Ultra-low sulfur diesel’s tendency to form sludge at faster rates than in the past is forcing the marketplace to adjust in ways not anticipated in the past.
It used to be that you could expect to store diesel fuel for fuels without an issue. Given the number of storage tanks out there, there are thousands and thousands of tanks and backup generators that have sat for years with fuel that’s ten or fifteen years old. There’s no telling the amount of diesel fuel tank sludge and microbes they have. And there's no telling what those have done to the fuel quality within. How confident would you be in your emergency generator if you knew the stored fuel inside was ten years old?
When fuel sits for long periods, chemical reactions have plenty of time to break the fuel down. The fuel gets exposed to oxygen and water, the heat from the environment provides the energy, a few unstable molecules form and they react with healthy fuel.
Why is ULSD worse in this respect than in the past? The processing of the fuel to remove the sulfur changes its composition, yielding components that are more sensitive to sludge formation. Not to mention a lot more sensitive to microbial growth (the sulfur used to inhibit this, but it’s not there anymore), which can break down fuel quality even faster.
Diesel fuel sludge is a problem for you on several fronts.
The best practice recommendations to ensure your systems aren’t affected by fuel sludge dropout are several old: treat the fresh fuel with a stabilizer, do annual fuel and fuel tank health checks, stay on top of water buildup, and keep biocide around to knock out microbial contamination. This last part is very important as today's ULSDs are inevitably going to develop microbial contamination. When that occurs, the only solution to fix that problem is to treat it with biocide to kill the microbes.