"It would be like never emptying the bag on a vacuum cleaner, Mark Thomas, director electrical and electronic engineering, Daimler Trucks North America (DTNA), says. "This reduces the effectiveness of the vacuum's ability to pick up dirt."
The clogging increases the pressure drop (backpressure) within the exhaust system, causing a variety of problems from increased stress on many internal engine components, says Schmidt. Problems include a lack of engine power and vehicle speed, poor fuel economy, overheating and ever-shortening intervals between system regeneration commands.
There is also the risk of permanently damaging the DPF, adds Thomas.
The regeneration process is typically achieved by burning off the trapped particulate matter. There are two types of regeneration: passive and active. With passive regeneration, particulate matter is continually burned off while a vehicle is driving using a combination of exhaust heat and a catalyst to combust the soot.
Active regeneration uses fuel introduced through the 7th injector or a supplemental heat source such as an electrical heater, flame-based burner or precious metal catalytic burner to combust (oxidize) the soot, says Saxman of Volvo. This only occurs when passive exhaust temperatures are either relatively low or high for short periods of time.
The active regeneration process often requires that the vehicle be stationary. It is much more rapid and occurs at temperatures of 1,100 degrees Fahrenheit or more, he notes.
Active regenerations typically won't be necessary for those applications where truck engines work hard enough to generate the heat necessary to continually burn off the trapped particulate matter. They may, however, be required for those applications where vehicles do a lot of stop-and-go operation or prolonged idling.
For 2010, a typical Mack highway tractor "may never see an active regen event as opposed to something around one every14 engine hours today," says Mack's McKenna. "Vocational trucks, dumps, mixers and roll-offs will see significantly reduced requirement for active regens - something around 300 to 400 engine hours."
Drivers will not notice passive regeneration, as the engine continues to operate normally. The only sign of any passive regeneration is an indicator light on the dashboard that illuminates.
No new steps need to be included in a vehicle's routine maintenance for 2010 DPFs. In fact, in SCR-equipped vehicles, the maintenance interval may be extended.
Over time, the DPF filter needs to be cleaned. Many truck and engine dealers have DPF cleaning technology and offer cleaning services to fleets of all sizes. There are also companies that offer DPF cleaning services.
Some truck OEMs offer DPF core exchange programs administered through their dealers. Through these programs, shops have readily available certified clean DPFs, which helps minimize vehicle downtime.
The Cummins distribution network, by way of example, has both new and ReCon diesel particulate filters in stock, as well as DPF cleaning machines.
A typical Class 8 DPF is a ceramic filter cartridge riddled with about 10,000 holes with 5,000 of them open and 5,000 plugged on each end forming a checkerboard, says Drew Taylor, national sales manager, FSX, a company that designs and manufactures diesel particulate filter cleaning machinery. The cells are deep dead end holes with a thin wall between the holes.
"The thin walls between the cells contain billions of micro-pores that allow gases to go through but not much in the form of particulates," he explains. "The filter runs at about 750 degrees Fahrenheit under ideal circumstances. When you take a filter off a truck, the inlet end should be black with soot and the outlet end should be so clean it will pass a white glove test."
DPFs become plugged with either ash or soot or a combination thereof, says Cole Waldo, FSX's chief operating officer. As the engine operates, it exhausts unburned hydrocarbons in the form of soot and small amounts of engine oil that contains unburnable elements called ash. Ash is a combination of metals and minerals.