Equipment Type

SCR Demands on Maintenance Strategies

Selective catalytic reduction will be more common in off-road engines, but changes in maintenance requirements may not be extensive

February 22, 2013

Reprinted with the permission of Equipment Manager magazine, the magazine of AEMP.

As engine and equipment manufacturers launch new generations of equipment to meet U.S. EPA Tier 4-Interim and -Final emissions regulations, equipment managers can rest assured that using new Tier 4-certified machines will have minimal impact on operations or maintenance.

To satisfy Tier 4 requirements, manufacturers face the dilemma of designing equipment to deliver maximum power and productivity, while also dramatically reducing particulate matter (PM) and nitrogen oxides (NOx) emissions.

When the engine is operating most efficiently for power, it produces minimal PM, but NOx levels are very high. Conversely, when cooled exhaust gas is recirculated back into the intake, NOx production is reduced but PM levels rise.

Engine manufacturers have two basic choices to achieve mandated emissions levels. Selective catalytic reduction (SCR) reduces PM formation in the combustion chamber and treats exhaust gases with diesel exhaust fluid (DEF) to eliminate pollutants. Cooled exhaust gas recirculation (CEGR) recirculates exhaust back into the engine to reduce NOx formation, and uses a particulate filter to capture pollutants.

Maintenance of SCR Technology

SCR technology has been well accepted for several years for on-highway diesel applications throughout North America and Europe. Most truck engine manufacturers have chosen SCR as their solution for reducing emissions. This proven technology has accumulated some 30 million highway miles on its way to becoming a trucking industry standard. SCR FAQs

In an SCR system—whether used for on- or off-highway equipment—the engine is tuned for maximum efficiency. The higher combustion temperatures reduce PM levels but increase NOx levels. SCR is an aftertreatment-only system that creates a chemical reaction by adding DEF, which is a urea formulation. This transforms the NOx into nitrogen and water, which occur naturally in the atmosphere. The SCR aftertreatment system includes a DEF supply module, a DEF tank, a dosing module and an SCR catalyst. No particulate filter is required because PM levels are low due to the higher combustion temperatures.

Rather than interfere with engine performance, SCR actually improves performance, because it allows the engine to breathe more freely. In fact, in many applications, SCR delivers enough improvement in fuel economy to offset upfront cost increases within the first year of operations.

Maintenance for SCR machines is easier than most fleet managers could ever have anticipated. The SCR system only requires regularly filling the DEF tank. A warning light signals when the diesel exhaust fluid level is running low. Refilling the DEF tank can be done as part of regular maintenance when checking fluid levels, or when refueling. Filters in the DEF circuit are usually easy to access and have a maintenance schedule equal to engine oil.

Equipment managers will notice little change in the cost or complexity of maintaining SCR-equipped machines. For example, these machines will continue using standard oils without any concern for switching to low-ash oils or other more expensive formulations. Fuel usage is not an issue because SCR engines do not require any special fuel.

Diesel Exhaust Fluid

DEF is a liquid-reducing agent that reacts with engine exhaust in the presence of a catalyst to convert smog-forming nitrogen oxides (NOx) into harmless nitrogen and water vapor.

DEF consists of high-purity urea (pure urea is solid at room temperature), dissolved and suspended within demineralized water. The ratio of the mix is approximately 32.5 percent urea and 67.5 percent water. The reason for the 32.5 percent solution is that it provides the lowest freeze point. If the DEF should freeze, the urea and water will thaw at the same rate, ensuring the solution does not become diluted. Field experience in North America has shown no significant problems with cold storage or cold starting and operating.

Urea is a nitrogen compound that turns to ammonia when heated. It is used in various industries, including as a fertilizer in the agriculture market. The urea used in agricultural applications is not as pure as the urea used in the production of DEF.

Because DEF is nontoxic, nonpolluting, nonflammable, nonhazardous, stable, colorless and has about the same alkalinity as baking soda, it is safe to handle and store. Equipment managers will need a strategy for monitoring DEF use, maintaining adequate inventories and storing it properly. We recommend indoor storage of DEF to help ensure constant storage temperatures. (See how Kokosing is handling DEF.)

Three years ago, DEF was not commonly available, but with the rapid development of a DEF market for use in over-the-road trucks and consumer vehicles, its availability is no longer a concern. Bulk suppliers can deliver DEF in tanker trucks, much the same as equipment fleets buy bulk fuel for storage at their shops and equipment yards. Retail availability is constantly expanding. DEF is available through the majority of truck stops and many equipment-related retail businesses throughout the country.

CEGR Machine Maintenance

CEGR technology requires maintenance of the diesel particulate filter (DPF), including regeneration, and changes in oil and fuel requirements. It is designed to last for thousands of hours, and it is accessible for easy replacement.

Typically, CEGR machines go through passive and manual regeneration cycles to heat the DPF to burn off accumulated particulates, which results in longer DPF life and improved performance. On many machines equipped with CEGR technology, passive regen occurs periodically during normal operation and has little impact on the operation. Manual regeneration, which sometimes is required daily depending on the application and nature of operation, takes 10 to 20 minutes and only requires the operator to ensure the machine is clear of combustibles before starting.

Some CEGR systems require the use of higher-spec, more expensive oil to deal with the effects of higher soot levels that result from lower combustion temperatures. Most manufacturers recommend using oil that meets the API CJ-4 oil specification. CJ-4 oil exceeds previous performance requirements and is specifically designed to protect emission control systems, help comply with emission standards, reduce engine wear and control piston deposits and oil consumption.

Also, CEGR engines with diesel particulate filters should use ultra-low-sulfur diesel fuel (15 ppm maximum sulfur) because even small amounts of sulfur can impair the filters’ effectiveness.

Because of the increased cooling requirements with CEGR systems, equipment managers and technicians will notice engine design changes such as larger oil coolers, larger oil pans, larger water pumps and radiators, and additional coolers. Although some CEGR-equipped machines will require more frequent oil changes, most manufacturers are increasing engine oil capacities to lengthen oil-change intervals.

Naturally, maintenance requirements vary by manufacturer and also by type of equipment. Equipment operating manuals have been expanded to cover Tier 4-Interim maintenance and service issues for vehicles that have either SCR or CEGR emission control systems. Technician training also is available through a variety of sources, including dealers, printed materials and online courses.

The bottom line in managing maintenance needs for Tier 4-compliant equipment is following practices that help achieve lower total cost of ownership, better performance and improved productivity.

Brad Stemper is solutions marketing manager for Case Construction Equipment.

 
 

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