Hydrogen Jet Flames Research Articles

Experimental study on flame behaviors and dynamic parameters induced by hydrogen jet flame in an enclosed compartment

Hydrogen is considered as one of the most superior future energy carriers due to its clean, low-carbon and extensive sources. However, a wide flammable concentration range and low ignition energy of hydrogen can cause potential safety hazards, including hydrogen jet flames. Currently, a series of hydrogen jet flame experiments were performed in an enclosed compartment with internal dimensions of 1.82 m (L) × 1.99 m (W) × 1.85 m (H), using different nozzle diameters and stagnation pressures. The results indicate that the combustion process can be divided into four stages, including growth stage, relatively stable stage, stretching stage, and self-extinguishing stage. The oxygen concentration in an enclosed compartment decreases rapidly with increasing stagnation pressure. The self-extinguishing time is positively correlated with the compartment volume and negatively correlated with the mass flow rate. Based on thermal equilibrium analysis, the correlations for average gas temperature rise and oxygen concentration were proposed.

A LES study on the instantaneous H2 jet-ignited combustion characteristics of H2/NH3 mixtures

This paper presents a Large Eddy Simulation (LES) study investigating jet flame ignition characteristics to achieve stable ammonia combustion for novel applications in gaseous ammonia/hydrogen-fueled engines with an active prechamber. The study investigated three cases with initial global equivalence ratios of 0.6, 0.8, and 1.0. Two main ignition modes were proposed, and five stages of coupled flame propagation processes were identified. The oscillation of supersonic hydrogen jet flame was investigated. The modes of flame-vortex interaction including vortex ring formation, along with the mechanism of highly reactive zone formation, were proposed. The effects of reactivity and turbulence transition on piloted ammonia flame were investigated to attain stable ammonia combustion and achieve a high heat release rate. The results showed that oscillations in the jet flame were strengthened at low global equivalence ratios with high hydrogen mass ratios. Enhancing propagation of initial and secondary vortex rings broadened highly reactive zones. Vorticity dissipated more rapidly at low equivalence ratios, leading to a stratified structure and enhanced piloted spherical flame. The Unsteady Flamelet Ignition Prediction (UFIP) sub-model of combustion was verified for the piloted ammonia flame, enabling a more comprehensive discussion of flame propagation tendencies.

Experimental Study of the Dynamics of Lean Premixed Hydrogen Flames in a Multi Jet Combustor

Abstract In this study, the flame dynamics of lean premixed hydrogen jet flames are experimentally investigated. Acoustic and optical measurements are used to capture the response of a bundle of jet flames to acoustic forcing. Using helium as a fuel surrogate, we simulate the change in acoustic properties in the burner during the determination of cold burner transfer matrix measurements. We investigate the influence of the equivalence ratio and the addition of methane as well as the interaction of the individual flames to evaluate the scalability of the results to systems with more flames. It is shown that the changes in the dynamic flame response can primarily be explained by the flame length, which changes both with the methane share and with the equivalence ratio. It can be observed that with small changes in the equivalence ratio, the flame length and the flame transfer function (FTF) change in the same way as with a small change in gas composition. To assess the scalability of these results, we deactivate some of the jet flames and analyze how the overall response to acoustic forcing changes. We find that the FTF phase is not affected by the number of active flames. Analyzing the respective gain values, significantly stronger responses are measured for a few flames, but only small difference can be measured above a certain number of neighboring flames so that the lab scale results can also be expected to be valid for industrial configurations with a high number of flames.

Investigation on the morphology and temperature distribution of hydrogen jet flames impinging on barrier walls

Hydrogen is often stored and transported in a high-pressure state, posing a risk of jet flames in the event of accidental leakage. Firewalls are commonly installed around high-pressure hydrogen storage and transportation equipment to protect surrounding facilities and personnel from the fire hazards caused by hydrogen leaks. By combining experimental and numerical simulation methods, this study investigated the effects of varying hydrogen release pressure, nozzle shape, nozzle-wall distance, and barrier height on the behavior of high-pressure hydrogen jet flames. A predictive model for the flame extension length after contact with the wall was proposed. The study found that when the wall height is sufficient to cause complete flame deflection, the temperature distribution near the wall exhibits a strong regularity. The temperature of the barrier wall below the nozzle height is higher than that above the nozzle height, indicating that enhanced thermal protection is needed in this region for practical applications.

