Ignition Of Hydrogen Research Articles

Detailed simulation of laser-induced ignition, spherical-flame acceleration, and the origins of hydrodynamic instability

Ignition of a lean hydrogen–oxygen premixture by focused-laser-induced breakdown and subsequent three-dimensional expanding-flame instabilities are simulated in high detail. Both diffusive–thermal and hydrodynamic (Darrieus–Landau) instabilities are active and accelerate the flame expansion. The fluid is a partially-ionized gas in local thermodynamic equilibrium with detailed kinetics and transport models, starting from initial conditions from an auxiliary simulation based on a two-temperature local thermodynamic non-equilibrium model. After the decay of the initial laser-induced plasma, the r ∼ t1.5 growth in time of the flame radius matches theory and experimental observations. Based on hydrodynamic theory for spherical-flame propagation, a global Karlovitz number is defined as the ratio of the hydrodynamic to flame-distortion time scales. It initially increases during the diffusive–thermal instability stage, then with the onset of significant baroclinic torque, this trend reverses, with vorticity production becoming the dominant mechanism of instability.

Numerical study on the mechanism of spontaneous ignition of high-pressure hydrogen in the L-shaped tube

There have been reports of ignition of high-pressure hydrogen during its sudden release for unexplained reasons and ignition mechanism still need to be further investigated. In this paper, mechanism of spontaneous ignition of high-pressure hydrogen during its sudden release into the L-shaped tube is investigated. LES, EDC model, 10-step like opening process of burst disk and 18-step detailed hydrogen combustion mechanism are employed. Three cases with burst pressures of 2.16, 6.21, and 9.10 MPa are simulated. It is found that shock wave is strongly reflected after it hits the tube corner wall, forming a reflected-shock-affected region and an energy conversion region with higher temperature, greater pressure and lower velocity. Afterwards, the reflected shock wave moving forward is reflected several times by the tube wall until it disappears and oblique shock is generated. After the hydrogen/air mixture enters the corner, it extends downstream along inner wall and separated from the main hydrogen/air mixture. The reflected shock wave moving backward interacts with the expansion waves and increases the temperature and pressure again, but spontaneous ignition cannot be initiated. Three mechanisms of spontaneous ignition of high-pressure hydrogen in the L-shaped tube are proposed eventually. The results reproduce the experimental spontaneous ignition conditions and positions, indicating that the numerical models can be applied as a tool for hydrogen safety engineering.

Effects of ignition location, obstacles, and vent location on the vented hydrogen-air deflagrations with low vent burst pressure in a 20-foot container

A series of experiments on vented lean hydrogen-air deflagrations with low vent burst pressure was performed in a 20-foot container. The effects of hydrogen concentration, ignition position, vent location, and obstacles were studied, and all tests were performed at about 290 K and 101 kPa. For the cases with end vent, three overpressure peaks of P1, P2, and P3 were recorded, resulting from the vent rupture, flame propagation to the vent, and the Helmholtz oscillation, respectively. Moreover, at the middle and later stages of the vented explosion, the acoustic oscillations with high-frequency were observed due to the thermo-acoustic-vibration coupling caused by the instability of lean hydrogen combustion. The peak overpressure for the case with the obstacle is lower than that without the obstacle. Vent rupture occurs quickly for front ignition and low hydrogen concentrations. For the tests with high hydrogen concentration such as 24 vol% and 28 vol%, since the polyethylene film can reach its static activation pressure and rupture, the peak overpressure is much larger. For the cases with the ceiling vents, only one overpressure peak P1, corresponding to the rupture of the vent cover, was recorded and its value increases with the hydrogen concentration. The obstacle causes the propagation direction of the flame to change, and resultantly the flame spreads upward and burns the polyethylene film, which decreases the internal overpressure rise time. This phenomenon is particularly evident for the tests with high hydrogen concentrations. Except for 16 vol%, the obstacle reduces the peak overpressure.

