Advancing Aftertreatment

The EU Stage V-compliant 2406J engine from Perkins is 65% smaller and 63% lighter than the Stage IV equivalent, even with the aftertreatment shown on top of the engine. (Perkins)

Regulations in North America and Europe may have settled for the moment, but the pressure is still on for development in aftertreatment.

Integrating SCR catalysts on DPFs is one approach for a compact, fuel-efficient, high-performance solution. The Corning DuraTrap AT filter is shown. (Corning)

“Emissions standards continue to expand beyond U.S. EPA and EU markets with countries such as China and India moving toward increasing air quality standards,” said James Schnuriger, Product Marketing for Perkins. “The need for aftertreatment systems continues to grow as emissions standards expand across the world.”

Europe has forged ahead with its Stage V off-road regulations, ending the regulatory harmony that existed with the U.S. Tier 4 Final and EU Stage IV. “With the establishment of U.S. Tier 4 Final and EU Stage IV regulations, low NOx and hydrocarbon (HC) have been important for many years,” explained Schnuriger.

However, as worldwide regulations evolve, especially in China and India, they are forcing engine makers and their suppliers to rethink the balance between NOx, CO2, and particulate matter (PM). Particulate control, for one, is growing in importance. Schnuriger noted that the EU Stage V and future China requirements focus on reducing particulate count. Referred to as particulate number, or PN, they regulate the number of particles that tailpipes emit rather than simply its mass.

“[These] drive the need for a diesel particulate filter (DPF) to reduce tailpipe particulate-number count,” he said.

Meeting each region’s requirements while offering a global, modular solution is a challenge, he added. “At Perkins, we’ve been able to achieve this goal by offering EU Stage V and U.S EPA Tier 4 Final compliance on a common hardware set.”

At key power nodes, Perkins offers multiple and unique aftertreatment offerings to give the company’s customers installation flexibility. “In all cases, the core engine technology is common for seamless integration, regardless of the emissions standard. Our machine customers want smaller, more cost-effective solutions,” he said.

Schnuriger also thinks the technology in substrates and washcoats have continued to advance to reduce cost and package size.

“We’ve taken advantage of these technologies, along with our own patented design technologies, to deliver smaller, lighter aftertreatment systems at EU Stage V,” he said, adding that it will be important for diesel exhaust fluid (DEF) and aftertreatment systems to continue to progress to support lower temperature NOx reduction, a growing requirement for the future.

Engineering challenges

Dr. Ameya Joshi, Director of Emerging Technologies and Regulations at Corning Inc., agrees that new regulations will force a move to DPFs in off-road machinery. However, another issue is likely to create more engineering challenges: in-use emissions measurements.

“Taking a broader view, the emphasis across the world is with actual in-use emissions,” he said. This mirrors the concerns about the worldwide light-duty fleet as well as commercial on-road and off-road vehicles as well. “So, not only are the standards getting tighter, but now the emphasis will be moving beyond dynamometer-based certification cycles,” he added. “China is taking an interesting approach in that their compliance program now emphasizes in-use surveillance rather than certification processes currently used in the U.S. and Europe.”

FEV’s Integrated Turbocompounding/Waste Heat Recovery, Electrification and Supercharging (FEV-ITES) system employs a turbocompound turbine, secondary compressor, and 48V electric motor/generator. (FEV)

China also has a unique situation in the tension between regulation and enforcement. They are trying a new approach with technology. “For example, China is doing this very interesting thing of remote transmission of onboard diagnostic (OBD) data,” Joshi said. “Putting a GPS unit on the machine is in the latest regulation that is coming up in 2020, requiring transmission of the location and altitude of the vehicle or machinery.” He also notes that this in-use compliance testing means they will pull off vehicles and equipment and for random testing.

One of the key technology challenges that many experts agree on is removing NOx from the exhaust when it is at a relatively low temperature. Joshi notes there are many ways to get earlier SCR activation, when the exhaust temperature is below 180°C (356°F).

“We are looking at close-coupled SCR and integrating the SCR with the DPF as potential technologies for moving the SCR substrate closer to the engine,” he said. Another is passive NOx adsorber material. “It holds and adsorbs the NOx at low temperatures and releases it at higher temperatures where the rest of the aftertreatment becomes active. Other technologies to watch are the use of heated urea dosing and multiple SCRs having their own dosing systems.”

Michael Franke, Director, Light-Duty Diesel and Commercial Engines at FEV North America, agrees that new regulatory proposals globally are trying to control real-world emissions even further to lower standards. “[This is] resulting in an expansion of powertrain and aftertreatment solutions while OEMs try to maintain probability and improve reliability,” he said. “For off-road machines, we expect DPF technology to be mandatory across power levels.”

He also expects future updates in NOx emission standards and potential greenhouse gas legislation to drive future system configurations. “Reducing cost will be a continuing challenge as new emission legislation is put in place,” he said.

Integrated sets of technologies will be important in meeting these challenges. For example, FEV’s Integrated Turbocompounding/Waste Heat Recovery (WHR), Electrification and Supercharging system, or FEV-ITES, employs a little bit of everything—turbocompound turbine, secondary compressor, 48V electric motor/generator—in a combined system approach, integrating these technologies in a single unit (see SAE technical paper 2018-01-0887 ).

System-level development that includes the engine, powertrain, and aftertreatment together is important. “Powertrain and aftertreatment system need to work synergistically,” Franke said, incorporating design, development, calibration, and validation concurrently. “The base engine’s calibration, engine-out emission levels and exhaust gas temperature level play a crucial role to keep the aftertreatment system at its peak performance.”

Simulation models play an important role at the design phase as well as during calibration and validation processes. Many state-of-the-art engine controllers use several embedded models to aid aftertreatment controls and diagnostic features.

Are there management problems integrating engineers from OEM and suppliers? “This may have been true just a few years ago, however, today applying an integrated approach throughout development, calibration and validation tasks is a must,” Franke said. “At FEV, our engineering teams are fully integrated to be sure all interactions and potential conflicts are continuously addressed.”