Experimental investigation on the development characteristics of high-pressure hydrogen jet flame under different ignition conditions

With the rapid development and application of hydrogen in the chemical and energy industry, the safety of hydrogen industrial facilities has been widely concerned. In this study, the safety of hydrogen accidently released from a high-pressure tube storage system (tube diameter:10 mm, storage tank volume:4 L) was explored experimentally. The combustion behavior of the transient hydrogen jet and explosion overpressure under self-ignition and electric spark induction were investigated. Besides, the explosion overpressure and jet flame evolution laws of the hydrogen cloud induced by the release of unsteady turbulent hydrogen jets into the open environment were analyzed. The results revealed that the peak value of hydrogen self-ignition explosion overpressure was higher than that of electric spark ignition overpressure. Compared with spark ignition, hydrogen self-ignition flame structures can be maintained for longer time. However, spark ignition at low release pressures was more likely to cause hydrogen ignition and explosion compared to self-ignition. Finally, the combustion behavior and potential hazards of the ignited free transient hydrogen jet under different ignition modes were analyzed. This study can provide a reference for the prevention and control of hydrogen explosion accidents in practice.

Burning behavior of hydrogen jet flame inhibited by a wire mesh screen

Hydrogen is recognized as a promising energy source and the potential risks associated with leakage and jet fire accidents should be considered. The objective of this study is to explore the feasibility of utilizing wire mesh to suppress hydrogen jet flames. The experiments of hydrogen jet fire with ignitors below and above the wire mesh were performed to explore the effect of wire mesh on the burning behaviors at different mesh numbers, mesh-to-nozzle distances, and fuel flow rates. Compared to the free jet flame, the length of jet flame under the action of wire mesh is decreased by 50–90 %. The flame with topside ignition fails to pass through the mire mesh due to the cooling effect of the fuel jet. Experimental results reveal that the state of the flow field in the impingement area plays an important role in determining the upper flame height. Both the upper flame height and the flame extension length beneath the screen decrease with mesh-to-nozzle distance. As the mesh porosity decreases, the flame extension length increases, however, the upper flame height decreases. Based on the classical theory of flow resistance through porous media, a new dimensionless model was developed to predict the characteristic flame lengths of the jet flame inhibited by wire mesh. The findings presented in this paper offer fresh insight into the safeguarding of jet fires.

Hydrogen Jet Flame Simulation and Thermal Radiation Damage Estimation for Leakage Accidents in a Hydrogen Refueling Station

With the rapid development of hydrogen energy worldwide, the number of hydrogen energy facilities, such as hydrogen refueling stations, has grown rapidly in recent years. However, hydrogen is prone to leakage accidents during use, which could lead to hazards such as fires and explosions. Therefore, research on the safety of hydrogen energy facilities is crucial. In this paper, a study of high-pressure hydrogen jet flame accidents is conducted for a proposed integrated hydrogen production and refueling station in China. The effects of leakage direction and leakage port diameter on the jet flame characteristics are analyzed, and a risk assessment of the flame accident is conducted. The results showed that the death range perpendicular to the flame direction increased from 2.23 m to 5.5 m when the diameter of the leakage port increased from 4 mm to 10 mm. When the diameter of the leakage port is larger than 8 mm, the equipment on the scene will be within the boundaries of the damage. The consequences of fire can be effectively mitigated by a reasonable firewall setup to ensure the overall safety of the integrated station.

