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How to Prevent Diesel Soot from Wreaking Havoc on Your Engine



Diesel soot wreaks havoc on engines and is one of the leading causes of costly breakdowns and unscheduled maintenance. Soot consists of a complex structure of pure, hard carbon, surrounded by a sticky layer of organic compounds that cause the particles to stick together and form deposits in your engine oil, turbo bearings, cylinder walls and EGR induction plumbing.


The Diesel Oxidation Catalyst (DOC) in the exhaust aftertreatment system removes the sticky layer and the Diesel Particulate Filter (DPF) traps the remaining carbon, with the exception of poisonous fine particles that pass right through into the atmosphere. The trapped particles in the DPF build up in the filter pores and are automatically heated to a high temperature to convert them to ash in a process called regeneration (regen) that occurs intermittently according to the engine design and calibration of the engine control module (ECM). The frequency of automatic regens will depend upon time of engine operation and the power demand history.


Regens are activated by the differential pressure sensors mounted on the DPF. They signal the need for regen because of high differential pressure. At that point, added fuel is inserted to heat up the exhaust in what is called a “thermal event”, lasting long enough to reduce the differential pressure, perhaps 10-30 minutes, all during the drive cycle. If that process doesn’t reduce the pressure sufficiently, you will get a signal to perform a “parked or forced regen”, lasting about 30 minutes. In a heavy-duty engine during long-haul service, regens will occur in frequency intervals of 20 hours or longer and are a good indicator of how well your DPF is performing. We’ve seen city buses with intervals of 10 hours because of their stop and go drive cycles. If regens are failing to clear the DPF, the engine will be subjected to power derates in increments of 5 mph until you are forced to “limp” into a shut down and perform a parked regen.


What can you do about your DPF loading and regen frequency? Keep tabs on your regen frequency, as you will get a signal on when regens are occurring. As soon as the intervals are dropping below 20 hours, you can perform your own parked regen at a convenient time to clear the filter. Eventually, the ash in the pores gets so bad that you must pull the DPF cartridge for cleaning in a special machine that probes each pore. If you are running stop and go drive cycles, such as in cities or on a bus, performing your own regens is a reasonable idea. This graph from California Air Resources Board indicates how the frequency of regens (in miles) varies with vocational application.


The graph below, also from CARB, indicates how heavy-duty diesel vehicle (HDDV) active regenerations have increased in their frequency by model year.


As for what you can do to reduce soot formation and regen frequency, SPI.Systems has a solution. Our studies indicate that the improved combustion created by the SPIER System can cut diesel soot formation by up to 50%. That means less filter maintenance and cleaner engines. Savings include fewer turbo failures, reductions in EGR system repairs and soot contamination, and longer engine life. The added benefit is that SPIER also reduces fine particle count by preventing their formation right in the cylinder, which means significantly fewer harmful emissions released into the atmosphere. In fact, using the SPIER System, diesel engines exceed EPA 2027 emission requirements.


Clearly, the negative impact of diesel soot on the environment and on engine performance can be minimized. That’s great news for the trucking industry because less contamination in critical engine systems means fewer breakdowns, lower maintenance costs, and more uptime, which are positive outcomes that fleet owners, mechanics, and drivers are always striving to achieve.

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