Hydrogen Jet Research Articles

Effect of leakage source condition on the unignited hydrogen released issuing through a horizontal realistic pipeline geometry

An unignited gas release experiment system for the schlieren visualization and concentration quantitative measurement is designed and built to investigate the diffusion and concentration distribution features of turbulent hydrogen jets issuing from a realistic pipeline geometry. Helium is used in place of hydrogen for safety reasons. The spatial and temporal evolution of the asymmetry of turbulent helium jets was studied. The influence mechanisms of the volumetric flow rate (Q), the ratio of orifice diameter to the inner diameter of pipeline (R), and the angle between the normal of the leakage orifice and the opposite direction of gravity (θ) on the asymmetric concentration distribution are revealed. The experimental results show that the diffusion angle (α) and the inclination angle (β) of the turbulent helium jet are the largest when Q is 15 SLPM, R is 0.3, and θ is 0°, and the asymmetric feature of the turbulent helium jet is obvious. As the Q increased, the slope k of the inverse helium concentration (1/volume fraction) and a scaled distance L (L = (x/d)·(ρa/ρ0)1/2) became small. The increase of Q aggravated the concentration attenuation caused by the volumetric flow rate and the asymmetry jet. As R increased, the slope k of the inverse helium concentration and a scaled distance L first decreased and then increased. The slope k got the minimum value when R was 0.3. The downward movement of the leakage orifice position increased the turbulent intensity near the leakage orifice. This work can provide theoretical support for accident prevention and emergency treatment of hydrogen leakage accidents in long-distance pipeline low-pressure hydrogen transportation.

Cavity effects on spontaneous ignition of pressurized hydrogen jets

The release of pressurized hydrogen jets can lead to spontaneous ignition, which poses a major challenge to the safe utilization of hydrogen energy. Previous studies have primarily focused on the spontaneous ignition of pressurized hydrogen released into tubes. However, in real industrial scenarios, pressurized hydrogen is usually released into the atmosphere or a complex equipment environment. Therefore, the effect of obstacles on spontaneous ignition needs to be considered. In this study, the spontaneous ignition of sudden releases of pressurized hydrogen entering various cavity shapes was modeled using the standard k-ω turbulence model, the eddy dissipation concept (EDC) model and a detailed 21-step chemistry model. The effects of the cavities on the jet flow fields and the spontaneous ignition were analyzed for various cavity shapes and release pressures. For the pressures considered in this study, the cylindrical cavity did not lead to ignition. The highest hydrogen jet temperature occurred in the contact region due to the shock wave reflection, after which spontaneous ignition could not occur due to the flow divergence. The pressurized hydrogen entering hemispherical and conical cavities enhanced the hydrogen-air mixing which led to combustible regions and the formation of multidimensional shock waves, which significantly increased the spontaneous ignition probability. The cavities created a high-temperature region inside the cavity that experienced ignition but the flames did not spread out of the cavity. The conical cavity produced lower flame temperatures than the hemispherical cavity but prolonged the flame lifetime. Higher initial hydrogen release pressures resulted in more violent multidimensional shock wave interactions and higher contact surface temperatures, which lead to earlier ignition times but with little impact on the initial location of the spontaneous ignition. The results of this study provide a scientific foundation for hydrogen safety codes, safe equipment designs and the development of industry codes and standards.

The role of the shock generator on the mixing performance of hydrogen jet released from the extruded transverse 3-lobe nozzle in a scramjet engine

The role of a shock generator in the fuel distribution of a scramjet engine is highly significant. In this article, the usage of the erected 3-lobe nozzle in the existence of a shock generator for fuel injection inside a supersonic combustion chamber is fully studied. A three-dimensional model of the extruded 3-lobe nozzle with two altitudes of 4 mm and 2 mm is produced to disclose the importance of the produced vortex upstream/downstream by the usage of the extruded injector. Comprehensive computational analysis is done to investigate the mixing efficiency and fuel diffusion of the proposed jet configuration. Impacts of the coaxial inward air jet on the hydrogen dispersion of the annual extruded 3-lobe injector are also revealed in the present research. The results of the flow structure indicate that the produced vortex upstream of the erected nozzle improves the fuel dispersion behind the hydrogen jet. Our findings show that the effects of injector height are more considerable than the use of an inner air jet for advance of the fuel mixing within the combustor of a scramjet engine.