Practical approaches for evaluating radiative heat from high pressure hydrogen flame

As the construction of hydrogen stations and other hydrogen-related facilities progresses, it becomes increasingly crucial for safety designs to account for scenarios where leaked hydrogen might ignite. Since a hydrogen flame is usually invisible, detection must rely on radiative heat or temperature. While it is possible to predict accurate radiative heat flux from a high pressure hydrogen jet flame through detailed numerical calculations of hydrogen combustion with its radiation, the objective of this study is to provide a simpler and more accurate prediction method. Previous experimental data of radiative heat flux, Qr from high pressure hydrogen jet flames were compiled, and a simple experimental equation Qr=1463.3(Lo/Lf)−2.32 was derived, where Lf and Lo represent the flame length and the distance perpendicular to the flame axis from the midpoint of the flame length to the observer, respectively. Radiative heat fluxes were computed through detailed numerical simulations using three types of water vapor radiation models: Goody's narrow random band model, the exponential broad band model by Edward and Elsasser's narrow regular band model. The temperature and water vapor partial pressure distributions obtained from numerical simulations were used as input conditions. The results were found to be in good agreement with the experimental equation. Moreover, a simple diagram representing the radiative heat flux from a hydrogen flame was derived using the method of cylinder-like approximation. The results of this study show that if the hydrogen pressure and leakage aperture diameter are given, the radiative heat flux at a certain distance can be predicted with high accuracy. Additionally, the average value of emissivity for the hydrogen diffusion flame was found to be on the order of 0.03.

Effect of temporal increase in equivalence ratio on combustion instability of a lean-premixed swirling hydrogen flame

The effect of temporal increase in the equivalence ratio on the combustion instability of a lean-premixed low-swirl hydrogen jet flame in a low-swirl combustor (LSC) is investigated in detail using a high-fidelity Large-Eddy Simulation (LES). The equivalence ratio is linearly increased from 0.3 to 0.5 over a duration of 0.4 s. The results show that the pressure oscillation amplitude in the combustor increases significantly when the equivalence ratio at the combustor inlet (ERCI) exceeds 0.42, and the maximum pressure amplitude and the combustion instability mode exhibit trends consistent with those in a previous experiment and numerical simulation conducted with the same LSC setup at a fixed equivalence ratio of 0.39. Temporal variations in the equivalence ratio and consequently the temperature inside the combustor cause the drastic amplification of pressure oscillation (when the ERCI exceeds 0.42) whose amplitude is larger than that at the fixed equivalence ratio (= 0.39). Prior to the onset of this exceptionally strong combustion instability, a transient irregular oscillation phenomenon comprising instantaneous changes in the pressure oscillation frequency is observed. While the pressure oscillations in the combustor and in the injector channel are in phase after the onset of strong combustion instability, they are in opposite phases during the occurrence of the irregular oscillation phenomenon prior to the onset of strong combustion instability. This irregular oscillation phenomenon predicted by the LES may play a crucial role in the mechanism of transition from stable combustion to combustion instability.

Experimental investigation on hydrogen jet flame behavior and temperature distribution with different shapes of outlet

Hydrogen's wide flammability range causes its high-pressure jet flames to exhibit large-scale, high-temperature characteristics, posing risks of casualties and property damage. This study investigates the impact of different nozzle shapes and release pressures on flame behavior and temperature distribution through high-pressure hydrogen jet flame experiments. Circular outlets (0.5–4 mm diameter) and rectangular outlets (aspect ratios 1 to 8) are used, covering release pressures from 20 to 220 bar. High-pressure hydrogen is released through a nozzle into ambient air, igniting to form a flame. Flame length, width, and axial temperature are measured. Findings indicate that visible flame size increases with release pressure. The models for dimensionless visible flame length and width, considering the dimensionless heat release rate, are proposed for different nozzle shapes. Additionally, the dimensionless temperature rise along the flame axis is observed to be a function of the dimensionless distance and dimensionless heat release rate.