Features of hydrogen and deuterium ignition over noble metals at low pressures

Hydrogen and deuterium combustion over Rh, Ru, Pd and Pt wires at total pressures up to 200 Torr and initial temperatures up to 500 °C is investigated in order to establish the temperature dependencies of autoignition limits over noble metal surfaces and to indicate the governing factors of gas ignition by a catalytic surface. It was found that Rh, Ru and Pd surfaces treated with 2H2 + O2 ignitions manifest the defects in the form of openings, which are located on surface defects. It was shown that before ignition, the catalytic wire is not heated up uniformly; and initial centers of the ignition occur.It was shown that Rh is the most effective catalyst of 2H2 + O2 ignition, the lowest ignition temperature over Rh coated Pd wire (Rh/Pd) was 210 °C, for Ru/Pd and Pd −300 °C, for Pt wire −410 °C at total pressures less than 200 Torr. A hysteresis phenomenon was observed over Ru/Pd, Pt and Pd wires; namely the ignition limit value measured over the wire when increasing temperature from a state of no ignition, is higher than the value measured when decreasing temperature from a state of autoignition. It was shown that Rh is the most effective catalyst of 2D2 + O2 ignition, in this case the lowest ignition temperature over Rh coated Pd wire (Rh/Pd) was 100 °C. It is more accurate to speak about ignition over noble metals hydrides/deuterides; thus, the lowest ignition limit of 2D2 + O2 over rhodium deuteride was 100 °C; thus, D2 is more flammable than H2 over Rh and Pd. The results obtained indicate the existence of a kinetic inverse isotope effect, which affects the reactivity of MeH and MeD, where Me =Rh, Pd.

Numerical study on the mechanism of spontaneous ignition of high-pressure hydrogen during its sudden release into a tube

Hydrogen is regarded as the promising energy carrier in the 21st century and high-pressure storage is selected as the best option. However, spontaneous ignition would be induced if high-pressure hydrogen is suddenly released. Three cases were numerically conducted to gain an insight into the mechanism of the spontaneous ignition and to validate against our previous experimental results. Result show that a hemispherical shock wave is first produced. Then it is reflected as reflected shock wave after hitting the tube wall and interacts with other reflected shock waves to form the Mach disk, shock triple point and a barrel shock. The height of the Mach disk gradually decreases and finally it disappears. Meanwhile, the shape of hydrogen jet changes from a forward convex shape to a backward concave shape and hydrogen/air mixture layer is formed near the tube wall and the center of the tube. The temperature of the shock-affected region gradually increases and its area thickens. After maintenance of high temperature for a period of time, spontaneous ignition firstly occurs at the tube boundary. Present numerical results not only reproduce the ignition conditions but also the ignition positions indicating that the model is an effective tool for hydrogen safety engineering.

Ignition of Hydrogen–Hydrocarbon (C1–C6)–Air Mixtures over the Palladium Surface at 1–2 Atm

In this paper, we report the results of studying the combustion characteristics of fuels containing a hydrogen–hydrocarbon (C1–C6, as in CH4, C2H6, C3H8, C4H10, C5H12, and C6H14) mixture with a fuel fraction of 0.6–1.2 in a mixture with air above the palladium surface at a total pressure of 1–2 atm. The propagation features of the flame front in mixed fuels are revealed, and the temperature dependences of the ignition limit over the palladium surface are determined. The observed separation of the CH and Na emission bands in time during the combustion of the 30% propane + 70% H2 + air mixture (the fuel fraction in the mixture with air is unity) was established to be caused by the occurrence of hydrodynamic instability of the flame when it touches the end of a cylindrical reactor.

