Search Results (67)

Hydrogen enrichment of compression ignition (CI) engines has emerged as a promising strategy to simultaneously enhance thermal efficiency and reduce carbon-based emissions. This study numerically investigates how hydrogen enrichment affects engine performance and emissions in methanol–diesel dual-fuel CI engines, a combustion mode gaining increasing attention for replacing fossil diesel with sustainable fuels, particularly in hard-to-abate sectors such as maritime transport. The simulations are based on the Unsteady Reynolds-Averaged Navier–Stokes (URANS) equations, incorporating the RNG k-ε turbulence model, the Eddy Dissipation Concept (EDC) for turbulence–chemistry interaction, and the G-equation for turbulent premixed flame propagation. The numerical model is validated against experimental data for in-cylinder pressure and heat release rate at 45% methanol substitution ratio (by energy). The results indicate that increasing the hydrogen enrichment ratio (HER, defined on an energy basis) from 5% to 20% raises the Sauter mean diameter (SMD) of the diesel fuel from 20.2 µm to 28.0 µm (+38%), driven by reduced aerodynamic breakup intensity associated with modified gas-phase properties under hydrogen enrichment. Furthermore, hydrogen’s elevated adiabatic flame temperature and superior mass diffusivity intensify combustion, raising peak in-cylinder pressure from 75.2 to 79.1 bar (+5.2%), amplifying the peak heat release rate from 129 to 211 J/°CA (+63.6%), and elevating maximum in-cylinder temperature from 1542 to 1735 K (+193 K). Under the investigated CFD operating conditions, these thermodynamic gains translate into an engine-level 6% improvement in indicated thermal efficiency and a 14% reduction in indicated specific fuel consumption (accounting for hydrogen, methanol, and diesel) at HER 20%. On the emissions front, CO₂ declines by 24% in direct proportion to the carbon-containing fuel mass displaced by hydrogen substitution, while NO_x increases approximately twofold from 0.10 g/kWh at HER 0 to 0.21 g/kWh at HER 20, driven by peak temperature elevation. These findings establish hydrogen-enriched methanol–diesel dual-fuel combustion as a viable pathway toward high-efficiency, low-carbon CI engine operation for heavy-duty transport applications. Full article

Port-area hydrogen refueling stations face low-frequency but high-consequence events when high-pressure leaks ignite as jet fires in wind-exposed, constrained environments. This study develops a consequence-based framework coupling theoretical screening, CFD combustion analysis, and hazard zoning to support separation-distance setting and emergency planning. A jet-fire model estimates flame-impingement distances for multiple leak diameters, and a weighted multi-point radiation model predicts heat-flux fields, from which lethal and irreversible-injury zones are delineated using thresholds of 7 and 5 kW/m², respectively. To move beyond wind-free screening, steady reacting-flow CFD is conducted for a representative release under four ambient conditions, with 4.34 m/s adopted as the representative wind speed for the windy cases based on Ningbo Port conditions. Validation against a visible-flame correlation defined by T ≥ 1573 K shows a deviation of 6.99%. Results show that radiation footprints expand markedly with diameter, with lethal and injury distances scaling approximately linearly within the studied range. Under wind, near-ground hot-plume extents defined by T ≥ 388 K and T ≥ 582 K depend strongly on wind direction and station geometry, whereas visible flame length is less sensitive. Additional sensitivity analyses indicate that the quasi-steady results are weakly affected by the selected ignition snapshot, while inclined releases modify projected plume/flame extents without altering the main engineering interpretation of the baseline case. The results support theory-based preliminary screening, but wind direction should be explicitly considered in exclusion-zone definition. Full article

