What experience has revealed about diesel particulate filters

What we know about diesel particulate filters we didn’t know back in august 2009.

The cover story in the August 2009 edition of Fleet Maintenance looked back on the first two years of 2007-EPA emission compliant diesel engines for commercial trucks. The EPA had mandated that starting in 2007 all new on-highway diesel engines must limit the emission of particulate matter (PM). To comply with this regulation, OEMs incorporated diesel particulate filters (DPFs) as part of a comprehensive emissions control system. DPFs trap diesel particulates (soot) in a diesel engine’s exhaust through an extensive filtering process. The PM collected is then oxidized to remove it from the DPF.

At the same time, ultra low sulphur fuel (ULSD) was introduced for use on 2007 or later model year diesel vehicles. A cleaner-burning diesel fuel that contains 97 percent less sulfur than low sulphur diesel, ULSD was developed to allow the use of the improved pollution control devices that reduce diesel emissions more effectively but can be damaged by sulfur.


There were record heavy duty truck sales of calendar year 2006 models to avoid the increased cost of the 2007 models due the mandated exhaust aftertreatment systems.

In the summer of 2009, the landscape remained heavily populated with pre-2007 trucks. Low-mileage 2006 models would be the hot commodity in the used truck market for years to come.

In 2009, information was beginning to trickle in about the DPF-equipped trucks. At the time, 2006 and earlier model year trucks dominated use in the trucking industry while 2007 and later models accounted for a much smaller segment.

Now, more than six years later, the rear view mirror can teach us a lot that we didn’t know then. The 2006 truck models have now mostly disappeared from use. Those few remaining in service are tired and spent, having racked up millions of miles. DPF trucks are now the norm.


The DPF technology is performing its job well if given proper care. Now, as in 2009, no longer do big rigs belch black smoke with the stench of diesel fuel in their wake. In addition, DPF-equipped trucks run quieter.

“Engineers have worked very hard over a long period of time to reduce emissions while preserving the efficiencies and advantages of the diesel engine,” notes John Wall, vice president and chief technical officer for Cummins (www.cummins.com).

All this has come with a price. In 2007, $5,000 to $10,000 got tacked onto truck sticker prices.


Many fleets were experiencing problems with their DPFs, due mainly to failing to properly care for them.

“Diesel engines in vehicles have earned a reputation for being dependable, for being powerful, for being energy efficient, and they last forever,” explains Gina McCarthy, assistant administrator, air and radiation, for the U.S. EPA.

But add an EPA-mandated DPF and diesel oxidation catalyst (a device that helps to control diesel emissions) and the only thing you can depend on is unscheduled downtime if you don’t clean the DPF on a regular, proactive schedule. Experience has shown that without proper cleaning the DPF works fine until it cracks, sinters, melts or just plain gets plugged with soot or hardened ash plugs.


In 2009, many questions remained unanswered. Today we have some answers.

1. The DPF technology and the emissions control systems are working. This technology is effectively filtering diesel exhaust. Diesel exhaust is a complex mixture of gases and PM that contains more toxic air contaminants.

Clear evidence is building that cleaner diesel exhaust helps remove a major health risk as prolonged exposure to diesel exhaust can increase the risk of cardiovascular, cardiopulmonary and respiratory disease and lung cancer.

2. Does a clean DPF improve fuel efficiency? Many fleets are now reporting fuel efficiency gains from 3 percent to as high as 5 percent when DPFs are cleaned regularly.

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