Hydrogen-oxygen Mixtures Research Articles

Calculation of continuous spin detonation of a hydrogen-oxygen mixture in an annular combustor with oxygen ejection

A closed mathematical model of continuous spin detonation in a H2-O2 mixture with oxygen ejection from the environment has been developed. The model takes into account the inverse effect of pulsation processes in the combustor on oxygen ejection. A numerical study was performed for a 10 cm diameter ramjet annular combustor with geometric dimensions corresponding to experiments. One-wave modes of continuous spin detonation were calculated and the flow structure was analyzed with variation in the specific hydrogen flow rate from 3 to 3.75 kg/(s·m2). Decreasing the flow rate of ejected hydrogen during continuous detonation in the combustor is found to lead to a monotonic decrease in the detonation velocity, wave front height, average static pressure, and equivalence ratio, but to an increase in the oxygen ejection coefficient. The results are validated against experimental data.

Influence of detailed mechanisms of chemical kinetics on propagation and stability of detonation wave in H2/O2 mixture

In the present paper, detonation in a stoichiometric oxygen-hydrogen mixture is simulated numerically using 4 detailed chemical mechanisms. The effect of chemical kinetics models on the stability of 1D detonation wave and 2D detonation wave propagating in a plane channel is investigated. The number of detonation cells formed in a channel of a given width at different degrees of overdrive is determined. Simulations are performed using a previously developed computational program based on high-order shock-capturing TVD schemes and a finite-rate chemistry solver. The program is implemented in C++ using the CUDA parallel computing platform for running on graphic processor devices (GPU), the open OpenMP standard for multi-threaded applications on multiprocessor systems with shared memory and the MPI protocol for data exchange between processors.

Detonation in the hydrogen-oxygen microfoam on the aqueous base

In the paper, the propagation of the detonation wave in the hydrogen-oxygen microfoam on the aqueous base is considered. Microfoam represents a two-phase system containing micron-sized gas bubbles filled with the hydrogen-oxygen mixture. These bubbles are dispersed in the water solution of surfactant (sodium dodecyl sulfate). The dependencies of detonation speed on the equivalence ratio and on the water content in the foam are obtained with the use of high-speed filming. It is found that the detonation speed slightly increases with the decrease in water content in the foam. Based on the pressure measurements, it is established that the detonation propagation in the foam is driven by relatively weak shock waves, which by themselves are not able to induce ignition of the hydrogen-oxygen mixture. To substantiate the fact of detonation existence in the microfoam a hypothesis of the cumulative collapse of gas bubbles under the shock wave action is proposed. The estimation for detonation speed in microfoam is analytically derived on the basis of simple phenomenological representations.

Combustion of heptane-in-water emulsion foamed with hydrogen-oxygen mixture

One of the perspective types of combined fuels is the oil-in-water emulsion foamed with the hydrogen-oxygen mixture. In this paper, the process of combustion of such a system obtained via hydrogen-oxygen mixture bubbling through the heptane-in-water emulsion is considered experimentally for the first time. The main goal of this paper is to study different regimes of foamed emulsion combustion at varying composition of hydrogen-oxygen mixture inside bubbles and heptane content in the emulsion. Flame speed is measured with the use of high-speed filming. It is shown that the use of hydrogen allows increasing the speed of flame propagation through the foamed emulsion, and at certain conditions even detonation onset becomes possible. The detonation in the foamed emulsion is determined by the effect of energy focusing during the collapse of gaseous bubbles. When using a lean hydrogen-oxygen mixture, the dependence of the total burning rate of the foamed emulsion on heptane concentration has a maximum. It is found that when using the stoichiometric hydrogen-oxygen mixture, the flame speed decreases monotonically with the increase in heptane concentration. In the case of a weakly reactive compound of the foamed emulsion, the regime of spinning detonation is possible.

