Flame Propagation Velocity Research Articles

Experimental investigation on explosion flame propagation of wood dust in a semi-closed tube

In order to explore flame propagation characteristics during wood dust explosions in a semi-closed tube, a high-speed camera, a thermal infrared imaging device and a pressure sensor were used in the study. Poplar dusts with different particle size distributions (0–50, 50–96 and 96–180 μm) were respectively placed in a Hartmann tube to mimic dust cloud explosions, and flame propagation behaviors such as flame propagation velocity, flame temperature and explosion pressure were detected and analyzed. According to the changes of flame shapes, flame propagations in wood dust explosions were divided into three stages including ignition, vertical propagation and free diffusion. Flame propagations for the two smaller particles were dominated by homogeneous combustion, while flame propagation for the largest particles was controlled by heterogeneous combustion, which had been confirmed by individual Damköhler number. All flame propagation velocities for different groups of wood particles in dust explosions were increased at first and then decreased with the augmentation of mass concentration. Flame temperatures and explosion pressures were almost similarly changed. Dust explosions in 50–96 μm wood particles were more intense than in the other two particles, of which the most severe explosion appeared at a mass concentration of 750 g/m3. Meanwhile, flame propagation velocity, flame propagation temperature and explosion pressure reached to the maximum values of 10.45 m/s, 1373 °C and 0.41 MPa. In addition, sensitive concentrations corresponding to the three groups of particles from small to large were 500, 750 and 1000 g/m3, separately, indicating that sensitive concentration in dust explosions of wood particles was elevated with the increase of particle size. Taken together, the finding demonstrated that particle size and mass concentration of wood dusts affected the occurrence and severity of dust explosions, which could provide guidance and reference for the identification, assessment and industrial safety management of wood dust explosions.

Impact of Wall Temperature in Large Eddy Simulation of Light-Round in an Annular Liquid Fueled Combustor and Assessment of Wall Models

Abstract The process of ignition in aero-engines raises many practical issues that need to be faced during the design process. Recent experiments and simulations have provided detailed insights into ignition in single-injector configurations and on the light-round sequence in annular combustors. It was shown that large eddy simulation (LES) was able to reliably reproduce the physical phenomena involved in the ignition of both perfectly premixed and liquid spray flames. This study aims at further extending the knowledge on flame propagation during the ignition of annular multiple injector combustors by focusing the attention on the effects of heat losses, which have not been accounted for in numerical calculations before. This problem is examined by developing LESs of the light-round process with a fixed temperature at the solid boundaries. Calculations are carried out for a laboratory-scale annular system. Results are compared in terms of flame shape and light-round duration with available experiments and with an adiabatic LES serving as a reference. Wall heat losses lead to a significant reduction in the flame propagation velocity as observed experimentally. However, the LES underestimates this effect and leads to a globally shorter light-round. To better understand this discrepancy, the study focuses then on the analysis of the near wall region. An a priori analysis underlines the shortcomings associated with the chosen wall law by considering a more advanced wall model that fully accounts for variable thermophysical properties and for the unsteadiness of the boundary layer.

Experimental study on the explosion-propagation law of coal dust with different moisture contents induced by methane explosion

This study aimed to explore the explosion-propagation law of coal dust with different moisture contents induced by methane explosion. An experimental system of explosion of mixed gas–coal and dust in a straight pipe was established in our laboratory. The evolution of overpressure and the flame-propagation law of deposited-coal-dust explosion with different moisture contents were then studied. Experimental results indicate that when the moisture content is less than 15.12%, the deposited coal dust in the pipeline explodes under the induction of gas explosion. Meanwhile, the total amount of deposited coal dust in the pipeline remains constant; the overpressure peak value and flame-propagation velocity after coal-dust explosion initially increase and then decrease with increased coal-dust moisture content. When the moisture content of the deposited coal dust is 9.57%, the overpressure and flame-propagation velocity of the depositional coal-dust explosion reach the maximum values of 0.766 MPa and 468.553 m/s, respectively. However, when the moisture content exceeds 20.28%, coal dust cannot induce an explosion, and the deposited coal dust can resist a gas explosion. Overall, this research provides theoretical references for methane-induced coal-dust-explosion resistance in coal mines.

