TORONTO, Ont. – Most of the attention surrounding the 2007 emissions-compliant heavy-duty engines has been focused on the performance of the engines themselves, but many questions still linger about the diesel particulate filters (DPFs) required to keep them clean.

While answers to some questions still remain elusive, at this year’s Canadian Fleet Maintenance Seminar three industry experts – Ron Hood of Tormont Cat, Steven de Sousa of Mack Trucks Canada, and Ryan Weary of Cummins Canada – shared their knowledge about what has been learned to this point about the ability of diesel particulate filters to handle the additional soot and ash created by the new engines.

Soot, a byproduct of incomplete combustion, is handled easily enough after it is collected in the diesel particulate filter. By elevating the exhaust temperatures soot is converted to vapour.

Ash, which is mainly a non-combustible residue of lubricating oil and, to a smaller degree, a by-product of the diesel particulate filter’s regeneration process, presents more of a challenge and the CFMS panel experts differed somewhat in what they considered acceptable strategies to dealing with it.

Powertrain analysis of what materials are making up that ash is still continuing but Mack Canada’s de Sousa said that preliminary indications show that anhydrite calcium sulfate is the major component, with a minor amount of zinc pyrophosphate. Both chemical components are neither toxic nor hazardous, he said.

A service indicator will alert the truck operator of required maintenance and the US Environmental Protection Agency requires full-size diesel particulate filters to be cleaned once per 150,000 miles or 4,500 hours (minimum). It has also recently established a minimum interval of 80,000 miles or 2,400 hrs for the scheduled maintenance of diesel particulate filters used in some space-constrained truck applications.

Hood explained how the diesel particulate filters are regenerated with Cat engines. Essentially low pressure fuel (approx. 250 psi) is delivered to an Aftertreatment Regeneration Device – basically a “self-contained furnace,” as Hood described it. The fuel is atomized in the combustor housing. Combustion is initiated with a sparkplug and the flame front provides the heat (620-650 Celsius) required for regeneration.

To reduce the quantity of ash a diesel particulate filter has to collect in the first place, Hood highly recommended using the new CJ-4 engine oils.

Weary, however, said Cummins is permitting the use of both CJ-4 oil and the older CI-4 oil.

“We’ve found that ash with CI-4 oils is not contributing to plugging of the diesel particulate filter at a rate that is significant. And there is an oil drain interval difference with CI-4 oils. Our motivation is to allow customers to maintain their current (CI-4) supplies,” Weary said.

He added that with CI-4 oils, although the diesel particulate filter will have shorter maintenance intervals, there is the opportunity to extend oil drain intervals by up to 5,000 miles. For example on the Cummins ISX, maintenance intervals with CJ-4 are as follows in the normal duty cycle:

* Oil and filter change – 25,000 miles (40,000 km)

* Cummins Particulate Filter – 200,000-400,000 miles (320,000-640,000 km)

Whereas ISX maintenance intervals with CI-4 in the normal duty cycle are follows:

* Oil and filter change – 30,000 miles (48,000 km)

* Cummins Particulate Filter – 150,000-350,000 miles (240,000-590,000 km)

What the experts did agree on was the need to ensure that diesel particulate filters be handled carefully and their components not be moved or altered from the OEM installation in any fashion.

Hood pointed out the diesel particulate filter can weigh up to 250 lbs, so it must be placed on a transmission or engine jack when removed. If the outside of the diesel particulate filter is dented or damaged, then the inside could also be damaged, he pointed out.

Moving or altering the DPF or its components will result in emission system malfunction or failure, said de Sousa and altering the emissions system is prohibited by law. It’s also important to note that dealers and/or body builders are not authorized to alter or modify the emissions system or any of the emissions related components.

All the experts also warned that while an “inhibit” switch can be used by the truck operator to prevent the diesel particulate filter from regenerating during an inconvenient time, extended operation with this switch activated may cause the diesel particulate filter to become completely full.

De Sousa said that the initial goal was to completely automate the regeneration process but some fleets didn’t want that for some instances and so the “inhibit” capability was built in.

“Eventually we probably will make it automatic,” he added.