An apparatus for producing tunable, repeatable, hydrogen–oxygen-deflagrative blast waves

The Hydrogen Unconfined Combustion Test Apparatus (HUCTA) was designed and built to study the blast waves produced from unconfined hydrogen/oxygen deflagrations. The HUCTA uses evacuated balloons of up to 2 m in diameter which are filled with a combustible combination of gaseous hydrogen–oxygen mixtures. The well-mixed gases are ignited with an electric spark at the center of the sphere, resulting in a gaseous deflagration propagating through the mixture and a shock wave produced in the air. The combinations of balloon size and fuel/oxidizer ratios allow for a wide range of blast waves to be produced. Overpressures are measured with standard blast gauges at a variety of locations, demonstrating a high degree of radial symmetry and repeatability in the shock wave pressures, as well as the ability to produce non-ideal shock wave pressure profiles under some conditions. The range of peak pressures and explosive impulses obtainable is described as a function of mixture ratio. High-speed retroreflective shadowgraphy is used to visualize shock wave propagation and coalescence in individual frames and digital streak images. Since HUCTA is elevated approximately 2 m off the ground, there is a significant area around the apparatus where non-noisy, un-reflected, symmetric blast waves propagate; this area is ideal for testing items whose response to blast waves is desired for safety considerations.

Convergence properties of detonation simulations

ABSTRACTWe present a high-resolution convergence study of detonation initiated by a temperature gradient in a stoichiometric hydrogen–oxygen mixture using the PENCIL CODE and compare with a code that employs a fifth order weighted essentially non-oscillating (WENO) scheme. With Mach numbers reaching 10–30, a certain amount of shock viscosity is needed in the PENCIL CODE to remove or reduce numerical pressure oscillations on the grid scale at the position of the shock. Detonation is found to occur for intermediate values of the shock viscosity parameter. At fixed values of this parameter, the numerical error associated with those small wiggles in the pressure profile is found to decrease with decreasing mesh width like down to . With the WENO scheme, solutions are smooth at , but no detonation is obtained for . This is argued to be an artifact of a decoupling between pressure and reaction fronts.

Continuous detonation of a hydrogen–oxygen gas mixture in a 100-mm plane-radial combustor with exhaustion toward the periphery

Regimes of continuous spin detonation and continuous multifront detonation in a hydrogen–oxygen mixture are obtained in a plane-radial combustor with an inner diameter of 100 mm and exhaustion toward the periphery. The fuel-lean limits of detonation in terms of the specific flow rate of the mixture are determined. For continuous spin detonation, transverse detonation waves and the flow in their vicinity in the combustor plane are reconstructed. The detonation wave is found to be significantly curved because of the increase in the tangential component of the velocity along the combustor radius. It is demonstrated that the scale effect is manifested only in the number of rotating waves. However, their velocity increases with increasing the combustor size. The velocity deficit of continuous detonation is 20–40% as compared to the velocity of the ideal Chapman–Jouguet detonation. (The smaller value corresponds to the fuel-lean mixture.)

Multi-Implicit Methods with Automatic Error Control in Applications with Chemical Reactions

Multi-implicit methods with a second derivative for stiff systems of ordinary differential equations are described. An algorithm for automatic step size control and selection based on multi-implicit methods of the eighth and sixth orders of accuracy is proposed. The efficiency of the variable step size methods is demonstrated as applied to nonequilibrium kinetics of chemical reactions describing an explosion of a hydrogen–oxygen mixture consisting of six species (H2, O2, H, O, OH, H2O).

Evaluation of the possibility of ignition of a hydrogen–oxygen mixture by erosive flame of the impulse laser

The paper presents the mathematical model of combustion initiation in a mixture of hydrogen and oxygen gases (oxyhydrogen) by a laser flare created near a metal barrier. For numerical resolution of the ‘hyperbolic’ part of Reynold’s equations system, we give a new nonlinear quasimonotone compact polynomial difference scheme of improved accuracy. Calculations of all the main parameters: the laser flare, the heating of the metal barrier, and the combustion processes in the hydrogen–oxygen system are performed.

Numerical simulation of shock and detonation waves in bubbly liquids

A well-posed mathematical model of nonisothermal, two-phase, two-velocity flow of a bubbly medium with chemically inert liquid and chemically inert or active gas bubbles is proposed. The model is based on the two-phase Euler equations with the introduction of an additional pressure at the gas-bubble surface, which ensures the well-posedness of the Cauchy problem for a system of governing equations, and the Rayleigh–Plesset equation for radial pulsation of gas bubbles allowing solutions of the soliton type that are realized in experiments to be obtained. The model is validated by comparing calculations of detonation wave propagation with experimental data in water or an aqueous solution of glycerin with bubbles of acetylene–oxygen mixture or with bubbles of argon–hydrogen–oxygen mixture for a volume gas content of 1–6%. The model is shown to provide satisfactory results for the detonation propagation velocity and detonation pressure profiles.

