Hydrogen-oxygen Mixtures Research Articles

Investigating nonstationary waves from the combustion and detonation of a hydrogen-oxygen mixture in the optical and terahertz ranges

New procedures for recording flame using the terahertz radiation of the Novosibirsk free electron laser (NFEL) are described that allow us to investigate the kinetics of nonstationary waves of combustion and detonation in a gas mixture. Schemes of experiments and the results from recording a propagating front of combustion produced by a hydrogen–oxygen mixture are presented. Experiments are performed in the 115 to 200 μm range of wavelengths. Investigations are conducted at the absorption lines of water and OH radical and with these lines tuned out. Recording in the 0.4 to 0.9 μm optical range of wavelengths is done simultaneously. Waves of combustion from a stoichiometric 2H2 +O2 mixture are investigated at the initial atmospheric pressure in a channel 40 mm in diameter. The measured velocities of the combustion wave lie in the range of 10 to 1500 m s–1.

Theoretical Study of Hydrogen Production from High Pressure PEM Electrolyzer Stack

Proton exchange membrane (PEM) electrolyzer is a promising technology and likely to be an important hydrogen generator. The ability to produce high purity-hydrogen and deliver it at a relatively high pressure is an important advantage of the PEM electrolyzer technology. The high pressure operation at the cathode cause hydrogen crossover from the cathode to anode and thus deteriorate of performance. In this work, PEM electrolyzer system to produce high pressure hydrogen with consideration of energy usage and hydrogen permeation is theoretically investigated. The electrochemical and hydrogen crossover model are coded by Matlab. The effect of pressure, temperature, current density and membrane thickness on designed stack performance is presented. The explosion limit of hydrogen-oxygen mixture is also taken into consideration to figure out optimal operating operation and parameter.

CFD analysis of hydrogen volumetric concentrations in a Hard Venting Containment System of a Mark II BWR

After the Fukushima Daiichi Nuclear Power Plant (NPP) accident, the analysis of severe accidents (SA) has become an important field of study in order to define appropriate severe accident management and emergency planning. The Station Blackout (SBO) scenario, in which all the external power is lost, is a reference to the simulation of a severe accident initiating event. All nuclear power plants are designed to face partially a SBO. However, a long SBO scenario can result in a beyond design basis accident and evaluations in order to define severe accident management guidelines (SAMGS) must be performed. The hydrogen generation due to the high temperatures of the melting core in contact with steam is an issue in the assessments of SA. Usually, in boiling water reactors (BWR), the primary containment has an inert atmosphere (with Nitrogen) in order to prevent a detonable hydrogen–oxygen mixture. However in a SA, the primary containment is highly jeopardized and can fail with the subsequent release of the inert atmosphere to the secondary containment where the hydrogen can be in contact with the oxygen of the air and a detonation may occur (as in Fukushima Daiichi NPP). An option in order to avoid a detonation inside the reactor building in the case of a primary containment failure is by means of the installation of a Hard Venting Containment System (HVCS). A methodology in order to assess the transport of gases (especially hydrogen, steam and nitrogen) inside the hard venting pipe has been developed. Taking the results of the MELCOR code, mainly mass fluxes as well as temperature and pressure fields inside the primary containment, a source term for the computational fluid dynamics (CFD) code GASFLOW is calculated in order to predict the hydrogen behaviour inside the venting system. The calculations performed with GASFLOW showed the risk of the occurrence of a detonation inside the venting pipe due to the hydrogen volumetric concentrations entering in contact with the air inside the venting pipe (if it is initially filled with air).

Effect of equivalence ratio on the velocity of rotating detonation

Rotating detonation engines having the advantages of high thermal efficiency, high specific impulse and simple structure, are being studied widely. Rotating detonation waves in hydrogen–oxygen mixture are experimentally and numerically studied here. Two pressure sensors at different positions in the combustor capture the detonation pressure signals in the experiments. Mass flow rates are measured by gas mass flow controllers and rotating detonation waves at different equivalence ratios are obtained. Both experimental and numerical results show that as the equivalence ratio increases, the velocity of the rotating detonation wave first increases and then decreases while the velocity of the detonation wave decreases monotonously according to the previous study.

Experimental proof of Zel'dovich cycle efficiency gain over cycle with constant pressure combustion for hydrogen–oxygen fuel mixture

The objective of work outlined in this paper was to prove experimentally the energy efficiency of Zel'dovich thermodynamic cycle (cycle with detonative combustion of fuel) by direct comparison of thrust performances of liquid-propellant rocket engine (LRE) prototypes operating in continuous-detonation and continuous-combustion modes using gaseous hydrogen as fuel and gaseous oxygen as oxidizer. For this purpose, a test rig and two LRE prototypes were designed and fabricated. It has been proved experimentally that Zel'dovich thermodynamic cycle with continuous-detonation combustion of hydrogen–oxygen mixture in two different LRE prototypes is more energy efficient than the cycle with continuous constant-pressure combustion of the same mixture, other conditions being equal. Thus, at predetermined limitations on supply pressures of fuel components and at a fixed mass flow rate of fuel mixture the specific impulse of the LRE prototypes operating in the continuous-detonation mode appeared to be 6–8% higher than the specific impulse of the same LRE prototypes operating in the continuous-combustion mode.

