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Contaminants Found on Diesel Fuel Storage Tank Filters

IASH 2011 – 12th International Conference on Stability, Handling and Use of Liquid Fuels

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Donaldson Company, Inc. | October 2011

3 case studies of observations made from field samples of diesel fuels taken from plugged storage tank filtration applications; takeaway = soft and deformable contaminants were primary cause and engines need to be protected from hard particulate smaller than 4 microns

  • ISO 4406 contamination code (defines number of particles per mm of fuel having diameter larger than 4, 6, and 14 microns) is 18/16/13 – newly delivered fuel rarely meets standard
  • Fuel delivered to bulk storage facility has average cleanliness level of 22/21/18, meaning if fuel is going to meet fuel injector and engine manufacture specification of better than 12/9/6 at the fuel injector, fuel must be at least 64-1000x cleaner than it was delivered to the bulk storage facility
  • Authors suggest changing standard to 14/13/11 for fuel leaving bulk storage facility
  • Volume of dirt exceeds empty volume of typical fuel filter can; filters must have efficiency rating of less than 4μm at a Beta ratio of 2,000 or more. This is the only rated filter provided that is capable of providing a cleanliness level of 14/13/11 at the tank on-vehicle
  • Case 1: Additive plugging of bulk fuel storage high efficiency filters
    • Small civil engineering company in Iowa experiencing on-vehicle fuel filter plugging – fuel was supplied to vehicles from 4 10,000 gallon above ground tanks with 30μm nominal filtration on the tank outlet
    • 3 tanks were clean and dry, one tank had microbial contamination
    • High efficiency filters were installed on inlet to prevent delivery of dirt into the system and on the outlet to prevent delivery or contamination into vehicles, and tanks were fitted with water absorbing breathers to prevent dust and water ingress as the tank breathes upon filling and emptying
    • From August 2009 through Winter 2010, fuel samples were taken every 2 feet throughout depth of the tank and evaluated for temperature, water content, and particulate analysis; temperature of headspace of tanks fluctuated from 80°F to less than 0°F over the different seasons, and throughout testing none of the tanks developed free water at bottom
    • Delivered fuel cleanliness was determined to be ISO 23/22/19, it was then pumped through high efficiency 4μm filters so that cleanliness level of fuel within tank was ISO 14/13/11
    • In April 2010 the stored fuel was dispensed by pumping through high efficiency 4μm filters, but filters plugged after pumping only 300 gallons
    • Analysis revealed all contaminants were soft and deformable, primarily made of carbon and oxygen (no evidence of hard particles) - carbonyl (-C=O) and hydroxyl (-OH) or amine (-NH) functional groups were present
    • Additives were found to be primary contaminants: n-hexadecamide and noctadecamide, compounds known to be additives in diesel fuel, were present
    • In other cases and in this one, these contaminants were found on inlet filters especially for winter fuel deliveries = they are understood to be known fuel additives, but not clear why in this case they were initially soluble in the fuel but their solubility decreased over time
  • Case 2: Plugging of low efficiency bulk fuel filters with biodiesel compounds
    • Quarry using 50/50 splash blend of ULSD/Biodiesel experienced plugging of low efficiency 32μm cellulose fuel filters placed on the outlet of their bulk fuel storage tanks
    • Soft, deformable contaminates made of carbon and oxygen – spectrum was different than Case 1, but did indicate presence of carbonyl and hydroxyl functionalities
    • Analysis showed presence of typical components/byproducts found in biodiesel: glycerin, fatty acid methyl esters, and monoglycerides
    • Monoglycerides were found to be primary fuel filter contaminants
  • Case 3: Precipitation of fuel additives and biodiesel compounds from laboratory fuels
    • Donaldson’s attempt to replicate soft contaminant filter plugging in the lab by investigating the fallout of additive and biodiesel compounds from a 5% blend of soy-based biodiesel and ULSD (B5)
    • Fuel was placed in lab refrigerator at 4°C overnight – there were several precipitates found in the cold samples, including a fluffy contaminant that did not readily settle out of solution and a white granular material that did settle out of solution – none of the precipitates readily went back into solution upon warming to room temperature
    • Analysis of contaminants revealed carbonyl, hydroxyl, and possibly amine/amide functionalities – monoglycerides and possibly an amine or amide additive were present
    • Similarity of contaminants found in lab experience to those found in field applications raises concern regarding stability of blends and additives – there is a need to address soft and deformable contaminants within fuel cleanliness specifications
  • Summary
    • Modern diesel engines need to be protected from all hard particles smaller than 4μm
    • Due to cleanliness of delivered fuels, on-vehicle fuel filtration will suffer from lack of capacity and therefore, filter life
    • Soft and deformable contaminants constitute the bulk of contaminates on filters on-vehicle and at bulk fuel storage facilities
    • The case studies show that the soft deformable contaminants arise from several mechanisms and sources and result directly from the fuel itself
    • Fallout (poor solubility) of additives and biodiesel components are shown to be problematic
    • Today’s fuel cleanliness standards and specifications do not address these contaminants

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