최재혁 교수

A numerical study was carried out to investigate the effects of methane (CH4), ethane (C2H6), propane (C3H8), butane (C4H10), and dimethyl ether (DME) on the combustion and emission characteristics of a four-stroke gas-diesel dual-fuel (DF) marine engine at full load. Three-dimensional simulations of the combustion process and emission formation inside the engine cylinder in the diesel and DF modes were performed using the AVL FIRE R2018a simulation software to analyze the in-cylinder pressure,

This letter presents a novel analytic model that accurately evaluates the performance of a single-hop IEEE 802.11 wireless LAN (WLAN). By using a closed queuing network, we model an IEEE 802.11 WLAN system that consists of a fixed number of stations and derive the saturated throughput of the IEEE 802.11 distributed coordination function (DCF). The ns-2 simulation results show that our new analysis model is very accurate in evaluating the performance of the IEEE 802.11 DCF.

In this paper, we study the performance of 802.11 wireless local area networks (WLANs) and propose a distributed packet scheduling scheme that improves the short-term fairness among stations in a WLAN. First, we present a completely different analytical model to analyze the performance of 802.11 distributed coordination function (DCF), which models the channel contention dynamics of an IEEE 802.11 system, rather than the individual user perspective adopted by most previous analytical works based

Previously the compound of ${\mathrm{Hg}}_{0.7}{\mathrm{Cr}}_{0.3}{\mathrm{Sr}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}$ was believed to exhibit an enhanced flux-pinning behavior compared to the pristine ${\mathrm{HgBa}}_{2}{\mathrm{CuO}}_{4+\ensuremath{\delta}}.$ As candidates for its origin, possible extended defects of a superlattice in the $c$ direction or a strong coupling deduced from a reduced distance between ${\mathrm{CuO}}_{2}$ planes have been proposed. To clarify these, we extensiv

Piston bowl geometry plays an important role in the fuel/air mixing quality which has a direct influence on the performance and emission characteristics of the engine. This work studied the effects of piston bowl geometry on the combustion and emissions of a four-stroke direct injection (DI) heavy-duty diesel marine engine. Three types of piston bowls with various parameters were numerically investigated, targeting to improve engine performance, fuel oil consumption, and emission characteristics

This study aimed to evaluate the environmental impact of using liquefied petroleum gas (LPG) in small fishing vessels by conducting a life cycle assessment (LCA) in Korea. For the first time in the country, LPG engines designed for small fishing ships were utilized in this study. In addition, this research examined the potential benefits of employing Bio LPG, a renewable LPG produced from two distinct raw materials (crude palm oil (CPO) and refined, bleached, and deodorized (RBD) palm oil), inst

Recent works in empirical 802.11 wireless LAN performance evaluation have shown that cross-layer interactions in WLANs can be subtle, sometimes leading to unexpected results. Two such instances are: (i) significant throughput degradation resulting from automatic rate fallback (ARF) having difficulty distinguishing collision from channel noise, and (ii) scalable TCP over DCF performance that is able to mitigate the negative performance effect of ARF by curbing multiple access contention even when

A numerical study was carried out to investigate the effects of injector spray angle (SA) and injection position (IP) on the combustion and emission characteristics of a two-stroke ME-GI marine engine at full load. Three-dimensional (3D) simulations of the combustion process and emission formations inside the cylinder of the engine operating in the diesel and DF modes were performed using the ANSYS Fluent simulation software to analyze the in-cylinder pressure, temperature, and emission characte

This work studied the effect of the injector spray angle (SA) on the combustion and emissions of a 4-stroke port-injection natural gas-diesel dual-fuel (NG-Diesel DF) marine engine to determine the optimal SA for the fuel injector, aiming to reduce exhaust gas emissions while keeping the engine performance. Three-dimensional (3D) simulations of the combustion process and emission formations occurring in the engine cylinder in both diesel and DF modes were carried out using the AVL FIRE R2018a co

We have studied the pressure effect on the superconductivity and magnetism of ${\mathrm{Ho}}_{1\ensuremath{-}x}{\mathrm{Dy}}_{x}{\mathrm{Ni}}_{2}{\mathrm{B}}_{2}\mathrm{C}$ for $x=0.1$ and $x=0.4$ by measuring its transport properties. While the superconducting transition temperature ${T}_{c}$ lies above the N\'eel temperature ${T}_{N}$ for $x=0.1,$ the ${T}_{c}$ lies below the ${T}_{N}$ for $x=0.4.$ The pressure changes the magnetic exchange integral ${J}_{\mathrm{sf}}$ and controls the pair br

A numerical study was conducted to investigate the effects of hydrogen and scavenging air temperature (SAT) on the combustion and emission characteristics of a 2-stroke heavy-duty dual-fuel (DF) marine engine at full load. The engine had a 700 mm bore fuelled with hydrogen–methane (H2-CH4) mixtures. Three-dimensional simulations of the combustion and emission formation inside the engine cylinder with various H2 contents in the H2-CH4 mixture were performed. ANSYS FLUENT simulation software was u