High Order Bubble Dynamics in Incompressible Liquid

A semi-analytical approximation to the solution of the radial Fourier equation describing liquid temperature dynamics in the vicinity of a spherical bubble is presented. This approximation opens a possibility to construct a computationally efficient bubble model that is flexible enough to simulate different bubble dynamics behavior like bubble growth, collapse, and oscillations. In turn, it allows development of two-pressure computer codes aiming at simulation of processes in liquid with bubbles that are important for industrial applications. The model is based on the system of ordinary differential equations (ODEs) and is presented together with results of simulations and comparison with some available experimental data. Additionally, scenarios like strong bubble parameter oscillations in largely subcooled water and abrupt liquid pressure change are considered. As respective simulations show, the latter may lead to subsequent hydrogen explosion if hydrogen–oxygen mixture is presented in the bubble. This may be important for boiling water reactor piping safety analysis.

Numerical comparison of hydrogen-air reaction mechanisms for unsteady shock-induced combustion applications

An unsteady shock-induced combustion (SIC) is characterized by the regularly oscillating combustion phenomenon behind the shock wave supported by the blunt projectile flying around the speed of Chapman-Jouguet detonation wave. The SIC is the coupling phenomenon between the hypersonic flow and the chemical kinetics, but the effects of chemical kinetics have been rarely reported. We compared hydrogen-air reaction mechanisms for the shock-induced combustion to demonstrate the importance of considering the reaction mechanisms for such complex flows. Seven hydrogen-air reaction mechanisms were considered, those available publically and used in other researches. As a first step in the comparison of the hydrogen combustion, ignition delay time of hydrogen-oxygen mixtures was compared at various initial conditions. Laminar premixed flame speed was also compared with available experimental data and at high pressure conditions. In addition, half-reaction length of ZND (Zeldovich-Neumann-Doring) detonation structure accounts for the length scale in SIC phenomena. Oscillation frequency of the SIC is compared by running the time-accurate 3rd-order Navier-Stokes CFD code fully coupled with the detailed chemistry by using four levels of grid resolutions.

Energy efficiency of a continuous-detonation combustion chamber

Systematic experimental and computational studies of the energy efficiency of continuous-detonation combustors (CDCs) have been performed. A small-size and a large-size CDCs using hydrogen as fuel and oxygen or air as oxidizer have been developed and tested. It was first experimentally proved that the Zel’dovich thermodynamic cycle with continuous-detonation combustion of a hydrogen-oxygen mixture in an annular combustor is more efficient than the Brayton thermodynamic cycle with continuous combustion of the mixture, other things being equal. The specific impulse of a small-size bench-scale rocket engine with a 50 mm diameter CDC operating in the continuous-detonation mode was 6–7% higher than that in the continuous combustion mode of operation. The measured fuel-based specific impulse for the large-size CDC of 406 mm diameter running on a hydrogen-air mixture was at a level of 3000 s. Three-dimensional calculations to optimize the structure and operation mode of the large-size CDC have shown that when running on a combustible mixture with a nearly stoichiometric overall composition, the specific impulse can be increased to ≈4200 s.

Effect of addition of oxygen and water vapor on fretting fatigue properties of an austenitic stainless steel in hydrogen

JIS SUS304 fretting fatigue test was done in high-purity hydrogen, an oxygen–hydrogen mixture and humidified hydrogen. The fretting fatigue strength in hydrogen was drastically changed depending on the oxygen level. Based on the XPS (X-ray photoelectron spectroscopy) analysis of the fretted surface, it was found that the fretting removed the original protection layer of the stainless steel, however, the addition of water vapor or ppm-level of oxygen produced an oxide layer on the fretted surface during the fretting that surpassed the removal effect of the initial oxide layer by fretting. In fact, a strong adhesion between the contacting surfaces occurred and no fretting wear particles were observed in the high-purity hydrogen. On the other hand, oxidized fretting wear particles were found in the oxygen–hydrogen mixture. Based on the geometry of contact used in this study, a severe concentration of the contact pressure arouse at the contact edge. This produces a compressive stress field in the specimen where the crack growth was suppressed. This stress concentration was relieved when fretting wear occurs. Therefore, the change in the fretting fatigue strength in hydrogen by the addition of oxygen is closely related to the change in the wear behavior.

