In 1859, when crude oil was discovered in Pennsylvania, the only product that oil refineries made from it was kerosene. That became the inexpensive alternative to whale oil, which lit the lamps of that era.
However, only a small portion of a barrel of crude had the right chemistry to be refined into this new lamp oil. The rest of that barrel produced other liquid by-products that no one had a use for or even named yet.
Enter a German engineer named Rudolf Diesel. In 1892, he received a patent on a reciprocating engine that operated by compression ignition, but he could not find a reliable fuel to power that engine. He began experimenting with refinery by-products and, in 1895, he found one that successfully fueled his engine. That type of engine, and the fuel that runs it, are still known by his name today.
A refinery is just a distillery, and operates the same way a “still” used to make whiskey does. Boil up the fermented mash to evaporate the alcohol, and let the alcohol condense and drip into a pot. A petroleum refinery heats the crude oil in a boiler with superheated steam. Then in the distillation tower, as the vapor cools down to about 300 degrees C, the diesel fuel condenses as a liquid.
Additional diesel fuel is produced by a chemical process called cracking, which breaks down the heavier hydrocarbon molecules of gas oil into the lighter molecules of diesel. And just like blended whiskey, which is composed of a number of different spirits, diesel fuel is blended as a mix of distilled diesel and cracked diesel.
Once this freshly made diesel fuel leaves the refinery it soon begins to degrade, and lose the qualities that make it operate a yacht’s engines and generators efficiently.
The fuel’s next stop, on the way from the refineries in Texas and Louisiana to Ft. Lauderdale, is a tank farm where the diesel is stored until it is shipped. Next, the fuel is sent via pipeline to load into the tankers bound for Port Everglades. Once the tanker arrives in port, the fuel is pumped into storage tanks to await local distribution.
Then the wholesalers use large tanker trucks to deliver the fuel to the retailer who finally delivers it to a yacht, either from a marina pump, fuel barge or small fuel truck. Unfortunately, contamination can creep into the fuel at every step along this supply chain.
Diesel fuel is hygroscopic, which means it readily absorbs water from moisture in the air. Much of this water becomes bound up with the fuel, but as the fuel sits in a tank, some of it dissociates and falls to the bottom.
Since water is heavier than diesel, the bottom of a fuel tank contains a layer of water and above it a layer of fuel. The boundary between these two layers, or fuel-water interface, presents ideal conditions for microbial growth.
Bacteria, fungus, yeast and mold living in the water feed on the rich hydrocarbons in the fuel. Some microbes form a slime that coats the walls of the tank and encourages larger colonies of bacteria to grow. If a large piece of biomass breaks off the tank wall, it can clog fuel lines and filters.
Water also contributes to corrosion in steel tanks, which causes rust particles to enter the fuel system. Additionally, the acidic waste products of microbial activity cause pitting and pinhole leaks in steel tanks and weakening of fiberglass tanks.
As diesel fuel ages, processes called re-polymerization and agglomeration occur. These are diesel’s natural tendency to reform as larger molecules of gums and resins that fall to the bottom of the tank and develop into asphaltenes or sludge.
All fuel tanks, from large storage tanks to engine supply tanks, are vented. The vent allows air pressure to equalize in the tank as the fuel is used. This vent also allows moisture and microbes from the air to enter the fuel.
Pipelines, ships tanks and tanker trucks that have not been cleaned properly all add to the possibility of dirty fuel getting delivered to a yacht. All it takes is just one weak link in that supply chain. The result may be a brew of water, organic and inorganic contaminants being pumped into a yacht’s fuel tanks along with the diesel you paid for.
Capt. Jeff Werner has been in yachting for more than 20 years on private and charter yachts, both sail and power. He is an instructor for RYA, MCA, USCG and US Sailing courses and owns Diesel Doctor (MyDieselDoctor.com). Comments on this column are welcome at firstname.lastname@example.org.