Study of shock train/flame interaction and skin-friction reduction by hydrogen combustion in compressible boundary layer

A numerical study is carried out to investigate the shock train/flame interaction and skin friction with boundary layer combustion in compressible boundary layer. The Transition k−kl−w model is employed as the turbulence model and the finite-rate model is selected as the combustion model. The results showed that the skin friction could be reduced by 50% through boundary layer combustion while the pure-mixing case can only bring about a 10% drag reduction. The ignition of hydrogen in the boundary layer leads to a rapid reduction in skin friction. When a shock wave intersects with the flame surface, in addition to the reflection, it is also refracted, which will cause the change of both skin friction and heat transfer to the wall. Studies on the effects of air/fuel temperature ratio reveal that both the skin friction and heat transfer increase with air/fuel temperature ratio. When the concentration of H2O increases in airflow, the skin friction is enhanced as the mixing and combustion between oxygen and hydrogen is suppressed with H2O addition. The results of changing the air/fuel pressure ratios show that at high airflow pressure, the distance between the flame and the wall is reduced, leading to increase of heat transfer to the wall.

Experimental study of end-vented hydrogen deflagrations in a 40-foot container

Experiments were conducted in an enclosure with the same overall dimensions as a 40-foot ISO container to study the vented hydrogen-air deflagrations. This work focuses on the effects of hydrogen concentration, ignition location and obstacles on the overpressure and the structural response of the container wall. For center ignition, three overpressure peaks, which resulted from the vent opening, Helmholtz oscillation and acoustic oscillation, respectively, were recorded inside the container without obstacles. However, with the increase of hydrogen concentration, the third overpressure peak disappears when the obstacles are added in the container. Unlike center ignition, only two overpressure peaks were observed for back ignition. Due to the difference in reactivity of hydrogen-air mixture, the first overpressure peak is generated by the vent burst for low hydrogen concentration, or the venting of flame for high hydrogen concentration. The overpressure induced by the flame-acoustic interaction was not monitored with the increase of the hydrogen concentration and the installation of obstacles for back ignition. The overpressure for back ignition is more influenced by the obstacles than that for center ignition, when hydrogen concentration is larger than 12%. The displacement-time curves share similar trends with the pressure-time curves. The first peak displacement changes linearly with the corresponding first peak overpressure. However, the displacement caused by the second overpressure peak is significantly increased, especially for high hydrogen concentration and back ignition in the case with two obstacles.

Experimental study on shock wave propagation and spontaneous ignition induced by high-pressure hydrogen suddenly released into T-shaped tubes

To investigate the influence of bifurcation structure in tubes on the spontaneous ignition of high-pressure hydrogen, a series of experiments were conducted. The tubes including T-shaped and straight tubes with the length of 0.7/1.2/1.7 m were tested. The burst pressure ranged from 4–10 MPa. The pressure and light signals in the tube and the external flame images were recorded. The results show that the T-shaped structure has a significant influence on the occurrence of spontaneous ignition. The critical release pressure required for self-ignition in short T-shaped tube was lower than that in straight tube, because the strong reflect shock wave near the bifurcation point heated the combustible mixtures near the contact surface. However, with the extension of the tube length, the critical pressure increased, because the distance between the leading shock and contact surface increased when the leading shock reached the bifurcation point. Consequently, the reflect shock cannot heat the combustible mixture near the contact surface, but the air instead. Besides, comparing with the straight tube, the formation of jet fire was inhibited in the T-shaped long tube (1.2/1.7 m) and the shock wave attenuated rapidly after pass through the bifurcation point.

Spontaneous ignition of high-pressure hydrogen and boundary layer characteristics in tubes

Hydrogen is efficient and environmentally friendly, but the danger of self-ignition resulted from the leakage of high-pressure hydrogen cannot be ignored. In this work, the self-ignition of high-pressure hydrogen released through different conditions was studied. 700-mm-length tubes with different diameters were adopted in our experiments. It summarized the characteristics of shock waves' attenuation and evolution process of hydrogen jets in tubes. In addition, effects of the boundary layer on the leading shock waves, the contact surface, and expansion waves were discussed. Results indicate that minimum pressure when self-ignition occurs for 15-mm-diameter tube is similar to 10-mm-diameter. And they have closely velocity of shock waves. Simulations show that the greater the release pressure, the more ignition products of hydrogen. Higher release pressure and smaller diameter can create a thicker boundary layer in micro shock tubes, and the boundary layer can lead to a change in the velocity of shock waves’ structures.

