While no jurisdiction has made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all on-road diesel engines will be fitted with them. The American 2007 heavy truck engine emissions regulations cannot be met without filters.
Particulate filters have been in use on non-road machines since 1980, and in automobiles since 1996. During combustion of the fuel/air mix, diesel engines produce a variety of particles generically classified as diesel particulate matter due to incomplete combustion.
The composition of the particles varies widely, dependent upon engine type, age, and the emissions specification that the engine was designed to meet.
Historically, diesel engine emissions were not regulated until 1987 when the first California Heavy Truck rule was introduced capping particulate emissions at 0.60 g/BHP Hour. Since then, progressively tighter standards have been introduced for both On-Road and Non-Road diesel engines.
While particulate emissions from diesel engines was first regulated in the United States, similar regulations have also been adopted by the European Union, most Asian countries, and the rest of North and South America World List of Standards.
While no jurisdiction has made filters mandatory, the increasingly stringent emissions regulations that engine manufactures must meet mean that eventually all on-road diesel engines will be fitted with them. The American 2007 heavy truck engine emissions regulations cannot be met without filters.
Enter today’s Diesel Particulate Filter (DPF).
The DPF, in most cases is around 12 inches in diameter and 3 feet long and weighs 50-60 pounds, depending on the engine size and manufacturer. DPFs on heavy duty tractors are located either along the frame rails or at the bottom of the exhaust stack.
Midrange trucks are more complicated. Because they are fitted with a wide variety of bodies and equipment, manufacturers have to use a split system, as on light trucks. But more often they’ll be a single-unit can, like those on heavies. Usually the can will go beneath the cab, off to the right. In some cases it will be under the steps on the curb side. The tailpipe runs rearward on the frame or up a rear corner on the cab.
How the DPF Works
The process is similar to a self-cleaning oven’s cycle: a filter traps the tiny particles of soot in the exhaust fumes. The filter uses a sensor that measures back pressure, or the force required to push the exhaust gases out of the engine and through to the exhaust.
As the soot particles in the particulate filter accumulate, the back pressure in the exhaust system increases. When the pressure builds to a certain point, the sensor tells the engine management computer to inject more fuel into the engine.
Exhaust heat from high-load highway operations will be enough to burn off soot in a process called passive regeneration. In stop-and-go operations, extra heat will be needed for what’s called active regeneration. This comes from injecting small amounts of fuel into the exhaust stream, or from a temporarily rich mixture in the cylinders.
When the fuel hits the oxygen catalyst, a reaction causes high heat, which then passes into the DPF and burns off the accumulated particulates. The entire cycle occurs within a few minutes and is undetectable by the vehicle’s driver.
Simple, no? But, we’re not through yet.
The ash from motor oil will collect in the DPF and have to be removed through special cleaning. Over-the-road tractors will probably not require cleaning before 200,000 to 300,000 miles; local trucks might go less than 100,000 miles.
How the OEM’s Approach Cleaning
Cleaning ash out of the DPFs will be a new service procedure. In most cases, cleaning will be done by removing the DPF element from the truck – an easy job, partly because parts will be made of stainless steel to resist corrosion, manufacturers say – and placing it on a special machine.
The console-like machine will blow compressed air at normal shop pressure (about 90 psi) through the filter in pulses. This will take about half an hour, during which the technician can perform other service work on the truck. Removal and reinstallation of the DPF will together consume another half hour and maybe less.
Caterpillar says that its DPF is unique in that it can be cleaned without removal from the chassis. Technicians will just need to hook the Caterpillar DPF cleaner to the inlet and outlet of the DPF and turn it on. The total time required for the service will be as long as needed for an oil change, and the two operations can be done simultaneously. The Caterpillar target for cleaning intervals is twice the EPA requirement for most applications.
Cummins says their ash cleaning machine runs on 110-volt power and uses standard shop air. Attachments are available to fit every size of particulate filter from Cummins and most other engine manufacturers. The cleaning, on average, takes less than 30 minutes with the total procedure taking 90 minutes or less, depending on how accessible the mounting of the DPF is on the vehicle.
Detroit Diesel (which also markets and supports Mercedes Benz MBE diesels) recommends filter cleaning with deionized water. This will be done on machines at Detroit’s remanufacturing centers.