Hydrogen combustion is known to be fast compared to traditional hydrocarbon fuels. The fast combustion leads to a higher thermal efficiency. In this research a 600 cc single cylinder hydrogen engine was tested at 1250 rpm, lambda = 2 and 3, and three load levels (load was represented by Manifold Absolute Pressure (MAP); MAPs tested were 75, 95 and 120 kPa) and compared to operation with gasoline and propane. The fast burn duration (Mass Fraction Burnt MFB10% to MFB90%) and the MFB 50% were determined and analyzed. The hydrogen MFB50% location for Minimum Timing for Best Torque (MBT) was found to occur at around the typical 8 Crank Angle Degrees (CADs) After Top Dead Center (ATDC). Measurements of ignition delay based on the fast data direct measurement of spark ignition coil current drop to the change in polarity of net heat release are presented. With shifts towards direct injection and higher injection pressures, consideration was given to the hydrogen pressurization penalty, where it was calculated that pressurizing hydrogen to 100 bar at the flow required for lambda = 2 operation is 2.3 bar, i.e., higher than the Friction Mean Effective Pressure (FMEP)! Furthermore, hydrogen is widely cited to have a higher heat loss than typical hydrocarbon fuels. In this paper, detailed analyses at lambda 2 and lambda 3 showed that hydrogen in fact has lower heat losses. Full article

The application of ammonia decomposition technology for hydrogen production enables hydrogen-enriched combustion in marine diesel-ignited ammonia engines. This study presents experimental and simulation investigations of a diesel-ignited ammonia engine operating with hydrogen-containing fuels derived from ammonia decomposition at various blending ratios. The combustion and emission characteristics of the engine were systematically examined, and a comparative analysis was conducted on the combustion behavior of the engine between using ammonia decomposition-derived hydrogen-containing fuel and pure hydrogen. The result shows that under constant engine output power, at 1200 rpm and 75% load, increasing the hydrogen energy rate results in largely unchanged cylinder pressure and heat release rate. The diesel substitution rate exhibits an initial increase followed by a decrease, while the energy consumption rate demonstrates the opposite trend. At 1500 rpm and 75% load, an increase in hydrogen enrichment leads to an earlier rise in cylinder pressure and heat release rate, a continuous increase in diesel substitution rate, and a consistent decrease in energy consumption rate. The early stage of in-cylinder combustion is dominated by diesel combustion, followed predominantly by the combustion of ammonia and hydrogen. Regarding the difference between using decomposition-derived hydrogen-containing fuel and pure hydrogen, within the hydrogen enrichment range of 0–20%, the discrepancies in intake composition and equivalence ratio between the two hydrogen-addition modes gradually widen but remain within 1.3%. Taking a hydrogen energy rate of 10.56% as an example, the differences in in-cylinder pressure and heat release rate between the two hydrogen-addition modes are not significant, indicating that the N₂ generated from ammonia decomposition has a relatively weak influence on the engine. With increasing hydrogen enrichment, NH₃ emissions gradually decrease, while NO emissions increase. For N₂O, hydrogen enrichment promotes its consumption, resulting in lower emissions. Under various hydrogen enrichment conditions, equivalent greenhouse gas emissions are mainly influenced by CO₂ emissions. Full article

The increasing efforts to decarbonise the energy sector have made it possible to reconsider advanced combustion modes that could simultaneously increase engine efficiency and meet stringent emission regulations. Reactivity-controlled compression ignition (RCCI) has emerged as a strong candidate due to its dual-fuel approach, which enables flexible control over in-cylinder reactivity and heat release patterns. Ethanol and hydrogen have recently attracted attention as a complementary low-reactivity and high-reactivity fuel pair within RCCI systems, typically implemented in a tri-fuel configuration using a small diesel pilot for ignition control. Therefore, most practical implementations operate as ethanol–hydrogen–diesel RCCI systems rather than pure dual-fuel ethanol–hydrogen modes. Research published between 2020 and 2025 provides a clearer picture of how these two fuels behave when used together in RCCI engines. Most studies report a noticeable improvement in the brake thermal efficiency of 4–7%. Particulate matter emissions reduce substantially from 20% to 50%. Lower carbon monoxide and hydrocarbon levels are often reported, and usually, a stable ignition is found throughout a wide range of operating conditions. However, if the combustion phasing is not properly controlled, hydrogen’s reactivity can lead to increased nitrogen oxide emissions, thus making it necessary to recirculate exhaust gases. Besides the challenges of combustion, practical aspects still remain as major hurdles. The problems of material compatibility between two fuels, hydrogen storage safety, and the requirement for low-carbon fuel production pathways can play a vital role in deciding commercialisation. To summarise, research findings point to the ethanol–hydrogen RCCI combination as a very promising route for the improvement of cleaner and more efficient engine technologies, provided the technical and logistical barriers can be addressed. Accordingly, this review primarily addresses ethanol–hydrogen–diesel tri-fuel RCCI architectures, while also discussing dual-fuel ethanol–hydrogen concepts where applicable in order to avoid conceptual overlap with spark-ignited ethanol–hydrogen systems. Full article

