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Antony John Nyongesa,설영윤,여실중 한국마린엔지니어링학회 2023 한국마린엔지니어링학회지 Vol.47 No.2
Research and development of marine equipment aimed at improving safety at sea has led to a significant reduction in the occurrence of marine accidents. Studies have revealed that installing a rope cutter device would prevent propeller entanglement, which is a major cause of accidents for small ships sailing in coastal regions. This study investigates the effects of rope cutter installation on the pressure distribution, flow streamlines, velocity vectors, cavitation, and thrust force produced by the propeller using the computa-tional fluid dynamics (CFD) approach. ANSYS Fluent, CFD software was used in this study and simulations were conducted under open sea conditions at a maximum continuous rating (MCR) using actual ship propeller dimensions. As a result, rope cutter installation led to a slight reduction of water flow velocity behind the propeller, lower vapor volume fraction by 5.02%, and lesser turbulence in the flow behind the propeller. There were no visible differences in the pressure distribution around the propeller. The average thrust force produced by the propeller was increased by 1.97% after rope cutter installation while the torque required to rotate the propeller with the rope cutter was higher by 0.965%. The findings indicate that the installation of a rope cutter has no adverse impact on the propeller's operation. This research revealed extra positive effects, including a decrease in vapor formation, water circulation behind the propeller, and a slight increase in the propeller's thrust force.
Antony John Nyongesa,김정국,이원주 한국마린엔지니어링학회 2023 한국마린엔지니어링학회지 Vol.47 No.6
Natural gas (NG) is a potential alternative fuel for a carbon-free transition. Currently, NG combustion in marine two-stroke engines is achieved using two dual fuel concepts namely, the high-pressure injection (HPDF) and low-pressure injection (LPDF). The LPDF engine concept can meet the Tier III emission regulations without any after-treatment devices. However, under low load condi-tions, it exhibits poor combustion characteristics and higher CO and HC emissions. The quality of the in-cylinder NG/air mixture is crucial for the premixed combustion nature of the LPDF concept. This study numerically evaluates the influence of adjustable-sized scavenge ports on the NG stratification in a large-bore marine two-stroke NG/diesel, dual-fuel engine. Originally, the engine port height was 211mm; the size was reduced to various port heights to analyze its influence on the NG/air stratification. The results showed a significant improvement in the in-cylinder dynamic, mixing, and turbulence properties. The swirl ratio, turbulence kinetic energy, and vorticity magnitudes were increased to a maximum of 16.56, 37.027, and 17.04%, respectively. However, owing to the reduced scav-enge port size, the trapped air mass in the cylinder was reduced slightly by 2.05%. This study provides a reasonable approach to improve the cylinder mixture formation to improve combustion efficiency in marine low-pressure gas dual-fuel engines.