Numerical simulation of leakage jet flame hazard of high-pressure hydrogen storage bottle in open space

The jet fire is a common type of fire accident in high-pressure hydrogen storage bottles. It is crucial to conduct research on the thermal radiation hazards resulting from on-board hydrogen storage bottle leaks, leading to jet fires within 35 MPa. Additionally, accurately and swiftly calculating the characteristic parameters of hydrogen jet flames, such as flame geometry and radiation heat flow, is of utmost importance. To study the jet fire hazard caused by high-pressure hydrogen storage cylinder leaks, a simplified model of the hydrogen storage cylinder was established using FLUENT software for numerical simulation analysis. The study analyzed the impact patterns of high-pressure hydrogen leakage jet flames under different scenarios, including leakage aperture, leakage pressure and ambient wind speed. The results demonstrate a positive correlation between the leakage aperture and pressure with the size of the jet flame and the extent of thermal radiation damage. The larger the leakage aperture and pressure, the larger the hydrogen jet flame size. The higher the peak value of the flame thermal radiation, the greater the hazard range. Additionally, the temperature of the stable axis of the jet flame rises with increasing leakage aperture. As the leakage pressure rises, the thermal radiation of the flame also increases. Conversely, as the ambient wind speed increases, the flame length, the burn radius, and the thermal radiation range decreases, but the high-temperature heat range expands. The empirical formula between flame length and leakage pressure and leakage aperture under different environmental wind speeds is obtained by data fitting, which can be used as a priori prediction of flame length under wind speed conditions.

Numerical study on the shock wave and vortex and their coupling effect on the behavior of the flame induced by the spontaneous ignition of high-pressure hydrogen release

High-pressure hydrogen storage is currently the mainstream way of hydrogen storage. However, the risk of spontaneous ignition and subsequent jet flame are serious obstacles to the wide application of hydrogen energy. To further reveal the interaction of shock waves, vortices and flame induced by the spontaneous ignition of high-pressure hydrogen release under the effect of release process and burst pressure, a numerical study is conducted by employing LES, RNG, EDC models and detailed hydrogen/air combustion mechanism. The qualitative and quantitative comparison of flow field and flame splitting process outside the tube between this numerical study and previous experimental results validate the numerical results. It is found that an initial vortex is formed at the edge of the jet. Then, several vortices are generated at the edge of the jet and ahead of the Mach disk. The number of vortices in the outer side of the barrel shock is larger when the opening time is shorter. After moving out of the tube, the flame front becomes hemisphere and the lateral edge has a hemispherical bulge which is induced by the initial vortex. The temperature is low and the hydrogen concentration is high in the high-speed region which is induced by the reflected shock wave, leading to the splitting of the flame into two parts: the first and the second half of the flame. However, the flame cannot be formed at the initial stage when the opening time increases to 150 μs and the flame area is larger than with smaller opening times. After splitting, under the affection of the vortices generated at the lateral side, the first half of the flame rotates backward and gradually merges with the second half of the flame, finally forming a complete hydrogen jet flame.

Modeling of jet spreading and flame hazard distances for high pressure hydrogen releases

Hydrogen is a promising clean and sustainable energy carrier. Hydrogen is usually stored at high pressure due to its low density. Hydrogen releases from high pressure storage can result in underexpanded jets that will mix with air, forming a large combustible cloud. If the jets are ignited, jet flames will form with a large hazard area. This study simulated hydrogen jets and jet flames for storage pressures of 1~70 MPa and nozzle diameters of 1~2 mm using the HyRAM software. The results show that the jet diffusion distance increased with the hydrogen stagnation pressure and the nozzle diameter. The diffusion distances were correlated with the nozzle diameter and the hydrogen stagnation pressure. The jet flames and thermal radiations were then analyzed to show that the flame length and hazard distance both increased with the stagnation pressure and nozzle diameter. Correlations for radiation major harm distance, harm distance and no harm distance were developed to predict the jet flame hazard range. The present study can provide references for the safety design of hydrogen applications.

Comparing the risk of third-party excavation damage between natural gas and hydrogen pipelines

Existing natural gas pipelines can facilitate low-cost, large-scale hydrogen transportation and storage, but hydrogen may entail safety challenges. These challenges stem from hydrogen’s different properties compared to natural gas, such as higher ignition probability, different flame behavior, and potential for hydrogen embrittlement. Although risk assessments for hydrogen pipelines are increasing, the impact of hydrogen on the risk of third-party excavation damage (TPD), the major cause of pipeline incidents in the U.S., has received little attention. This work presents the SHyTERP model for Safe Hydrogen Transportation and Excavation Risk Prevention for Pipelines. The model incorporates causal models, excavation damage and pipeline failure statistics, and validated physical models of hydrogen and natural gas release and jet flame behavior. Through four case studies, the model compares the TPD risks of hydrogen and natural gas pipelines, offering insights and recommendations for the safe implementation of hydrogen in existing pipelines.

