Hydrogen-oxygen Mixtures Research Articles

Influence of quantum effects on the initiation of ignition and detonation

A theoretical analysis that allows one to quantify the quantum corrections to the rate constants of endothermic reactions associated with an increase in the high-energy tails of the momentum distribution functions at high pressures due to a manifestation of the uncertainty principle for the energy of the colliding particles at a high collision frequency is performed. The initiation of ignition of hydrogen-oxygen mixtures is investigated and special series of experiments on the initiation of detonation waves of condensation in carbon suboxide and acetylene at elevated pressures near the low-temperature limits have been carried out. The experimentally observed deviations in the Arrhenius dependences of the induction periods of the initiation of hydrogen ignition and detonation waves of condensation are shown to be well described by the proposed quantum corrections.

Effect of oxygen addition on fretting fatigue strength in hydrogen of JIS SUS304 stainless steel

Fretting fatigue test of SUS304 austenitic stainless steel was performed in air, in hydrogen gas, and in oxygen–hydrogen mixture. The fretting fatigue strength is more significantly reduced in hydrogen as compared to air. An increase in the fretting fatigue strength was found in the mixture. The mechanisms were investigated focusing on crack initiation. As the result, the crack initiation limit was significantly lower in hydrogen than in air, and increased in the mixture. The tangential force coefficient in the mixture is similar to that in air. The morphology of the fretting damage in the mixture was similar to that in air. These results indicated that the adhesion between contacting surfaces was prevented by addition of oxygen.

Microstructure evolution during silicon oxidation at room temperature under composite ion beam irradiation

In this work, we studied the silicon microstructure evolution during its oxidation under composite beam ion irradiation at room temperature. It was found that when the composite ion beam was formed by hydrogen and dry oxygen mixture at low doses (∼1018cm−2), a porous silicon layer was formed. During irradiation, the pore size gradually reduced and at a dose of ∼1020cm−2 pores disappear completely, and an uniform layer of silicon oxide was formed. If residual gases and hydrogen are used to generate a composite ion beam, the formation of porous silicon is not found. The final thickness of irradiation-induced silicon oxide corresponded to the projected range of protons at a given energy in both cases.

Improvement of a Propulsion Equipment with a Supersonic Nozzle for Single Pulse Detonation

A pulse detonation engine (PDE) is one of candidates of aerospace engines for supersonic cruse. In the paper, a supersonic nozzle ejector is designed to increase thrust of single pulse detonation for methane-oxygen and hydrogen-oxygen mixtures. The design method is based on the conventional characteristic method and inlet condition is averaged value of detonations of methane-oxygen and hydrogen-oxygen mixtures. Comparison of thrusts with a design nozzle and no nozzle (straight- type) is conducted to ensure the designed nozzle performance. Furthermore, the flow velocity, temperature and velocity of the designed nozzle are calculated to ensure its appropriateness with the commercial software ANSYS CFX. Consequently, we succeed in increasing the thrusts of the single pulse detonation with the nozzle, which are 1.4 and 2.0 times as large as ones of straight- type for methane-oxygen and hydrogen-oxygen mixtures respectively.

Specific features of the kinetics of H2-O2-O2(a 1Δ g ) mixtures: I. formation and quenching of electronically and vibrationally excited (A′) molecules in H2-O2-O2(A 1Δ g ) mixtures at a temperature of 300 K

Available data on the kinetic processes in H2-O2-O2(a 1Δ g ) mixtures are analyzed theoretically, and the ranges in which the rate constants of these processes can vary are determined. The processes of energy transformation in an O2(a 1Δ g )-H2-H-HO2 system in the approximations of the fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state are considered. The experiments on the quenching of singlet delta oxygen (SDO) molecules O2(a 1Δ g ) excited in a microwave discharge at a temperature of 300 K and pressure of 6 Torr in a lean hydrogen-oxygen mixture are simulated (by a lean fuel mixture is meant a mixture in which the ratio of the fuel to the oxidizer mass fraction is less than the stoichiometric ratio, which is 2: 1 for a hydrogen-oxygen mixture). It is shown that, over the experimental observation times, the SDO quenching frequency depends on the concentration of molecular hydrogen, the residual odd oxygen fraction in the gas flow, and the ratio between the rate constants of kinetic processes involving HO2 and HO2* radicals. Simulations of the microwave discharge and the transport of excited oxygen along the drift tube make it possible to determine the residual odd oxygen concentration in the gas flow. Recommendations on the choice of the rate constants for the O2(a 1Δ g ) + HO2)A″, v3″ = 0) ↔ O2 + HO2*(A′, v3′ = 1), HO2*(A′v3′ ≤ 1) + O2(a 1Δ g ) → HO2*(A′,v3′ ≥ 6) + O2, and HO2*(A′,v3′ ≤ 1) + O2(a 1Δ g ) → H + O2 + O2 processes are given. It is shown that, in the case of slow quenching in a H2-O2-O2(a 1Δ g ) mixture at a low temperature, the intensity of hydrogen oxidation is enhanced due to the reaction + HO2*(A′,v3′ ≤ 1) + O2(1Δ) → H + O2 + O2.

