A small combustion chamber was developed and manufactured for empirical combustion testing of several alternative fuels developed to meet IMO emission limits for fuel oil used in ships. The combustion chamber consists of four independent tanks and a circulation system with a two-stage heating function owing to the high viscosity and temperature of ship fuel. A gun-type burner is mounted on the side of the combustion chamber, which possesses a cylindrical shape and a capacity of less than 300 L. This device was manufactured in accordance with several variables such that the basic stage performance and simulation tests of each fuel could be sufficiently completed before performing the combustion test to simulate the engines of large ships. To conduct an initial experiment using the developed combustion chamber, low-sulfur MGO with a sulfur content less than or equal to 0.05% was chosen, and ideal operating parameters were selected according to the measurement tests based on load control. The exhaust gas temperature differed by approximately 10.7% as a result of burning MGO at a burner load state of 80–100%. The use of a normal oxygen concentration of 4% helped remove approximately 14.31 ppm of nitrogen oxide and 1.91% of carbon dioxide. The maximum combustion efficiency was 70.17%, indicating the chamber’s potential for use in a variety of combustion tests of alternative fuels for ships in the forthcoming years.
Computer numerical control (CNC) lathes are optimized for machining workpieces into rotating shafts or cylindrical shapes of structures. However, because rotating mechanical parts are used on CNC lathes, vibration from spindles, servomotors, hydraulic pumps, and feed screws occurs. Therefore, periodic preventive maintenance is required to minimize vibrations. Additionally, alignment, balance, and adjustment operations are necessary for parts that perform linear or rotational movements. Thus, this study adjusts the tension of the V-belt that drives the spindle of the CNC lathe, analyzes the primary components and the vibrations occurring at the spindle and servomotor, and measures the surface roughness to identify the cutting quality according to the impact of the belt tension. The experimental results show that the peak value of the vibrating component increases as the cutting speed increases. We demonstrate that the optimal vibration characteristics and excellent surface roughness values are achieved at a relatively looser belt tension than the standard value. In particular, at a feed speed of 0.05 mm/rev, a cutting speed of 250 m/min, and a depth of cut of 0.8, the surface roughness in loose tension was reduced by up to 143.9% compared to tight tension. Additionally, the optimum processing quality is achieved at a cutting depth of 0.6 and 0.8 mm, corresponding to a turning insert nose R-value of 0.4 mm, and at cutting speeds ranging from 200 to 250 m/min.
Alternative marine fuels are needed to help reduce the exhaust emissions of ships. In this study, we performed an analysis to verify the potential applicability of a fuel based on Bunker-C oil, a low-grade marine heavy oil, as a novel alternative marine fuel. Bunker-C oil and water were mixed in the presence of a 0.8–1.2% emulsifier in four steps from 0% to 25% to produce a special type of emulsified fuel oil. Confocal microscopy images of samples after stabilization for approximately three days at room temperature showed no variation in the pattern at the 0% condition with no water, but a relatively homogenous mixed state of water droplets was found across all domains at the 5–25% conditions. The open-source software Image-J indicated the extraction of 166, 3438, and 5636 water droplets with mean diameters of 1.57, 1.79, and 2.08 μm, as well as maximum diameters of 7.31, 21.41, and 25.91 μm, at the 5%, 15%, and 25% conditions, respectively. For all three conditions, the mean particle diameter was approximately 2 μm, below the 20 μm reported in previous studies, with uniform distributions. This suggests that the mixed state was adequately homogenous.
In this study, we conducted onboard noise measurement experiments under the conditions of anchoring, sailing, casting, and hauling to determine whether noise generated in the G/T 1000-ton fishing trawler triggers zone-specific effects upon vessel operation. It was shown that most accommodation areas of the trawler comfortably met the IMO acceptance criteria regardless of the sailing condition, but most of the stern area, where the fishing actually occurs, exceeded the permitted limit of 75 dB (A). Furthermore, the statistical analysis revealed a significant difference (p < 0.05) only in the bow and the stern, which are both open areas. In the case of the former, improvements were deemed possible due to the influence of the fluid emission noise from the seawater piping in the bow, and the acceptance criteria were also appropriate. However, in the case of the latter, a significant difference was seen in hauling conditions, and on-site analysis confirmed frictional noise from hydraulic oil in the trawl winch and between the chains and the metal hull, leading to the conclusion that various improvements are required, such as the mandatory wearing of safety equipment by workers and stricter legal standards for permitted noise levels.
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