fo systems

Fuel to be used is first transferred from storage tanks to a settling tank in which it is heated to allow some water and sludge to settle out by gravity and be drained off. The fuel is then passed through the purification system and discharged to a daily tank. There are usually two daily tanks, used alternately, one in use while the other is being recharged. Settling and service tanks are lagged to conserve heat.

A recommended standard of treatment for residual fuel to be used in a large engine requires two centrifuges of adequate capacity operating in series. The first acts as a purifier to remove water, solubles, sludge etc while the second acts as a clarifier to remove solids. The purifier must be fitted with the correct disc or dam to match the oil density. The oil is heated before purification (max. temp. 98°C) and the rate of throughput is limited to assist efficient separation. Both centrifuges must be cleaned frequently. Such systems can operate effectively on oils of densities
up to 0.99. Westfalia also advocate using a similar system on their unitrol system with heavily contaminated fuels with densities above 0.991

From the service tanks the treated oil is pumped through a pressurised fuel system to the engine. With the oil temperatures necessary for high viscosity fuel, and the possibility that a trace of water may still be present, it is necessary to maintain the engine pump suctions and circulating connections under pressure to inhibit boiling, gasification and cavitation.

The sketch above illustrates a fuel oil supply and return system incorporating a heater and viscotherm. By-passes, valves, and duplex pumps and filters have been omitted for simplicity. However, both the heater and the viscotherm would be fitted with a by pass, and the heater steam supply could be controlled by hand if required. There will be more than one heater to allow for redundancy, and there would be two supply pumps and two booster pumps.

Fuel leaves the settling tank via a quick closing valve and passes through the change over valve and suction filter before entering the mixing column, where it mixes with fuel from the return line before being pumped through the heater by the booster pumps. After the heater the fuel viscosity is monitored by the viscotherm. An amplified output signal from the viscotherm operates the heater control valve. The fuel then enters the engine fuel rail via a set of backflushing filters. The fuel is continuously recirculated back down a return line to a mixing column, from where it enters the system once again; this ensures that the fuel in the fuel rail is kept at the correct temperature to maintain the desired viscosity. The system will be lagged to prevent unnecessary heat loss, and may well be fitted with trace heating.


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