- Microbial Growth
- Fuel Degradation
Clean fuel is necessary for the proper function of modern equipment. Without it, you risk increased downtime and inflated maintenance costs. This is especially true with newer equipment, which requires extremely clean fuel in order for the manufacturer to meet their government mandates for clean emissions. Additional fuel quality challenges have arisen due to recent changes to fuel chemistry itself, further increasing the need for efficient filtration.
Dirty Fuel Damages Engines
Dirty fuel will cause premature parts failure in equipment of any age. Because of the extremely high pressures, this damage is even more pronounced in newer equipment with HPCR fuel systems. Hard particulate is commonly referred to as “dirt”, but is in fact made up of a wide variety of materials found at job sites (coal, iron, salt, etc.), generated by fuel tanks and lines (rust, corrosion, etc.) and inside engines (carbonatious materials and wear particles).
Damage Caused by Hard Particulate
Hard particulate causes problems with moving parts in the fuel system. This can lead to starting problems, poor engine performance, idling issues and potentially complete engine failure.
The spray pattern generated by the HPCR injector is critical for proper combustion and overall fuel system performance. It must be extremely precise in terms of quantity, distribution and timing. Ball seat valves are sealed with balls that are only 1mm in diameter. A good seal is absolutely necessary for proper injection. Damage from erosive wear, such as shown below, will cause over fueling, leading to decreased fuel efficiency and eventually shut you down altogether.
Pump performance can also be compromised by scoring and abrasive wear. These issues are magnified by the tighter tolerances and extreme pressures in HPCR engines. In these circumstances, it is the smallest particles (1-5 microns in size) that cause the most damage, virtually sand blasting part surfaces.
How Does Dirt Get Into Fuel?
Dust and dirt are all around us, especially on job sites. Fuel fuel is fairly clean when it leaves the refinery, but becomes contaminated each time it is transferred or stored. Below you will find some of the key contributors of fuel contamination:
Pipelines: Most pipelines are not new, and certainly not in pristine condition. Corrosion inhibitors are added at most refineries to help protect pipelines, but rust and other hard particulate is nevertheless picked up by the fuel that flows though them.
Barges and rail cars: How often are they drained and scrubbed out? What was in the last load? Where did it come from? How much of it was still in the tank when your load was picked up? How long was it in transit? Is the tank hermetically sealed? There are lots of opportunities for contaminants to make their way into the fuel.
Terminal tanks: Terminal tanks usually see a high rate of turnover, so there is not much time for the fuel to pick-up contamination from outside ingress. Has the tank ever received a “bad load” from a pipeline or a barge? Has larger dirt had a chance to settle on the bottom of the tank? How often has it been cleaned out? Was it just filled? Did the bottom get churned up in the process? How full was the tank when your fuel was loaded into the delivery truck? There are many variables that can affect fuel cleanliness.
Delivery trucks: All the same issues that apply to stationary tanks also apply to tanker trucks, except that truck tanks never get a chance to settle. In addition, have you ever considered how much dirt gets into that tanker while it is delivering fuel to a customer, potentially a customer in an extremely dusty environment? As fuel flows out, air is sucked in to displace it. Is there anything protecting the inside of the tank from all the dust in the air? Generally not. Venting is typically completely unprotected, as seen in the image to the right.
Storage tanks: Onsite bulk storage tanks typically see less rapid turn-over than terminal tanks. In addition to those issues, yard and jobsite tanks can also develop serious problems with other sources of contamination, such as the ingress of dirt and water, condensation, rust, corrosion, microbial growth, glycerin fall-out and additive instability. Time and temperature become big factors affecting fuel quality.
Dispensing process: How far does your fuel need to travel between the bulk tank and the dispenser? The more pipe it runs though, the more potential there is for contamination. Are your dispenser nozzles kept clean? Are they ever dropped on the ground? Then what? What about the vehicles’ fuel tank inlets, are they clean? Think about the extremely tight tolerances in your fuel system, then take another look at housekeeping issues. You will see them through new eyes.