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.

Effects of energy-share and ambient oxygen concentration on hydrogen-diesel dual-fuel direct-injection (H2DDI) combustion in compression-ignition conditions

This study investigates the ignition and combustion characteristics of interacting hydrogen (H2) and diesel surrogate jets under simulated compression-ignition engine conditions. The experimental setup includes two converging single-hole injectors in an optically accessible constant-volume combustion chamber (CVCC). The parameters varied in the study are fuel injection durations and ambient O2 concentrations (10 to 21 vol.%). The results show that a longer interaction between the diesel products and the H2 jet is required to achieve ignition of the H2 jet at lower O2 concentrations. Once ignited, the flame stabilises near or at the nozzle, except under the lowest ambient O2 condition of 10 vol.% where a lifted flame is observed. The lift-off response, however, is influenced by the relative injection duration of the fuels, with the interaction between the incoming H2 jet and the diesel combustion recession products possibly playing a role. The interaction between the jets also affects the recorded intensity and the distribution of the diesel fuel jet soot zone.

Concentration fluctuations and flammability of cryo-compressed hydrogen and methane jets

Compressed hydrogen stored at cryogenic temperatures has a much higher density than room-temperature storage, which enables large-scale hydrogen storage and transport. An understanding of the release of cryogenic hydrogen from pressurized vessels is needed to evaluate the risk and safety concerns with the use of this fuel. The present work extends the analysis of previous experimental studies that measured the gas concentrations of cryo-compressed hydrogen jets and methane jets using a laser Raman scattering diagnostic system. Since the Raman signals are very small, a denoising algorithm was applied to significantly reduce the noise to enable statistical analysis of the data. The transient features of the turbulent jets were characterized by their concentration intermittencies and probability density functions (PDFs). A two-part PDF was developed to predict the bimodal features of the jet concentration distributions. Then, the flammability factors of the cryogenic jets were calculated based on the intermittency and the PDF.

Fuel mixing enhancement of transverse coaxial air and fuel jet by upstream shock wave on in scramjet engines: numerical study

In this study, computational fluid dynamics (CFD) is used to disclose the impacts of upstream shock waves on fuel mixing of cross coaxial air and fuel jet at a scramjet engine. This study has tried to investigate the impact of three different lobe injectors (2-lobe, 3-lobe, and 4-lobe nozzle) on the fuel penetrations along the scramjet combustor. The supersonic air stream is M = 4 while cross hydrogen and air jet are released in sonic velocity. This study uses CFD simulations to analyze the effects of upstream shock waves on fuel mixing in the transverse coaxial jet and assess their potential for improving combustion efficiency. The results demonstrate that the usage of upstream shock waves significantly increases shock interactions and augments the vortex region downstream of the jet. Our results show that the impacts of shock waves on the penetration of fuel jet released from the coaxial lobe nozzle are substantial.

Improved Delayed Detached Eddy Simulation of Combustion of Hydrogen Jets in a High-Speed Confined Hot Air Cross Flow II: New Results

The improved delayed detached Eddy simulation (IDDES) approach used in the part I of this investigation to study the self-ignition and combustion of hydrogen jets in a high-speed transverse flow of hot vitiated air in a duct is extended in the following directions: (i) the wall boundary conditions are modified to take into account the optical windows employed in the experiments; (ii) the detailed chemical kinetic model with 19 reactions is used; (iii) a nonlinear turbulence model is implemented in the code to capture the secondary flows in the duct corners; (iv) the wall roughness model is adapted; (v) the synthetic turbulence generator is imposed upstream of the fuel injection. As a result of improving the mathematical and physical problem statements, a good agreement between the simulation and the experimental database obtained at the LAERTE workbench (ONERA) is achieved.