Counter-current hydrogen–oxygen vortex combustion chamber. Thermal physics of processing

The expediency is substantiated for the use of a vortex counter-current circulation flow of water steam and the stoichiometric hydrogen-oxygen mixture as a source of heat generation. That flow is essential for the purpose of making efficient models of high-temperature combustion chambers for the cogeneration cycles.An experimental investigation was carried out of hydrogen-oxygen mixture combustion in a counter-current combustion chamber-superheater. Operating range values of heat power were obtained. A maximum temperature of the superheated steam at the combustion chamber outlet was 1350 K. There were determined the optimal modes of hydrogen-oxygen mixture outflow ensuring its steady combustion in the counter-current flow core of the water steam.

MHD effects in continuous spin detonation

Conversion possibility of the chemical energy of combustion products of a hydrogen–oxygen mixture into electrical energy with the use of continuous spin detonation has been demonstrated for the first time in an MHD system. The specific conductivity of detonation products in the region of rotation of the detonation front was measured to be ~3 · 10–2 Ω–1 m–1. The structure of transverse detonation waves was examined, their velocity was measured (2220 ± 50 m/s), and the flow in their vicinity was studied.

Numerical investigation of oblique detonation structure in hydrogen-oxygen mixtures with Ar dilution

Two combustible mixtures, H2-O2-Ar and H2-O2-N2, are widely used in detonation research, but only the latter has been employed in oblique detonation wave (ODW) studies. In this study, ODWs in H2-O2-Ar are simulated to investigate their structural characteristics using reactive Euler equations with a detailed chemistry model. Similar to ODWs in H2-O2-N2 mixtures, two observed structures are dependent on incident Mach numbers. However, in mixtures of 2H2 + O2 + 7Ar, the structures are sensitive to inflow static pressure P0, different from the structures in H2-O2-N2 mixtures. Based on flow field analysis, the ratio of induction and heat release zone lengths RL is proposed to model the difference induced by dilution gas. Generally, RL is large in N2 diluted mixtures but small in Ar diluted mixtures. Low RL indicates that induction is comparable with the heat release zone and easily changed, resulting in pressure-sensitive structures. When the dilution gas changes gradually from N2 to Ar, the ratio RL increases slowly at first and then declines rapidly to approach a constant. The variation rule of RL is analyzed and compared with results from calculations of a constant volume explosion, demonstrating how different dilution gases influence ODW structures.

Equations for Engineering Calculations of the Thermodynamic Properties of High-Temperature Dissociated Steam

A system of equations is developed to calculate the properties of dissociated steam in the temperature and pressure ranges of 1250–3400 K and 0.01–10.00 MPa. These equations are based on detailed tables for dissociated steam compiled for a mixture of atoms of hydrogen and oxygen, hydroxyl OH, molecules of hydrogen and oxygen, and steam at a reference temperature of 0 K. Since the expansion of dissociated steam in a thermal engine results in its transformation into its common form, the equations for the parameters of dissociated or nondissociated steam uses the same reference temperature, i.e., the water triple point of 273.16 K. A system of equations for the calculation of dissociated-steam properties is derived with the generalized thermodynamic equation, which takes into account the change in the chemical potential and the composition of the mixture during steam dissociation, the Gibbs energy equation, differential thermodynamic equations, and equations for calculation the properties of nondissociated steam. To minimize the deviation of the steam properties calculated by the proposed equations from the table values, the considered temperature and pressure ranges have been divided into three regions. The deviation of the steam properties calculated by the proposed equations from the table values does not exceed 0.05–0.09%. The developed equations can be used in calculations of the processes of cooling of burners and combustion chambers during the combustion of hydrogen–oxygen mixtures, as well as cycles of heat engines that use high-temperature steam as a working fluid at temperatures over 1250 K.

Evaluation of wall heat loads in the region of detonation propagation of detonative propulsion combustion chambers

This paper deals with evaluation of wall heat loads that occur in a region of detonation propagation in a detonative propulsion combustion chamber. The heat loads were assessed for two types of detonation engine: pulse and rotating detonation. The results were compared to experimental data published in the literature. The procedure undertaken is based on an experimental investigation of heat transfer behind a single detonation wave that was conducted using a detonation tube. Fast response thermocouples were used to measure hot gas side wall temperature and this enabled the researchers to obtain values of heat flux behind a detonation wave propagating through gaseous, homogeneous, stationary mixtures of various compositions and initial pressures. Two mixtures were studied: H2-O2 and CH4-O2. In the case of the hydrogen-oxygen mixture a theoretical investigation was also conducted, where heat flux was obtained on the basis of inviscid CFD calculations supplied with an analytical model of Sichel and David. Numerical results include the expansion wave as well as the influence of wall temperature on the detonation chamber wall heat loads.

