Figure No. 8 Fuel into Ship's Tanks
Fuel tanks must be inspected regularly to make sure that they are free of water and/or hydro carbon sludge. They should be cleared from rests of the previous batch as far as possible for reasons given before: compatibility and indisputable composition and / or origin.
Fuel tanks must not be used for ballast water and vice versa for quality and environmental reasons.
As said before, fuels of different origin and bunkered at different times must not be mixed, not with each other, and not with distillates like MDO in an attempt to improve the quality.
3.7 The Fuel Treatment System
The two most important precondition s for an unproblematic fuel treatment are:
- The equipment must be of satisfactory capacity to clean the worst fuel quality the engine is specified for by the OEM.
- The ship's crew must have the competence to run and optimize the fuel treatment system according to the critical variables of the fuel.
The policy to save money by fitting separators smaller than theoretically required or to install one settling tank instead of two dramatically increases the probability of engine damage due to insufficiently cleaned fuel. It is a matter of common sense, therefore, to challenge classification societies to request the capacity of separators and settling- / service tanks such, that these can cope with border line fuels.
Settling tanks should have the shape that allows water to definitely settle at the deepest point. Their capacity should give the water the time necessary for the process. Temperatures should be as high as possible with the aim to increase the difference in density between fuel and water. Water and sludge settling must be drained off regularly and it is difficult to understand why water sensors and subsequent alarms are not fitted generally.
Best practice is to install three heavy fuel oil separators: the first one as a purifier and the second one as a clarifier. The third one should be on stand by, to be operated additionally in case of excessive water, sludge or particles content of the fuel. Anything less significantly increases the probability of problematic fuels being delivered to the engine with subsequent damage.
Service tanks have to hold the fuel cleaned and preheated there should again be two, with one being supplied from the separators and the other feeding the final fuel service system. The service tanks have to act as buffers during shorter engine stops as well as to supply the engine during interruption in the feed from the separators. Some ships have one service tank only, this results in the probability of no treated fuel being available in case of malfunction of one or more separators.
The final fuel service system must be dimensioned to provide sufficient fuel oil of adequate injection viscosity to the engine under full load conditions. This is in first line a question of satisfactory heat transfer capacity. Deficiencies in this area can result in poor injection and poor combustion with resulting mechanical, economical and environmental problems.
In summary, it must be said for the fuel treatment system:
- The attempt to save money in initial investment results in a lifetime lack of flexibility in buying fuels.
- Efficient treatment systems make the fuel bunkered " a few $ per ton better".
3.8 The Engine - Ignition and Combustion
The genuine principle of the Diesel engine is that the fuel - when injected and with temperatures and pressures high enough - will ignite and burn completely. There are problematic fuels, however, which will not, or - eventually - cumbersome. The probability that such will happen is less significant, but quite a share of fuels are of a quality, that results in retarded or irregular ignition under start up and low load conditions.
