Over the years, ClassNK has made extensive failure investigations and incorporated the results into the classification rules, and presented the information on failures to other concerned parties. The objective of the presenting this information is to share the knowledge between related parties in order to avoid the future failures, and this paper was prepared towards this aim. In this paper, case studies on propellers, crankshafts, main engine bearings and coupling bolts have been selected as a failure in marine propulsion systems. The case studies together with detailed information including the results of investigations and the cause of failure will be of interest to marine engineers and other concerned parties.
Semi-built-up and solid crankshafts, as a main part of diesel engines, have been subjected to increasingly severe service conditions to meet such engine requirements as higher output and more compact size. This has driven crankshaft manufacturers to improve the fatigue strength, quality, and reliability of crankshafts. This paper describes technical developments and recent trends, such as improved steel-making processes, new materials with higher strength, and new fillet hardening processes.
Growth of a fungus, which was isolated from the sludge at the bottom of a ship's fuel tank for Marine diesel oil, was examined. A lot of sludge had been stacked on the wire-mesh filter in the fuel strainer. In this ship, the commercially available dispersant, YUNIC #555D, was being used continuously to reduce the sludge formation in Marine diesel oil. The microscopic observation of the sludge revealed the mycelia of the fungus. The volume concentration of the dispersant in the sampled fuel oil containing sludge was estimated to be 1/300- 1/400, which was 25-67 times higher than that recommended by the company. This dispersant might have contributed to an increase in the growth of the isolate in Marine diesel oil. Hence we examined the additional effect of the dispersant on the growth of the isolate in Marine diesel oil. It was found that the isolate could grow in Marine diesel oil alone. Growth repression of the isolate, however, was observed even in the presence of 117100 of the dispersant as a final volume concentration. We examined another dispersant, SPA·LAZAE® that did not have any effect on the growth of the isolate.
For the purposes of engine maintenance, it is very important for engineers to collect acoustic information on abnormalities from the equipment running noise. However, in the engine room of a ship it is difficult to collect the acoustic information as the noise levels can be as high as 100 dB. In this study, the authors investigated the ability to listen to a specific sound against a disturbingly loud background noise. We found that combustion noise disturbed the detection of other sounds (non-combustion noise) . Consequently, we recorded shell noise by microphone, and transformed the sound to electronic data. We then instantaneously attenuated the combustion noise in the sound data and played it from a speaker. This method enabled reduction of listening disturbance (masking phenomenon) due to combustion noise. A hearing support system incorporating an algorithm for the above data processing was accordingly constructed to help distinguish acoustic information from background engine room noise.
Premixture combustion mainly occurs in gasoline engines but it had also occurred in diesel engines at the previous combustion. Gasoline engines have been used as marine engines especially for pleasure boats. The mechanism of premixture combustion helps to reduce air pollution and fuel consumption. It also helps to know the mechanism of previous combustion which generates noise and heat loss in diesel engines. This work has studied the effect of flow characteristics to the flame structure during premixture combustion. A constant volume combustion chamber was designed to research the relationships between combustibility and flow characteristics by changing the gas velocity to study its effect on flame shape. Gas velocity was measured by LDV system, combustion pressure was measured by pressure indicator and flame shape was studied by a television camera. The results showed that the main cause of the complexity of flame shape is the turbulence intensity of gas flow.