Fuel Quality

During the last fifteen to twenty years, diesel fuel characteristics in the United States have undergone numerous changes that can have a severe impact on operations and profitability. Standard diesel fuel specifications, however, have undergone very little change during the last several decades. Technology demands, market trends and processing changes have seriously affected the use and storage of No. 1 and No. 2 fuels. The specifications which have been in effect for the past 50 years were very general guidelines which required the fuel to pass a limited number of tests designed to measure how fuel performed under controlled conditions and very tolerant engine and storage systems. The limited number of tests that make up the current specifications do not cover many physical properties that severely impact storage and operation today.

Further changes are being forced by future emissions regulations. Diesel composition and specifications will be forced to change in order to comply with these regulations. These changes include restrictions on certain fuel components, such as sulfur and aromatics, which have an unfavorable effect on exhaust emissions. However, they currently do not address the negative impact on certain fuel characteristics, nor do they address the side effects on other important properties when producing these new fuels.

A successful business that consumes middle distillate fuels must develop a program to regularly test and treat fuels in order to protect and maximize it’s bottom line interests. This program should ensure proper housekeeping and fuel performance enhancement that meets their localized needs.

Below is a brief summary of contaminants and fuel components that could potentially be present in fuel.

Entrained Water
One of diesel fuel's most favorable characteristics is its natural ability to shed water and thus prevent fuel/water emulsions. Recently, however, many diesel fuels have shown a disastrous tendency to absorb and hold large quantities of water. These fuel/water emulsions greatly reduce the effectiveness of fuel/water separators and rapidly plug fuel filters. Typical causes of entrained water levels include microbial activity, surfactants, alcohols, particulates, and poorly designed fuel additives. 

Free Water
Poor housekeeping is probably the largest contribution to the free water problem. Water enters bulk fuel tanks via condensation, carry-over from fuel distribution systems, leakage through the fill cap, spill contaminant valve or piping. The fuel water interface can raise to the fuel draw level when water bottoms are allowed to build up. This can allow significant quantities of water to be pumped into vehicle fuel tanks.

In either case, moisture promotes microbial activity, fuel/water emulsions, rust and corrosion. The more water dispersed in fuel or present in the fuel system, the greater the tendency for ice crystals to form and grow when the fuel temperature falls below the freezing point of water.

Free Water and Sediment test method D2709

Particulates
The more commonly recognized particulate contaminants found in diesel fuel are rust, dirt and sludge. However, diesel fuel can also form its own solid particulate contamination as it undergoes complex chemical changes known as oxidation and polymerization. In addition to oxidation, certain microbes grow in fuel. Their waste products contribute to the overall particulate contamination.

Particulates become trapped on filter surfaces, tank walls and fuel lines. The result is a shortened fuel filter life, dirty fuel tanks, clogged lines, and plugged screens. Recently many fleets have seen fuel filters plugged with "black goo", which can be caused by the particulates, which are often a result of thermally unstable fuel. The fuel filter may not trap finer particulates that may cause fuel system wear, plunger damage, increased deposit formation and premature fuel pump wear.

Surfactants
Surfactants are substances that reduce the surface tension of /fuel/water and thereby promote fuel/water emulsions. The surface-active compounds come from various sources, including refinery treatment chemicals, naturally occurring materials not removed from the crude oil, pickup from other products in the distribution system, poorly formulated additives, lubrication oil blended into the fuel and even microorganisms.

Surfactants need to receive increased attention by fleet operators because they are instrumental in causing slow water settling in fuel storage tanks and preventing the coalescing of water by fuel/water separators. Surfactants will also disperse microorganisms, rust, dirt and water throughout the fuel system. Certain types of surfactants actually cause fuel filter restriction simply by giving the fuel an electrical charge.

Microbial Contamination
The most common means by which microbes enter the fuel system is through air drawn into the tank as fuel is dispersed or used, as in the case of vehicle tanks. Other sources of inoculation are ground water encroachment, portable fuel transfer piping or hoses, or the delivery of the fuel itself.

As bacteria and fungi reproduce, they form a biomass, which accumulates at fuel/water interfaces, tank surfaces, filters or any place in the fuel system where microscopic droplets of water exist. As metabolic waste and dead cells accumulate, they settle out as sludge. If sufficient sludge builds up, particles will be drawn out of the diesel fuel. As a result, filters and orifices may become clogged. More often, filter and line plugging results from bio-film formation on transfer line walls and filter surfaces. Reduced filter life also goes unrecognized in many operations where chronic microbial contamination goes unrecognized. It is only after biomass production is inhibited and the consequent longer filter life is achieved that the existence of the problem is recognized.

Occasionally, catastrophic failures, such as engine shut down due to fuel starvation, provide convincing evidence of the importance of contamination control. One of the more sinister aspects of the filter-plugging problem is that often the bio-film is nearly transparent and goes unnoticed. Microbial induced corrosion can severely damage main storage tanks, vehicle tanks and fuel lines. This is usually noticed when catastrophic failures occur. Another effect of flow restriction is increased engine wear. Non-uniform flow causes variation in combustion within cylinders. Increased piston wear rates and increased torque on camshafts translate into higher maintenance costs.

Peroxides
The refinery process used to produce low sulfur fuel can lead to unexpected consequences. One area of concern is the increased tendency for some severely hydrotreated fuels to form peroxide levels high enough to be incompatible with fuel system components. Peroxide formation in severely hydrotreated aviation fuel has been recognized for some years. Problems of fuel system elastomer hardening and cracking from exposure to high peroxide levels in aviation fuel have been experienced in the field. The tolerance of aviation fuel systems to various levels of peroxide was investigated in the laboratory. This has led to the specification for limiting peroxides in some military fuels and in the requirement for the addition of antioxidants if the fuel contains hydrotreated components.

Recent studies have found that a large number of low sulfur diesel fuels have the tendency to form high levels of peroxides. These studies should also raise concern that high peroxide levels could, in fact, damage fuel system components. With the initial introduction of low sulfur fuel, many fleets experienced fuel system elastomer failures. Peroxide formation in low sulfur fuels may be a problem for many years to come. 

Housekeeping practices can make the difference between success and failure. The most successful companies have a program that includes good housekeeping practices, regular fuel analysis, and the proper application of additives.

Call 1-800-228-3848 to speak to our highly trained service representatives.