Influence of an acoustic resonator on flame propagation regimes in spark initiated H2 combustion in a cylindrical reactor near the lower detonation limit

It is experimentally shown that an acoustic resonator like Helmholtz's resonator connected with a cylindrical reactor can provide a significant flame acceleration under spark initiation in lean (15%) hydrogen–oxygen mixtures close to the lower detonation limit.

Specific features of the kinetics of H2-O2-O2(a 1Δ g ) mixtures: II. Quenching of O2(a 1Δ g ) excited in a discharge behind the shock front at temperatures of 500–1020 K

Results of experiments on the quenching of singlet delta oxygen (SDO) O2(a 1Δ g ) in lean hydrogen-oxygen mixtures at temperatures of 500–1020 K and pressures of 26–90 Torr behind the shock front are analyzed theoretically. The processes affecting SDO quenching are simulated taking into account the temporal characteristics of the experiment and various mechanisms of energy transformation in an O2(a 1Δ g )-H2-H-HO2 system. It is demonstrated that the approximations of both fast and slow (in comparison with the vibrational relaxation time of the HO2 radical) quenching of the electronically excited state of the radical are in good agreement with the experimental data on the effective rate constant of SDO deexcitation at temperatures of up to 700 K. It is shown that the available data on the kinetics of reactions involving SDO in H2-O2-O2(a 1Δ g ) mixtures overestimate the SDO quenching rate in comparison with the experimental results obtained at temperatures above 850 K. The decrease in the rate constant of the reaction H + O2(a 1Δ g )→ products by one order of magnitude makes it possible to match the simulation results to the experimental data. The existence of the processes restoring SDO in the presence of atomic hydrogen that are not considered in the current models of the H2-O2-O2(a 1Δ g ) kinetics is supposed.

Modeling and simulation of hydrogen combustion in engines

Hydrogen being an ecological fuel is very attractive now for engines designers. It is already actively used in rocket engines. There exist plans to use hydrogen in pulse detonation engines. However, peculiarities of hydrogen combustion kinetics, the presence of zones of inverse dependence of reaction rate on pressure, etc. prevent from wide use of hydrogen engines. Computer aided design of new effective and clean hydrogen engines needs mathematical tools for supercomputer modeling of hydrogen–oxygen components mixing and combustion gas dynamics.The paper presents the results of developing verification and validation of mathematical model and numerical tool making it possible to simulate unsteady processes of ignition and combustion in engines of different types and to study its peculiarities. First, verification and validation of the chemical kinetic models for hydrogen oxidation were carried out through investigations on the ignition delay time on pressure, temperature, and equivalence ratio for hydrogen-oxygen mixtures. Then, the developed solver was used to model pre-mixed and non-premixed combustion and detonation related phenomena including deflagration to detonation transition.

Specific features of the oxidation of hydrogen and methane near the third ignition limit in quartz and metal reactors

Heat release during the sublimit reaction, induction period, and explosion in stoichiometric hydrogen-oxygen and methane-oxygen mixtures near the third ignition limit is measured. It is shown that, for the hydrogen-oxygen reaction, the third limit pressure, sublimit reaction rate, and reaction rate during the induction period depend not only on the state and nature of the reactor wall surface, but also on the sequence of introduction of the reactants. It was found that heat released during the induction period is close to that released during the explosion. Changing the order of introduction of the explosive mixture components into the reactor leads to a drastic change in the dark reaction rate. It was found that the main reaction (90%) in detonating gas below the ignition limit and during the induction period occurs with the participation of the reactor wall surface. The main product of the heterogeneous reaction is hydrogen peroxide, which accumulates and, together with the initial mixture, creates conditions for ignition. An analysis of the results and literature data suggests that the ignition of detonating gas is a degenerate process (in N.N. Semenov’s terminology). For the methane-oxygen reaction, the third limit pressure, as well as the rates of the sublimit and induction-period reactions, depend on the state and nature of the reactor wall surface, while being independent of the order of introduction of the reactants.

