Search Results (35)

To mitigate explosion hazards arising from hydrogen leakage and subsequent mixing with air, the injection of inert gases can substantially diminish explosion risk. However, prevailing research has predominantly characterized inert gas dilution effects on explosion behavior under quiescent conditions, largely neglecting the turbulence-mediated explosion enhancement inherent to dynamic mixing scenarios. A comprehensive investigation was conducted on the combustion behavior of 30%, 50%, and 70% H₂-air mixtures subjected to jet-induced (CO₂, N₂, He) turbulent flow, incorporating quantitative characterization of both the evolving turbulent flow field and flame front dynamics. Research has demonstrated that both an increased H₂ concentration and a higher jet medium molecular weight increase the turbulence intensity: the former reduces the mixture molecular weight to accelerate diffusion, whereas the latter results in more pronounced disturbances from heavier molecules. In addition, when CO₂ serves as the jet medium, a critical flame radius threshold emerges where the flame propagation velocity decreases below this threshold because CO₂ dilution effects suppress combustion, whereas exceeding it leads to enhanced propagation as initial disturbances become the dominant factor. Furthermore, at reduced H₂ concentrations (30–50%), flow disturbances induce flame front wrinkling while preserving the spherical geometry; conversely, at 70% H₂, substantial flame deformation occurs because of the inverse correlation between the laminar burning velocity and flame instability governing this transition. Through systematic quantitative analysis, this study elucidates the evolutionary patterns of both turbulent fields and flame fronts, offering groundbreaking perspectives on H₂ combustion and explosion propagation in turbulent environments. Full article

Numerical simulations reveal the combustion dynamics of hydrogen-blended natural gas (H-BNG) in semi-open spaces. In the typical semi-open space scenario, increasing the hydrogen blending ratio from 0% to 60% elevates peak internal pressure by 107% (259.3 kPa → 526.0 kPa) while reducing pressure rise time by 56.5% (95.8 ms → 41.7 ms). A vent size paradox emerges: 0.5 m openings generate 574.6 kPa internal overpressure, whereas 2 m openings produce 36.7 kPa external overpressure. Flame propagation exhibits stabilized velocity decay (836 m/s → 154 m/s, 81.6% reduction) at hydrogen concentrations ≥30% within 2–8 m distances. In street-front restaurant scenarios, 80% H-BNG leaks reach alarm concentration (0.8 m height) within 120 s, with sensor response times ranging from 21.6 s (proximal) to 40.2 s (distal). Forced ventilation reduces hazard duration by 8.6% (151 s → 138 s), while door status shows negligible impact on deflagration consequences (412 kPa closed vs. 409 kPa open), maintaining consistent 20.5 m hazard radius at 20 kPa overpressure threshold. These findings provide crucial theoretical insights and practical guidance for the prevention and management of H-BNG leakage and explosion incidents. Full article

To study the emission intensity of OH during H₂/CH₄/air mixtures explosion, experiments were performed inside a 20 L spherical closed tank. The pressure history and flame propagation characteristics of H₂/CH₄/air mixtures explosion were recorded and analyzed. The effects of the volume fraction of hydrogen and equivalence ratio on explosion pressure, flame radius, and emission intensity of OH were surveyed. The results show that after α > 0.6, hydrogen started to take a leading role in the explosion pressure and flame propagation of H₂/CH₄/air mixtures. The effect on the high equivalence ratio of H₂/CH₄/air mixtures is more obvious, which makes the reaction of H₂/CH₄/air mixtures explosion faster and more dangerous. The emission intensity of OH at 308.9 nm is strongest, with 282.8 nm being the earliest and 347.2 nm being the latest. As the volume fraction of hydrogen increases, the I_max and (dI/dt)_max of OH continue to increase, and at a higher equivalence ratio, the I_max of OH begins to rise sharply from α = 0.6. As the equivalence ratio increases, I_max and (dI/dt)_max of OH increase first and then decrease. The important sources of OH emissions in the H₂/CH₄/air mixtures explosion are the reaction of R38 and the reverse reaction of R84. Full article

The spread of fires on the facades of high-rise buildings is highly influenced by atmospheric wind conditions, particularly in strong wind environments. A strong wind environment refers to the situation where the wind speed reaches level 6 or above, or the wind speed is between 10.8 m/s and 13.8 m/s. We conducted an in-depth study of the characteristics of flame spread on the facades of high-rise buildings under strong wind conditions. A nested coupling method based on WRF (Weather Research and Forecasting) and CFD (computational fluid dynamics) software (Ansys Fluent 2021) was used. The mesoscale meteorological simulation software WRF was utilized to obtain regional airflow variation data within a radius of 2 km around the high-rise building. Subsequently, these data were coupled with the CFD software (Ansys Fluent 2021) to simulate and obtain realistic wind field data within a 400 m range around the building. Finally, these realistic wind field data were used for FDS (Fire Dynamics Simulator) fire simulations and model experiments to accurately replicate building fire scenarios under strong wind conditions. The results indicate that using grid nesting for boundary condition division would help to improve the accuracy of fire spread characteristics on the facades of high-rise buildings under strong wind conditions. For a high-rise building, both headwinds and tailwinds promote vertical and horizontal flame spread, with a more significant impact on vertical flame spread speed. Side winds enhance horizontal flame spread but inhibit vertical flame spread. These findings provide a reference for the effective design of fire protection systems for the facades of high-rise buildings. Full article