Onboard fuel tanks: Contamination continues even after the fuel is in the equipment. What has that tank seen in the past? Has it been left stagnant for long periods? What kind of protection is there on the equipment’s air intake vents? Heavy equipment does hard, dirty work.
Engines: Unfortunately, even if the fuel in your tank could be perfect, additional contamination is generated by the fuel system itself. Wear particles are created by mechanical friction. High heat and extreme pressure generated inside the modern engine, lead to coking and the creation of carbon products at the injector. Much of this internally produced particulate is returned to the fuel tank along with the unburned fuel.
Water is the Enemy of Fuel Engines
Water has always caused rust and corrosion of fuel system components and infrastructure. Modern fuel systems are so much less tolerant than lower pressure systems, that manufacturers now specify zero free water must reach the engine.
Water causes damage to both fuel tanks and engine parts. Rust and corrosion in the tank create hard particulate that is passed along in the fuel, causing engine wear. Component life is also shortened by water etching, erosion, cavitation and spalling, such as:
Rust: In contact with iron and steel surfaces water produces iron oxide (rust). Rust particles that get into the fuel, like other hard particulates, will cause abrasive wear to parts. Premature wear can cause part failures.
Corrosion: Corrosion is one of the most common causes of injector problems. Water combines with acids in the fuel to corrode both ferrous and non-ferrous metals. This is made worse when abrasion exposes fresh metal surfaces that readily corrode. The injector shown on the left was installed new but failed in under 300 hours due to rapid corrosion.
Abrasion: Water has lower viscosity than fuel, therefore providing less of a lubricating “cushion” between the opposing surfaces of moving parts. This leads to increased abrasive wear.
Etching: Etching is caused by water-induced fuel degradation which produces hydrogen sulfide and sulfuric acid that “eat” metal surfaces.
Pitting and Cavitation: Pitting is caused by free water flashing on hot metal surfaces. Cavitation is caused by vapor bubbles rapidly contracting (imploding) when exposed to sudden high pressure, which causes them to condense back into a liquid. These water droplets impact a small area with great force, causing surface fatigue and erosion.
Spalling: Occurs due to hydrogen embrittlement and pressure. Water is forced into microscopic cracks in metal surfaces. Then, under extreme pressure, it decomposes and releases hydrogen in a “mini-explosion” which enlarges the cracks and creates wear particles.
Ice: Free water in fuel can freeze, creating ice crystals that behave just like any other hard particulate. They can create wear in fuel systems and (in large volumes) clog fuel filters. A fuel filter’s job is to protect the engine by stopping hard particulate. Engines and filters do not differentiate between dirt and ice. Damage caused by ice can be hard to correctly diagnose since the ice will melt and disappear long before a lab examination can occur.
Indirect Damage Caused by Water
Soft Solids: Water is polar. Certain chemicals in additives are polar. Hydrocarbons are non-polar. This means that water and polar chemicals are attracted to each other. In the presence of free water, the chemical molecules will sometimes disassociate themselves from the hydrocarbon chain of the additive and combine with water molecules to form a new substance. The new material is a soft solid that precipitates out of the fuel and can rapidly clog filters or create engine deposits. See additive stability for more information.
Microbial Growth: Like most living organisms, bacteria and fungi (molds) need both food and water to survive. If free water is present microbial growth can proliferate, creating slimes that foul your fuel and acids that corrode your tank and fuel system.
Fuel Oxidation: Free water accelerates the oxidation process and encourages the formation of acids, gums and sediments known generally as fuel degradation products.
Indirect Damage Caused by Water
All fuel contains some percentage of dissolved water. The water molecules remain part of the fuel until there are too many of them. The point at which the fuel can hold no more water is called the saturation point. The quantity of water in fuel is measured in ppm (parts per million). As long as the water stays below the saturation point as dissolved water it is typically not too much of an issue.
Significant problems start when water separates from fuel and becomes free or emulsified water. Emulsified water is another form of free water; the droplets are simply so small as so well mixed into the fuel that they remain suspended rather than dropping to the bottom. There are no “droplets” when water is fully dissolved in fuel.