Ignition of hydrogen–oxygen and stoichiometric hydrogen–methane–oxygen mixtures on hot wires at low pressures

It was found that the ignition temperatures of H2–O2 and H2–CH4–O2 mixtures at a low pressure on heated Pd, Pt, Nichrome and Kanthal wires at 40 Torr increase with a decrease in H2 concentration; only a heated Pd wire shows the pronounced catalytic action. Numerical calculations allowed us to reveal the role of an additional branching step, viz. H + HO2 → 2OH.

Theoretical justification of utilization of forest waste by incineration in a composition of bio-water-coal suspensions. Ignition stage

The results of the theoretical studies of the ignition processes of a completely new class of fuel for thermal power plants—Bio-water-coal fuel (Bio-WCF) based on coals of varying degrees of metamorphism, water and forest waste (forest combustible fuel – FCM) have been presented.A mathematical model of the processes of heat and mass transfer that occur during the induction period of time has been developed. The model differs from the known ones in a detailed description of the kinetics of the physicochemical processes occurring in the boundary layer and in the particle. The numerical simulation of the ignition process has been carried out and the ignition delay times (tign) have been calculated. According to the results of the theoretical studies, the influence of the kinetics of gas-phase reactions proceeding in the induction period of time has been established. It has been shown that OH radicals can be active centers-catalysts of the chemical reactions of ignition and combustion of hydrogen (H2), methane (CH4) and carbon monoxide (CO).The basic laws of the physicochemical processes occurring on the surface of a particle (after evaporation of moisture) of Bio-water-coal fuel have been established. It has been shown that secondary reactions of incomplete oxidation of carbon by atmospheric oxygen (with the formation of CO), water vapor (with the formation of CO (or CO2) and H2), hydrogen (with the formation of CH4) do not significantly affect the particles ignition characteristics and conditions (maximum deviations of the values ignition delay times do not exceed 6%).

Experimental study on cryo-compressed hydrogen ignition and flame

This paper presents a hydrogen ignition experiment conducted to establish safety standards for high-pressure hydrogen handled at the hydrogen stations for fuel cell vehicles (FCV). In the experiment, cryogenic hydrogen pressurized to over 80 MPa was leaked from a pinhole nozzle, and the blast pressure at the ignition and the flame length during steady combustion were measured. The hydrogen supply equipment used in the experiment has a maximum flow rate of 100 kg/h, a maximum discharge pressure of 90 MPa, and a temperature adjustment range of 50 K–300 K. Four types of pinhole nozzles with different outlet diameters, viz. 0.2 mm, 0.4 mm, 0.7 mm, and 1.0 mm were used to leak the hydrogen. In the experiment, the effects of the pinhole nozzle diameter, hydrogen supply pressure and temperature, and an igniter location on the blast pressure and flame length were evaluated. The igniter being appropriately positioned, once a steady flame was formed, combustion continued even if the ignition source was turned off, which necessitated the stopping of hydrogen supply to extinguish the fire. As a result of the experiment, it was found that the blast pressure and the flame length can be expressed as the correlation equations of the hydrogen leakage flow rate. However, even if the leakage flow rate was the same, we found that the flame length increases with decreasing the hydrogen supply temperature. We presented a correlation equation for the cryo-compressed hydrogen flame length that is about 30% longer than the previously presented equations for 300 K hydrogen flame.

Controlling the Combustion, Exploding, and Detonation of Gases by Means of Chemical Kinetics

Ways are considered of preventing fires and explosions of methane–air mixtures in coal mines and elsewhere, the ignition and explosion of hydrogen–air mixtures, and the transition of combustion to detonation in the current model of a ramjet. The results from interdepartmental tests are presented along with experimental data illustrating the destruction of a stationary detonation wave by small impurities of lower hydrocarbons.