One of the most widely used processes in ship hull plate manufacturing is the flame forming process (FFP). In this work, the fabrication of saddle-shaped specimens with FFP using a spiral irradiating pattern is studied experimentally. The deformation of the deformed plates by FFP based on the spiral irradiating pattern is affected by process parameters such as the pitch of spiral passes (PSP), the radius of the starting circle (RSC), and the number of irradiation passes (NIP). However, in this work, the effects of process parameters on the deformation of SSS are statistically examined by the design of experiment (DOE) method based on response surface methodology (RSM). The experimental and statistical results show that the deformation of flame-formed SSS increases with the increase in RSC and NIP and the decrease in PSP. In addition, the results of the optimization procedure demonstrate that the maximum value of deformations of flame-formed saddle-shaped specimens is achieved by adjusting the process parameters as follows: PSP = 10 mm, RSC = 75 mm, and five NIPs. Full article

The automotive industry is under increasing pressure to develop cleaner and more efficient technologies in response to stringent emission regulations. Hydrogen-powered internal combustion engines represent a promising alternative, offering the potential to reduce carbon-based emissions while improving efficiency. However, the accurate estimation of in-cylinder pressure is crucial for optimizing the performance and emissions of these engines. While traditional simulation tools such as GT-POWER are widely utilized for these purposes, recent advancements in artificial intelligence provide new opportunities for achieving faster and more accurate predictions. This study presents a comparative evaluation of the predictive capabilities of GT-POWER and an artificial neural network model in estimating in-cylinder pressure, with a particular focus on improvements in computational efficiency. Additionally, the artificial neural network is employed to predict the equivalent flame radius, thereby obviating the need for repeated tests using dedicated high-speed cameras in optical access research engines, due to the resource-intensive nature of data acquisition and post-processing. Experiments were conducted on a single-cylinder research engine operating at low-speed and low-load conditions, across three distinct relative air–fuel ratio values with a range of ignition timing settings applied for each air excess coefficient. The findings demonstrate that the artificial neural network model surpasses GT-POWER in predicting in-cylinder pressure with higher accuracy, achieving an RMSE consistently below 0.44% across various conditions. In comparison, GT-POWER exhibits an RMSE ranging from 0.92% to 1.57%. Additionally, the neural network effectively estimates the equivalent flame radius, maintaining an RMSE of less than 3%, ranging from 2.21% to 2.90%. This underscores the potential of artificial neural network-based approaches to not only significantly reduce computational time but also enhance predictive precision. Furthermore, this methodology could subsequently be applied to conventional road engines exhibiting characteristics and performance similar to those of a specific optical engine used as the basis for the machine learning analysis, offering a practical advantage in real-time diagnostics. Full article

Minimum ignition energy (MIE) has been extensively studied via experiments and simulations. However, our literature review reveals little quantitative consistency, with results varying from 0.324 to 1.349 mJ for ϕ = 1.0 and from 0.22 to 0.944 mJ for ϕ = 0.9. Therefore, there is a need to resolve these discrepancies. This RANS study aims to partially address this knowledge gap. Additionally, it presents other flame evolution parameters essential for robust combustion design. Using the reactingFOAM solver, we predict the threshold energy required to ignite the fuel mixture. For this, the single step using the Arrhenius law is selected to model ignition in the flame kernel of stochiometric and lean CH₄/air mixtures, allowing it to develop into a self-sustained flame. The ignition power density, an energy quantity normalised with volume, is incrementally varied, keeping the kernel critical radius r_s constant at 0.5 mm in the quiescent mixture of two equivalence ratios ϕ 0.9 and 1.0, for varied operating pressures of 1, 5, and 10 bar at the constant initial temperature of 300 K. The minimum ignition energy is validated with twelve independent 1-bar datasets both numerically and experimentally. The effect of pressure on MIEs, which diminish as pressure rises, is significant. At ϕ = 1.0 (and 0.9), the flame temperature reached 481.24 K (457.803 K) at 1 bar, 443.176 K (427.356 K) at 5 bar, and 385.56 K (382.688 K) at 10 bar. The minimum ignition energy was validated using twelve independent 1-bar datasets from both numerical simulations and experiments. The results show strong agreement with many experimental findings. Finally, a mathematical formulation of MIE is devised; a function of pressure and equivalence ratio shows a slightly curved relationship. Full article