An Experimental Investigation on the Ignition Sensitivity and Flame Propagation Behavior of Mixed Oil Shale–Coal Dust

ABSTRACT To evaluate the ignition sensitivity of mixed oil shale–coal dust, understand the flame propagation behavior of these mixtures during combustion and provide further reliable parameters for preventing explosion or combustion accidents associated with oil shale and coal dust, the ignition sensitivity of the mixed oil shale and two kinds of coal dust samples is examined for different mixing ratios,, using a dust layer minimum temperature test apparatus, a Godbert–Greenwold furnace, and a vertical glass tube; the flame propagation behavior of the mixed dust is observed in a vertical combustion tube and their flame propagation process is recorded with a high-speed video camera. The results show that the ignition sensitivity increases with increasing oil shale content for the mixed dust of oil shale and coal #1. . Under the same experimental conditions, both the flame front position and propagation velocity increase with oil shale content. However, for the mixed dust of oil shale and coal #2, the minimum ignition temperature of mixed dust, the minimum ignition energy of dust cloud did not change significantly with the change of oil shale, and the maximum flame front position did not differ greatly. The distribution of functional group in the mixed oil shale and two kinds of coal dust is tested using Fourier transform infrared spectroscopy (FT-IR). The result indicates that before combustion, the content of the -CH2- and -CH3 groups in the mixed dust of oil shale and coal#1 gradually increases with increasing oil shale content while the content of the -CH2- and -CH3 groups is relatively high in the mixed dust of oil shale and coal #2; aliphatic -CH3/-CH2 and oxygen-containing functional groups are key determinants for dust combustion intensity.

Suppression effects of ultrafine water mist on hydrogen/methane mixture explosion in an obstructed chamber

The mitigation effects of ultrafine water mist on hydrogen/methane mixture explosions with hydrogen fraction (ϕ) of the range from 0% to 60% were experimentally studied in a vented chamber with obstacles. The spraying time, droplets size of water mist and the volume ratio of hydrogen were varied in the tests, and the key parameters that reflect the explosion characteristics such as the flame propagation imagines, flame propagation velocity, and explosion overpressure were obtained. The results show that the ultrafine water mist presents a significant mitigation effect on hydrogen/methane mixture explosions. The flame propagation structures are similar under the condition of without and with ultrafine water mist while the flame temperature is declined by the physical and chemical inhibition by ultrafine water mist. In addition, the mitigation effect increases with the increase of water mist flux. As a result, the maximum flame speed and overpressure of ϕ = 30% hydrogen/methane mixture explosion are declined by 33.3% and 58.4% under the condition of spraying for 2 min with 15 μm ultrafine water mist, respectively. Besides, the mitigation effects of ultrafine water mist on ϕ = 30% hydrogen/methane mixture explosion descends evidently with the increase of the droplets size of the range from 6 μm to 25 μm, which due to the easier evaporation and the greater total droplets surface area of the smaller water mist. However, the explosion mitigation effect of ultrafine water mist on the hydrogen/methane mixture actually descends with the increase hydrogen fraction.

Aluminium/tin (IV) oxide thermite composite: sensitivities and reaction propagation

ABSTRACT Thermites are energetic composites made of metal and oxidizer particles that react according to an exothermic reaction and release large amounts of energy. Many possible metal and oxidizer couples exist in the literature. Here, the performance of the aluminum reducing metal and tin (IV) oxide (SnO2) combination was reported as a function of the fuel/oxidizer mass ratio. The Al/SnO2 energetic composite, in stoichiometric conditions, was insensitive to impact, sensitive to friction and extremely sensitive to electrostatic discharge. The combustion velocity was determined to be close to 600 m/s. Changing the stoichiometry affected both the sensitivity thresholds to the friction test (160 N to > 360 N) and flame propagation velocity (480–588 m/s) of the Al/SnO2 composite. These results are reported for the first time.

Investigation on the effect of bluff body ball on the combustion characteristics for methane/oxygen in micro combustor

A micro combustor inserted with a bluff body ball was developed and compared with the conventional combustor. The combustion characteristics (flammability limits, stable flame propagation and combustion efficiency) of methane/oxygen mixture in the micro combustor with bluff body ball were experimentally and numerically investigated. The results show that bluff body ball could broaden flammability limits of methane/oxygen mixture in the combustor. When inlet velocity was 0.7 m/s, the flammability limits in the combustor with 1 mm bluff body ball had equivalence ratios of 1.2 and 2.05 and that in the combustor with 2 mm bluff body ball had equivalence ratios of 1.5 and 2.68, which are larger than that in conventional combustors. The bluff body ball beneficially decreased the propagation velocity of the stable flame thereby making the gases burn completely. When the inlet velocity was 0.5 m/s, the combustion efficiency of the combustor inserted with a bluff body ball was 82.899% which was 2.7% higher than that of conventional combustor. However, the difference in combustion efficiency between the combustor with and without a bluff body ball decreases as the inlet velocity increases. When the velocity increased to 1.25 m/s, the difference was 0.75%.

