Here is an older article about Cummins and how their system works.
When talking about diesel particulate filters (DPFs), there is absolutely no relation between regeneration and the need for cleaning.
Apparently, a number of folks are not quite sure just what that means or if it’s actually true. A recent conversation with Zack Ellison, the director of customer support at Cummins, began by him saying, “There’s a lot of confusion in the marketplace on how regeneration relates to the need for cleaning a diesel particulate filter. The two are completely independent of each other.”
With that said, let’s go back to the beginning. In just over a half a year, to comply with 2007 emissions regulations, all new commercial diesels will be equipped with some kind of aftertreatment device, more commonly referred to as DPFs. While these devices have been widely used on transit buses for years, they’re new to the trucking industry and apparently are causing some confusion. In general, DPFs will be installed on trucks in place of mufflers and will be needed because 2007 emissions regulations dramatically limit the particulate material that can be emitted in exhaust.
Just like the mufflers they replace, DPFs come in a variety of proprietary designs. All of them will be designed to collect particulate matter without obstructing the flow of exhaust gases. And, they do their jobs very efficiently, but, like any other filter, as they collect material, back pressure will increase unless some way is incorporated in the system to control this.
“Regeneration, which takes place in the presence of heat and a precious metal catalyst in the DPF, is the name given to how we eliminate the soot or carbon from the DP,” Ellison says. “During regeneration, the trapped soot, which is carbon, is converted to carbon dioxide (CO2). Some people think that after we burn off the soot during regeneration, we’re left with ash. That’s not correct. It’s important to understand that there is no residue left behind from the regeneration operation.”
It’s also important to understand that regeneration takes place automatically. No driver input is required nor will a driver know that the process is taking place.
“Passive regeneration means that you don’t have to add anything to the exhaust stream,” Ellison says. “The heat of the exhaust, combined with heat generated by the chemical reaction within the DPF, is enough to convert the carbon to carbon dioxide.”
Active regeneration, during which a small amount of diesel fuel is injected into the exhaust, will be required only if the exhaust temperature is too low because of lightly loaded conditions. Such a situation will not be encountered in most highway applications, but might well be required in city operations where engines have lower exhaust temperatures because they are not working as hard as they are in over-the-road applications.
“I’d say, for 99 percent of our over-the-road customers, they will never need to add fuel to the exhaust stream,” Ellison says. “That, of course, is good for fuel economy. In 30 highway test vehicles, we have yet to experience the need to add fuel for regeneration.” Even in the case of active regeneration of the DPF, no driver action is required.
So what’s all the talk about cleaning DPFs? Recall we said that these filters are very good at removing any solid material from the exhaust stream. A very small portion of that material will come from the additive package in the lube oil. This is what is referred to as “ash.” The amount that gets into the exhaust is directly related to how much oil is burned in the engine and how much of the additive doesn’t burn.
To address that situation, all engine manufacturers are designing their 2007 engines to burn exceptionally little oil, and the new CJ-rated oil that will be used in these engines will decrease ash content from 1.5 percent to 1 percent.
Still, some ash will be trapped; so filters will need cleaning by reverse flow of high-pressure air in a machine designed for the task–a process that takes about an hour and a half. By law, this cannot be required in fewer than 150,000 miles.
Ellison says that Cummins systems are designed to run 200,000 to 400,000 miles before cleaning is required.
That sounds like once in a lifetime to me!
Tom Gelinas
Editorial Director
Fleet Equipment May 1, 2006