The accurate determination of the potential impact radius is crucial for the design and risk assessment of hydrogen pipelines. The existing methodologies employ a single point source model to estimate radiation and the potential impact radius. However, these approaches overlook the jet fire shape resulting from high-pressure leaks, leading to discrepancies between the calculated values and real-world incidents. This study proposes models that account for both the mass release rate, while considering the pressure drop during hydrogen pipeline leakage, and the radiation, while incorporating the flame shape. The analysis encompasses 60 cases that are representative of hydrogen pipeline scenarios. A simplified model for the potential impact radius is subsequently correlated, and its validity is confirmed through comparison with actual cases. The proposed model for the potential impact radius of hydrogen pipelines serves as a valuable reference for the enhancement of the precision of hydrogen pipeline design and risk assessment. Full article

The understanding of the boundary layer flame flashback (BLF) has considerably improved in recent decades, driven by the increasing focus on clean energy and the need to address the operational issues associated with flashback. This study investigates the influence of the Lewis number (Le) on symmetric flame shapes under the critical conditions for a laminar boundary layer flashback in cylindrical tubes. It has been found that the transformation of the flame shape from a mushroom to a tulip happens in a tube of a given radius, as the thermal expansion coefficient and Le are modified. A smaller Lewis number results in a local increase in the burning rate at the flame tip, with the flame being able to propagate closer to the wall, which significantly increases the flashback propensity, in line with previous findings. In cases with a Lewis number smaller than unity, a higher thermal expansion results in a flame propagation happening closer to the wall, thus facing a weaker oncoming flow and, consequently, becoming more prone to flashback. For Le > 1, the effect of the increase in the thermal expansion coefficient on the flashback tendency is much less pronounced. Full article

A new co-rotating electrochemical machining method is presented to machine the complex structure inside annular parts such as flame tubes and aero-engine casings. Due to the unique shape and motion of electrodes, it is difficult to accurately compute the electric field intensity in the machining area. In this paper, the complex electric field model is simplified by conformal transformation, and the analytical solution of electric field intensity is exactly calculated. A material removal model is built on the basis of the electric field model, and the dynamic simulation of the material removal process is realized. The effects of the cathode radius, applied voltage, feed rate and initial interelectrode gap on the interelectrode gap (IEG) and material removal rate (MRR) are analyzed. The simulation results indicate that the MRR is always slightly less than the feed rate in a quasi-equilibrium state, resulting in a slow reduction in IEG. In addition, the final machining state is not affected by the initial IEG, and the MRR in a quasi-equilibrium state is determined by the feed rate. Several comparative experiments were carried out using the optimized processing parameters, in which the MRR and IEG were measured. The convex structures were successfully machined inside the annular workpiece with optimum machining parameters. The experimental results are in good agreement with the theoretical results, indicating that the established model can effectively predict the evolution process of MRR and IEG. Full article

Gasoline–air mixture explosions mostly occur in buried tank rooms, which are annular cylindrical confined spaces with circular arches. In this paper, explosion experiments at different gasoline–air mixture volume fractions are carried out in an annular cylindrical steel bench with a circular arch curvature radius of 900 mm and an annular half-perimeter to radial width ratio of 12π. The results show that the development process of explosion overpressure is clearly divided into four stages after first-order differentiation treatment. Compared with other types of confined spaces, 1.70% is still the most dangerous gasoline–air mixture volume fraction. However, this type of confined space has a larger inner surface area in the same volume condition, which will inevitably increase the heat absorption rate, reduce the chemical reaction rate, and slow down the flame propagation speed. Meanwhile, this spatial structure will inevitably make the explosion flames collide, which will promote positive feedback coupling between explosion flames and pressure waves, making the explosion more violent and dangerous. These results can provide theoretical and technical support for the explosion prevention design of buried tank rooms. Full article