Large-Eddy-Simulation of Turbulent Non-Premixed Hydrogen Combustion Using the Filtered Tabulated Chemistry Approach

Abstract With air traffic expected to grow 5% annually until the year 2030, alternative fuels such as hydrogen are being investigated in order to tackle the current environmental crisis. Due to safety concerns, future hydrogen combustion chambers will require new designs of injection systems and are expected to operate under multimode combustion regimes. From a large-eddy-simulation (LES) perspective, a prerequisite for the shift toward new hydrogen combustion chamber technologies is a robust turbulent combustion model capable of functioning in non-premixed conditions. Turbulent combustion modeling using flame front filtering is a well-developed strategy in premixed combustion (filtered-tabulated chemistry for large-Eddy-simulation (F-TACLES)). This approach has been extended to non-premixed flames however, it suffers from high flame filter size sensitivity. Moreover, thin hydrogen flame fronts will result in lower resolution on the LES grid, potentially amplifying this issue. In order to address the feasibility of the non-premixed F-TACLES model applied to hydrogen fuel, simple one-dimensional and two-dimensional laminar counterflow diffusion flames are computed. The model is then tested on the three-dimensional Sandia hydrogen jet flame with a Reynolds number of 10,000. Simulations and a priori tests show that tabulated subgrid-scale correction terms are stiff and can result in nonphysical results, however the model is capable of correctly reproducing non-premixed flame structures for small filter sizes.

Macroscopic flame and flow structures in hydrogen and methane multi-regime combustion

The current experimental investigation focuses on the macroscopic structures of CH4/air and H2/air flames operated on the Darmstadt multi-regime burner adapted for hydrogen operation. Building upon previous research on lean-burn limits, this study utilizes simultaneous PIV and OH-PLIF measurements to examine notable differences in flame and flow structures. Six flame cases are studied, focusing on CH4/air and H2/air jet flames at equivalence ratios of 1.4, 2.2, and 3.5. It is observed that the hydrogen slot 2 flames exhibit unique behavior under ultra-lean conditions, demonstrating thermodiffusive effects that generate finger-like structures. Despite receiving less thermal support from the slot 2 flame, hydrogen jet flames burn faster and resist flame extinction in high-velocity regions. The extensive heat release from fuel-rich H2 jets maintains a stable location compared to CH4 jets at the same equivalence ratio, altering local flow dynamics. Additionally, the study identifies a reshaped primary inner recirculation zone (IRZ) and a secondary IRZ in H2/air flame cases, which is absent in CH4 flames. The interplay between the jet flame and the primary IRZ results in visible flame enhancement in slot 2, indicating preheating and fuel enrichment effects. Overall, this research provides comprehensive insights into the distinct combustion behavior and flow structures of CH4 and H2 flames on a multi-regime burner.

Experimental study of self-extinguishing behavior of hydrogen jet fires in the confined space with a ceiling vent

With the widespread utilization of hydrogen energy, the hydrogen safety issues, especially hydrogen jet fires, should be much paid attention to, since the latter present high temperature and radiation in confined space. Hydrogen jet fire experiments were conducted with various release rates and vent sizes in a confined space with ceiling vent to investigate the hydrogen jet flame height, oxygen concentration, and self-extinguishing time. The results show that, the large vent sizes with low hydrogen release rates result in well-ventilated hydrogen jet fires. As the vent size decreases or the hydrogen release rate increases, the hydrogen jet flame evolves from a well-ventilated one to one having self-extinguishing behavior with under-ventilation. The combustion process can be divided into four stages: the growth stage, the quasi-steady stage, the stretch stage and the self-extinguishing stage. The flame height increases with the hydrogen release rate at the quasi-steady stage, and the vent size has almost no effect. However, in the case of under-ventilation, the flame height at the stretch stage is determined by the joint actions of vent size and hydrogen release rate, and the flame height is positively connected with the size of the ceiling vent. The oxygen concentration and self-extinguishing time decrease dramatically as the vent size and hydrogen release rate increase. The parameter Q˙VA1/3 is proposed to reflect the coupling effects of hydrogen release rate and vent size, and the correlations of oxygen concentration and self-extinguishing time are determined with Q˙VA1/3.