Hydrogen, a promising clean energy carrier, needs safe detection due to its flammability. Conventional electrical hydrogen sensors have drawbacks like high operating temperatures, poor selectivity and ignition risks. We propose an optical sensor using long-period fiber gratings (LPGs) coated with Pt-SiO₂ nanomaterials. It works via catalytic reaction: H₂ reacts with O₂ on Pt nanoparticles, releasing heat that shifts LPG’s resonant wavelength. Structural characterization showed porous SiO₂ with uniform Pt, ensuring efficiency and stability. Experiments proved it sensitively responds to 0.5–2.5% H₂ (max wavelength shift 7.544 nm), with fast response/recovery, good repeatability/reversibility. Logistic fitting (R² = 0.999) confirmed strong correlation. This sensor, safe, sensitive and stable, has great potential for real-time H₂ monitoring in critical environments. Full article

Hydrogen, a promising alternative to conventional fuels, presents significant combustion hazards due to its low minimum ignition energy (MIE) and wide flammability range (4–75 vol.%). The risks are amplified with liquid hydrogen (LH₂), which has an extremely low boiling point (20.3 K) and high diffusivity. Once released, LH₂ vaporizes rapidly and mixes with ambient air. This process forms a cryogenic and highly flammable cloud, which significantly increases ignition and explosion hazards. Therefore, a comprehensive understanding of the MIE of cryogenic hydrogen–air mixtures is crucial for quantitative risk assessment. This work develops and validates a numerical algorithm for predicting the MIE of hydrogen–air mixtures at cryogenic temperatures (down to 93 K) across a wide range of hydrogen concentrations (10~50 vol.%) and oxygen concentration ratios [O₂/(O₂ + N₂) = 21~52%]. By coupling a detailed H₂/O₂ reaction mechanism with a large eddy simulation (LES) turbulence model, this algorithm demonstrates high reliability and accuracy. The results indicate (1) an exponential increase in MIE with decreasing initial temperature; (2) a U-shaped dependence of MIE on hydrogen concentration, with the minimum occurring near 25% hydrogen concentration; (3) an asymptotic dependence of MIE on oxygen concentration ratio, particularly at 40% hydrogen concentration. The initial temperature has the greatest influence on MIE; hydrogen concentration is the second; and the oxygen concentration ratio has the weakest influence. This study provides a theoretical framework and a practical computational tool for assessing and mitigating cryogenic ignition associated with LH₂ leakage, thereby enabling safer application of liquid hydrogen technologies. Full article

This study investigates the thermal decomposition, ignition, combustion, and gasification processes of composite fuels derived from anthracite coal and pine sawdust. The research highlights the non-additive behavior of composite fuels, demonstrating enhanced reactivity and combustion efficiency compared to simple mixtures. Thermogravimetric analysis (TGA) revealed distinct stages of thermal decomposition, with composite fuels exhibiting combined processes of volatile release and coke residue decomposition, unlike mixtures. Ignition experiments in a vertical tubular furnace showed reduced flash delay times for composites, attributed to the formation of active surface centers during mechanical activation. Flare combustion studies confirmed more stable and complete combustion of composites, achieving higher temperatures and improved flame stability. Plasma gasification experiments indicated that composite fuels provide more uniform gas evolution, with higher yields of hydrogen (H₂) and carbon monoxide (CO), while reducing nitrogen oxide (NO) emissions. The findings underscore the potential of composite fuels for optimizing energy efficiency and reducing environmental impact in coal-fired power plants, supporting the transition to sustainable energy solutions. Full article