The joint American–Russian Space Experiment Flame Design (Adamant) was implemented on the International Space Station (ISS) in the period from 2019 to 2022. The objectives of the experiment were to study the radiative extinction of spherical diffusion flames (SDF) around a porous burner (PB) under microgravity conditions, as well as the mechanisms of control of soot formation in the SDF. The objects of the study were the normal and inverse SDFs of gaseous ethylene in an oxygen atmosphere with nitrogen dilution at room temperature and pressures ranging from 0.5 to 2 atm. The paper presents the results of transient 1D and 2D calculations of 24 normal and 13 inverse SDFs with and without radiative extinction. The 1D calculations revealed some generalities in the evolution of SDFs with different values of the stoichiometric mixture fraction. The unambiguous dependences of the ratio of flame radius to fluid mass flow rate through the PB on the stoichiometric mixture fraction were shown to exist for normal and inverse SDFs. These dependences allowed important conclusions to be made on the comparative flame growth rates, flame lifetime, and flame radius at extinction for normal and inverse SDFs. The 2D calculations were performed for a better understanding of the various observed non-1D effects like flame asymmetry with respect to the center of the PB, flame quenching near the gas supply tube, asymmetrical flame luminosity, etc. The local mass flow rate of fluid through the PB was shown to be nonuniform with the maximum flow rate attained in the PB hemisphere with the attached fluid supply tube, which could be a reason for the flame asymmetry observed in the space experiment. The evolution of 2D ethylene SDFs at zero gravity was shown to be oscillatory with slow alterations in flame shape and temperature caused by the incepience of torroidal vortices in the surrounding gas. Introduction of the directional microgravity, on the level of 0.01$g$, led to the complete suppression of flame oscillations. Full article

The predictions of turbulent burning velocity parameterizations for non-unity Lewis number flames have been assessed based on a single-step chemistry Direct Numerical Simulation (DNS) database of premixed Bunsen flames for different values of characteristic Lewis numbers ranging from 0.34 to 1.2. It has been found that the definition of the turbulent burning velocity is strongly dependent on the choice of projected flame brush area in the Bunsen burner configuration. The highest values of normalized turbulent burning velocity are obtained when the projected flame brush area is evaluated using the area of the isosurface of the Reynolds averaged reaction progress variable of 0.1 out of different options, namely the Favre averaged and Reynolds averaged isosurfaces of reaction progress variable of 0.5 and integral of the gradient of Favre and Reynolds averaged reaction progress variable. Because of the axisymmetric nature of the mean flame brush, the normalized turbulent burning velocity has been found to decrease as the burned gas side is approached, due to an increase in flame brush area with increasing radius. Most models for turbulent burning velocity provide comparable, reasonably accurate predictions for the unity Lewis number case when the projected flame brush area is evaluated using the isosurface of the Reynolds averaged reaction progress variable of 0.1. However, most of these parameterizations underpredict turbulent burning velocity values for Lewis numbers smaller than unity. A scaling relation has been utilized to extend these parameterizations for non-unity Lewis numbers. These revised parameterizations have been shown to be more successful than the original model expressions. These modified expressions also exhibit small values of L₂-norm of the relative error with respect to experimental data from literature for different Lewis numbers, higher turbulence intensity and thermodynamic pressure levels. Full article

Nowadays, an accurate and precise description of the combustion phase is essential in spark-ignition (SI) engines to drastically reduce pollutant and greenhouse gas (GHG) emissions and increase thermal efficiency. To this end, computational fluid dynamics (CFD) can be used to study the different phenomena involved, such as the ignition of the charge, combustion development, and pollutant formation. In this work, a validation of a CFD methodology based on the flame area model (FAM) was carried out to model the combustion process in light-duty SI engines fueled with natural gas. A simplified spherical kernel approach was used to model the ignition phase, whereas turbulent flame propagation was described through two variables. A zero-dimensional evolution of the flame kernel radius was used in combination with the Herweg and Maly formulation to take the laminar-to-turbulent flame transition into account. To estimate the chemical composition of burnt gas, two different approaches were considered—one was based on tabulated kinetics, and the other was based on chemical equilibrium. Assessment of the combustion model was first performed by using different operating points of a light-duty SI engine fueled with natural gas and by using the original piston. The results were validated by using experimental data on the in-cylinder pressure, apparent heat release rate, and pollutant emissions. Afterward, two other different piston bowl geometries were investigated to study the main differences between one solution and the others. The results showed that no important improvements in terms of combustion efficiency were obtained by using the new piston bowl shapes, which was mainly due to the very low ($+4\%$) or null increase in turbulent kinetic energy during the compression stroke and due to the higher heat losses ($+20\%$) associated with the increased surface area of the new piston geometries. Full article

Explosion isolation flap valves are one of the most used explosion protection systems in process industries; research is essential to improve them and to minimise both human and material losses when dust explosions take place. In this regard, there is little knowledge on the effect of bends in the functionality of these protective systems; hence, the main aim of this work is to bridge this gap. Large-scale dust explosions were performed, using three different types of dust: metal dust and two types of organic dust. In order to analyse the effect of bends in the functionality of these protective systems, results using a straight duct and one with bends were compared for each dust tested. In addition, the influence of the bend radius on aluminium dust explosions was also evaluated. The results indicated that the effect of bends depended on the explosive characteristics of the dust. However, for aluminium and maize starch dusts, bends led to higher pressures and flame velocities. Relevant information is provided to help decision-making when designing these valves. Moreover, such data can be used for consideration in the discussions held by the task force entrusted with developing the standard used to assess their functionality. Full article