- Microbial Growth
- Fuel Degradation
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…)