Automated & Mobile Diesel Fuel Polishing & Cleaning, Preservation & Equipment. Fuel Storage Seminars.

Diesel Fuel Quality

Diesel Fuel Quality & Understanding The Source Of Today’s Stability Problems
Catalytic Cracking and Fuel Stability
Today’s refineries produce higher yielding products while the life of many stored fuels has dropped from years to months.
Fuel and heating oil service professionals with many years of experience remember a time when fuel seemed to last longer. They claim a dramatic increase in unscheduled service calls due to dirty filters and clogged nozzle and fuel injection system failures.
Increasingly, we’re realizing that the increasing fuel-related service calls can be traced to changes in the refining process.

Until the 1970’s most fuel oil was produced using traditional methods of distillation. This process yielded 60% light and middle distillates and 40% heavy products. The energy crisis of 1973 and again in 1979, pressured refiners to explore ways to increase yields of middle distillates like diesel and heating oils. These shortages and pressure to increase yield from current supplies meant the introduction of Fuel Cracking, a process by which long molecule chain (heavy) oils are "cracked" into shorter chains. The results increased yields of lighter and more valuable fuels such as gasoline, kerosene and heating oil at lower costs. But cracking has been a mixed blessing for fuel oil dealers and users. It increased the supply, helping to moderate prices. However, the “new” blended fuel with its artificially broken chains is much more unstable.

Prior to the 1970’s, a simple distillation process produced most heating oil. This fuel sample is almost 35 years old and has produced virtually no sediment.

Shortages and pressure to be produce more high value product from the same quantity of crude oil caused refiners to catalytic cracking, a process by which long chain (heavy) oils are “cracked” into shorter chains. The results increased yields of lighter and more valuable fuels such as gasoline, kerosene and heating oil at lower costs. But cracking has been a mixed blessing for fuel oil dealers and users. It increased the supply, helping to moderate prices. However, the “new” blended fuel with its artificially broken chains is much more instable.

Re-polymerization: In the world of diesel fuel, this is a keyword

During the catalytic cracking process long chain hydrocarbon molecules are broken into shorter chains, which are refined and blended into additional gasoline, kerosene, on and off road diesel fuels and heating oil. Unlike their natural counterparts, the artificially cracked chains have “active ends” – (bonds) which have been broken and which are susceptible to recombining with other unstable molecules. When cracked and or blended fuels are stored, these molecules begin recombining, in a process known as re-polymerization.

This process results in increasing the size and mass of the fuel particle. Often the repolymerized chains join with other chains (agglomerate) eventually into visible particles.
These organic compounds that first form insipient solids continue to grow, turning into black particles (tank sludge) that settle in tanks, clog filters and damage system components.

Although re-polymerization begins at a sub-microscopic level, as long-chain hydrocarbons begin to re-form they agglomerate and form visible sediment. The sample on the right shows the result of this process. The sample on the left was treated with a stabilizer and dispersant to inhibit re-polymerization.

The extent of fuel problems is illustrated in the graph below. Water, biological contaminants
and rust continue to create fuel storage problems and work as catalysts in the process.
Their impact has been dwarfed by problems caused by re-polymerization.

Traditional Problems Still Exist

Although re-polymerization is by far the most significant threat to stored fuel, other more traditional problems remain.

Oxidation
When exposed to air or water, fuel combines with oxygen. In many cases, the result is harmless darkening in color. Oxidation can also result in sediment formation. Many older fuel stability tests still use oxidation as a key indicator.

Bacteria and Fungus
Biological contaminants will grow in fuel tanks, particularly if water is present. Bacterial or fungal contamination as a primary cause of operational problems is much rarer than commonly believed.

Water & Rust
The presence of water and sulfate reducing bacteria cause H2Shydrogen sulfide, leading to rust, corrosion seen as pitting. Water is a necessity for microbial activity, which in turn leads to ionization of the water, making it more corrosive. This phenomenon is known as microbial induced corrosion (MIC). Microbial contamination is one of the accelerating factors in “fuel quality degradation”.

Main Menu