Self-ignition Mechanism Research Articles

Research on the flow characteristics and self-ignition mechanism of high-pressure hydrogen jets in bifurcated tubes

This manuscript provides insights into the characteristics of shock wave propagation and flame development mechanisms in bifurcated tubes due to accidental leakage from a high-pressure hydrogen storage unit in the energy and chemical industries. Incorporating the non-stop working process of tube plugging in gas transportation in industrial production, two types of bifurcated tubes with axial and normal blocking are designed. The experimental results indicate that, compared to straight tube, both types of blocking tube structures can effectively reduce shock wave pressure intensity at the nozzle. Under the initial burst pressure of 8 MPa, the lowest shock wave pressure at the nozzle of the axially blocking tube is just 0.47 MPa. However, the peak shock wave pressure inside the blocking tubes is higher, and the ignition critical pressure is lower. Within the axially sealed blocking tube, flame quenching is observed, offering experimental support for mitigating the development of continuous jet fires outside of high-pressure hydrogen tubes.

Mechanism of self-ignition and flame propagation during high-pressure hydrogen release through a rectangular tube

The dynamic mechanisms of self-ignition and flame propagation during high-pressure hydrogen release through a rectangular tube were experimentally investigated using pressure records, flame detection and high-speed photographs. Experimental results show that the minimum burst pressure for self-ignition decreases with an increase in axial distance to the diaphragm and then remains at an almost constant value. The self-ignition onset at the same location of the tube exhibits a certain randomness even if the intensity of the shock wave produced in the tube is similar. Multiple ignitions were observed at the early stage of hydrogen release. They usually had difficulty to sustainably develop and were extinguished owing to oxygen deficiency. At a subsequent stage, the ignition kernel appears again and grows rapidly in the axial and radial directions, finally converging to a complete flame across the tube width. It was found that the radial growth rate of the flame was lower than the axial growth rate.

Research progress on the self-ignition of high-pressure hydrogen discharge: A review

As one of the most promising fossil energy substitutes, hydrogen energy is receiving increasing attention, and it has been greatly developed in recent years. However, hydrogen safety issues limit the large-scale application of hydrogen energy. Since 1922, the issue of self-ignition of high-pressure hydrogen discharge has gradually become the focus of attention of scholars in the field of hydrogen energy. Particularly fruitful research results have been obtained in the past 20 years, showing that the minimum discharge pressure of hydrogen self-ignition is approximately 2 MPa. In particular, the discharge tube shape and bursting disc rupture have a significant effect on the characteristics of hydrogen self-ignition. Moreover, the study of the hydrogen self-ignition mechanism under special working conditions has been extended by shock-induced ignition theory. Initial conditions mainly affect the critical pressure of hydrogen self-ignition by changing the formation, development and propagation of shock waves. Finally, the deficiencies and future research trends in research methods, self-ignition characteristics, and dynamic mechanisms are analysed.

Mechanism of self-ignition of pressurized hydrogen flowing into the channel through rupturing diaphragm

The paper considers numerically the mechanism of hydrogen self-ignition occurring when hydrogen flows into the channel through gradually rupturing diaphragm. The analysis focuses on the near-critical self-ignition regimes arising at initial hydrogen pressure ∼60 atm that is marginal for self-ignition occurrence for selected channel geometry. Numerical simulation reproduces two types of ignition kernels observed experimentally. Both types of kernels arise on the contact surface between the released hydrogen and air heated behind the outrunning shock wave. In the initial stage the self-ignition kernels arise on the side contact surface interacting with channel walls and compression waves reflected from the walls. However, because of oxygen deficit these ignition kernels are extinguished. In the subsequent stage the self-ignition kernel arises in the region where the side contact surface penetrates into the boundary layer heated behind the shock wave. The further evolution of the ignition kernel is provided by the vortical structures evolving at the side contact surface and defining the mixing of hydrogen with air as well as the sustained supply of the mixture into the ignition kernel.

