Diesel Fuel and the Sources of Problems
by Michael D. Holloway, MLT I, OMA I, CLS
Manager Strategic Accounts & External Training, Tribology

Industry surveys show that diesel fuel contaminants are the #1 cause of poor engine performance. Condensation, rainwater and seepage can cause water contamination in fuel. The presence of water in the fuel causes poor combustion, clogged filters, promotes rust and corrosion formation, increases the likelihood of fuel line freeze ups, and enables bacterial and fungal growth.

Water in fuel storage tanks is a major problem, particularly for companies who have to store large amounts of fuel for stand-by, back-up generator systems. Water from condensation due to temperature changes contributes to rust that forms within the void between the level of fuel and the tank. This rust falls away and causes sediment within the fuel. Other sources of water ingress are through poorly maintained manhole access points. These can fill with water and seepage can occur through filler caps, breather points, tank lids and faulty seals. Faulty tanks and cracked pipe work can all contribute to contamination problems within storage tanks.

There are many types of bacteria and fungus that feed on the hydrocarbons in diesel fuel. Bacteria and fungus enter fuel through water contamination or air vents. Biological growth causes slime formation and eventually dead bacteria will clog filters and injector tips. The microbes produce acids which can cause leaking storage tanks and worn injectors. From the terminal tank to the diesel engine tank the potential sources of contamination are not only water but dust from the environment through storage tank breathers and engine fuel tank breathers. Engine builders and fuel injection equipment manufacturers have found that the particles greater than 4 microns and greater than 6 microns are particularly critical to the durability of the fuel injection system. Fuel injectors now have tolerances in the 2 um to 3 um range. Final fuel filtration now targets 2 microns and up which is why plugging is a bigger issue now than ever before.

To maximize the efficiency and effectiveness of filtration, many engine manufacturers adopted the recommendation of the World Wide Fuel Charter that fuel supplied to engines meet the ISO 4406 code of 18/16/13 maximum for respectively 4, 6, and 14 micron particle sizes. Many engine manufacturers recommend that if the fuel does not meet the ISO cleanliness code of 18/16/13 in bulk storage, additional filtration be applied before the fuel is delivered to the equipment's fuel tank. The recommend ISO cleanliness of fuel at the injector is 12/9/6. If the fuel to the tank exceeds 18/16/13 then onboard filtration will not get the fuel to 12/9/6 at the injectors, and fuel filter plugging will occur.

The fuel cleanliness issues start at the refinery. There the fuel output filtration is typically between 50 and 80 micron. Particles smaller than this are unfiltered and remain in the fuel. The contamination continues when the fuel is taken from the refinery as it may go through several more transfers before reaching the final place. The tank, boats, tankers, barrels can all contribute to dirt and water ingress. The most damaging particle size in a lubricated system such as an engine is between 5 to 15 microns. For fuel systems, particles in the 2 to 3 micron sizes are the most abrasive size and are the cause of shortened component life. A 2 micron particle is the perfect fit between micro-machined clearances and would actually grind away on metal surfaces, causing accelerated wear resulting in a drop in pump pressures and injector erosion.

Many years ago the maximum diesel fuel system pressures rarely exceeded 3000 psi. Today's advanced systems can be as high as 30,000 psi and therein lies the problem. The high pressures combined with the opportunity for increased wear of the injector housing leads to fuel entering the combustion chamber pre or post combustion. When this occurs there is a build-up of soot and/or fuel dilution of the engine oil leading to reduced viscosity and increased engine wear.

The following various tests that can be performed on diesel fuel in order to gain an understanding of emerging problems:

Water and Sediment: Water and sediment lead to rust, corrosion and filter blockage as well as wear on pumps and injectors.

Viscosity: The viscosity affects fuel spray atomization and fuel system Immediate and lubrication. It also affects fuel system leakage.

Ash: Ash can contribute to bore polishing of the liners and valve seating problems

Cetane Number: The cetane number test measures ignition quality affects cold starting.

Fuel Stability: This test indicates potential to form insoluble gums, abrasive particles, and immediate gum/residues in the fuel during storage due to aging degradation.

HFRR: The High Frequency Reciprocating Rig tests the lubricity of fuel. Reduced sulfur concentrations has reduced diesel fuel lubricity which may contribute to increased wear.

ALS can test diesel fuel for these properties as well as many more. Contact us to learn more about how ALS can assist with your diesel fuel management program.