Aqueous DPF Cleaning - Why and how
DPF devices are simple in principle; trap particulate matter found in the exhaust stream in a honeycomb structure to allow the particles to "cake" and burn up easier. In doing so, solid particles are burnt to gaseous emissions that can be converted into a more environmentally friendly exhaust stream. Not everything in the exhaust stream can burn up, though. Soot burns off, ash does not. Ash is the incombustible byproduct of additives found in fuel or oil. A few examples of incombustible ash are anti-wear oil additives like zinc or oil detergents such as calcium. Soot is commonly black, where ash normally has a red, gray, or white tint.
Regens and conventional bake-and-blow methods are effective against soot, however, compacted ash cannot be removed using heat and air as it is incombustible. Ash is commonly not a loose dust like the name suggests, but rather a hard metallic plug deep inside the cell structure of the DPF. Accumulated ash does not pass through the filter, either. It will restrict airflow at any point that ash has accumulated within the filter.
For a fleet or repair facility, high ash content within the DPF can cause recurring regens, high backpressure, and ultimately downtime. Regeneration burns soot, but does not eliminate compacted ash. As ash accumulates over time, backpressure increases, which can be detected as high differential pressure. Restriction within the DPF will shorten intervals between regens until component replacement or cleaning is necessary. Restriction from ash within the exhaust system can also damage critical components if left unaddressed, such as turbochargers, sensors, and cylinder heads due to increased backpressure, increasing component strain and ultimately shortening the lifespan of expensive components.
Most dealerships and repair facilities use an air based bake-and-blow method. While effective against soot and some loose ash, compacted ash is largely untouched, and any kind of contamination found within the filter is typically grounds for an immediate red tag and rejection of the filter. Coolant residue does not bake out, and oil or fuel contamination is typically too great of a fire hazard for the dealership to execute a bake. Common bake cycles peak at ~1,200f, well above the flash point of diesel fuel and oil. In the event of a fuel or oil contaminated filter, a fire from within the filter may deform, crack, or even melt a DPF. Aqueous cleaning can help remove certain contaminants without the high temperatures of a bake cycle, allowing suitable filters to be cleaned after proper assessment.
Where other cleaning methods fail to clean ash, aqueous cleaning shines. By soaking the DPF in water, the ash deposits are able to detach from the cell walls. A stream of low pressure, high volume water can then be used to push out cell plugs and residual ash coatings. Typically, no additional chemicals are needed, and waters neutral pH means that filter material and integrity is preserved better than bake-and-blows or chemical treatments.
Our preferred aqueous cleaning system, the EnviroMotive Evacuflush, uses a recirculating water system to clean DPF filters by hand. Unlike fully automated cabinets that distribute water across the filter face, the Evacuflush allows us to target specific troublesome areas, giving us greater control over the cleaning process. High volume, low pressure water is used to flush out soot, ash, and contaminants by gently flushing and recirculating into a holding tank. The reclaimed water is treated to help separate contaminates, which collects into a catch basin for disposal. The cleaned water is then passed through a series of filters before being reused again. Reclaimed soot, ash, and any other byproducts that are removed from the water are disposed of within regulation.
At Greenmile DPF Cleaning, our EnviroMotive Evacuflush system allows us to use a hands on aqueous cleaning process to target accumulated deposits throughout the filter. Combined with restriction and flow testing, this approach helps us evaluate filter condition, restore airflow, and help customers make informed decisions about cleaning versus replacement.
Backsplash image by by Daniel Sinoca on Unsplash
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