It is said that the degree of generation of the corrosive wear is reduced as the output and temperature of the modern engines are higher, but there are some reports that the corrosive wear occurred at a lower part of the cylinder liner. Such a corrosive wear is practically coped with by the increase of liner temperature and/or increase of the cylinder oil feed rate. It is confirmed by the company to which the author belongs that the cylinder oil of 80BN containing a certain anti-wear additive is effective in reducing the corrosion wear. (Fig. 9.1)

Fig. 9.1 Effect of BN and liner temperature on corrosion wear

(2)　System Oils

The system oil of BN5-6 is generally used in Japan, but in Europe, there are some owners who prefer the system oil of BN10-12. The positioning of high BN system oils may be different among engine manufacturers and lubricant suppliers but the system oil of BN8-12 is listed in Table 3 of CIMAC Number 15, 1997, 4.7 Selection Criteria for System Lubricants for the selection. It is necessary to make sufficient consultaion with the engine manufacturer and the lubricant supplier in selecting the system oil.

The increase in both viscosity of the used oil and BN is an issue that has been a growing problem over the last 20 years thus the monitoring of oil condition of the system oil in use is important. The condition of the system oil in use should be regularly sampled and comprehensively evaluated, taking into consideration other properties of the system oil in use. What must be recognized is that attention has to be paid not to the absolute values of the test results, but to the chronological trend and sudden change of the results. A modern analysis service needs to offer a comprehensive range of testing including that by infrared ray spectros-copy¹⁾. More reaserch work in this area to link engine problems directly to analysis results is needed.

In the quality control of the system oil in use, the control standards are available at each engine manufacturer and each lubricant supplier and a good reference is included in CIMAC Number 15, 1997,8 QUALITY LIMITS OF SYSTEM OIL IN USE.

　

9.2.2　Lubricating Oils for Trunk Engines

Recently, troubles have been caused by unburnt low-quality fuel contaminating the engine oil in large-size and middle-speed trunk engines. A large amount of black sludge is generated in the crank case (Fig. 9.2), and deposits in the purifier for the lubricating oil are increased. Also the fuel oil mixed in the engine oil degrades the performance of the lubricating oil. Modem trunk piston engine oils with improved detergency and dispersancy provide excellent compatibility with the low-quality fuel oil, containing high levels of asphaltenes, and (Fig. 9.3). The overall effect is to keep the internals of engines clean. The determination of the quantity of the urburnt fuel in the lubricating oil is difficult through the regular analysis methods. As for the analysis method, there are a RFD (Residual Fuel Detection) method by Mobil and the report by Shell²⁾

Fig. 9.2 Crank case where black sludge is deposited (3,000 hrs)

Fig. 9.3 Crank case using lubricating oil of improved quality (6,000 hrs)

In Europe, the problem of the liner lacquering still occurs with high-output engines (fishing boats) where MGO (Marine Gas Oil) is used. It seems that the quality of European MGO (low sulfur content, high aromatic content, low-combustion property), the engine model and the engine load pattern combine to create poor combustion conditions. The quality of the lubricating oils involved do have an impact on lacquer formation and this is recognized by European engine builders. Their approval listings reflect their service experience with high and low quality lubricants.

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