Modeling investigation on transient behaviors of gaseous ammonia jet flow with direct injection

This study investigates the characteristics of gaseous ammonia jets under an injection pressure of 0.8 MPa and an ambient pressure of 0.1 MPa, using LES and RANS simulation approaches to inform applications of ammonia in internal combustion engines. A three-dimensional constant volume chamber model was established, and the Dynamic Structure model was applied in LES modeling with AMR techniques. The near-nozzle transient structures were successfully captured. Furthermore, a direct comparison between LES and RANS simulation was made, and main jet characteristics were investigated. LES outperforms RANS in predicting the instantaneous structures of ammonia jets and provides a more distinct visualization of oblique shock waves and diamond-like shock cells. RANS excels at displaying averaged features with a smoother distribution curve that represents self-similar characteristics. Additionally, the transient characteristics of ammonia and hydrogen jets were compared. The vortex formation and mixing process in ammonia jets occur at a much slower rate compared to hydrogen jets. Meanwhile, transient vortex ring behaviors were analyzed in detail, including their development tendencies regarding initial, secondary, and broken vortex formation. It is revealed that petal-like swirling movements are strongly correlated with the air–fuel mixing process.

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.

A system for plasma density variation based on a gas-dynamic source of a molecular beam

A description is given of a system for plasma density variation based on a gas-dynamic source (GDS) of a molecular beam, designed to test the modes of replenishment and quenching of plasma in the vacuum chamber of the KTM tokamak. Experimental studies have been conducted to determine the flow parameters of a hydrogen jet in vacuum on a segment of a vacuum chamber of a KTM tokamak at a pressure at the inlet to a supersonic nozzle of 5 MPa and 6 MPa. The results of calculating the parameters on the axis of the hydrogen flow are presented: Mach number, concentration of hydrogen molecules, hydrogen flow rate. An analysis was made of the design adaptation of GDS on the vacuum chamber of the KTM tokamak, and a conclusion was made about the possibility of using GDS of a molecular gas flow to test the modes of replenishing and quenching plasma on the KTM tokamak.

Effect of crossflow impinging type throttling mechanism on combustion characteristics of a strut-based scramjet combustor

Efficient mixing of fuel-air, improved combustion performance, and flame stabilization are the critical events for the successful operation of scramjets that must be realized within the short residence time. One of the significant concerns is flame blow-off during the start-up stage even with the presence of the flame holders. To counter it, an innovative mechanism of air-throttle injection has been proposed and investigated through computational fluid dynamics in the present study. In the proposed mechanisms, a strut is used as a base flame holder, and a provision is made to inject the air in the transverse direction behind the strut's base. Two- and three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations have been solved using the k-ω SST turbulence model for reacting and non-reacting flows. A finite-rate/eddy-dissipation combustion model is selected to include the effects of turbulence-chemistry interaction. It was observed from the simulations that the impingement of hydrogen jet and the transverse throttled jet generates the vortices and recirculation zones. Improved fluid-dynamics associated with the impinging action of the air-throttle has been studied by considering argon as a surrogate for air; also, the enriched oxygen (due to air throttling) around the hydrogen jet makes fuel-air mixture more flammable. These fluid dynamics and chemistry aspects are responsible for the superior performance of air-throttling mechanisms. The proposed mechanism showed 46 % reduction in combustor length to reach the combustion efficiency of more than 95 %. The maximum improvement of mixing efficiency is 48 % observed at downstream of the throttle base over the non-throttled condition. Further the effectiveness of the proposed throttling mechanism is demonstrated to show a promise for holding the flame even at a higher Mach number, i.e., M=4.5. The ignition is achieved at a shorter distance in the air-throttling case, resulting in 28 % reduction in ignition length. The air throttling within the two-shear layer may reduce the ignition delay associated, and the flame can be held immediately downstream of the injector. Additionally, a three-dimensional flow field was also analysed to study the flow characteristics around the transverse jet. In the 3-D flow field, the circulation profiles indicated that the stronger vorticity was generated during the air-throttling than without air-throttling.