An experimental study on the mechanism of self-ignition of high-pressure hydrogen

In the present study, the self-ignition of high-pressure hydrogen released in atmospheric air through a diaphragm is visualized under various test conditions. The experimental results indicate that the hydrogen that jets through the rupturing diaphragm is mixed with the heated air near the tube wall. The self-ignition event originated from this mixing. The self-ignition was strongly dependent on the strength of an incident shock wave generated at the diaphragm rupture. As a result, a cylindrical flame that formed after the self-ignition shows a tendency to become longer as it propagates in the downstream direction. The head velocities of the hydrogen-air mixture and the cylindrical flame are consistent with that of a contact surface calculated from the measured shock speed. A modified self-ignition mechanism is proposed based on the experimental observations.

D121 管内高圧水素噴流による自着火機構(OS-10:火災・爆発(2))

This paper deals with a self-ignition mechanism of high-pressure hydrogen jet in a tube filled with air. Although the self-ignition phenomenon is expected to clarify for industrial safety, the ignition mechanism in a tube still has not been known well. In this study, the direct photographs of flame behaver initiated by the self-ignition are captured by a high speed camera. The flame propagation histories are obtained from the pressure and light sensors. Additionally, a numerical simulation is performed to understand the ignition process induced by hydrogen jet in detail. As the results, a self-ignition occurs at the region where the contact surface interacts with the local high-temperature region which is built by the shock wave reflects from the sidewall of tube.

Examination of Low-Temperature Oxidation of Low-Rank Coals, Aiming at Understanding Their Self-Ignition Tendency

With the aim at understanding the self-ignition mechanism of low-rank coals, low-temperature oxidation behaviors of three coals were investigated by measuring the weight change, gas formation rate, heat generation rate, and change of functional groups during the oxidation at the heating rate of 5 K/min in a helium stream containing 22% oxygen. Detailed examination of the initial stage of oxidation below 200 °C that will be closely related to the self-ignition clarified the following: the reactions occurring are the intake of oxygen into aliphatic carbons as peroxides and the decomposition of the peroxides forming carboxyls and H2O. For two low-rank coals tested, the former process was rapid enough and only the latter decomposition reaction of the peroxides to form carboxyl groups was observed, which resulted in the monotonous weight decrease and the H2O production. For a high-rank coal tested, the former process solely occurred below 140 °C and the former process was faster than the latter process below 2...

G0510306 3次元数値解析による高圧水素噴流の管内における自着火機構の解明([G051-03]流体工学部門一般セッション(3),流体工学部門)

G0510306 3次元数値解析による高圧水素噴流の管内における自着火機構の解明([G051-03]流体工学部門一般セッション(3),流体工学部門)

A flow visualization study on self-ignition of high pressure hydrogen gas released into a tube

Hydrogen is known as one of the green energy sources for fuel cells and hydrogen-fueled cars in the next generation. The storage of high-pressure hydrogen gas conditions is preferred to its storage in cryogenic liquid state. However, cases of unidentified self-ignitions were reported, notably when the high-pressure hydrogen gas suddenly leaked out. Only a few of numerical simulations have shown visually the processes of the self-ignition inside a tube. This paper presents a flow visualization study to investigate the self-ignition mechanism in a test tube i.e. how the ignition process is initiated and the flame propagates. In addition to visualization, measurement of a number of pressure and light sensors installed in the tube supported the analysis of the self-ignition and flame propagation. The test result showed that self-ignition takes place at the boundary layer behind the front center of mixing zone at first, and the flame propagates to the front of mixing zone and tail of the mixing zone along the boundary layer. It showed that self-ignition is accompanied with complex mixing induced by shock interaction with the mixing front. It is also suggested that the self-ignition boundary has a certain critical threshold of static pressure at the boundary layer, based on various burst pressures of hydrogen.

