrogen and water.
What is DEF?
Diesel Exhaust Fluid (DEF) is one of the key elements involved in the SCR process. It is a nontoxic solution of 67.5 percent water and 32.5 percent automotive grade urea. DEF helps to convert NOx into nitrogen gas and water vapor. It is stable, colorless, odorless, and meets accepted international standards for purity and composition.
What is Urea?
Urea is a compound of nitrogen that turns to ammonia when heated. It is used in a variety of industries, including as a fertilizer in agriculture. Urea is naturally occurring, but is also commonly made from natural gas.
- Why not use a 100 percent urea solution? DEF provides the highest degree of practical NOx reduction in real life automotive conditions. Using DEF at a 32.5 percent solution in water is cost-effective. Also, it allows the engine to perform at the highest levels of efficiency and at the widest range of climatic temperatures – anything above 12ºF.
- With a freezing level at 12ºF., should drivers in very cold temperatures be concerned? While freezing may be one of the biggest concerns with SCR, DEF thaws quickly without changing its efficacy, and should warm-up quickly using the heat of the engine.
- Is DEF toxic or hazardous? No. By comparison, other automotive fluids such as diesel fuel, brake fluid, antifreeze and transmission fluid are all more toxic. The EPA classifies DEF as “non-hazardous.”
- How does SCR and DEF increase fuel efficiency? Since the SCR works after combustion, your engine can run at higher NOx levels. This means it can run hotter, so you won’t lose fuel efficiency to heat rejection, and there will be less particulate matter going into the DPF filter. When particulate matter does build up, you can run DPF regenerations at lower temperatures, so you burn even less fuel.
- How much DEF will I need? One gallon of DEF is used about every 300 miles. The typical tank ranges in size from 6 to 23 gallons depending on the truck’s application which means you can go up to 7,000 miles between fill-ups.
- Will my truck stop if I run out of DEF?
- No. Under no circumstances will the engine shut down or be prevented from restarting as a result of running out of DEF. If your DEF tank runs dry, a potential de-rate inducement could be activated.