Experimental study on induced accelerated combustion of premixed hydrogen-air in a confined environment

The study on induced accelerated combustion of premixed hydrogen-air in a confined environment is of great significance for the efficient utilization of hydrogen energy in internal combustion engines. The accelerated flame induced by the orifice plate is more stable and easy to control, which is beneficial to achieve controlled and rapid turbulent combustion. In this work, the accelerated combustion process induced by the orifice plate, and the influence of the orifice structure and initial conditions on the flame propagation and combustion characteristics were investigated by constant volume combustion bomb and schlieren method. The results show that the combustion process induced by the orifice plate consists of three stages: the initial stage of propagation, the accelerated stage of the orifice plate, and the end combustion stage. The reduction in aperture induces greater turbulence intensity and increases the perturbation of the orifice plate to the flame, resulting in a substantial increase in flame propagation speed through the orifice plate. As the initial pressure and the equivalence ratio increase, the velocity of turbulent flame induced by the orifice plate and the change rate of the velocity before and after the orifice plate increase. As the initial temperature increases, the turbulent flame propagation velocity does not change much, and the velocity change rate before and after the orifice plate decreases. The effect of the initial conditions on flame acceleration induced by the orifice plate is essentially the influence of flame propagation speed and instability. The greater the flame propagation speed and the stronger the flame instability, the stronger the induced turbulence and the greater the influence of the turbulent flow disturbance, and the greater the velocity of the turbulent flame induced by the orifice plate. There exists an optimum aperture for the shortest combustion duration at any initial conditions, but the optimal diameter is not sensitive to changes in initial conditions. The effect of orifice-induced combustion acceleration is remarkable, and the combustion durations induced by each orifice plate are shortened by more than 50%.

Explosion mitigation of methane‐air mixture in combined application of inert gas and ABC dry powders in a closed compartment

AbstractThe explosion is one of the most serious safety incidents occurring in the application of the gas methane in industrial process. The new developments in attenuating the destruction and environmental hazard of this explosion are conducted using the combined inert gas and ABC dry powder. The explosive characteristic parameters including flame configuration, velocity of flame propagation, explosion pressure, and pressure rising rate are quantified and revealed. The difference of explosion mitigation effect of ordinary and ultra‐fine ABC dry powders are examined based upon the specific surface area and the settling velocity. As the concentration of ordinary or ultra‐fine ABC dry powder increases, the explosion pressure initially increases and decreases afterwards, indicating that there is an optimal mass concentration of explosion mitigation for both powders. The effect of ignition delay time on the explosion mitigation of ultra‐fine ABC dry powder is characterized on the basis of the turbulent lever and the dry powder particle settling state. Moreover, the mechanisms of explosion mitigation with CO2 and the ultra‐fine ABC dry powder are fully revealed both on the physical and chemical properties. The present research provides basic data and theoretical guidance for prevention and controlling of gas explosion accidents.

Flame propagation and pressure characteristics of polymethyl methacrylate dust explosions in a horizontal pipe

To reveal the characteristics of flame propagation and pressure in organic dust explosions during pneumatic transportation, 30 μm polymethyl methacrylate (PMMA) dust explosions with different airflow velocities were experimentally conducted in a horizontal pipe. The results showed that dust flame transited from the luminous flame with a continuous structure to discrete flames as flame propagating. After the appearance of the discrete flames, flame propagation velocity increased sharply owing to the positive feedback coupling between combustion and expansion. With the increase of dust concentration, the average flame propagation velocity, maximum flame temperature, temperature rising rate, maximum pressure, and maximum rate of pressure rise increased and then decreased. These explosion characteristics (except for the maximum flame temperature) increased significantly with the increase of airflow velocity. When airflow velocity increased from 6.39 m/s to 13.3 m/s, the peaks of average flame propagation velocity increased from 23.9 m/s to 38.2 m/s; the peaks of maximum pressure and maximum rate of pressure rise were increased by 1.9 and 6.1 times respectively. In addition, it was found that the optimum dust concentration decreased as airflow velocity increased. Furthermore, the relationship among flame propagation, temperature, and pressure was discussed in detail.

