With implementation of the 2007 Environmental Protection Agency diesel emissions regulations comes the use of diesel particulate filters (DPFs). These aftertreatment devices, used by every Class 8 truck manufacturer, will require periodic maintenance, creating a potential new revenue stream through service support.
But as with any new technology, both customers and technicians will have questions. The following guide will help you answer those questions as you prepare to meet the future service needs of DPF-equipped vehicles.
How it works
The purpose of a DPF is to catch diesel particulate matter before it escapes into the air through the exhaust. Inside the DPF is a honeycomb-shaped mesh or grid made of a ceramic material called cordierite. It can withstand high temperatures and doesn’t carry heat away like metal does. This is ideal because the soot must be kept hot for the DPF to work.
Some passages through the structure are open and others are closed. As the exhaust gas weaves through the open passages, the filter walls capture particles of carbon soot, while the exhaust, with unused oxygen in it, flows through.
Diesel exhaust gets pretty hot when the engine is under load because the burning fuel in the cylinders heats the air. As a result, under normal cruising conditions, the exhaust will heat the DPF and keep it hot.
Most engine makers further the heating process by using a DOC, or diesel oxidation catalyst, located just in front of the DPF and part of the same assembly. The DOC contains a noble metal that speeds up burning, just like the catalytic converter in a car. It accelerates combustion of the hydrocarbons and soot passing through, releasing energy and heating the exhaust beyond its normal temperature as it enters the DPF. In the up to 600-degree F heat and under the stream of exhaust and oxygen flowing past, the particulates burn off as fast as they accumulate in the filter. This is called passive regeneration and is the more important mode of cleaning the DPF on most trucks.
In the case of Caterpillar, rather than adding a DOC, the entire DPF is impregnated with a catalyst material to heat up the air and accelerate combustion of the soot, probably because the exhaust in ACERT engines is cooler.
Either way, end of soot problem. Well, almost.
Low load regeneration
Under certain operating conditions, such as crawling through city streets or heavy traffic, the exhaust is too cool to burn the soot in the DPF so it builds up and begins clogging it, creating backpressure When backpressure becomes higher than normal, a tiny bit of finely atomized fuel pumps into the exhaust. When the fine fuel mist and warm exhaust meet the DOC or catalyzed Caterpillar DPF, the fuel ignites, heating the exhaust to almost 1,000 degrees F and burning off the accumulated soot, in a process called active regeneration.
This process is automatic, though most trucks provide in-cab indication when it is occurring.
The amount of fuel required to accomplish this is so small that engine makers say fuel economy is not affected in nearly all applications. Even when regeneration is needed frequently, the impact should be very small.
Caterpillar’s system monitors the regeneration event to make sure the DPF operates at the right temperature.
Detroit Diesel adds an intake throttle valve, which accelerates regeneration by reducing airflow through the engine, thus increasing exhaust temperature with a minimum of added fuel.
Clean Gas Induction
Caterpillar ACERT engines cool the intake air and favorably affect the combustion process, reducing nitrogen oxide (NOx). But the 2007 standards are so tight, Cat added a different form of EGR. Clean Gas Induction will pipe a smaller amount of exhaust back into the engine than regular EGR systems. CGI does not require an exhaust gas cooler on the engine, and it takes the exhaust from behind the DPF through a pipe integral with that assembly after removal of most of the soot.
New oil, fuel standards
The need for servicing arises because of ash in the exhaust, which does not burn but will accumulate slowly in the DPF.
Ash doesn’t come from fuel but from the engine oil. It’s there only because of TBN (Total Base Number) additives. These are antacids like Alka Seltzer that are in the oil only because the sulfur that’s naturally in fuel creates acids. TBN neutralizes the acids, or counters their effects, so they won’t destroy the engine’s internal parts. One thing that will help here is ultra low sulfur diesel.
Because sulfur can poison a DPF, the oil industry lowered the sulfur content of fuel to 15 parts per million. This way, the DPF will likely last the life of the truck.
Removing more sulfur will make fuel cost a little more and slightly decrease energy content and miles per gallon, but it will help the ash situation. Less acid is good for the engine, as well.
The 2007 engines also use a new grade of diesel engine oil called CJ-4. It is a better oil in every respect, and contains much less ash because, with less sulfur, there will be much less acid in the oil for the TBN additives to neutralize. Since all highway trucks will be running the same ULSD, the oil is backward compatible, working fine in older engines.
DPF service requirements
The small amount of ash left in the oil eventually leaves a fine coating on the DPF, resulting in backpressure and the need to clean the unit because the ash won’t burn even when extremely hot. Sensors detect the gradual increase in backpressure and warn the driver when the unit has to be cleaned.
DPFs require cleaning no more often than every 150,000 miles, but nearly all engine makers estimate that under favorable operating conditions (trucks getting good fuel economy and not suffering from high oil consumption), the cleaning interval is about twice that long.
Cleaning is almost always done with high-velocity air under pressure. Air is forced through the DPF from back to front, and the ash is collected and disposed of. This requires a specially designed, high-powered vacuum device already for sale for aftermarket use.
The standard cleaning process involves removing the DPF. Although heavy enough to require a floor jack, most are installed using band clamps that can quickly be removed, allowing the unit to slide out. Cleaning takes as little time as an oil change on most vehicles – about a half hour’s labor.
DPF technology is here and every Class 8 truck manufactured this year through 2009 will be equipped with one. Integrating DPF cleaning into your suite of services will create a new revenue source and expand the value of your business to customers.
OEM DPF Cleaning Procedures
Procedures and requirements for cleaning the DPF differ by engine manufacturer. For instance:
- Caterpillar – The Caterpillar DPF is unique in that it can be cleaned without removal from the chassis, said Caterpillar engineers.
Technicians simply hook the cleaner to the inlet and outlet of the DPF and turn it on. The total time required for the service is as long as needed for an oil change, and the two operations can be done simultaneously. Cat DPF cleaning devices are available for purchase.
- Cummins – The Cummins’ ash cleaning machine runs on 110-volt power and uses standard shop air. Attachments will be available to fit every size of Cummins particulate filters and most other engine manufacturers. This will help control costs because repair shops will need to buy only one cleaning machine.
The cleaning, on average, should take 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. It will be possible to exchange Cummins DPFs between vehicles or replace them with a Cummins Recon DPF.
- Detroit Diesel – Detroit Diesel’s DDEC IV predicts when DPF cleaning is needed, allowing the operator or owner to plan ahead for service. Detroit’s studies show the best cleaning with the filter removed; the engineers designed the unit so removal and replacement would take only 30 minutes.
Detroit requires that the DPF first be regenerated on the vehicle. Total air cleaning will take two to three hours. Detroit also has designed its DPF so it can be washed with a liquid. Remanufactured DPFs cleaned in this manner will be available as Detroit Diesel remanufactured parts.
- International Truck and Engine Co. – Warren Slodawske, manager of emissions certification and compliance, said the International DPF needs cleaning at 150,000 miles or 4,500 hours, whichever comes first. He said it is easy to remove, “Just loosen the mounting bolts and slide it out,” he expained.
- Mack – Mack’s DPF like most of the others, has band clamps for quick removal. Dave McKenna, product manager-marketing, said cleaning should take less than 30 minutes. Mack’s system triggers active regeneration automatically, but the driver also can initiate it.
- Volvo – Volvo said its DPF can be serviced with a standard transmission jack, and technicians with the proper tools and training will be able to service it.
