Few things in trucking draw more scrutiny and scorn than a diesel engine’s after treatment system.
The adjustment from pre-Selective Catalytic Reduction (SCR) engines to the modern clean diesel era has been a painful – and somewhat expensive – one, but OEMs have worked to ease those woes through evolutions of engineering.
“System design isn’t mandated, just the end result,” says Ash Makki, product marketing manager for Volvo Trucks North America.
A transition to a single canister design, which allowed engineers to repackage aftertreatment components so that all the features from a dual canister setup could be placed into one, has cut almost 100 pounds out of Cummins’ system.
“You still have the same functionality but packaged much more efficiently in a smaller envelope,” says Jim Nachtman, heavy duty marketing manager for Navistar, who uses Cummins-designed Single Module system that is designed to be up to 60 percent smaller and 40 percent lighter than the previous EPA 2013 solution.
The weight savings for Mack’s single-unit ClearTech One and Volvo Trucks’ One Box is approximately 17 pounds compared to the previous two-unit solution.
“The reduction in weight is the result of combining the previously separate diesel particulate filter (DPF) and selective catalytic reduction (SCR) system into a single package,” says Scott Barraclough, Mack Trucks technology product manager.
Detroit’s 1-Box emissions system combines the SCR catalyst, the diesel oxidation catalyst (DOC), diesel particulate filter (DPF) and diesel exhaust fluid (DEF) into one compact component and is the longest-tenured single canister solution on the heavy-duty market.
Weight savings aside, moving away from a duel canister design comes with other benefits.
Barraclough say trucks equipped with Mack ClearTech One get an extra 11 additional inches of frame rail space.
“That space is definitely valuable,” Makki says, adding the extra frame rail space makes room for auxiliary power units and other add-ons without needing extra wheelbase. “On the vocational side, that is priceless.”
The smaller size also comes with service benefits. Nachtman says single canister units are easier to maintain, whether that is in the removal of overall system or simply servicing it.
“It’s just a tub that has the pieces in it,” he says, “so you can disassemble it and replace just the needed components.”
Makki estimates service time for the diesel particulate filter – the top part of the unit – have dropped by at least 50 percent.
“We created what you would call a side door with clamps,” he says. “All they have to do is remove the shield and slide that canister out.”
Volvo’s One Box features a Copper-zeolite coating that improves the flow temperature of the NOx, improving conversion and making the system more robust in the long term.
Makki says the coating also reduces hydrocarbon slippage from the DPF, minimizing the poisoning of the SCR.
“The soot level is reduced drastically,” he adds.
The system’s smaller size also improves fuel economy in that it has less surface area to heat.
“It needs to be hot to do active regens,” Nachtman says, “so it gets hot quicker, and stays hotter. When you need to do regen, they occur with less fuel burned.”
The compact design is also less restrictive, allowing exhaust gas to flow more freely.
Diesel Technology Forum Executive Director Allen Schaeffer says over a 5-year period, the newest generation commercial vehicles have saved 4.2 billion gallons of diesel fuel, and reduced 43 million metric tons of carbon dioxide (CO2), 21 million metric tons of nitrogen oxides (NOx) and 1.2 million metric tons of particulate matter.
As diesel engines continue to be refined by OEMs to further drop emissions, Makki says he can foresee aftertreatment systems continuing to shrink.
“I could see in the future going to smaller DPF because the engine itself is cleaner,” he says.
“You don’t need to filter as much of what is coming out of the engine because what is coming out of them is much cleaner.”