Korea, Republic of

As the global transition to carbon neutrality accelerates hydrogen energy has emerged as a key alternative to fossil fuels due to its potential to reduce carbon emissions. Many countries including Korea are constructing hydrogen refueling stations; however safety concerns persist due to accidents caused by equipment failures and human errors. While various accident analysis models exist the application of the root cause analysis (RCA) technique to hydrogen refueling station accidents remains largely unexplored. This study develops an RCA modeling map specifically for hydrogen refueling stations to identify not only direct and indirect causes of accidents but also root causes and applies it to actual accident cases to provide basic data for identifying the root causes of future hydrogen refueling station accidents. The RCA modeling map developed in this study uses accident cause investigation data from accident investigation reports over the past five years which include information on the organizational structure and operational status of hydrogen refueling stations as well as the RCA handbook. The primary defect sources identified were equipment defect personal defect and other defects. The problem categories which were the substructures of the primary defect source “equipment defect” consisted of four categories: the equipment design problem the equipment installation/fabrication problem the equipment reliability program problem and the equipment misuse problem. Additionally the problem categories which were the substructures of the primary defect source “personal defect” consisted of two categories: the company employee problem and the contract employee problem. The problem categories which were the substructures of the primary defect source “other defects” consisted of three categories: sabotage/horseplay natural phenomena and other. Compared to existing accident investigation reports which identified only three primary causes the RCA modeling map revealed nine distinct causes demonstrating its superior analytical capability. In conclusion the proposed RCA modeling map provides a more systematic and comprehensive approach for investigating accident causes at hydrogen refueling stations which could significantly improve safety practices and assist in quickly identifying root causes more efficiently in future incidents.

The adoption of H2 fuel in gas turbine systems is steadily increasing as part of the transition toward cleaner energy sources. However its unique combustion characteristics pose significant challenges in managing combustion instability. This study examines the acoustic behavior of H2-CH4 mixed-fuel combustion instability using a model gas turbine combustor. To simulate instability situation of mixed fuel multi-mode acoustic excitation experiments are performed with the fixed fundamental forcing at the combustor's resonance frequency (∼160 Hz) together with additional variable forcing at 250 Hz and 1000 Hz which are the representative instability modes of CH4 and H2 flames respectively. In some cases highly risky signal amplification is observed. For example when the amplitude ratios of forcing at 160 250 and 1000 Hz are 1:9:0 the response reaches up to 106.15 kPa at the other frequency of 1750 Hz. This phenomenon is confirmed by attribution of the interaction of the overlapping mode frequencies and the node and antinode position of standing wave with no such amplification observed at other experimental conditions. Consequently the optimal sensor location is expected to vary with changes in the co-firing ratio and conditions and identifying these optimal positions is essential for reliable monitoring and successful implementation of H2 co-firing technology.

The present investigation aims to provide a comparative assessment of using hydrogen-enriched wood waste-derived producer gas (PG) for a dual-fuel diesel engine fueled with a 20% Jatropha biodiesel/80% diesel blend (BD20) with the traditional mode. The experiments were conducted at 23°bTDC of injection timing 240 bar of injection pressure 17.5:1 of compression ratio and 1500 rpm of engine speed under various engine loads. Gas carburetor induction (GCI) port injection (PI) and inlet manifold injection (IMI) methods were used to supply H2-enriched PG while B20 is directly injected into the combustion chamber. Among all the combinations the IMI method provided the highest brake thermal efficiency of 30.91% the lowest CO emission of 0.08% and smoke opacity discharge of 49.26 HSU while NOx emission reached 1744.32 ppm which was lower than that of the PI mode. Furthermore the IMI method recorded the highest heat release rate of 91.17 J/°CA and peak cylinder pressure of 83.29 bar reflecting superior combustion quality. Finally using the IMI method for H2-enriched PG in dual-fuel diesel engines could improve combustion efficiency reduce greenhouse gas emissions and improve fuel economy showing that the combination of BD20 with H2-enriched PG offers a cleaner more sustainable and economically viable technology.

Raney Ni (R-Ni) electrodes are used as hydrogen evolution reaction catalysts in alkaline water electrolysis (AWE). However they are not durable because of reverse current-induced oxidation and catalyst damage from H2 bubbles. Reverse current triggers Ni phase changes and mechanical stress leading to catalyst delamination while bubbles block active sites increase resistance and cause structural damage. These issues have been addressed individually but not simultaneously. In this study a P-doped Ni (NiP) protective layer is electroplated on the R-Ni electrode to overcome both challenges. The NiP protective layer inhibits oxidation reducing Ni phase changes and preventing catalyst delamination. Enhanced surface wettability minimizes nucleation and facilitates faster bubble detachment reducing bubble-related damage. Electrochemical tests reveal that NiP/R-Ni exhibits a 26 mV lower overpotential than that of R-Ni at −400 mA cm−2 indicating higher catalytic activity. Accelerated degradation tests (ADTs) demonstrate the retention of the NiP/R-Ni catalyst layer with only a 25 mV increase in overpotential after ADT which is significantly less than that of R-Ni. Real-time impedance analysis reveals the presence of small rapidly detaching bubbles on NiP/R-Ni. Overall the NiP protective layer on R-Ni simultaneously mitigates both reverse current and H2 bubble-induced degradation improving catalytic activity and durability during AWE.

