Source: by Ray Bohacz for Successful Farming | April 9, 2019
Advancements that have produced record crop yields along with the disease and drought tolerance that you enjoy on your farms today comes with a price of complexity. In like fashion, the quest to reduce diesel emissions brings to the shop a host of systems and service procedures that must be understood. In the profit-sensitive industry that is agriculture, it is imperative that you do not allow emission controls to create costly failures or downtime.
Depending on the use, horsepower, and year of production, the modern diesel has little in resemblance to those of the past due to the integration of emissions reduction equipment. These systems are identified with acronyms such as EGR (exhaust gas recirculation), DOC (diesel oxidation catalyst), DPF (diesel particulate filter), and SCR (selective catalytic reduction).
EGR, SCR, DOC, AND DPF EXPLAINED
EGR is a design function of the engine that introduces inert exhaust gas to the combustion chamber to act as a filler. This lowers combustion pressure and heat for a reduction in oxides of nitrogen emissions (NOx).
SCR further diminishes NOx though the injection of DEF (diesel exhaust fluid), which is a specific mix of urea and water.
DOC is employed to reduce carbon monoxide and hydrocarbon emissions along with sulphur-based exhaust particulates. In simple terms, this is known as diesel soot. The soot then enters the DPF where it is stored and burned off at an elevated temperature. This converts the soot to ash. The conversion takes places in the DPF with heat that is generated in the DOC during a process called regeneration.
The DPF is nothing more than a trap as you would place in a cornfield to determine moth population. If you never emptied that trap, it would fill up and become useless. Cleaning a DPF is emptying the trap (often the DPF is identified as a soot trap in literature) since it can only hold so much ash.
As the exhaust gases leave the turbocharger (or exhaust port on normally aspirated engines), it will first travel to the DOC, then the DPF, and on to the SCR.
Diesel fuel is used to produce heat either via injection during the exhaust stroke of the engine or preferably with a dedicated injector that is fitted to the intake stream of the DOC. Depending on the criteria deemed by the engine manufacturer, regeneration (or the conversion of the soot to ash) can take place based on the following:
• The amount of fuel consumed by the engine.
• Mileage or hours of use.
• The differential in pressure between the inlet and exit of the DPF.
The differential pressure method is considered the most desirable. This method will only evoke a regeneration when there is enough soot to impede exhaust flow and degrade engine performance. The other two methods employ no other metric to confirm the condition of the DPF.
During operations that create sufficient exhaust heat (over 575°F. ), the engine control unit (ECU) will evoke a passive regeneration. This is the most desirable method to convert the trapped soot to ash. It requires the engine to be under a defined operating state. If this state is not seen and the ECU deems a regeneration is required, then an active procedure is commanded. It will usually require the vehicle or equipment to be stopped.
The ECU commands a high idle speed and the fueling of the DOC once a minimum temperature of approximately 575°F. is reached.
Whereas a passive regeneration can take anywhere from 20 to 40 minutes, an active protocol can take upwards of one hour or longer. More important, the truck or farm machine must be parked and not in use. The most desirable procedure is the passive regeneration, since it keeps the unit in service and is the gentlest on the DPF. If the ECU requires an active (or sometime referred to as a forced regeneration) and you ignore the message, the engine’s power will be derated until the procedure is performed and with some calibrations, may stall or stop running.
By keeping the engine running properly, performing scheduled maintenance, and using high-quality and properly additized fuel, the amount of soot produced by the engine will be so low that a passive regeneration will keep everything in line.
DOWNSIDE OF ACTIVE REGENERATION
A problem comes up if the engine doesn’t get the use necessary to evoke a passive regeneration. This is common with trucks or equipment exposed to short duty-cycle or light load service (for example, a truck that is used to feed cattle or has a sprayer nurse tank on it). Also, the diesel pickup you bought that just goes to town and back will most likely never evoke a passive regeneration, and you will need to employ active regeneration.
The DPF looks externally like a muffler, but it has an interior of precious metals that resembles a tight honeycomb. This matrix holds the soot. As it fills, exhaust flow will decrease with a corresponding pressure differential and degraded engine performance. The purpose of the regeneration process is to burn off the collected soot and let it become ash and fall from the matrix. It is important to recognize that the ash will remain in the DPF and eventually need to be removed. That requires the use of special equipment and cannot be accomplished in your shop.
DPF CLEANING PROCEDURE
The nationwide travel center and diesel repair facility company TA/Petro (ta-petro.com) invited me to attend a daylong class on DPF and DOC cleaning procedures, taught by one of its technical trainers, Daniel Mustafa. The company has five cleaning locations in key areas of the country and can fully restore both the DOC and DPF to like-new working order. In addition, they provide pick-up and delivery service. You can remove the components from the truck or farm machine and let TA/Petro service them. The cost to fully clean the DPF is $350; it’s $49 for the DOC.
The procedure for cleaning either the DOC or DPF involves four pieces of dedicated equipment. It begins with an airflow test and weighing of the components. This is followed by a mechanical cleaning with air pressure and a dedicated tool, a check of the matrix’s integrity with a lightbox, baking the components in an application-specific oven at 1,000°F. for approximately 12 hours with a computer controlled cool-down rate, and a second flow test.
The TA/Petro service also repairs any worn or damaged mounting or sensor bungs, and provides new gaskets or clamps, as needed. The cleaned DOC and DPF are then delivered to your farm and are ready to go into service.
By taking advantage of services like this, you can keep all your equipment working properly.
Read more about Machinery Repair and Maintenance at Successful Farmer.