Equipment World Digital Magazine
Issue link: http://read.dmtmag.com/i/885126
October 2017 | EquipmentWorld.com 50 marriage of mechanical engineering and chemistry. And the systems are de- signed to be transparent to the end user with minimal maintenance requirements, save for the DEF refills. But you need to be aware of several things: • The amount of DEF you will need to run your Tier 4 Final machine. • The most appropriate storage and dispensing protocols. • The importance of DEF purity. • How to keep your DEF clean. (Note that diesel engines 74 horsepower and below don't require SCR or DEF and use simpler technolo- gies to meet their exhaust emission targets.) Estimating DEF use DEF consumption is cal- culated as a percentage of fuel burn. Most OEMs claim 2 to 7 percent. So, an engine with SCR, on average, will go through two to seven gallons of DEF for every 100 gal- lons of fuel consumed. The variance is due to operating conditions and the balance OEMs strike between SCR and other exhaust emission technol- ogies in the engine. Most manufacturers size their DEF reservoirs to hold enough fluid to last through one to two tanks of fuel, says Brad Stemper, product man- ager, Case Construction Equipment. Backhoes and skid steers typically have smaller DEF tanks, and with intermittent use, they may only need refills engines | continued Oxidation Catalyst DEF Dosing System NH 3 Oxidate Catalyst Urea SCR PM NO x CO HC CO 2 N 2 H 2 O PM Engine Exhaust In an SCR system, the engine exhaust is piped through a series of catalysts and filters and dosed with DEF. It then exits the exhaust stack as harmless nitrogen, water, carbon dioxide and a small amount of particulate matter. On larger machines, DEF tanks (note the blue filler cap) are sized so that you refill with DEF every one or two diesel refills. On smaller machines, the DEF tank may be sized to last a week or so.