Suppression characteristics of double-layer wire mesh on wheat dust flame

Dust explosion accidents frequently occur in dedusting pipes of wheat dust, causing huge casualties and property losses. In this paper, a vertical pipeline of combustion experimental platform was established to obtain the effects of working conditions and double-layer wire mesh parameters on wheat dust flame propagation. The results show that the double-layer wire mesh has an obvious suppression effect on the flame propagation of wheat dust. At the combination of the same mesh number, both the peak flame temperature and the maximum flame propagation velocity decreased with the increasing of the mesh number, and the flame quenching phenomenon occurs at 80 mesh. At the combination of different mesh numbers, the flame temperature at the upper-density and lower-sparseness combination is lower than that at the upper-sparseness and lower-density combination under all working conditions. The flame temperature difference (ΔT) gradually increases with the increasing of mesh number difference, and the maximum ΔT appears at the mesh difference of 40 mesh. As the separation distance increases, the flame temperature rises, and the suppression effect is best at the separation distance of 1cm. The peak combustion pressure is negatively linear with the separation distance.

Flame propagation characteristics and explosion behaviors of aluminum dust explosions in a horizontal pipeline

The effects of airflow velocities, particle sizes, and dust concentrations on the flame propagation characteristics and explosion behaviors of aluminum dust explosions in a horizontal pipeline were experimentally investigated. The results showed that the distributions of the airflow velocity and turbulence integral length both exhibited convex parabolic distributions. After ignition, the flame propagation velocities of 5μm and 30μm aluminum dust explosions both experienced acceleration processes. The positive feedback coupling among the combustion, expansion, and turbulence governed the acceleration mechanism. The flame propagation characteristics and explosion behaviors were significantly affected by the airflow velocity. As the airflow velocity increased from 6.4m/s to 13.3m/s, the maximum average flame propagation velocity increased from 60m/s to 140m/s. Moreover, the maximum explosion pressure increased from 36kPa to 83kPa, and the maximum explosion impulse increased from 78Pa.s to 576Pa.s.

Investigation of the measurement characteristics of a multiple-ion-probe method for a propagating methane–oxygen–nitrogen flame

The multiple-ion-probe measurement method is a method to measure a propagating flame using ion probes installed on the wall surface of a combustion chamber. The dynamic behavior of the propagating flame along the wall surface can be regenerated from the dataset of flame signals from individual ion probes. Although this method only captures flames near the wall surface, the flame propagation behavior can be indirectly visualized. Because this method can attain very high temporal resolution, it can provide precise measurements of high-speed phenomena such as knocking in spark-ignition engines and detonation in detonation combustors. This study aimed to investigate the ability of a developed 64-channel multiple-ion-probe measurement system to characterize a propagating flame. To this end, three flames with substantially different propagation velocities were measured using the proposed multiple-ion-probe measurement system. During the experiments, methane–oxygen stoichiometric mixtures diluted with different amounts of nitrogen were used. The flame propagation velocity varied within the range of several m/s for a turbulent flame to 2.4 km/s for detonation by varying the dilution ratio of nitrogen. In the case where a mixture with a nitrogen mole fraction of 0.71 was used, a phenomenon of repeating stagnation and reacceleration of the propagating flame was observed. Furthermore, the phenomenon considered to be flame quenching was also observed near the wall. In the case of no dilution (nitrogen mole fraction = 0.00), multiple-ion probes with an installation interval of 1.5 mm indicated that the velocity fluctuated within the range of −500 m/s to +2000 m/s with respect to the Chapman–Jouguet detonation velocity of 2390 m/s. Experiments involving soot foil recording conducted in parallel confirmed that this velocity fluctuation was derived from the detonation cell structure and that micro-explosions in the detonation front could be captured using the multiple-ion-probe method.

Combustion Mechanism of Alloying Elements Cr in Ti-Cr-V Alloys.

The combustion velocity and the mechanism for a series of Ti-Cr-V alloys with different chemical compositions are studied by a promoted ignition combustion test corresponding to different oxygen pressures to investigate the influence of alloying elements, such as Cr and V, on combustion behavior. The microstructures and composition distributions of the alloying elements in the reaction and oxide areas are observed and analyzed. The thermogravimetry analysis results show that the oxidation mass gain decreases with the increasing Cr content, and the oxidation resistance obviously increases from 10 Cr to 20 Cr. The combustion velocity decreases with increasing Cr content, and it is concluded that elevated Cr content can effectively retard the flame propagation velocity. Importantly, for the Ti-Cr-V alloys, the Cr and V elements accumulate in the melting zone and reduce the heat created by combustion.