Low-Temperature Formation of a WO<sub>3</sub> Thin Film by the Sol-Gel Method Using Photo-Irradiation and Fabrication of a Flexible Hydrogen Sensor

Hydrogen has been recently attracted much attention with respect to high energy-conversion efficiency and low environmental burden. However, hydrogen gas is dangerous due to an explosive gas and a fast combustion rate. Therefore, the development of hydrogen sensor with high accuracy and reliability that can detect hydrogen easily is required. Especially, a flexible hydrogen sensor is useful because it has a high degree of freedom with respect to the shape of location in which the sensor is to be located. A flexible hydrogen sensor—namely, a WO3 thin film formed on a PET film by the sol-gel method using photo irradiation—based on gasochromism of WO3 was developed. By irradiating a thin film, which was prepared by using WO3 precursor solution synthesized by the sol-gel method, with ultraviolet rays, a high-purity WO3 film could be prepared on PET at low temperature. The sensor was structured as a polystyrene (PS) film containing palladium (Pd) laminated on a WO3 film. The WO3 layer was porous, so the PS containing Pd atoms solution penetrated the WO3 layer. WO3 reacted with hydrogen gas and instantly turned blue as the transmittance of the WO3 layer changed. The sensor showed high reactivity even for hydrogen concentration below 4% (1%, 0.5%, 0.25%, and 0.1%), which was the lower limit of hydrogen ignition, and a linear relationship between hydrogen concentration and change in transmittance was found. Moreover, the resistance of the WO3 film significantly and instantaneously changed due to hydrogen-gas exposure, and the hydrogen concentration and resistance change showed a linear relationship. It is therefore possible to quantitatively detect low concentrations of hydrogen by using changes in transmittance and resistance as indices. Since these changes occur selectively under hydrogen at room temperature and normal pressure, they form the basis of a highly sensitive hydrogen sensor. Since the developed sensor is flexible, it has a high degree of freedom with respect to the shape of location in which the sensor is to be installed

Low-Temperature Formation of a WO<sub>3</sub> Thin Film by the Sol-Gel Method Using Photo-Irradiation and Fabrication of a Flexible Hydrogen Sensor

Hydrogen has been recently attracted much attention with respect to high energy-conversion efficiency and low environmental burden. However, hydrogen gas is dangerous due to an explosive gas and a fast combustion rate. Therefore, the development of hydrogen sensor with high accuracy and reliability that can detect hydrogen easily is required. Especially, a flexible hydrogen sensor is useful because it has a high degree of freedom with respect to the shape of location in which the sensor is to be located. A flexible hydrogen sensor—namely, a WO3 thin film formed on a PET film by the sol-gel method using photo irradiation—based on gasochromism of WO3 was developed. By irradiating a thin film, which was prepared by using WO3 precursor solution synthesized by the sol-gel method, with ultraviolet rays, a high-purity WO3 film could be prepared on PET at low temperature. The sensor was structured as a polystyrene (PS) film containing palladium (Pd) laminated on a WO3 film. The WO3 layer was porous, so the PS containing Pd atoms solution penetrated the WO3 layer. WO3 reacted with hydrogen gas and instantly turned blue as the transmittance of the WO3 layer changed. The sensor showed high reactivity even for hydrogen concentration below 4% (1%, 0.5%, 0.25%, and 0.1%), which was the lower limit of hydrogen ignition, and a linear relationship between hydrogen concentration and change in transmittance was found. Moreover, the resistance of the WO3 film significantly and instantaneously changed due to hydrogen-gas exposure, and the hydrogen concentration and resistance change showed a linear relationship. It is therefore possible to quantitatively detect low concentrations of hydrogen by using changes in transmittance and resistance as indices. Since these changes occur selectively under hydrogen at room temperature and normal pressure, they form the basis of a highly sensitive hydrogen sensor. Since the developed sensor is flexible, it has a high degree of freedom with respect to the shape of location in which the sensor is to be installed

