Diesel builders have endeavored to produce an engine that operates cleaner without generating an overabundance of toxins. The machine is a significant internal combustion engine, yielding excellent fuel mileage, exceptional torque and is extremely reliable. The engine design can be applied to a small two-door passenger automobile or gigantic earthmovers and beyond.
World engineers have worked continuously to improve diesel exhaust emissions. In the first days of diesel engines, soot, ash, nitrous oxide, and other harmful particulates billowed from their tailpipes. In recent decades, two major emission technologies have come into play.
- Diesel exhaust fluid (DEF) has negated detrimental effects of nitrous oxide
- Diesel particulate filters (DPF) curtail soot, ash and other carbon-based pollutants.
In this article, we will discuss drive to clean exhaust systems and how they operate.
Drive to Clean Exhaust System: What is it?
This message will pop up on an operator’s information screen, informing them the DPF is overloaded and requires cleaning, NOW.
Duramax DPF cleaning has the same message. Chevrolet displays “Cleaning Exhaust Filter Keep Driving.” With increasing EPA regulations, every diesel on the highway is required to be outfitted with a DPF.
The diesel particulate filter is built inline to the exhaust pipe. The DPF burns soot from the engine into ash and is trapped by a filter. As more and more residue builds up in the filter, it must be cleaned. This cleaning process is called regeneration or regen for short. DPF filter cleaning is automatic if the operator maintains sufficient speed. Regeneration occurs at 100 to 500-mile intervals. Several issues may affect excessive regeneration.
- Stop and go driving.
- Short driving distances.
- Turning the engine on and off by remote.
- Aftermarket air filters, air boxes, cold air kits, and exhaust add-ons.
Modern warning system technology is nothing short of remarkable. Today’s digital vehicles are equipped with hundreds of sensors, communicating every conceivable condition, and making repairs easier. A service technician can diagnose problems quicker, with greater certainty. Operators need to pay attention to any DPF messages:
- Exhaust Filter Overloaded, Drive to Clean
- Exhaust Filter at Limit Drive to Clean Now
Overlooking DPF warning message can lead to a trip to your dealer’s service department. An example message that may show if you ignore warnings is “Exhaust Filter Over Limit, Service Now”. If the operator sees this message on their screen, there will be a 20% to 30% cutback in torque. Regeneration is disabled, and a certified technician must clean the filter.
Additional messages related to DPF cleaning:
- Exhaust Filter at Limit, Clean Now
- Exhaust System Overheated, Stop Now
- Exhaust Filter Drive Complete
Regeneration: Active, Passive and Operator Command
Diesel particulates burn off at 600 degrees Celsius and above. Onboard active systems use extra fuel or extra power to the DPF’s electrical structure to complete this burn-off. Regeneration is the process of eliminating built-up soot and ash from the DPF filter. Every diesel builder has different procedures or displays messages for this process. However, the fundamental objective is the same. Each regeneration cycle will last between 9 to 20 minutes.
- Passive Regeneration: Passive cleaning of a DPF filter utilizes normal exhaust temperatures and nitrous oxide as the catalyst. This mode of regeneration is automatic and straightforward. Filter cleaning happens during normal driving. Warning messages will appear, prompting the operator to drive above the 30-mph speed for roughly 20 minutes.
- Active Regeneration: Pressure sensors detect soot overload if driving patterns have not adequately cleaned a DPF filter under passive regeneration. An engine control module informs the system to clean the filter using active regeneration. Exhaust temperatures are raised to dispose of pollutants. During active regeneration, raw fuel is injected into the diesel oxidation catalyst (DOC) system to burn off soot and ash in the DPF. Driver intervention is not needed for either of the above regeneration processes.
- Operator Command Regeneration: If your diesel-equipped vehicle cannot maintain speed for passive or active regeneration, a driver must use operator command. This method allows an operator to initiate regeneration at idle. The particulate filter must be at 100% load for the operator command to work. 1) Start the vehicle and bring it to operating temperature. 2) Press the information display button and follow and understand the prompts. 3) Answer yes to start the process and exhaust positioning. 4) Once an operator regeneration has commenced, the engine will rev to 2000 rpm. 5) Regeneration process ends, the engine and cooling fan will return to normal. The exhaust system will be hot. The complete regeneration takes about 30 minutes.
Diesel Particulate Filter (DPF)
Two primary pollutant control systems exist on modern diesel engines. Diesel exhaust fuel (DEF) and Diesel particulate filters (DPF). Under certain conditions, a DPF will remove 85% to 100% of the particulate matter coming from diesel exhaust. The filter must be maintained continually, or the DPF will not function correctly.
Diesel soot is generated from incomplete combustion of diesel fuel. Carbon and other particulates vary, depending on engine type, size, and fuel used. Particulate filters have been employed since the mid-1970s and used in vehicles since 1985.
Several filter technologies are in use today:
- Cordierite is the most common material. Ceramic-based cordierite has excellent filtering properties, inexpensive and thermally efficient.
- Silicon carbide is the second most common filtering material. The silicon carbide has a higher melting point, but not as thermally efficient.
DPF filters have developed into the most economical means to capture and dispose of diesel particulate matter. Regeneration techniques have been able to prolong the life of filters, by “burning off” soot and other carbon particles. Thermal regeneration is by far the most complete and efficient form of operating particulate filters.
The continued progress of DPF and DEF systems are growing pains for emission regulations. In the 60s, there were no automotive standards to control what was coming out of the tailpipe. Americans could see the impact of dirty diesel fuel, from the billows of black smoke gushing out of exhaust pipes.
Current EPA regulations, which took effect in 2010 have reversed the trend. Modern diesel engines run much cleaner and operate at higher efficiencies.
The 2010 EPA regulations for diesel engines was by far the most significant clean-air regulation in our lifetime. It is believed, the standards will reduce carbon and nitrous oxide emissions by 1 million tons per year. It is equivalent to removing 35 million passenger cars from the highway. The drive to clean exhaust system is one of those wonders that gets the job done.