A fast POD prediction method for hydrogen leakage at different pressures

The complexity of hydrogen leakage at different pressures leads to the challenge of developing a prediction method for both low pressure and supercritical pressure hydrogen leakage. In this paper, a reduced-order model (ROM) based on proper orthogonal decomposition (POD) is developed to rapidly predict the hydrogen dispersion caused by leakage in small holes at different pressures. The subsonic and underexpanded hydrogen jets are simulated and verified with experimental data. Numerical results of some pressures are collected as POD snapshots and POD interpolation methods are performed to predict the velocity and hydrogen concentration distributions at desired unsampled pressures. Different sample plans with different sampling intervals and sample numbers are investigated. POD-linear, POD-spline, and POD-RBF (radial basis function) interpolations are compared. The results show that the POD-linear and POD-spline methods can accurately predict the velocity and hydrogen fraction at different pressures, and both are better than the POD-RBF method. The relative errors in predicting the hydrogen mole fraction between the POD-linear and POD-spline methods and the simulation results are 2.26% and 2.37%, respectively. Best of all, the POD interpolation method proposed in this work significantly reduces the time required for prediction, costing only 3.3 ms.

Explosion free in fire self-venting (TPRD-less) Type IV tanks: Validation under extreme impinging 70 MPa hydrogen jet fire conditions

High-pressure hydrogen jet fire from a storage tank impinging another tank located nearby is a worst-case incident scenario. This could result in storage vessel rupture with catastrophic consequences implying life and property loss. The concept of microleaks-no-burst (μLNB) performance of hydrogen storage tanks of Type IV is explained. In this study, the breakthrough safety technology of explosion free in fire self-venting (TPRD-less) tank with nominal working pressure (NWP) of 70 MPa is validated again st the most extreme fire conditions of an impinging hydrogen jet from 70 MPa tank. The results of the successful performance of self-venting tank in momentum-dominated hydrogen impinging jet fire are analysed. This work expands further the experimental validation domain of the explosion free in fire self-venting tanks to scenario of impinging fire of the highest applied intensity of HRR/A = 19.5 MW/m2.

Pressure-based large-eddy simulation of under-expanded hydrogen jets for engine applications

An assessment of Large-Eddy Simulations (LES) of non-reactive under-expanded hydrogen jets by using a pressure-based algorithm is presented. Such jets feature strong compressible discontinuities often considered to be best dealt with by a density-based solver. The crucial contribution of this work is to evaluate the suitability of the pressure-based solver to correctly describe the flow field of gaseous hydrogen jets for engine applications, despite the presence of shock waves in the under-expanded near-orifice region. Inherently, the paper aims at providing guidance on the corresponding numerical aspects to simulate these flows. Hydrogen jets in an argon atmosphere at three different injection pressures are simulated and the results are compared to experiments in literature. Jet tip penetration and cone angle are the main investigated parameters. A good match is found, confirming the solidity of the proposed model. Different LES sub-grid scale models and discretisation schemes are then investigated in order to find the best approach in terms of accuracy and required computational cost. In particular, it is found that the WALE model coupled with a 4th-order cubic scheme for the convective terms yields the most suitable configuration.

