Editor’s note: The second in a two-part series of articles discussing new Tier 4 emissions requirements and technology to meet them.
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|Mechanics Corner: Tier 4 Interim technology solutions take different approaches|
|Columns - Mechanics Corner|
|Friday, 16 September 2011 07:33|
In this article, we’ll take a look at technology solutions manufacturers are employing to achieve Tier 4- mandated emissions reductions.
Agricultural producers should understand the basics of the two technologies being implemented to meet Tier 4 Interim requirements: selective catalytic reduction (SCR) and cooled exhaust gas recirculation (CEGR).
In an SCR system, the engine is tuned for maximum efficiency. The higher combustion temperatures reduce particulate matter (PM) levels but increase nitrogen oxide (NOx) levels. SCR is an after-treatment-only system that creates a chemical reaction by adding diesel exhaust fluid (DEF).
This transforms the NOx into nitrogen and water, which occur naturally in the atmosphere. No particulate filter is required because PM levels are low due to the higher combustion temperatures.
SCR allows for a quiet system that is separate from the main engine function and does not compromise horsepower or torque. It does not interfere with engine performance and actually improves performance, because it allows the engine to breathe more freely.
The SCR after-treatment system requires the addition of diesel exhaust fluid (DEF). The after-treatment system is composed of a supply module, a DEF tank, a dosing module and an SCR catalyst.
The second technology option for meeting Tier 4 Interim requirements is the cooled exhaust gas recirculation approach. In a CEGR system, exhaust gases are cooled, blended with fresh air and then returned to the cylinder, lowering combustion temperatures and dramatically reducing NOx.
The cooler combustion temperature results in a higher PM level, which is then reduced through the use of an after-treatment diesel particulate filter (DPF) system.
The DPF requires periodic regeneration for optimal operation. This re-gen process is usually automatic, without requiring operator intervention.
Clean-burning small engines already Tier 4-certified
As we get closer to Tier 4 Final standards for small engines, we expect to see solutions that combine external EGR with after-treatment provided by a particulate oxidation catalyst (POC).
Tier 4 Interim is a three-year to four-year rolling requirement, the first phase of which became effective on January 1, 2011, for off-road diesels of more than 174 hp (130 kW). Tier 4 Interim requirements for engines down to 75 hp (57 kW) take effect in 2012.
Technology approaches will differ because large engines run hotter than small engines, which means the small engines won’t have as many cooling-related issues to address. Another potential solution for small engines will take a kind of “EGR-lite” approach, including the use of a DPF but without the need for an additional cooling apparatus.
SCR boosts fuel economy
Tier 4 technology will not add any complexity to the operation of the machines. Operators will find it easy to check DEF levels on SCR-equipped machines and to check the DPF on a machine featuring CEGR technology.
SCR is low on maintenance but does require filling the DEF tank every third time you fill the fuel tank. There’s some thought being given to providing an extra DEF supply with the machine.
One operational difference operators will encounter in machines with CEGR technology is the occasional need for letting the CEGR system actively regenerate the particulate filter, which requires taking the machine out of its application and parking it in a safe location during the re-gen process. This can usually be done at the beginning or end of a work shift and will typically require about 30 minutes to complete.
Of the new models we introduced since January 1, 2011, Case F Series wheel loaders use an SCR solution, and Case C Series excavators use a CEGR solution.
We see advantages to both technologies, and we are applying the solution that achieves the lowest operating costs, depending on each model’s engineering characteristics and application requirements. Our solutions integrate each model’s engine, hydraulic and electronic systems to achieve the most efficient and powerful performance.
Eventually, we expect to migrate equipment to SCR technology as we approach the deadline for Tier 4 Final certification. This will involve coordination and planning among our global product development partners.
By choosing models that use SCR to achieve Tier 4 Interim certification, agricultural producers can be confident of achieving the benefits today of what we believe will be the standard technology for years to come.
More Tier 4 information
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