Experimental investigation of hydrogen jet flame inhibition by nitrogen jet

With the rapid development of hydrogen energy and the increase of the risk of hydrogen jet fires, a reliable fire protection technology is required to extinguish hydrogen jet flame efficiently. An experimental investigation was carried out to study the inhibition of a hydrogen jet flame by a nitrogen jet. The impact angle, nozzle diameter and nozzle position of the nitrogen jet were the variables. The flame characteristic parameters were analyzed, including the flame length, deflection height and deflection angle. The results show that the inhibited flame length was always positively correlated with the vertical distance between the nozzles. The increase of the impact angle had a significant inhibitory effect on the flame length. Besides, the explanatory factor was used to describe the influence of various initial release conditions on flame inhibition and was calculated by the combination of the explanatory variables, such as impact angle, impact stroke and impact height. The flame length reduction ratio, deflection height reduction ratio and dimensionless deflection angle are positively correlated with the explanatory factor. It means that the jet flame is more easily extinguished under a larger explanatory factor. The critical parameter of the explanatory factor for extinguishing the hydrogen jet flame was verified experimentally.

Effect of distance of vertical barrier wall and release temperature on the hydrogen jet flame width and temperature distribution induced by impingement of ignited release of cryogenic hydrogen

Cryogenic storage option is one of the important ways of storing hydrogen, but under-expanded ignited releases of cryogenic hydrogen could easily lead to jet fires, causing serious damage to people and properties. Barrier walls are important means to reduce the severity of cryogenic hydrogen jet flames, however, its effect on the cryogenic hydrogen jet flame and related temperature distribution are still unclear. In this work, the effect of the distance of barrier wall (0.20, 0.25, 0.30, 0.35 and 0.40 m) and release temperature (140, 180, 220, 260 and 300 K) on the hydrogen jet flame width and temperature distribution is investigated experimentally. It is found that the flame width in the horizontal and vertical direction and the temperature on the vertical barrier wall increase with the decrease of the distance to the nozzle and release temperature. The normalized flame width and inverse excess maximum temperature on the barrier wall increases linearly with the scaled distance considering nozzle diameter and release temperature. The temperature distribution is normalized as Gaussian distribution both in the horizontal and vertical direction, while the excess temperature is higher upward than that of downward. The results can provide a theoretical basis and data support for the blocking of jet fires formed by cryogenic hydrogen ignited releases.

Experimental investigation on the development characteristics of explosive overpressure induced by high-pressure hydrogen jet flame

Accidental release of high-pressure hydrogen can induce the self-ignition, and the spontaneously combusting flame can eventually induce a non-premixed jet flame or even explosion. In this study, the explosion overpressure characteristic of hydrogen jet flame outside the pipeline was investigated. Experiments were conducted on high-pressure hydrogen release pipelines with a diameter of 10 mm and pipeline lengths of 750, 1450 and 2200 mm, respectively, under different hydrogen release pressure. The impact of different initial conditions on the peak value of high-pressure hydrogen jet explosion was systematically investigated. The external pressure signals and flame images were completely collected. The results show that the external explosion overpressure decreased with the increase of axial distance away from the nozzle. When the length of the pipeline increased, the peak value of the overpressure was also gradually decreased. Meanwhile, as the high-pressure hydrogen burst pressure increased, the overpressure rose first and then decreased. With the increase of release pressure, when the hydrogen pressure exceeded 8 MPa, the hydrogen flow in the tube formed a blocked flow, so the increase of external explosion overpressure became slow. This topic can provide a reference for the safety development of the high-pressure hydrogen storage system.