Characterization of Naturally Aged Iron Nanopowder Produced by Electrical Explosion of Wires

Iron nanopowder obtained by electrical explosion of wires, passivated by air and stored for a long time (up to 18 years) under natural conditions are characterized. The characterization of iron nanopowder was made using X-ray diffraction analysis (XRD), scanning electron microscopy, X-ray fluorescent spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis and the test on flame propagation velocity in a bulk layer. XRD analysis revealed that the main crystalline phase in the studied powder is α-Fe. Iron oxide phases in the surface layer are amorphous. The crystalline iron oxide peak with low intensity was observed only in the powder after storage for 18 years. The iron nanopowder stored for a long time under natural conditions are found to be stable towards oxidation by air at ambient temperature. However, at the heating the iron nanopowder possesses high reactivity. Atmospheric air humidity is considered to be an important factor influencing the activity of iron nanopowder during heating and combustion.

Experimental and kinetic modeling investigation on the laminar flame propagation of ammonia under oxygen enrichment and elevated pressure conditions

Ammonia is attracting more and more attentions due to its role as both a carbon-free fuel for gas turbines and an effective H2 carrier. Only a limit number of investigations on the laminar flame propagation and laminar burning velocity of ammonia have been performed on elevated pressures, which were focused on ammonia/air mixtures and suffered strong buoyancy effect. In this work, laminar flame propagation of ammonia/O2/N2 mixtures covering wide ranges of equivalence ratios, oxygen contents and initial pressures was investigated in a high-pressure constant-volume cylindrical combustion vessel. The oxygen enrichment speeds up the spherically expanding flames and consequently reduces buoyancy effect on the laminar flame propagation of ammonia. The laminar burning velocity was observed to increase with the increasing oxygen content, but decrease with the increasing initial pressure. A kinetic model of ammonia combustion consisting 38 species and 265 reactions was constructed from previous models with updated rate constants of important reactions. The present model can reasonably reproduce the laminar burning velocity data in this work and literature, as well as the ignition delay time and speciation data in literature. Based on the model analysis, effects of oxygen enrichment, equivalence ratio and initial pressure on laminar burning velocities of ammonia were analyzed in detail. It is revealed that the enhanced flame propagation with oxygen enrichment is mainly due to the increase of adiabatic flame temperature which in turn leads to higher concentrations of key radicals like H, OH and NH2. For NH3 and its major decomposition products like NH2 and NH, reactions with oxygenated species such as OH, O, O2 and NO are generally more important in the lean flames, while the role of reactions with H, NH and NH2 becomes crucial in the rich flames. The calculated pressure dependent coefficient indicates that NH3/O2/N2 flames exhibit clear pressure dependence, while this pressure dependence is weaker than those of the hydrocarbon and biofuel flames.

Application of flame arrester in mitigation of explosion and flame deflagration of ventilation air methane

Fugitive methane emissions from underground coal mines are considered a potent greenhouse gas source with a large global warming potential. Application of ventilation air methane thermal oxidiser technology reduces this risk to a large extent. However, it imposes the risk of accidental fires and explosions in the mine site which may claim many lives and cause massive property damage. As such, the necessity of employing safety barriers such as flame arrester seems crucial to protect the mine against the accidental flames and explosion propagation originated from the thermal oxidiser.The aim of this work was to evaluate the effectiveness of an inline flame arrester for the mitigation of methane explosions in a large scale detonation tube. The results corresponding to this study indicated that the flame arrester was capable to effectively mitigate the explosion flames of 5%, 7.5% and 9.5% methane air mixtures (for a 10 m fuel filled section). The flame arrester reduced the pressure wave velocity by 88% and 40% for the explosions of methane-air mixtures of 7.5% and 9.5% methane, respectively. The flame propagation velocities for the 7.5% and 9.5% methane concentrations reduced approximately 32% and 44%, respectively. A significant pressure build-up was observed upstream of the flame arrester when compared with a duct without flame arrester. In addition, the build-up pressure was relatively higher for larger methane concentrations (e.g. 9.5%). These observations highlights that the maximum design pressure of an industrial process plant must be carefully considered when implementing an inline flame arrester due to the possibility of a sudden pressure increase cause by an explosion.

