GENERATOR DAMAGE
paper. Since there are few microbes, there was minimal acid created, so there was little corrosion. With the introduction of surfactants,
Micelle formation prevents the free- standing bottom layer of water from existing. Instead, the Micelles clump to form what is called an invert layer; this layer can be several inches thick. Microbes can grow all throughout this layer, as opposed to just at the thin layer at the water/diesel interface. This thick Micelle layer is very conducive to microbial growth. More microbes produce more acids. To give an idea of how much more
growth volume microbes now have, a package of paper for a home printer is approximately one inch thick and holds 200 sheets of paper. Each inch of Micelle layer provides 200 times the growth volume for microbes, compared to diesel before ULSD. There could be multiple inches of the Micelle layer. The microbial growth volume has dramatically increased; more microbes make more acids, greatly acidifying the diesel (see Fig 5).
Micelle damage to injectors Injector damage has two vectors: l Acidified fuel corrodes all injector metal components; needles, orifices, fuel quantity reservoir, as well as pistons and valves.
l Micelles bypass traditional filters; water droplets scour the injector orifice and needles at 35,000 + psi.
This injector damage greatly increases the risk of backup generator failure (see Fig 6). The damage to orifices and needles disrupts the spray patterns into the cylinder, increasing emissions and fuel use, and reducing power.
Predicting levels of damage There are two main factors that can help predict the amount of corrosion and Micelle damage caused to a storage tank and emergency backup engine: one, the length of time the fuel is stored (1 year, 5 years, 10 years, etc), and two, the concentration of the surfactant used (B4, B5, B10, B20, etc). B4 means the addition of four per cent by volume of biodiesel, and B20 is a 20 per cent addition of biodiesel by volume. The combined effect of these two factors is discussed below.
Surfactant concentrations B4: Samples from field testing over 12 years show unfiltered B4 storage requires around five years for significant contamination of fuel to occur, and by 10 years the fuel has severe contamination, and is well above diesel storage limits for water (as measured by Karl Fisher titration, ASTM D6304), TAN (Total Acid
IFHE DIGEST 2024
Polar head a c Water droplet b d
Nonpolar tail
Figure 2. Surfactants: a) schematic of surfactant molecule showing polar head and nonpolar tail; b) schematic of invert-emulsion Micelle encapsulating water droplet and nonpolar tails extending into the medium (i.e., fuel); c) schematic of invert emulsion Micelles dispersed in fuel; d) photo of 10 mL each fuel and water – left: before shaking; right: 24h after shaking (note stability of invert emulsion).
Number as measured by ASTM D664), and particulate (as measured by ISO 4406). Fuel stored for 10+ years has shown water at 3,000 to 30,000 ppm (generator warranty 200 ppm), TAN of .29 (limits .08), and particulate counts of 25/23/18 (limits 18/16/13). B20: In 2020, the United States Air
Force (USAF) commissioned a yearlong study of B20 storage: In situ linkage of fungal and bacterial proliferation to microbiologically influenced corrosion.4 According to the study, one tank was
pulled after only nine months: “… tank SE 3, which was removed from
the study after nine months due to severe microbiological contamination that required mitigation.” (p2) From the report’s conclusions:
Injector damage greatly increases the risk of backup generator failure
“… Together, they illustrate the
susceptibility of fuels containing biodiesel to microbial proliferation (fouling), fuel biodegradation, and MIC of associated infrastructure. Here though, we were able to directly link the presence and prevalence of biofilms to pitting corrosion in actively operating B20 storage tanks.” (p10)
Effect of time of storage B20 has severe contamination after one year. B4 has severe contamination after 10 years. Other blends (B5, B10) will show severe contamination between these ranges; B10 can be expected to have severe contamination after two years, and B5 after eight years.
Micelle control, SAE J1488 Filtration The Society for Automotive Engineering International (SAE) sets many international standards, such as for engine oil (example SAE 10W40), and for diesel filtration. In 2010, SAE updated their filtration standard for diesel filtration, J1488, to be suitable for testing filtration of biodiesel blends, to address Micelle
Figure 3. Corroded ULSD equipment: Corroded carbon steel submersible turbine pump (STP) shaft removed from pump housing, CA-1 (left); brass ball float extractor cage plug, NY-2 (middle); aluminium drop tube, NC-1 (right).2
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