Role of ozone doping in the explosion limits of hydrogen-oxygen mixtures: Multiplicity and catalyticity

Effects of ozone doping on the Z-shaped explosion boundary of stoichiometric hydrogen-oxygen mixtures are computationally studied. Results show that with increasing ozone doping and within a small range of increment, the explosion limit transitions from the Z-shaped response with two turning points to responses exhibiting four, six, four, two and none turning points. By modifying the rate coefficients of the sensitive reactions within the ozone sub-mechanism, four reactions are identified to control the above highly non-monotonic behavior, and that the system transitions to the H2O3 chemistry as the limit becomes monotonic and overall more explosive. The practical implication is that there exists a critical range of ozone doping such that the mixture is more sensitive to unstable burning for lower levels of doping, with the associated multiple transition states, while the facilitating role of ozone catalyticity is fully realized with just slightly higher levels of doping, resulting in overall stronger explosive burning.

The propagation mechanism of detonation wave in a round tube filled with larger blockage ratio orifice plates

In this study, the detonation propagation mechanisms for the stoichiometric hydrogen-oxygen mixture are explored systematically in a circular tube with 6-m in length and an inner diameter of 90-mm. The continuous orifice plates with BR = 0.93 are adopted to investigate the characteristics of detonation diffraction, failure and initiation. High-speed piezoelectric pressure transducers are used to obtain the average velocity, and the smoked foil technique is adopted to record the detonation cellular patterns. The results indicate that three various propagation regimes can be observed, i.e., steady detonation, quasi-detonation and fast flame. In the smooth tube, only the steady detonation and fast flame modes are seen. When the initial pressure is greater than the critical value, the detonation can propagate at about the theoretical CJ velocity. Near the critical pressure, a sudden velocity drop is observed. Of note is that the single-headed spin and double-headed detonation cannot occur because of the limitation of the aspect ratio. In the tube filled with obstacles, the averaged wave velocity is decayed severely. Only the mechanisms of the quasi-detonation and fast flame can be seen. In the quasi-detonation mode, the critical value of d/λ is greater than 7.36, which is far larger than 1. Two different detonation ignition regimes produced by the shock reflection from the wall are observed, i.e., the initiation positions occur in the vicinity of the tube wall and the surface of the orifice plate.

Influence of Flame Suppressants on the Level of Nonequilibrium Radiation during Ignition of Hydrogen-Oxygen Mixtures behind Shock Waves

The nonequilibrium radiation occurring during ignition of a 10% stoichiometric hydrogen-oxygen mixture with flame suppressant additives diluted with argon behind shock waves was studied. Instead of the expected reduction in the super-equilibrium radiation of active radicals in the ignition zone, the addition of halogenated flame suppressants led to increased UV radiation around wavelengths of 220 and 411 nm characteristic of the HO2 radical and H2O2 and H2O molecules. Therefore, the hypothesis about the suppression mechanism due to quenching of the excited HO*2 radical is not confirmed, and the effect of flame-suppressing additives is due to the binding of H and O atoms.

On the Effect of Combustion Inhibitors on the Level of Non-Equilibrium Radiation during Ignition of Hydrogen Oxygen Mixtures behind a Shock Wave

On the Effect of Combustion Inhibitors on the Level of Non-Equilibrium Radiation during Ignition of Hydrogen Oxygen Mixtures behind a Shock Wave

Simulating the regimes of oblique detonation waves arising at detonation initiation by a small-diameter projectile

Initiating detonation in a reactive hydrogen-oxygen mixture by a spherical projectile of small diameter, flying with velocity exceeding the Chapman-Jouguet one, has been studied numerically. The mathematical model is based on the given kinetic scheme for the description of chemical reactions. At verification of the computational algorithm, the flow regimes and the detonation cell size were compared for numerical and experimental data. The agreement between the calculated and the experimental flow patterns and the quantitative correspondence of the modes of existence of inclined detonation waves have been obtained.