Injection timing in low-pressure hydrogen direct injection (H2LPDI) engines plays a critical role in optimising gas jet structure and mixture formation due to the complex and transient nature of ambient air flow and density inside the cylinder. This study systematically investigates the macroscopic characteristics of gas jet development at five distinct injection timings from 210 to 120 ◦CA bTDC with the intake valve closure (IVC) as a reference point in a motored inline four-cylinder spark-ignition engine at 2000 rpm and 160 Nm load using low-pressure injection of 3.5 MPa. Optical access was made with two endoscopes: one for high-speed imaging and the other for laser insertion to realise laser shadowgraph imaging of the gas jet delivered using a side-mounted outwardopening pintle nozzle injector. The experimental results reveal spatial and temporal variations in jet morphology penetration spreading angle and mixture dispersion as a function of injection timing. Pre-IVC injection (210 ◦CA bTDC) produced a narrow mean cone angle of ~40◦ and the highest penetration-rate proxy (0.49) whereas postIVC injection (120 ◦CA bTDC) retained a wider ~53◦ cone yet reduced the penetration rate to 0.28 while increasing the sheet-based mixing index from − 0.084 to − 0.106. Pre-IVC injection occurring under low ambient pressure and with active intake airflow was found to produce elongated jets with enhanced penetration and mixing rates though accompanied by substantial cyclic variations. Conversely post-IVC injection was strongly influenced by a fully developed tumble flow which redirected the jet trajectory towards the pent-roof and facilitated mixing through increased turbulence. However the elevated air density constrained the jet penetration. At-IVC injection resulted in a more uniform and stable jet structure. However the lack of convective flow constrained the overall mixing effectiveness. Quantitative analysis of jet spreading angle pixel intensity gradient and centroid movement using 100 consecutive cycles confirms the critical role of injection timing in shaping the gas jet development as suggested by the images.

Ammonia represents a promising alternative fuel and hydrogen carrier for power generation due to its advantages in storage and transportation compared to those of hydrogen. However challenges persist in the direct use of ammonia in solid oxide fuel cells (SOFCs) particularly with respect to performance degradation—an issue that necessitates comprehensive investigation at the full-stack scale. This study examines a ten-cell full-size SOFC stack under various operating conditions to evaluate the viability of ammonia as a direct fuel. Experiments were conducted using pure ammonia pure hydrogen fully reformed ammonia and 50 % pre-reformed ammonia at three operating temperatures (660◦C 710 ◦C and 760 ◦C). Performance was characterized through current–voltage curves electrochemical impedance spectroscopy and continuous monitoring of residual ammonia in the exhaust using Fourier-transform infrared spectroscopy. A 200-hour durability test was performed to assess long-term stability. The results demonstrated that at temperatures of ≥ 710 ◦C ammonia-fueled SOFCs performed comparably to hydrogen-fueled configurations within typical operating ranges (0.2–0.5 A/cm2 ). The stack achieved optimal performance at 55–80 % fuel utilization. The ammonia-fueled configurations exhibited different voltage behaviors at higher fuel utilizations compared with those of the hydrogen-fueled configurations. The residual ammonia concentration in the anode off-gas remained well below the safety thresholds. Long-term testing demonstrated an initial degradation that eventually stabilized at a more sustainable rate. These findings validate ammonia as a viable fuel for SOFC stacks when operated at appropriate temperatures (≥710 ◦C) and optimal fuel utilization offering a pathway toward sustainable carbon-free ammonia energy systems.

Lift–cruise-type unmanned aerial vehicles (UAVs) powered by hydrogen fuel cells often integrate secondary energy storage devices to improve responsiveness to load fluctuations during different flight phases which necessitates an efficient energy management strategy that optimizes power allocation among multiple power sources. This paper presents an innovative fuel cell DC–DC converter (FDC) design for the hybrid power system of a lift–cruise-type UAV comprising a multi-stack fuel cell system and a battery. The novelty of this work lies in the development of an FDC suitable for a multi-stack fuel cell system through a dual-input single-output converter structure and a control algorithm. To integrate inputs supplied from two hydrogen fuel cell stacks into a single output a controller with a single voltage controller–dual current controller structure was applied and its performance was verified through simulations and experiments. Load balancing was maintained even under input asymmetry and fault-tolerant performance was evaluated by analyzing the FDC output waveform under a simulated single-stack input failure. Furthermore under the assumed flight scenarios the results demonstrate that stable and efficient power supply is achieved through power-supply mode switching and application of a power distribution algorithm.

With growing global demand for sustainable decarbonization hydrogen energy systems have emerged as a key pillar in achieving carbon neutrality. This study assesses the greenhouse gas (GHG) reduction efficiency of Republic of Korea’s hydrogen ecosystem from a life-cycle perspective focusing on production and utilization stages. Using empirical data—including the national hydrogen supply structure fuel cell electric vehicle (FCEV) deployment and hydrogen power generation records the analysis compares hydrogenbased systems with conventional fossil fuel systems. Results show that current hydrogen production methods mainly by-product and reforming-based hydrogen emit an average of 6.31 kg CO2-eq per kg H2 providing modest GHG benefits over low-carbon fossil fuels but enabling up to a 77% reduction when replacing high-emission sources like anthracite. In the utilization phase grey hydrogen-fueled stationary fuel cells emit more GHGs than the national grid. By contrast FCEVs demonstrate a 58.2% GHG reduction compared to internal combustion vehicles with regional variability. Importantly this study omits the distribution phase (storage and transport) due to data heterogeneity and a lack of reliable datasets which limits the comprehensiveness of the LCA. Future research should incorporate sensitivity or scenario-based analyses such as comparisons between pipeline transport and liquefied hydrogen transport to better capture distribution-phase impacts. The study concludes that the environmental benefit of hydrogen systems is highly dependent on production pathways end-use sectors and regional conditions. Strategic deployment of green hydrogen regional optimization and the explicit integration of distribution and storage in future assessments are essential to enhancing hydrogen’s contribution to national carbon neutrality goals.