Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/908212
AGGREGATES MANAGER / December 2017 17 engines," says Ryan Cawelti, manager of Worldwide Engine Market Planning at John Deere Power Systems. "John Deere has been on a journey to deliver engines that meet Final Tier 4 emissions over the last 20 years. We have used a building block approach that has allowed us to add scalable technology to meet each subsequent emissions regulation." The industry introduced a combina- tion of technologies and aftertreatment systems to meet Tier 4 regulations. To achieve the needed Nitrogen Oxide (NOx) and particulate matter (PM) reductions, different combinations of the following technologies are used: High-pressure common rail (HPCR) fuel system: The HPCR fuel system was introduced during the Tier 2 emissions phase and provides constant control over fuel injection vari- ables such as pressure, timing, duration, and multiple injections. The HPCR fuel system provides higher injection pressures, resulting in more efficient combustion, which, in turn, leads to a reduction in particulate matter. Cooled-exhaust gas recirculation (EGR): Cooled-EGR was introduced with the start of the Tier 3 engines. The sys- tem mixes measured amounts of cooled exhaust gas with incoming fresh air back into the intake manifold to lower the engine's exhaust temperature, thereby reducing NOx emissions to an acceptable level. The use of cooled-EGR enables smaller SCR systems when used to meet Tier 4 emissions regulations. Diesel oxidation catalyst (DOC) and diesel particulate filter (DPF): Many Tier 4 engines feature an exhaust filter that contains a diesel oxidation catalyst and a diesel particulate filter. The DOC reacts with exhaust gases to reduce carbon monoxide, hydrocarbons, and some particulate matter. DPFs operate in conjunction with a diesel ox- idation catalyst that is located upstream of the particulate filter. The downstream DPF forces exhaust gases to flow through porous channel walls, trapping and holding particulate matter. Trapped particles are eventually oxidized within the DPF through a continuous cleaning process called passive regeneration, using exhaust heat created under normal operating conditions. Selective catalytic reduction (SCR) system: The SCR system uses a urea-based additive, often referred to as diesel exhaust fluid (DEF). DEF is injected into the exhaust stream prior to the SCR catalyst, which then converts NOx in the exhaust stream into nitrogen and water, helping to further reduce NOx emissions. Each of these systems dynamically interact with each other to adapt to various operating conditions and ensure Tier 4 emissions compliance. Three practices for a well-performing system There are three primary maintenance practices operators should keep in mind with Tier 4 engines: system cleanliness, proper storage and handling, and using the correct materials. 1. System cleanliness: Cleanliness is essential when using diesel exhaust fluid (DEF) to ensure reliability of the SCR system. This includes making sure storage tanks and any equipment used to handle or transport DEF are clean and free of debris. "Treat the DEF circuit like a hydraulic circuit. Taking precautions to preserve the cleanliness of the fluid will help ensure a trouble-free system in the long run," says Bryan Wood, manager of OEM Applications at John Deere Power Systems. Ensuring a clean system also includes setting aside containers to use only for DEF. Operators can benefit from using specialized DEF equipment, such as totes, stainless steel pumps, and fuel lines, as DEF can be corrosive to certain materials such as steel, iron, zinc, nickel, copper, aluminum, and magnesium. DEF contamination, even with trace amounts of metals, can damage the catalyst in the SCR system. 2. Proper storage and handling: Proper storage and handling of DEF are critical, as they can directly im- pact the fluid's quality. "Users should be aware that there is a shelf life for DEF, and it will start to degrade de- pending on how well it's preserved during storage," Wood says. DEF freezes around 12 degrees Fahrenheit, and it cannot be directly exposed to sunlight. However, DEF can still be used, even if it freezes solid. On the engine or equipment, the DEF tank is equipped with a heating element that uses engine coolant to thaw DEF in temperatures below 12 degrees Fahrenheit. Do not use antifreeze fluid products to win- terize pumps, nozzles, and hoses, as the residual antifreeze fluid can damage the SCR system. 3. Using the correct materials: The last maintenance practice users should observe is using the correct materials, including fuel and engine oil that is specified for off-highway applications. Through the various off-highway emissions stages, engine oil has been specifically formulated to reduce the buildup of ash in the diesel particulate filter, which differs from engine oils used for on-highway vehicles. Using the correct fuel, although routine, is crucial in keeping the exhaust system running smoothly on a Tier 4 engine. "Fuel filtration needs have increased as we've moved to high-pressure common rail fuel systems. Using diesel fuel that meets operator manual specifications is essential to assure adequate filter life and keep the fuel system operating efficiently," Wood says. "In addition, excess sulfur content in the fuel will reduce efficiency of the SCR system and lead to diagnostic trouble codes and unscheduled machine downtime. It is critical to use fuels with sulfur contents that meet ultra-low sulfur diesel (ULSD) specifications." Other than taking extra precau- tions to ensure system cleanliness and proper storage, other basic maintenance practices, such as abiding by proper service intervals and using the correct fluids, remain the same from Tier 3.