The influence of swirling of a flow with axial countercurrent on the process of burning of hydrogenoxygen mix in the stream of water steam

The paper presents comparative results of the numerical research of the combustion of stoichiometric hydrogen-oxygen mixture in the medium of water steam using various ways of mixing fuel components in the flame tube of a tubular combustion chamber.The geometry of the mixing chamber that makes it possible to achieve the highest values of combustion efficiency and temperature uniformity at the exit of the combustion chamber is defined.

Умови виникнення сферичної детонації в воднево-кисневій суміші

Initial detonation conditions required for fast chemical reactions to take place at the front of a spherical explosive wave have been determined. A simple relation describing the critical detonation temperature for various pressures in the hydrogen-oxygen mixture was obtained. Using the known formulas for a shock transition, the critical temperature was coupled with the initial conditions in a static environment, such as the pressure, temperature, and hydrogen content in the mixture.

Kinetic mechanism of combustion of hydrogen–oxygen mixtures

Based on the analysis of the databases published in the scientific literature and concerned with the reaction rate constants in the H2/O2 system, a new kinetic mechanism is suggested for describing the processes of ignition, combustion, and detonation in hydrogen–oxygen gaseous mixtures. Attention is mainly focused on consideration of a low-temperature region (T < 1000 K) where a chain of reactions of the formation and subsequent decomposition of hydrogen peroxide plays the major role in the system ignition. The proposed mechanism has been tested by comparing computational results with available data on measurement of the ignition-delay time in shock tubes.

About works on research of stationary and non-stationary waves of burning in the hydrogen-oxygen mix on the Novosibirsk Free Electron Laser

This work presents schemes, techniques of experiments and the first results on registration of burning front of hydrogen-oxygen mixture with the use of terahertz radiation. The problems of choice of absorption lines, on which registration is carried out, are discussed. The investigation of distribution of absorption at wavelength of 166.81 microns over the cross-section of stationary hydrogen-oxygen flame above the burner is carried out. In the dynamic experiment, the diagrams of flame propagating along the pipe obtained with both pyrodetector and Shottky detectors were compared.

Study of collisional deactivation of O2(b 1Σ g + ) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

Collisional deactivation of O2(b 1Σ g + ) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H2/O2 mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b 1Σ g + state of O2 molecules deactivation rates are measured in a 4.3 vol % H2 mixture at the number density of 2 amg in the temperature range 291–850 K. The physical deactivation is shown to dominate in the collisions of H2 with O2(b 1Σ g + ) and O2(a 1Δ g ) up to temperatures of 780–790 K at time delays up to 10 μs after the excitation pulse. The parameters of the obtained temperature dependence of the (b 1Σ g + state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200–400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H2O molecules which appear as the mixture, as the result of the dark gross reaction with O2 molecules in the ground state, O2 + 2H2 → 2H2O. The measurements show that this reaction results in complete transformation of H2 into H2O at temperatures of 790–810 K.

Hydrogen-air mixing-layer ignition at temperatures below crossover

This paper addresses ignition histories of diffusion flames in unstrained hydrogen-air mixing layers for initial conditions of temperature and pressure that place the system below the crossover temperature associated with the second explosion limit of hydrogen–oxygen mixtures. It is seen that a two-step reduced chemical-kinetic mechanism involving as main species H2, O2, H2O, and H2O2, derived previously from a detailed mechanism by assuming all radicals to follow a steady-state approximation, suffices to describe accurately the ignition process. The strong temperature sensitivity of the corresponding overall rates enables activation-energy asymptotics to be employed for the analysis, following the ideas developed for mixing-layer ignition by Liñán and Crespo in 1976 on the basis of one-step Arrhenius model chemistry. When the initial temperatures of both reactants differ by a relative amount that is of the order of or smaller than the ratio of this temperature to the effective activation temperature, the chemical reaction is seen to occur at a significant rate all across the mixing layer. The ignition time is then determined as a thermal runaway in a parabolic problem describing the evolution of the temperature increment and the H2O2 concentration, with local accumulation, chemical reaction, and transverse convection and diffusion, all being important. By way of contrast, when the air side is sufficiently hotter than the hydrogen side, as often occurs in applications, ignition occurs in a thin layer close to the air-side boundary, enabling a simplified description to be developed in which the ignition time is determined by analyzing the existence of solutions to a two-point boundary-value problem involving quasi-steady diffusion–reaction ordinary differential equations.