Экспериментальное исследование и численное моделирование распространения пламени по поверхности пластины ПММА

Introduction. Polymer materials are widely used, however the actual object is to provide polymers combustion ­model to predict their behavior under fire, and reducing flammability. The work is devoted to the experimental ­study and numerical simulation of flame propagation over the surface of horizontally and vertically placed slabs of polymer in still air. Methods. The object of the investigation was cast polymethylmethacrylate (PMMA). The experiment was focused on measurement of the spatial distributions of the temperature and species concentrations of the PMMA pyrolysis and combustion products in the gas-phase over the surface of PMMA. Temperature was measured by micro­thermocouple with diameter of 50 microns. Probe mass-spectrometry was used for the measurement of the spa­tial distribution of species concentrations in the flame. Results and discussion. The main species (mehylmethacrylate (MMA), O2, CO2, H2O, N2, C2H4 (ethylene), C3H6 (propylene)) were identified and their concentration profiles were measured on the different distance from the flame front. The chemical structure of the flame was established to be in good agreement with the thermal one. The size of the “dark zone” of the flame, in which the temperature near the surface of the polymer is minimal, correlated well with the size of the oxygen-free zone. The mass burning rate, the velocity of flame propagation, the width of the pyrolysis zone and the temperature distribution in the condensed phase were also measured. Based on the experimental results, densities of conductive and radiation heat fluxes from the flame to the fuel surface were deter­mined. Calcula­tion of the radiation heat flux density was carried out under the assumption of an optically thin ­model. Modeling of the horizontal flame propagation over the PMMA surface was carried out using a two-dimen­sional conjugated laminar combustion model that takes into account one-step reactions — the decomposition reaction of PMMA in the condensed phase and the oxidation of decomposition products in the gas phase. Modeling of the vertical flame propagation over the PMMA surface was carried out using economical model of FDS. Conclusion. The model was shown to describe satisfactorily the experimental data such as the mass burning rate, flame propagation velocity, as well as the temperature distribution and concentration of species near the flame front.

Влияние скорости распространения и ширины зоны турбулентного пламени на концентрацию несгоревших углеводородов и полноту сгорания топлива в двигателе с искровым зажиганием

The investigation considers how combustion efficiency and exhaust gas (unburnt hydrocarbon) toxicity are linked to the fundamental flame propagation characteristics (flame propagation velocity and reaction zone width). We present combustion efficiency and unburnt hydrocarbon concentration as functions of fundamental flame propagation characteristics, maximum flame temperature, flame failure temperature and thickness of the unburnt fuel layer adjacent to the combustion chamber walls. Comparing combustion efficiency computed according to the equation proposed to combustion efficiency derived by using an experimentally obtained indicator diagram showed that the data are in good agreement. We studied the connection between unburnt hydrocarbon emission and combustion efficiency. We detected that increasing combustion efficiency leads to lower unburnt hydrocarbon emission, which is explained by reduction of the unburnt fuel ratio in the layer adjacent to the wall. We propose a new technique for calculating unburnt hydrocarbon amount in engine exhaust gases. We show that our technique makes it possible to determine the chemical composition of the air-fuel mixture and the values of flame propagation characteristics that ensure a decrease in unburnt hydrocarbon emission. The results of our study may be used to develop or refine methods of increasing combustion efficiency of composite fuels and reducing exhaust gas toxicity in combustion chambers of internal combustion engines and other power plants.

Experimental study of shock wave propagation and its influence on the spontaneous ignition during high-pressure hydrogen release through a tube

An experimental study of shock wave propagation and its influence on the spontaneous ignition during high-pressure hydrogen release through a tube are measured by pressure transducers and light sensors. Results show that the pressure behind a shock wave first increases, and subsequently remains near constant value with an increase of the propagation distance. That is, a certain propagation distance is required to form a stable shock wave in the tube. In the front of the tube, the minimum value of pressure behind the shock wave (Pshock) required for spontaneous ignition decreases with the increase in axial distance to the diaphragm. However, the minimum Pshock remains nearly a constant value in the rear part of the tube. Moreover, the critical values of shock Mach number (MS) for spontaneous ignition decrease with the increase in tube length. And the ignition delay time decreases with the increase of the MS. As the ignition kernel grows in size to a flame, it propagates downstream along the tube with velocity greater than the theoretical flow velocity of the hydrogen-air contact surface. The flame propagation velocity relative to tube wall increases with MS. When the self-sustained flame exits from the tube, a rapid non-premixed turbulent combustion is observed in the chamber. The combustion-wave overpressure increases with the increase of the MS.