A Hydrogen detectors Wireless network for monitoring the gas ambient in a laboratory

A system to monitor the hydrogen contents in the atmosphere present in the various sections of a crystal growth laboratory has been built. When hydrogen is used in the processes carried out in a laboratory it is important to monitor its content because the oxygen-hydrogen mixture is highly flammable and/or explosive. The system emits a warning when the Hydrogen concentration increases and if the concentration rises above 1% in vol. it shuts down automatically any process that is using hydrogen. The design and performance of the system is reported here.

Laser-Induced Breakdown and Detonation in Particle-Laden Systems

Simulation of the interaction of a laser pulse with gas-droplet and gas-particle mixtures plays an important role in environmental and engineering applications. The injection of liquid droplets or metal particle causes optical breakdown on the individual droplet or particle and leads to a drop of the detonation minimum pulse energy of the mixture. Mathematical models of various stages of the optical breakdown are developed and applied to the analysis of laser-induced breakdown in particle-laden systems. The numerical calculations are based on an in-house computer code using the finite-volume method and high-resolution scheme. The threshold of optical breakdown and its dependence on contributing factors (droplet radius, location of droplet, total energy and time of laser pulse, radius of laser spot) has been studied. Minimum pulse energy of detonation was computed in the hydrogen-oxygen mixture with metal particles and liquid droplets.

Rotating Detonation Instabilities in Hydrogen-Oxygen Mixture

Rotating detonation engines are studied more and more widely because of high thermodynamic efficiency and high specific impulse. Rotating detonation of hydrogen and oxygen was achieved in this study. Rotating detonation waves were observed by high speed cameras and detonation pressure traces were recorded by PCB pressure sensors. The velocity of rotating detonation waves is fluctuating during the run. Low frequency detonation instabilities, intermediate frequency detonation instabilities and high frequency detonation instabilities were discovered. They are relevant to unsteady heat release, acoustic oscillations and rotating detonation waves.

Conjugated processes of the chemical transformation of sulfur dioxide under the effect of chain gas-phase reactions

The effect sulfur dioxide has on the dynamics of the spontaneous ignition of hydrogen-oxygen mixtures is studied. Additives of SO2 have no negative effect on spontaneous ignition and undergo chemical conversion to form elemental sulfur. The results are analyzed using the theory of branched chain reactions along with data on SO2 conversion under the action of chain reactions of hydrocarbon oxidation and slow hydrogen oxidation. The transformations classified as parallel reactions from the viewpoint of formal kinetics could actually be conjugated radical-chain processes.

Numerical estimation of the thrust performance on a rotating detonation engine for a hydrogen–oxygen mixture

The numerical simulations of 2D and 3D rotating detonation engines for a hydrogen–oxygen mixture are performed using a detailed chemistry model. The comparison of 2D/3D flow fields for the same injection conditions indicates that the overall flow structures are in agreement for the two simulations and that both rotating velocities are approximately 96% of the CJ value. However, Isp for the 2D RDE is approximately 10s larger than Isp for the 3D RDE. The grid resolution study indicates that the higher grid resolution produces detonation cellular structure; however, its effects on Isp are approximately a few seconds. Although Isp in the 2D smallest scale for higher mass flow is approximately 10s larger than that of the other large scales, Isp for low mass flow is not affected by the scale. However, 3D scale effects are important because the radius of curvature along the circumferential direction changes, which affects the propagation of the rotating detonation. Because Isp and thrust are governed by the stagnation pressure and the micro-nozzle area ratio, the mass flow rate from the injector also depends on these parameters. Isp and thrust for RDE are found to be correlated with the mass flow rate, similar to the case of a conventional rocket engine. This result indicates that the two important parameters, A∗/A and p0, can be replaced by one parameter, i.e., the mass flow rate.

Numerical Modeling of the Ignition of Hydrogen–Oxygen Mixtures Under Nonequilibrium Conditions

A numerical study has been made of the intensification of combustion in hydrogen-oxygen mixtures with a low-temperature nonequilibrium plasma, when the concentration of the active particles in the mixture (atoms, radicals, ions, and excited particles) is much higher than their equilibrium concentrations. Primary emphasis has been placed on the influence of higher-than-average concentrations of electronically excited O2(a 1Δg) molecules and O( 1Δ) atoms on the acceleration of the process of ignition. Electron-beam irradiation of the fuel mixture and the action of a high-voltage nanosecond discharge on it were selected for comparison of the efficiency of different types of plasma initiation of combustion.

Physicomathematical modeling of detonation suppression by inert particles in methane-oxygen and methane-hydrogen-oxygen mixtures

Based on the developed physicomathematical model of detonation attenuation and suppression in a methane-oxygen mixture by means of addition of a cloud of inert particles, the influence of the volume fraction of particles and their diameter on the detonation wave velocity is analyzed. Detonation limits in terms of the volume fraction of particles in methane-oxygen and methane-hydrogen-oxygen mixtures are found. A comparison with our previous data on suppression of detonation in a hydrogen-oxygen mixture shows that the critical volume fractions of particles resulting in detonation wave suppression in the methane-hydrogen-oxygen mixture are greater than those in the hydrogen-oxygen mixture.