How Does Water Get Into The Fuel?
Water can come from a wide variety of sources, some of which can be extremely difficult to control.
- On delivery from supplier
- Free water fall-out (beyond saturation point)
- Condensation in tank
- Leakage into tank (rain, pressure washing, ground water…)
- Ingress from atmosphere (humidity)
- Human error (unprotected vents, fill ports, seals…)
Microbes Eat Fuel and Multiply
Microbes are present everywhere, but without food and water they cannot multiply; fuel is food. When there is free water in the tank, the microbes have everything they need to grow, fouling fuel and damaging tanks in the process. By some estimates, a microbial colony can consume up to 1% of your fuel investment, while destroying the rest.
Microbes Need Food and Water
Microbial colonies proliferate at the interface between fuel and free water that has settled to the bottom of the tank. This creates a “rag layer” which gives them everything they need to thrive. Warm temperatures will accelerate the growth of microbial colonies. Microbial growth can occur in any fuel. Biofuel, being made from plant and animal fats, makes especially good food for these bugs and contributes to the increased incidence of biological growth problems seen in recent years. Bugs can grow in petro fuel as well. Stagnant fuel is especially at risk.
Degraded Fuel Becomes Unstable
With time the microbial colony proliferates beyond control. This leads to acid formation, rust, corrosion and filter plugging. Fuel degrades to the point that it can form a slimy sludge that is unusable as fuel.
This process can occur in a bulk storage tank or in a piece of equipment that is left idle for a long period of time. To the right is a classic example of what is called filter “leopard spotting”, which requires the filter to be exposed to both microbes and water. The black spots are microbial colonies. Live or dead, microbes will clog filters and damage fuel systems. It is important to eliminate bugs completely and permanently.
Fuel Has A Shelf Life
ULSD and biofuel both have reduced stability in storage compared to traditional high sulfur fuel. While it is true that removing sulfur improves stability, the hydro-treating process also tends to destroy naturally occurring antioxidants. As a result, some ULSD fuels may require the addition of a stabilizer to prevent the formation of peroxides that lead to soluble gums. Shelf life recommendations for petro fuel and biofuel blends are less than a year, and sometimes as low as 2 months, depending on factors below.
Consequences of Unstable Fuel
Oxidative instability in petro fuel or biofuel leads to the formation of fuel degradation products. These include:
Gums: sticky varnishes that contribute to corrosion and injector deposits, causing over or under fueling
Sediments: particulate that clogs filters and causes abrasive wear to fuel pumps and injector.
Acids: cause corrosion of tanks and fuel systems, leading to hard particulate formation and premature parts failure.
Thickeners: increase fuel viscosity, leading to incomplete combustion and reduced fuel economy
Common consequences of fuel degradation include loss of power, increased fuel consumption, premature filter plugging, damaged fuel pumps / injectors and increased maintenance costs. Generally speaking, fuel degradation decreases the combustion quality of fuel. You may notice symptoms such as black smoke, harder starts and reduced engine performance.
Fuel Degradation in Storage
Time is the enemy of diesel fuel quality. Oxidative instability can occur slowly during long-term storage or be accelerated by warm temperatures, the presence of free water and contaminants. This degradation can lead to high acid number, high viscosity and the formation of gums and sediment (fuel degradation products). Biofuel is especially susceptible to the effects of higher temperatures. Data sets vary, but a good rule of thumb is that the oxidation rate increases 2.2 times for every 18°F/10°C.
Example: biofuel blend stored at various temperatures
68°F/20°C: marginally OK after 6 months
77°F/25°C: degraded after 6 months
86°F/30°C: degraded after 4 months
Water in fuel can accelerate the oxidation process, but even worse are the effects of the microbial infestations that can grow as a result of water in the tank. These bacteria and fungi literally feed off your fuel, leaving behind acids and various forms of black, sticky, slimy materials that corrode your tank and plug your fuel filters. Whatever the contributing factors fuel degradation cannot be reversed, the key to success is to prevent it before it occurs with good fuel handling practices.