The Aftertreatment Equation

Heat issues with '07 aftertreatment devices.


Alternatively, Caterpillar offers the Caterpillar Regeneration System (CRS). "The combuster provides heat directly into the exhaust and into the diesel particulate filter," says Mike Dozier, Kenworth chief engineer. "The CRS is mounted just after the turbocharger in the traditional turbo pipe location. It works with the same control system methodology where it is identifying, based on temperature, when the diesel particulate filter needs to be regenerated."

Since Kenworth uses both Caterpillar and Cummins engines, it has witnessed both the dosing and burner approaches to aftertreatment devices. "At this point, from a standpoint of application and performance, I haven't seen anything that indicates a significant difference one way or another," says Dozier. "We are seeing excellent results from both."

Operators will not likely notice the automated regenerations during operation. "Other than indicator lights telling them it is happening, it will be largely transparent," says Dozier.

Initially, a black cloud hanging over the use of catalyzed particulate filters was the realization that you would need to clean out the ash. "Ash will accumulate in the low part of the particulate filter," says Matsil. "At some point, you are going to have to remove that ash. That is a service item."

The EPA set minimum limits of 110,000 to more than 150,000 miles between cleanings, depending on the size of the truck. But manufacturers report being able to greatly exceed these limits. In vocational applications, it could be years before you need to clean ash out of the particulate filter.

"There is maintenance, but they are not maintenance intensive," says McKenna.

HOT PIPES

An area of concern with regeneration is the heat coming out of the exhaust. "During an active regeneration, the exhaust plume gets up around 1,000° F," says Morelli.

"One area we are concerned about is this concept of having real hot exhaust gases coming out of the tailpipe during regeneration with a horizontal exhaust system," says Matsil. "During our development programs, we have actually melted and puddled the asphalt underneath the vehicle during regeneration."

To help prevent these extremely hot emissions during regeneration, exhaust aftercooling devices are being developed.

"Kenworth has developed an exhaust temperature reduction device," says Dozier. "The manufacturers are also working together to develop driver interface systems to help further control the regeneration process."

General Motors is also developing an exhaust cooler. "We are going to design and validate an exhaust cooler device, which we will mount downstream or after the diesel particulate filter, that will cool the exhaust gases," says Matsil. "It is a patented device we have developed that will allow us to mix and blend air. Some manufacturers are actually looking at pumping in air with an auxiliary compressor."

Freightliner, as well as other manufacturers, are working on similar solutions. "We have a diffuser that we have looked at for our horizontal exhaust," says Morelli. "In our testing, we have found that when you mix the exhaust plume with ambient air with any kind of swirl, it cools off six inches to the side and 12 inches to the back very quickly. We are pursuing that solution, and it has been very effective so far getting that hot exhaust down to a much lower level."

FEEL THE HEAT

With only a few months to go before these systems appear on production trucks, time is of the essence. Manufacturers will need to solve their heat issues before 2007 trucks can take their places in vocational fleets.

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