The Autoignition of Nuclear Reactor Power Plant Explosions

Abstract Explosive research proves that there is a common cause for most explosions in nuclear reactor power plants during normal operations and accident conditions. The autoignition of flammable hydrogen is a common cause for nuclear power plant explosions, where complex corrosion processes, nuclear reactions, and thermal-fluid transients autoignite explosions. Research evaluated increasingly complicated accidents. First, piping explosions occurred at Hamaoka and Brunsbuttel. Fluid transients compressed oxygen and flammable hydrogen to heat these gases to autoignition, where resultant explosions shredded steel pipes. This identical mechanism was responsible for pipe and pump damages to U.S. reactor systems since the 1950s, where water hammer alone has been assumed to cause damages. Small explosions inside the piping actually cause damages during nuclear reactor startups and flow rate changes. Second, explosions are caused by thermal-fluid transients during nuclear reactor restarts, following accidental nuclear reactor meltdowns. Disastrous explosions destroyed nuclear reactor buildings (RBs) at Fukushima Daiichi. Previously considered to be a fire, a 319 kilogram hydrogen explosion occurred at Three Mile Island (TMI). The explosion cause following each of these loss-of-coolant accidents was identical, i.e., after meltdowns, pump operations heated gases, which in turn acted as the heat source to autoignite sequential hydrogen explosions in reactor systems to ignite RBs. Third, the Chernobyl explosion followed a reactor meltdown that was complicated by a high energy nuclear criticality. The hydrogen ignition and explosion causes are more complicated as well, where two sequential hydrogen explosions were ignited by high-temperature reactor fuel.

Effect on hydrogen risk of total amount of inert gas during post-inerting in AP1000 NPP

To study the hydrogen risk at severe accident of LB-LOCA of cold leg in 1# SG compartment with gravity injection failure and hydrogen igniters without power in AP1000 NPP, we investigate the effect of total amount of inert gas on reducing hydrogen risk during AP1000 post-inerting. The total amount of inert gas is 42 tons, 56 tons and 70 tons respectively. We analyze the average volume fraction of hydrogen, flame acceleration factor and deflagration to detonation transition factor in 1# SG compartment and in the upper space of containment, and the pressure in containment. The results show that, post-inerting can reduce hydrogen risk in containment at severe accident, the more the total amount of inert gas is injected, the lower the possibility of FA and DDT is. Moreover, we must ensure that containment filtration and discharge system is functioning normally at accident conditions to prevent containment from overpressure.

Risk Assessment of Hydrogen Fuel Cell Electric Vehicles in Tunnels

The need to understand the risks and implications of traffic incidents involving hydrogen fuel cell electric vehicles in tunnels is increasing in importance with higher numbers of these vehicles being deployed. A risk analysis was performed to capture potential scenarios that could occur in the event of a crash and provide a quantitative calculation for the probability of each scenario occurring, with a qualitative categorization of possible consequences. The risk analysis was structured using an event sequence diagram with probability distributions on each event in the tree and random sampling was used to estimate resulting probability distributions for each end-state scenario. The most likely consequence of a crash is no additional hazard from the hydrogen fuel (98.1–99.9% probability) beyond the existing hazards in a vehicle crash, although some factors need additional data and study to validate. These scenarios include minor crashes with no release or ignition of hydrogen. When the hydrogen does ignite, it is most likely a jet flame from the pressure relief device release due to a hydrocarbon fire (0.03–1.8% probability). This work represents a detailed assessment of the state-of-knowledge of the likelihood associated with various vehicle crash scenarios. This is used in an event sequence framework with uncertainty propagation to estimate uncertainty around the probability of each scenario occurring.

Ignition of hydrogen–methane–air mixtures over Pd foil at atmospheric pressure

The ignition temperature of a mixture of 40% H2 in air over Pd (70 °C, 1 atm) is ∼200 °C lower than that over a Pt surface (260 °C, 1 atm). In addition, Pd foil ignites mixtures (30–60% H2 + 70–40% CH4)stoich + air; Pt foil cannot ignite these up to 450 °C. The effective activation energy of ignition over Pd was estimated at ∼3.5 kcal mol−1.