Marine Engineering
Online ISSN : 1884-3778
Print ISSN : 1346-1427
ISSN-L : 1346-1427
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SPECIAL ISSUE : Year Book “Progress of Marine Engineering Technology in 2020”
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SPECIAL ISSUE : Development of Internal Combustion Engines for Environmental Conservation
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  • Yoshitane Takashima
    2021 Volume 56 Issue 4 Pages 612-617
    Published: July 01, 2021
    Released: August 03, 2021
    JOURNALS RESTRICTED ACCESS

    In order to understand what occurs in a pre-chamber gas engine, we focused on the combustion process and attempted visualization of combustion from inside and outside of the pre-chamber. The vibration of pressure in the pre-chamber is synchronized with that of light intensity, and vibration is a phenomenon that occurs in the pre-chamber. It was confirmed that when the nozzle diameter was reduced, combustion in the main chamber was delayed due to relighting after jet light disappeared. It was confirmed that the vibration and light cycle at the combustion of the pre-chamber were synchronized from the bottom view.

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  • Arata Kimura, Junichi Kudou, Tomohiro Yuzui, Hiroko Itoh, Hideyuki Oka
    2021 Volume 56 Issue 4 Pages 638-645
    Published: July 01, 2021
    Released: August 03, 2021
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    Liquefied petroleum gas (LPG) is one of the promising alternative fuels which satisfy environmental requirements of ship fuels. However, since LPG is heavier than air and tends to accumulate on the floor, there are concerns about possible fire accidents in case of leakage. Although international regulations provide ventilation requirements to prevent such accidents, the actual diffusion behavior of leaked LPG is not well understood. In this study, the ventilation analysis was performed by using the Computational Fluid Dynamics (CFD) model on the assumption that fuel was leaked in an engine room. The parameters of the case study included a source diameter of leakage, a temperature of the leaked gas and a direction of the ventilation duct. The ventilation efficiency was assessed by comparing temporal variations in the average concentration of LPG in the engine room calculated with the CFD and a simple completely-mixing model. From these comparisons, it was found that the three parameters had a strongly influence on the ventilation efficiency.

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  • Hirofumi Yamashita, Tatsushi Kudo, Yasuhito Nakatake, Hiroshi Tanaka, ...
    2021 Volume 56 Issue 4 Pages 646-652
    Published: July 01, 2021
    Released: August 03, 2021
    JOURNALS FREE ACCESS

      In this study, we investigated the effects of Air Fine Bubble A-heavy oil (AFBA) on fuel consumption of and NOx emissions from high-speed diesel engines. Air Fine Bubbles (AFBs) from a pressurized dissolution-type Fine Bubble Mixing Unit (FBMU) were mixed into fuel to measure their size distribution. The results found that changing the amount of air supplied to the FBMU could control the number, diameter and void fraction of AFBs. When conducting an experiment with a high-speed diesel engine, the use of AFBA reduced fuel consumption by up to 6.1 % and by 2.0 % in the load average and cut NOx emissions by up to 19.6 % and by 10.5 % in the load average. These reductions were likely caused by the promotion of premixed-like combustion and lower combustion temperatures triggered by AFBA. The effects of reductions in fuel consumption and NOx emissions were more evident when void fractions increased. Simulation of spray combustion in a cylinder was performed to examine the impact of AFBs-induced atomization of spray droplets on the promotion of premixed-like combustion. The results showed that premixed-like combustion was promoted by AFBA due to not only the atomization of the spray droplets, but also precipitating air at the local pressure drop region in the fuel injection nozzle that promoted cavitation as bubble nuclei.

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  • Hiroki Hakamada, Soma Toguchi, Akinori Zukeran, Kohei Murakami, Hiroyu ...
    2021 Volume 56 Issue 4 Pages 653-658
    Published: July 01, 2021
    Released: August 03, 2021
    JOURNALS FREE ACCESS

      Electrostatic precipitators have been developed to remove particulate matters containing a large amount of black carbon that are emitted from ships and diesel generators. In order to keep them functioning in a highly efficient manner, it is necessary to wash away dust collected at the electrode. From this point of view, we investigated ways to burn carbon black using microwaves. In this study, carbon black dust was irradiated with microwaves after calculating the distribution of microwave intensity. We also measured the absorption power and temperature of carbon black and concentrations of CO generated in this process. Furthermore, we studied the influence of O2 concentrations and traveling waves on the combustion rate. The results indicated that the absorption of microwaves led to an increase in the temperature of the carbon black dust and CO concentrations. Although the combustion rate decreased in accordance with a reduction in O2 concentrations, the carbon black dust burned even when the O2 concentration was 13%, which is almost the same as those of exhaust gas. It was also demonstrated that traveling waves contributed to more uniform combustion of the dust.

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