Flame behavior and temperature distribution of coupled fire induced by the interaction of hydrogen jet flame and pool flame

Once fires occur unexpectedly at the oil-hydrogen integrated refueling stations, there is a high likelihood that they will escalate into a coupled fire, resulting in unpredictable casualties and property losses. In this work, experiments on coupled fire induced by hydrogen jet flame and a heptane pool flame were conducted with different nozzle diameters and release pressures. It has been found that there is a critical diameter above which the hydrogen jet can be ignited instantly. This critical diameter is determined by the release pressure and the location of the pool flame. The heat release rate is greater than that of the single pool flame, and it reaches its highest point at 0.2 MPa. Compared to a single fire, the height of the flame decreases while the length of the flame increases, a prediction model is proposed for the dimensionless flame length and width, taking into account the ratio of the heat release rate of the hydrogen jet flame to the heat release rate of the pool flame. The temperature of the coupled fire reaches its highest point at 0.2 MPa and increases as the nozzle diameter. And it decreases with the increase in the distance when Y= 0 m. However, it increases with the increase of the distance when Y= 0.05 m due to the inclination of the flame.

Experimental investigation on the behaviors and temperature distribution of cryogenic hydrogen jet flames

The jet flame resulting from the ignition of released cryogenic hydrogen is a threat to the surrounding people and facilities. However, the behaviors and temperature distribution of cryogenic hydrogen jet flame are still unclear. In this study, experiments are conducted at different release temperatures and release pressures. It has been found that the length and width of the jet flame increase as the release pressure increases and the release temperature decreases. The prediction model of cryogenic hydrogen jet flame length and width considering release pressure and temperature is proposed. The temperature of the cryogenic hydrogen jet flame increases with the increase of the release pressure and decrease of the release temperature as well. The temperature on the centerline can be expressed as a function in flame calibers, and the critical separation distance can be calculated based on three criteria. The dimensionless jet flame temperature distribution presents a three-stage distribution.

Flame stabilization characteristics of turbulent hydrogen jet flame diluted by nitrogen

Hydrogen is already widely produced and used in the industry. NOx formation during the combustion of hydrogen can be reduced by adding nitrogen. Nonetheless, this comes at the cost of decreased flame stability, which constrains the applicability of hydrogen. Therefore, the flame stabilization characteristics of nitrogen-diluted hydrogen jet flame at varying dilution concentrations (10%–50%) were investigated using thin-lipped nozzles with diameters of 2, 3, and 5 mm. The experimental results show that the nitrogen-diluted jet flame becomes bluer and the flame height and width decrease with the dilution concentration. Due to the incomplete combustion at downstream of the diluted jet flame, the classical prediction model using the dimensionless flame Froude number (Frf) overpredicts the flame height of nitrogen-diluted hydrogen jet flame. The model, ρeSLhμe=50(ueSL)g(ρeρ∞), can effectively predict the flame lift-off distance of diluted hydrogen jet flames, where SL is the corresponding laminar combustion speed in the lean mixture zone (Φ = 0.91). A unified prediction model of blowout limit based on the Damköhler number for diluted hydrogen and hydrocarbon jet flames was proposed for the first time. This study helps to better understand the instability mechanism of diluted hydrogen.

Comparative molecular dynamics study of liquid hydrogen annular jets in subcritical and supercritical environments

In this paper, the injection characteristics of a liquid hydrogen propellant jet under subcritical and supercritical operating conditions are comparatively studied at the molecular scale using molecular dynamics methods in the context of spacecraft propulsion systems. To control the temperature and pressure within the environment and nozzle respectively, two sub-computational domains are set up for separate modeling. The sub-computational domain merging process eliminates the broken molecular bonds by using the computational domain reduction in the x-direction. The jet velocity, density and other physical property distributions at different temperatures and pressures were comparatively studied. It is found that the rate of change of the radial density of the jet under supercritical conditions is small. Based on this, the surface area and volume of the liquid phase region of the jet were extracted and calculated. Compared to result of subcritical case, the volume of the liquid hydrogen jet in the supercritical environment is reduced by 1.9%, while the surface area is increase by 6.7%. To explain the variation in the surface area due to molecular diffusion, the molecular stress results revealed that the stress in the hydrogen jet in supercritical environment is only 88.9% of that in subcritical environment.