Continuous detonation in a supersonic flow of a hydrogen-oxygen mixture

The problem of continuous spin detonation in a supersonic flow in a flow-type annular combustor is considered in a two-dimensional unsteady formulation. The dynamics of the detonation wave in a hydrogen-oxygen mixture with isentropic and shock-wave compression of the flow in the input diffuser is studied. It is shown that the mass flow rate of the mixture through the combustor decreases as continuous spin detonation is formed, and a steady regime with a “detached” shock wave is observed at the entrance of the supersonic diffuser. For a contoured combustor, the limit from above is obtained for the Mach number of the incoming supersonic flow at which a continuous detonation regime is obtained.

Propagation mechanisms of supersonic combustion waves

The propagation of a supersonic combustion wave in an obstructed channel is investigated using high-speed schlieren photography. Experiments were carried out in a 2.54cm wide by 7.82cm tall channel with equally spaced 1.91cm tall fence-type obstacles mounted on the top and bottom surfaces. Tests were carried out with stoichiometric hydrogen–oxygen mixtures over an initial pressure range of 8–30kPa. The high-speed video shows that combustion wave propagation in the quasi-detonation propagation regime is very complex involving coupled local explosions, not all of which involve detonation initiation. For the most reactive mixtures (d/λ>6.5) a sustained detonation propagates through the channel with some weakening due to diffraction around obstacles. For less reactive mixtures (6.5>d/λ>2) detonation propagation is intermittent, where the detonation fails due to diffraction around the obstacles and then is re-initiated at the channel centerline following the collision of two transverse shock waves. The transverse shock wave originates from a detonation that forms immediately following shock reflection off the top and bottom obstacle faces. Detonation initiation occurs at the corner, where the channel wall and obstacle meet, as a result of shock focusing and propagates into the unburned gas ahead of the flame. For mixtures where d/λ<2, the wave propagation is governed by the outcome of the shock reflection off the obstacle pair (top and bottom). If shock reflection off the obstacle pair initiates an explosion at the obstacle face, the collision of the resulting two transverse shock waves produces a local explosion at the channel centerline after each obstacle resulting in an average lead shock velocity roughly equal to the isobaric speed of sound of the products. If shock reflection does not result in ignition of the gas at the obstacle face, the resulting propagation is in the choked flame regime.

On the influence of low initial pressure and detonation stochastic nature on Mach reflection of gaseous detonation waves

The two-dimensional, time-dependent and reactive Navier–Stokes equations were solved to obtain an insight into Mach reflection of gaseous detonation in a stoichiometric hydrogen-oxygen mixture diluted by 25 % argon. This mixture generates a mode-7 detonation wave under an initial pressure of 8.00 kPa. Chemical kinetics was simulated by an eight-species, forty-eight-reaction mechanism. It was found that a Mach reflection mode always occurs for a planar detonation wave or planar air shock wave sweeping over wedges with apex angles ranging from \(5^\circ \) to \(50^\circ \). However, for cellular detonation waves, regular reflection always occurs first, which then transforms into Mach reflection. This phenomenon is more evident for detonations ignited under low initial pressure. Low initial pressure may lead to a curved wave front, that determines the reflection mode. The stochastic nature of boundary shape and transition distance, during deflagration-to-detonation transition, leads to relative disorder of detonation cell location and cell shape. Consequently, when a detonation wave hits the wedge apex, there appears a stochastic variation of triple point origin and variation of the angle between the triple point trajectory and the wedge surface. As the wedge apex angle increases, the distance between the triple point trajectory origin and the wedge apex increases, and the angle between the triple point trajectory and the wedge surface decreases exponentially.

Induction for multiple rotating detonation waves in the hydrogen–oxygen mixture with tangential flow

Abstract Rotating detonation engines are studied more and more widely because of high thermodynamic efficiency and high specific impulse. Generally one detonation wave exists in the engines but sometimes multiple detonation waves appear, as is complicated and difficult to explain. Increasing the number of rotating detonation waves uniforms the flow field and weakens the combustion instabilities. A controllable way to induce multiple detonation waves is introduced here. Rotating detonation engine runs with a single detonation wave or multiple detonation waves were both conducted. Pressure sensors were used to record the pressure traces of rotating detonation waves and gas flow controllers controlled the flow rates of reactants. Tangential flow of reactants from the predetonator produces shock waves moving upstream, inducing multiple rotating detonation waves when there is axial flow of reactants from the head of the combustor. The maximum number of detonation waves is subject to the flow rates.