Polishing fuel first step to keep maintenance costs at bay

Nov 20, 2015 by Capt. Jeff Werner

Have you ever heard anyone say this: “We don’t have problems with our fuel because our boat is always moving, and we burn through the diesel in our tanks very quickly.”

It is not uncommon to hear that reaction when questioning a captain or engineer about the cleanliness of the diesel fuel aboard their yacht. There are plenty of misconceptions about diesel fuel maintenance, and this is probably the most widespread one.

Diesel fuel is the lifeblood of the main engines and generators aboard every yacht. Ideally, fuel should be polished and the tanks cleaned whenever the yacht is refueled, or monthly if the yacht is not fueled frequently. Implementing and strictly adhering to a fuel preventive maintenance program is a simple and inexpensive alternative to the cost of repairing severely damaged high pressure pumps, injectors and pistons.

The bulkhead mount is one type of fuel polishing, a part of a regular fuel maintenance program onboard yachts. PHOTO FROM MYDIESELDOCTOR.COM

The bulkhead mount is one type of fuel polishing, a part of a regular fuel maintenance program onboard yachts. PHOTO FROM MYDIESELDOCTOR.COM

Microbial contamination of diesel fuel is a fact of life. As a general rule, whenever diesel and water come into contact in a fuel tank, microbes will start to proliferate. Since water is heavier than diesel fuel, it accumulates at the bottom of a tank. The interface between the heavier water and lighter diesel provides the ideal environment for bacteria, mold or other fungi to grow.

Unless this growth is held in check, the result will be clogged filters, tank sludge and injector failure.

Naval architects understand this problem. They design fuel tanks with pick-up tubes many inches above the bottom of the tank. This keeps the sludge, water and particulate matter that settle to the bottom from being sucked up into the engine.

Eventually, the height of the contaminants will rise to a point above the pick-up tube and get pumped through the fuel system and into engines or generators. The immediate result is that the primary and secondary fuel filters get plugged and engine performance drops since the engine is being starved for fuel.

To avoid this problem, the best solution is the installation of an onboard system that will polish the fuel and clean all the tanks. Fuel polishing systems can be powered by direct current or alternating current, depending on the available electrical supply aboard the yacht and the pumping capacity of the system.

The fuel polishing process can be automated with a fully programmable control unit or operated with manually controlled timers depending on one’s budget. The ideal tank cleaning system has dedicated pick-up and return tubes plumbed into each tank, including the day tank. The dedicated pick-up tube is placed lower in the tank than the normal pick-up tube for the engines. This allows more water and sludge to be suctioned up during the fuel polishing process, which assures a better job of tank cleaning.

The best tank cleaning systems are multi-stage systems that use a variety of inline fuel conditioning and filtration technologies, and they don’t rely on just one process, such as a centrifuge.

The first phase of fuel polishing is to pass the fuel through a magnetic conditioner that breaks apart large clusters of hydrocarbon contaminants. Permanent magnets generate a very weak electrical field that separates the bonds holding together the large wax and asphaltene molecules so they are more combustible.

The next phase is a water separator or centrifuge that removes free water.

This step is followed by circulating the fuel through a disposable particulate filter that removes organic and inorganic matter greater than 30 microns in size.

The last phase is final filtration in which particles down to a diameter of three microns or less are removed. This is the most critical step in the fuel cleaning process since particulate contamination is the No. 1 cause of failure in electronically controlled common rail fuel delivery systems in diesel engines.

During the fuel polishing process, an additive is used to dissolve sludge and slime that accumulates on the walls and baffles of the tanks. This procedure assures that mold and bacteria are removed from all tank surfaces.

Once the tank is cleaned and the fuel is polished, an additional dose of fuel additive is mixed into the tank to help guard against future microbial contamination. Use of a full spectrum additive during this step will also add lubricity to the diesel fuel, prevent corrosion, reduce carbon build up and stabilize the fuel.

Fuel polishing is the major component of a fuel maintenance program aboard a yacht. Combined with regular fuel testing, diesel engines will run trouble-free longer, which means less repair costs. And that makes you a hero in the eyes of the yacht owner.

Capt. Jeff Werner has been in yachting for almost 25 years. Contact him through MyDieselDoctor.com.