When AGCO’s Massey Ferguson 5713SL won a Tractor of the Year award at Agritechnica last November, one of the features that impressed the judges and helped the tractor win was the new, compact SCR exhaust emissions system.
The Donaldson Company, known to many farmers as a filter brand, is actually the manufacturer behind that particular system. The Donaldson All-In-One compact selective catalytic reduction (SCR) exhaust treatment system is one of the new, more compact “single can” designs to be introduced, along with the likes of Cummins’ EcoFit Single Module. They wrap up everything in a much smaller package than was available with older designs. So AGCO engineers could tuck the All-In-One away under the cab of the 5713SL and use the resulting vacant real estate in the engine compartment to create a steeply sloping tractor hood, which improves forward visibility for the driver.
Most Tier 4 Interim emissions systems consist of two canisters, one that contains a diesel oxidation catalyst (DOC) and an airflow mixer where diesel exhaust fluid (DEF) is injected. Then, another one downstream in the exhaust flow holds the SCR catalyst. Together, they take up a lot of space under hoods.
“Naturally, there was a desire to try and figure out how to integrate those two cans into one package,” says Gary Simons, engineering director for exhaust emissions at Donaldson. “That was how the All-In-One evolved, to have a single can that contained the DOC, as well as the DEF mixer and the SCR catalyst, all in one relatively easily mountable body. To meet Tier 4 Final we took three distinct functions, if you will, and rolled them into one can.”
One of the reasons other systems use two separate cans is the need to have a fairly long distance between the DEF injector and the face of the SCR catalyst in order to allow enough time for a uniform ammonia distribution to be created in the exhaust flow before it reached the catalyst.
“So it’s not just a matter of shoving it into a smaller package,” explains Simons. “It’s getting it to improve its efficiency and getting it to work in a smaller package at the same time. The new part of this, by getting it as compact as we have, is we’ve saved a lot of volume in the design.”
Here’s how Donaldson managed to do that.
The improved design
The first stage of the system forces the incoming exhaust to pass through a metal-bodied DOC.
“A diesel oxidation catalyst (DOC) works similarly (to a catalytic converter on a car),” he continues. “It converts some of the gases, primarily some of the carbon monoxide and the hydrocarbons. It eliminates those. Then it will also convert some of the NOx (nitrogen oxides) from NO to NO2. And that gets broken down when it goes through the SCR system.”
Louvres downstream from the annular (doughnut shaped) DOC create a swirling airflow as the exhaust gases pass through it. That turbulent flow allows for complete mixing when the exhaust flow reaches the DEF injector. The exhaust flow changes direction 180 degrees before it gets blended with the DEF. The exhaust gas and DEF mixture passes back through the centre opening in the DOC and flows out through the SCR catalysts. “The DEF distribution is pretty uniform at that point,” Simons adds. “Uniformity is what you’re looking for to get the highest level of efficiency out of your SCR catalyst. Ultimately the SCR catalysts are there to break down NOx. It breaks it down to nitrogen and water.”
They also ensure none of the ammonia created from conversion of the Urea content in the DEF injection escapes into the atmosphere.
Unlike some other single can solutions from other companies, the Donaldson All-In-One system doesn’t rely on a diesel particulate filter (DPF), which means the entire system is maintenance free, and there is no need to buy an expensive replacement filter when the engine hours start to rack up.
“There is no service required on this system,” Simons confirms. “If they can meet the standard without a DPF, it seems many of the manufacturers are going in that direction. There were quite a number (of brands) that chose not to use DPFs, because of the cost and service issues.”
Eventually, buyers of all brands of equipment in the future will likely find a single can emissions system fitted to their equipment. Donaldson’s can be scaled to work with tractors all the way up to high horsepower models, according to Simons. “The range of our product in this configuration can go from 80 kiloWatts up to 350 (107 to 469 horsepower) or higher,” he says. “We can reach combines too. We believe this is one of our platform products that will be a good solution for Tier 4 Final, which is out today.”