Self-ignition of hydrogen releases through electrostatic discharge induced by entrained particulates

Abstract The potential for particulates entrained in hydrogen releases to generate electrostatic charge and induce electrostatic discharge ignitions was investigated. A series of tests were performed in which hydrogen was released through a 3.175-mm diameter orifice from an initial pressure of 140 bar. Electrostatic field sensors were used to characterize the electrification of known quantities of iron oxide particulates deliberately entrained in the release. The ignition experiments focused on using charged particulates to induce spark discharges from isolated conductors and corona discharges. A total of 12 ignition events were observed. The results show that electrification of entrained particulates is a viable self-ignition mechanism of hydrogen releases.

Cavitation-induced ignition of cryogenic hydrogen-oxygen fluids

The Challenger disaster and purposeful experiments with liquid hydrogen (H2) and oxygen (Ox) tank breaches demonstrated that cryogenic H2/Ox fluids always self-ignite in the process of their sudden mixing. Here, we propose a cavitation-induced self-ignition mechanism that may be realized under these conditions. In one possible scenario, self-ignition is caused by the strong shock waves generated by the collapse of pure Ox vapor bubble near the surface of the Ox liquid that may initiate detonation of the gaseous H2/Ox mixture next to the gas-liquid interface. This effect is further enhanced by H2/Ox combustion inside the collapsing bubble in the presence of admixed H2 gas.

Collisionless reconnection: mechanism of self-ignition in thin plane homogeneous current sheets

Abstract. The spontaneous onset of magnetic reconnection in thin plane collisionless current sheets is shown to result from a thermal-anisotropy driven non-relativistic magnetic electron Weibel-mode, generating seed-magnetic field X-points in the centre of the current layer. The proposed mechanism is of larger generality. It also works in the presence of magnetic guide fields.

Mechanism of Self-Ignition of Titanium Alloys in Oxygen

It is proposed that the ignitability of titanium alloys in oxygen, characterized by critical ignition pressure, is determined by critical temperature, i.e., the temperature to which juvenile surface fragments can be heated during metal fracturing. This hypothesis is supported by comparison of calculated critical temperatures with critical ignition pressures measured experimentally for various titanium α-alloys. Key words: titanium alloys, uvenile surface, oxygen, self-ignition, fracture.

Chemical amplifier, self-ignition mechanism, and amoeboid cell migration.

Chemical amplifier, self-ignition mechanism, and amoeboid cell migration.

Self-ignition mechanism for coal

1. A fundamentally new hypothesis is suggested for occurrence of self-ignition in coal. 2. The hypothesis obtained is checked by calculations for a linear unit and a structural unit of coal. 3. The probability of forming seats of self-ignition at a distance from the combustion front is higher than close to it. 4. Conditions for forming seats of self-ignition do not require transfer of coal into a plastic state and application of a possible hypothesis of cumulative collapse of gasfilled bubbles with release of the required energy (apart from the case of μ2=402). 5. On the basis of the hypothesis suggested it is possible to suggest a mechanism of forced intensification of coal seam combustion by converting it into coal detonation.

Closed-vessel hydrogen-air explosions at high pressures

As one of the most promising fossil energy substitutes, hydrogen energy is receiving increasing attention, and it has been greatly developed in recent years. However, hydrogen safety issues limit the large-scale application of hydrogen energy. Since 1922, the issue of self-ignition of high-pressure hydrogen discharge has gradually become the focus of attention of scholars in the field of hydrogen energy. Particularly fruitful research results have been obtained in the past 20 years, showing that the minimum discharge pressure of hydrogen self-ignition is approximately 2 MPa. In particular, the discharge tube shape and bursting disc rupture have a significant effect on the characteristics of hydrogen self-ignition. Moreover, the study of the hydrogen self-ignition mechanism under special working conditions has been extended by shock-induced ignition theory. Initial conditions mainly affect the critical pressure of hydrogen self-ignition by changing the formation, development and propagation of shock waves. Finally, the deficiencies and future research trends in research methods, self-ignition characteristics, and dynamic mechanisms are analysed.