The global transition toward low-carbon energy and transportation systems positions hydrogen as a key clean and versatile energy carrier. However, ensuring the safe handling and storage of hydrogen—particularly in its liquid form LH₂)—remains a critical challenge to large-scale deployment. Accidental releases of LH₂ can lead to rapid dispersion, cryogenic hazards, and increased risks of ignition or detonation due to hydrogen’s low ignition energy and wide flammability limits. This review synthesizes recent advances in the understanding and modelling of LH₂ safety scenarios, emphasizing the complementary roles of Computational Fluid Dynamics (CFD) and Machine Learning (ML). The paper first outlines the fundamental physical processes governing cryogenic hydrogen leaks, spills, and jet releases, followed by an overview of current storage and sensing technologies. Special consideration is given to safety implications arising from the differences between open and enclosed environments and the fact that existent sensing technologies present deficiencies at low temperatures. CFD-based studies are reviewed to illustrate how these methods capture complex flow and dispersion dynamics under diverse operational and environmental conditions, supported by a summary of existing experimental investigations used for model validation. The emerging role of ML is then examined, focusing on its integration with CFD simulations and sensor networks for predictive risk assessment, real-time leak detection, and the development of digital twins. Finally, integrated CFD–ML-sensor systems are discussed as a pathway toward a physics-informed, data-driven framework for advancing hydrogen safety and reliability. Full article

The global shift towards cleaner energy sources is driving the adoption of hydrogen as an environmentally friendly alternative to fossil fuels. Among the forms currently available, Liquid Hydrogen (LH₂) offers high energy density and efficient storage, making it suitable for large-scale transport by rail. However, the flammability of hydrogen poses serious safety concerns, especially when transported through confined spaces such as railway tunnels. In case of an accidental LH₂ release from a freight train, the rapid accumulation and potential ignition of hydrogen could cause catastrophic consequences, especially if freight and passenger trains are present simultaneously in the same tunnel tube. In this study, a three-dimensional computational fluid dynamics model was developed to simulate the dispersion and explosion of LH₂ following an accidental leak from a freight train’s cryo-container in a single-tube double-track railway tunnel, when a passenger train queues behind it on the same track. The overpressure results were analyzed using probit functions to estimate the fatality probabilities for the passenger train’s occupants. The analysis suggests that a significant number of fatalities could be expected among the passengers. However, shorter users’ evacuation times from the passenger train’s wagons and/or longer distances between the two types of trains might reduce the number of potential fatalities. The findings, by providing additional insight into the risks associated with LH₂ transport in railway tunnels, indicate the need for risk mitigation measures and/or traffic management strategies. Full article

Aluminum hydride (AlH₃) is a promising candidate for enhancing the combustion performance of liquid fuels due to its high energy density and exceptional hydrogen storage capacity. This study investigated the ignition and combustion characteristics of μ-AlH₃ particles in kerosene droplets using TG-DSC analysis, high-speed imaging, laser ignition, and combustion product characterization, with comparisons to micron- and nano-aluminum powders. Results showed that the exothermic combustion of hydrogen released from AlH₃ decomposition lowered the primary oxidation temperature of aluminum, leading to more intense combustion with smaller ejected particles. The particle size of kerosene droplets containing AlH₃ rapidly decreases due to the escape of hydrogen. The heat released by the combustion of hydrogen significantly accelerates the combustion of droplets, and the fastest combustion rate is observed at a concentration of 1% AlH₃. The combustion products of kerosene droplets containing AlH₃ are smaller than those of kerosene droplets containing aluminum, indicating that their combustion efficiency is higher. A combustion model for AlH₃-based kerosene droplets was developed, demonstrating less than 10% error in predicting ignition delay and burning rates. These findings provide valuable insights for the application of AlH₃ in liquid fuels. Full article

Lithium iron phosphate (LFP) batteries have become a popular choice for energy storage, electrified mobility, and plants. All lithium-based batteries produce flammable vent gas as a result of failure through thermal runaway. LFP cells produce less gas by volume than nickel-based cells, but the composition of this gas most often contains less carbon dioxide and more hydrogen. However, when LFP cells fail, they generate lower temperatures, so the vent gas is rarely ignited. Therefore, the hazard presented by a LFP cell in thermal runaway is less of a direct battery fire hazard but more of a flammable gas source hazard. This research identified the constituents and components of the vent gas for different sized LFP prismatic cells when overcharged to failure. This data was used to calculate the maximum homogenous concentration of gas that would be released into a 1.73 m³ test rig and the percentage of the lower explosive limit (LEL). Overcharge experiments were conducted using the same type of cells in the test rig in the presence of remote ignition sources. Ignition and deflagration of the vent gas were possible at concentrations below the theoretical LEL of the vent gas if it was homogeneously mixed. Full article

