Fig. 6 Cylinder liner wear history
Fig. 7 Al+Si content in fuel oil
Fig. 8 Particles in fuel from service tank
Fig. 9 Element distribution by fluorescent X-ray analysis
Fig. 10 Count of F.O. 2nd filter back flash
Fig. 7 shows the aluminum (Al) + silicon (Si) contents in fuel oil for these series vessels. Statistics show that cylinder liner excessive wear occurred after using the fuel oil with more than 30ppm of Al+Si contents in bunkering fuel.
Fig. 8 shows SEM analysis results of fuel oil sampled from fuel oil service tank. And Fig. 9 shows the element distribution by fluorescent X-ray analysis results. These figures show that most of the particles consist of Al and Si (FCC catalytic fines).
Fig. 10 clearly shows that counts of fuel oil 2nd filter back flashing per day rapidly increased in rough sea condition. This means that the catalytic fines accumulated on the bottom of the tank during steady sea condition, are agitated during rough sea condition. And finally, these highly concentrated impurities with catalytic fines come into fuel supply line.
Therefore, in order to prevent the catalytic fines from entering into the combustion chamber, installation of auto-backflach type fine filter with 5〜10 μm mesh size could be only one practical countermeasure.
3.2 Improper Combustibility
Fig. 11 shows the results of combustion comparison test between the fuel #B bunkered at U.S.A. West Coast and fuel #J bunkered at Europe, which clearly shows that the combustibility of the fuel #B has following adverse effects on piston running behavior.
1] Ignition delay
2] Too strong penetration and poor propagation.
3] Inhomogeneous flame and flame attack to the liner wall
4] High unburned carbon generation rate
5] Longer heat release duration
The test engine is depicted in Fig. 12, which is uni-flow scavenged two-stroke engine with 190 mm bore and 350 mm stroke. This engine has a reinforced acrylic resin piston crown and combustion can be observed through the piston crown and mirror. The high-speed camera records the combustion phenomena.
The properties of the fuel oil are shown in Table 1.
In the total database of fuel analysis, there is another evidence, which shows the abnormality of this fuel. The relation between density and micro carbon residue is known as one of the indexes of the combustibility. Fig. 13 clearly shows that the fuel supplied by #B has higher density in spite of lower micro carbon residue.
