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Additional information

The purpose of the following information is to show the relationship between

the quality of heavy fuel oil, heavy fuel oil processing, the engine operation

and operating results more clearly.
Economical operation with heavy fuel oil within the limit values specified in

the table entitled

The fuel specification and corresponding properties for

heavy fuel oil

is possible under normal operating conditions, provided the

system is working properly and regular maintenance is carried out. If these

requirements are not satisfied, shorter maintenance intervals, higher wear

and a greater need for spare parts is to be expected. The required mainte-

nance intervals and operating results determine which quality of heavy fuel oil

should be used.
It is an established fact that the price advantage decreases as viscosity

increases. It is therefore not always economical to use the fuel with the high-

est viscosity as in many cases the quality of this fuel will not be the best.
Heavy fuel oils with a high viscosity may be of an inferior quality. The maxi-

mum permissible viscosity depends on the preheating system installed and

the capacity (flow rate) of the separator.
The prescribed injection viscosity of 12 – 14 mm

/s (for GenSets, L16/24,

L21/31, L23/30H, L27/38, L28/32H: 12 – 18 cSt) and corresponding fuel

temperature upstream of the engine must be observed. This is the only way

to ensure efficient atomisation and mixture formation and therefore low-resi-

due combustion. This also prevents mechanical overloading of the injection

system. For the prescribed injection viscosity and/or the required fuel oil tem-

perature upstream of the engine, refer to the viscosity temperature diagram.
Whether or not problems occur with the engine in operation depends on how

carefully the heavy fuel oil has been processed. Particular care should be

taken to ensure that highly-abrasive inorganic foreign matter (catalyst parti-

cles, rust, sand) are effectively removed. It has been shown in practice that

wear as a result of abrasion in the engine increases considerably if the alumi-

num and silicium content is higher than 15 mg/kg.
Viscosity and density influence the cleaning effect. This must be taken into

account when designing and making adjustments to the cleaning system.
The heavy fuel oil is pre-cleaned in the settling tank. This pre-cleaning is

more effective the longer the fuel remains in the tank and the lower the vis-

cosity of the heavy fuel oil (maximum preheating temperature 75 °C in order

to prevent the formation of asphalt in the heavy fuel oil). One settling tank is

suitable for heavy fuel oils with a viscosity below 380 mm

/s at 50 °C. If the

heavy fuel oil has high concentrations of foreign material or if fuels according

to ISO-F-RM, G/K380 or K700 are used, two settling tanks are necessary,

one of which must be designed for operation over 24 hours. Before transfer-

ring the contents into the service tank, water and sludge must be drained

from the settling tank.
A separator is particularly suitable for separating material with a higher spe-

cific density – such as water, foreign matter and sludge. The separators must

be self-cleaning (i.e. the cleaning intervals must be triggered automatically).
Only new generation separators should be used. They are extremely effective

Man L23/30DF, Project Manual

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