Hydrogen–gasoline dual-fuel spark ignition (SI) engines represent a promising transitional solution toward cleaner combustion and reduced carbon emissions. In a previous study, a predictive engine model was developed to simulate the performance and combustion characteristics of such systems; however, its accuracy was constrained by the use of estimated combustion parameters. This study presents an experimental validation based on high-resolution in-cylinder pressure measurements performed on a naturally aspirated SI engine operating with a 20% hydrogen energy share. The objectives are twofold: (1) to refine the combustion model using empirically derived combustion metrics, and (2) to evaluate the feasibility of moderate hydrogen enrichment in a stock engine configuration. To facilitate a more accurate understanding of how key combustion parameters evolve under different operating conditions, Vibe function was fitted to the ensemble-averaged heat release rate curves computed from 100 consecutive engine cycles at each static full-load operating point. This approach enabled the extraction of stable and representative metrics, including the mass fraction burned at 50% (MFB50) and combustion duration, which were then used to recalibrate the predictive combustion model. In addition, cycle-to-cycle variation and combustion duration were also investigated in the dual-fuel mode. The combustion duration exhibited a consistent and substantial reduction across all of the examined operating points when compared to pure gasoline operation. Furthermore, the cycle-to-cycle variation difference remained statistically insignificant, indicating that the introduction of 20% hydrogen did not adversely affect combustion stability. In addition to improving model accuracy, this work investigates the occurrence of abnormal combustion phenomena—including backfiring, auto-ignition, and knock—under enriched conditions. The results confirm that 20% hydrogen blends can be safely utilized in standard engine architectures, yielding faster combustion and reduced burn durations. The validated model offers a reliable foundation for further dual-fuel optimization and supports the broader integration of hydrogen into conventional internal combustion platforms. Full article

Pressure relief devices are critical for the safe release of pressurized hydrogen. To address the risk of spontaneous ignition during a high-pressure release, three-dimensional (3D) numerical simulations are systematically conducted to investigate the effects of burst conditions on spontaneous ignition behavior. Eight simulation cases are considered, involving two opening processes (instantaneous and 10-step-like), three burst disk shapes (flat, conventional domed, and reverse domed), and five opening ratios (1, 0.8, 0.6, 0.4, and 0.2). The 10-step-like opening enhances jet turbulence and promotes flame merging between the boundary layer and jet front, intensifying combustion. Domed structures cause a high-velocity region behind the leading shock wave, altering jet front evolution. Compared with reverse-domed disks, flat and conventional domed disks generate stronger vortices and a larger shock-heated area, resulting in more severe combustion and elevated fire risk. As the opening ratio decreases, both shock wave strength and propagation velocity drop significantly, and spontaneous ignition does not occur. The opening ratio has minimal influence on the distance traveled by shock-induced heating. These findings offer meaningful guidance for the design and manufacture of pressure relief devices for the safe emergency release of hydrogen. Full article

This study investigates the effects of varying hydrogen percentages in fuel blends on combustion dynamics, engine performance, and emissions. Experimental data and analytical equations were used to evaluate combustion parameters such as equivalent lambda, in-cylinder pressure, heat release rate, and ignition timing. The findings demonstrate that hydrogen blending enhances combustion stability, shortens ignition delay, and shifts peak heat release to be closer to the top dead center (TDC). These changes improve thermal efficiency and reduce cycle-to-cycle variation. Hydrogen blending also significantly lowers carbon dioxide (CO₂) and hydrocarbon (HC) emissions, particularly at higher blend levels (H0–H5), while lower blends increase nitrogen oxides (NO_x) emissions and risk pre-ignition due to advanced start of combustion (SOC). Engine performance improved with an average hydrogen energy contribution of 12% under a constant load. However, the optimal hydrogen blending range is crucial to balancing efficiency gains and emission reductions. These results underline the potential of hydrogen as a cleaner additive fuel and the importance of optimizing blend ratios to harness its benefits effectively. Full article