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Aftertreatment System Designs Will Evolve to Meet Customer and Emissions Requirements
The cross section of a compact, fully insulated Stage V/Tier 4 Final DOC+DPF+Mixer+SCR system.
DONALDSON COMPANY INC.
Increasingly stringent emissions regulations and customer needs will bring about the need for new aftertreatment system technologies. By Sara Jensen
Aftertreatment systems have become an integral component of engines today due to the implementation of increasingly stringent emissions regulations. “In the last decade, aftertreatment systems used by our global OEM customers have become increasingly complex and more densely packaged,” said Korneel De Rudder, Development Manager, Europe at Donaldson Co.
This increased complexity is necessary to meet the ever-tightening emissions standards being implemented in the U.S., Europe and other parts of the world he said. “As a result, there are more catalysts and sensors incorporated into a given package size,” De Rudder explains. “For many off-road machines, because under-hood space is limited, we need to be creative to fit these new components onto the machines–and the components need to be more densely packaged.”
Donaldson has focused on developing components and systems which allow for less “dead” volume
JOHN DEERE POWER SYSTEMSEngine manufacturers continue to advance aftertreatment and
engine designs to meet current and future emissions regulations.
inside the afterteatment system. “With earlier generation systems, ‘dead’ volume was often used to increase the residence time of the DEF (diesel exhaust fluid; also called AdBlue), which enhanced its decomposition and mixing in the exhaust gas,” he said.
Determining how to develop and use the aftertreatment system is integral as well, said Alex Eden, Product Marketing Manager for Small Engines at Perkins Engines Co. Ltd. Manufacturers can choose to have a smaller diesel particulate filter (DPF) and larger selective catalytic reduction (SCR) or vice versa. They can also choose to focus their development efforts on the combustion system to make it a very clean system, which helps to reduce emissions and can help reduce the size of the aftertreatment system. “You have to think of aftertreatment as part of the entire system and take a systems approach that looks at satisfying the customer’s need for power, product, price and packaging, while also meeting emissions standards.
Mark Borst, Product Marketing Manager for Large Engines at Perkins Engines Co., said that when Tier 4 Final came into effect in the U.S., the company chose to include a DPF on its larger engines even though it was not required to meet the regulation. The company felt including a DPF was beneficial for meeting the emissions regulation and allowed it to commonize its engines once the EU’s Stage V standard was put in place.
“OEM customers buying our engines, Tier 4 Final or Stage V, get the same installation. They know the size, they know the package, they know what they have to accommodate,” said Borst. “Aftertreatment is just as integral to their machine as it is to our engine.”
Recent advancements in aftertreatment systems
Eric Hruby, staff engineer, Power Unit Development at John Deere, said that since the implementation of Tier 4
Final, the company has worked on advancing its aftertreatment system designs based on real-world experiences and customer feedback. “Our efforts have been focused on improving customer value in vehicle integration, visibil-
ity, service life, product reliability and fuel consumption,” he said.
To help ease installation and improve visibility, the company has integrated the diesel oxidation catalyst (DOC) and DPF, as well as the SCR and ammonia oxidation catalyst (AOC) into a single module. Development of a compact DEF mixer is a key technology enabler, which allowed John Deere to achieve this more compact aftertreatment system design. In addition, the company was able to use an advanced SCR coating on high porosity substrates to improve SCR catalyst activity. This reduced thermal mass and pressure drop to help broaden the operating temperature window for effective oxides of nitrogen (NOx) reductions in a smaller package said Hruby.
Improving the washcoat and substrate of the SCR over the years has benefited packaging of the aftertreatment. Doing so even by a small percentage enables better engine system optimization by either increasing power for the same package size or decreasing package size to fit into compact machines, said Eden.
Combining the SCR and DPF functions into a singular SCR-on-Filter Substrate (SCRoF) is becoming more common as a means of meeting system packaging challenges said Gary Simons, Engineering Director, North America at Donaldson Co. Inc. “Because SCRoF substrates have higher porosity than DPFs and SCRs, they are more fragile. Canning them requires careful management of the installation forces and the substrate mat holding pressures.”
As aftertreatment system packages get larger and more complex, De
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Rudder also noted they tend to have more surface area. This larger external surface can lead to heat rejection issues. Proper insulation will become more critical and those designs will need to be refined. DEF/AdBlue mixing is an important aspect of aftertreatment systems, as well, said De Rudder. “It is commonly expected the ammonia (NH3) uniformity requirements need to exceed 0.990 to meet emission standards. This level of performance is expected with little or no DEF/AdBlue crystallization.”
This crystallization is a recurring challenge with many aftertreatment systems he said. While some crystallization is possible, minimizing its occurrence and impact is the goal for all equipment manufacturers. De Rudder said the industry currently struggles with defining a specification for consistent testing of crystallization. However, Donaldson has developed its own test cycle to measure crystallization so it can apply appropriate mixer solutions to minimize its occurrence.
“Because it is more likely to generate crystallization/deposits during challenging duty cycles, at Donaldson we often recommend that mixers are designed to allow for effective function even during demanding duty cycles – rather than an unoptimized system that will result in a greater risk of deposits,” said De Rudder.
Compact, modular exhaust gas aftertreatment systems have become essential in the off-highway equipment industry said Klaus Schrewe, Head of Innovation and Strategic Product Management, HJS Emission Technology GmbH & Co. KG. This is due to the numerous applications within the industry that have their own unique needs and machine designs. Having a compact and modular design allows OEMs to place the engine and aftertreatment system in a way that best
fits the design of a piece of equipment without impacting operator visibility or machine performance.
“The range of user profiles in the NRMM (non-road mobile machine) area is much wider than in on-highway applications, from extremely long lowload operation to almost continuous full load,” said Schrewe. “
He said the company has used a simulation-based development cycle in combination with testing rigs to meet specific customer requirements. Doing so enables the company to develop systems with a high degree of maturity in a short amount of time even when the customer has complex requirements.
Further technology developments will be necessary
“During the last 15 years, global emission regulations have evolved rapidly,” said De Rudder. “Because the industry rushed from one legislation to the next, this may have led to some over-engineering, with little time devoted to cost and product optimization.”
However, now there is more time being given between emissions regulations, which is better enabling the industry to optimize aftertreatment systems and harmonize between different platforms he said. OEMs too have been better able to focus their design efforts on optimized products and functionality instead of meeting tight emissions regulation deadlines.
Additionally, many in the industry see passenger car and heavy-duty on-highway standards merging at the EURO 7/VII level. “If, and when, this happens, there will be questions regarding how the next Stage/Tier off-road standards can be harmonized with the on-highway EURO VII limits,” said De Rudder and Simons.
In general, further technological developments will be necessary for aftertreatment system designs whether that be to meet customer requirements or future emission regulations.
Going forward, Hruby said John Deere sees a need in the industry for advancements in SCR catalyst technologies, as well as improved selectivity of ammonia oxidation catalyst, DEF mixing and exhaust sensing technologies.” |
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