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DPF: The Time Bomb Under Your Diesel

We'll Show You How To Disarm the $8,000 Disaster That's Under Your Pickup

Text By Jason Thompson, Photography by Diesel Emission Technologies

No one has ever taken a deep breath and said, “Man, I wish this air was a little less clean.” Whether we like it or not, vehicle emissions regulations are not going to let up any time soon. That means all new diesels sold for on-highway use will need functioning emissions equipment. Trust us when we say: This is not the end of the world. But there are some facts that owners of ’07-and-newer diesels need to know.

History Is Repeating Itself
This is not the first time automotive enthusiasts have felt the growing pains of working with emissions equipment on our vehicles. In the ’60s, automotive emissions were nearly unregulated. In order to reduce air pollution, America decided to mandate vehicle tailpipe standards that were radically cleaner than before. The new laws didn’t specifically require manufacturers to add catalytic converters and air injection systems—but that’s the technology automakers chose to meet the new standards. Back then, enthusiasts felt wronged by the new hardware that showed up under their cars. They complained about reduced fuel economy, overheating, too much complexity, and poor vehicle performance. The catalytic converters, EGR components, and air pumps made working under the hood much more difficult—so hard-core enthusiasts ended up removing them. Sound familiar?

Owners of ’07-and-newer diesels will recognize this story all too well. Many of you are downright angry that your truck came with additional emissions equipment you didn’t ask for. You feel like that stuff doesn’t belong on your diesel—and that you should take it off. But what happens if you do? And what if (like our muscle car predecessors) you ever need to repair or replace the diesel particulate filter (DPF) under your truck? Many of us have no idea what this stuff does, how long it lasts, and what it’ll cost to replace.

Why Do We Need a DPF?
Diesel engines (well, all engines really) emit pollutants into the air we breathe. And by “pollutants” we mean chemicals and compounds that wouldn’t otherwise end up in our air in the quantity and concentration we create with our vehicles. To reduce the amount of these pollutants in our air, ’07-and-newer diesel engines have been fitted with a filter in the exhaust pipe to capture soot particles. This matrix of materials (a composite of cordierite, silicon carbide, or metal fibers), called a diesel particulate filter (DPF), traps the particulates (soot) flowing out the exhaust pipe.

What Happens To The Trapped Particles?
All DPFs capture soot until they fill up and create too much backpressure. At that point, DPFs use one of two approaches to regenerate (clean) themselves: active or passive. Passively regenerating DPF systems are commonly found in the retrofit marketplace for construction equipment. In these applications, the vehicle’s duty cycles and temperature profiles can be observed prior to filter installation. Passive systems rely on precious metal-coated substrates to heat the normal exhaust flow to temperatures that trigger regeneration. Although more sensitive to duty cycle and temperature, once installed, these DPF systems are considered to be more user friendly, as they do not require fuel additives, have no moving components, and only need to be serviced for annual cleaning.

DPF With Active Regeneration
Alternatively, light-duty diesel trucks have very different duty cycles, and therefore Ford, GM, and Dodge have all come to market with active DPF systems. Active regeneration of these DPFs is employed when the exhaust temperatures are too irregular for a passive system to regenerate consistently. Active regeneration is accomplished by changing parameters in the engine to increase the exhaust temperatures in the DPF. This requires precise knowledge of engine parameters and access to the engine control unit. Because of this, the engine management approach is performed by the OEMs that have direct access and control over their engine design.

Among the active strategies used are: late or post-injection of fuel into the combustion chamber, changes to the turbo boost, changes to the EGR valve, intake air throttling, and retarding the injection timing. All these methods can raise the exhaust temperature, but they also have negative impacts on the vehicle’s fuel economy, power, and engine wear.

Post-injection (late-cycle injection) in particular causes increased engine wear by diluting the engine oil film with fuel. Some of the other methods also decrease available oxygen in the exhaust, which impacts the soot-oxidizing ability of the particulate filter. Lastly, much of the heat generated by increasing the combustion chamber temperature is lost to engine coolant and engine components, thus decreasing fuel economy.

Cleaning vs. Regenerating: They Aren’t Really the Same Thing
Every DPF technology currently available utilizes what’s called a wall-flow filter that’s positioned in the exhaust system. As the exhaust gases pass through this filter, emissions of particulate matter (PM), carbon monoxide (CO), and hydrocarbons (HC) are trapped in the filter and reduced by more than 90 percent. This trapped diesel particulate matter (DPM) settles inside the filter walls until temperatures reach levels that allow for DPM combustion. The process of combusting these trapped particulates inside the filter without an intolerable buildup of engine backpressure is called filter regeneration. People who think of this as a self-cleaning (we did) for the DPF are practicing a little wishful thinking. To truly clean the DPF involves taking the filter out of the exhaust system and putting it in a special cleaning chamber.

Passive DPF and Active Diesel Injection
The alternative to using post-injection in the cylinders is heating the exhaust stream directly. This is achieved by heating the exhaust with an extra fuel injector positioned upstream from a catalytic oxidizer (the current Duramax uses this approach). The combusting fuel increases exhaust temperature needed to carry out the reaction. This is the most efficient method of increasing exhaust temperature and typically uses 35 to 50 percent less fuel than the post-combustion injection technology (fuel sprayed into the engine’s cylinder after top dead center) used by Ford, GM, and Dodge. This method minimizes engine wear since no changes to the engine performance—through engine management or increased power generation—is required. For retrofit or OEM replacement programs, this is also the simpler and less costly approach.

What if I Have to Replace My Exhaust?
The cost of replacing the DPF- and catalyst-equipped exhaust system on an ’07-and-newer diesel is projected to approach $7,000. That’s a lot of money for a new exhaust! Fortunately, the aftermarket has stepped up to the plate. Diesel Emission Technologies (DET) now offers solutions to replace the factory (non-cleanable) diesel particulate filters we’re used to dealing with—at a much cheaper price.

Your Guide To Air Pollution
Nitrogen Oxides (NOx): A pollutant that causes smog and acid rain. It can harm humans and vegetation when the concentrations are sufficiently high. It may cause lung damage and the degradation of breathing passages and lungs. It’s created when nitrogen molecules combine with oxygen in the presence of extreme heat.
Particulate Matter (PM): Contributes to smog formation and has been found to be carcinogenic. It causes nose and throat irritation, as well as lung damage. It’s caused by incomplete combustion (too much fuel, not enough heat, and not enough oxygen). This is the major thing a DPF catches.
Hydrocarbons (HC): A pollutant that can reduce the ability of blood to deliver oxygen to vital tissues. It is known to impact the cardiovascular and nervous systems. It’s caused by incomplete combustion.
Carbon Monoxide (CO): Poisonous, carcinogenic, and contributes to smog formation. It’s caused by incomplete combustion.
Carbon Dioxide (CO2): A nontoxic gas mainstream science believes is contributing to global warming.

SOURCES
Diesel Emission Technologies
714-782-7107
www.dieselemissiontechnologies.c
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By Jason Thompson
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