Effect of wall conditions on DDT in hydrogen–oxygen mixtures

Detonation in ducts is usually studied assuming adiabatic walls because of the high kinetic energy due to the incoming flow being supersonic. In the present work, numerical simulations of deflagration-to-detonation transition (DDT) using a detailed chemical reaction model are performed under adiabatic and isothermal boundary conditions in a tube with no-slip walls. The results show a local explosion driving DDT, which occurs near the tube wall in the case of an adiabatic wall, but close to the flame front in the case of an isothermal wall. Furthermore, to examine the effects of a turbulent boundary layer, a simulation using the Baldwin–Lomax turbulence model is carried out. In the case of the isothermal wall, there is again a local explosion near the tube wall, which leads to detonation. In summary, the present study confirms that the boundary conditions affect the transition to detonation and that the boundary layer is a key component of DDT.

An analysis of the explosion limits of hydrogen-oxygen mixtures

In this study, the essential factors governing the Z-shaped explosion limits of hydrogen-oxygen mixtures are studied using eigenvalue analysis. In particular, it is demonstrated that the wall destruction of H and HO2 is essential for the occurrence of the first and third limits, while that of O, OH, and H2O2 play secondary, quantitative roles for such limits. By performing quasi-steady-state analysis, an approximate, cubic equation for the explosion limits is obtained, from which explicit expressions governing the various explosion limits including the state of the loss of non-monotonicity are derived and discussed.

Detonation Transition Around Cylindrical Reflector of Pulse Detonation Engine Initiator

To achieve reliable transmission of detonation waves to a pulse detonation engine combustor (detonation chamber), the authors propose a pulse detonation engine initiator that uses a cylindrical reflector downstream of a predetonator exit. The detonation wave propagates around the reflector to change the wave shape in three transition stages: from a planar detonation wave in the predetonator to an expanding cylindrical detonation wave, from the cylindrical wave to a planar toroidal detonation wave, and from the toroidal wave to a planar detonation wave in the detonation chamber. The cylindrical wave propagates along a cylindrical path between the reflector and front wall of the detonation chamber, and the toroidal wave propagates along an annular path between the reflector and sidewall of the detonation chamber. The purpose of this study was to examine the influence of the gap width of the annular path on the transition stages from cylindrical to toroidal and from toroidal to planar. A series of experiments that filled the entire test section with the driver gas mixture (stoichiometric hydrogen–oxygen mixture) showed that the expanding cylindrical detonation wave was sufficiently strong to survive the rarefaction waves from the corners of the reflector at all of the investigated annular gap widths (5, 10, 15, and 20 mm) and was transmitted to the planar toroidal wave successfully in all cases. When the strength of the cylindrical detonation wave was under a supercritical condition for diffraction at the reflector corner, the necessary filling distance for the driver gas was predicted well by the Whitham theory. A second series of experiments showed the influence of the annular gap width on the detonation transition from the planar toroidal detonation wave to the planar detonation wave. Two different types of detonation transitions termed “continuous transition” and “temporal quenching” were observed. The threshold value of for continuous transition is approximately four.

Modeling of detonation wave propagation through a cloud of particles in a two-velocity two-temperature formulation

Processes of suppression and quenching of detonation in a hydrogen-oxygen mixture by means of inserting inert particles into the flow field are numerically studied within the framework of a two-velocity two-temperature model of mechanics of heterogeneous media. The wave pattern in an inert cloud of particles, induced under the action of shock and detonation waves, is determined. The validity of using a one-velocity model for the description of detonation suppression and quenching by clouds of coarse particles is demonstrated. The effect of the volume fraction and diameter of moving particles on the detonation wave velocity is found. The limiting transition from a frozen detonation flow, which is formed in the case of large particle diameters, to an equilibrium flow formed in the case of small particle diameters is studied. Geometric limits of detonation are determined, and a comparison with similar results predicted by the one-velocity model is performed.

Laminar Flame Speed and Ignition Delay Time Data for the Kinetic Modeling of Hydrogen and Syngas Fuel Blends

Laminar flame speeds and ignition delay times have been measured for hydrogen and various compositions of H2/CO (syngas) at elevated pressures and elevated temperatures. Two constant-volume cylindrical vessels were used to visualize the spherical growth of the flame through the use of a schlieren optical setup to measure the laminar flame speed of the mixture. Hydrogen experiments were performed at initial pressures up to 10 atm and initial temperatures up to 443 K. A syngas composition of 50/50 by volume was chosen to demonstrate the effect of carbon monoxide on H2-O2 chemical kinetics at standard temperature and pressures up to 10 atm. All atmospheric mixtures were diluted with standard air, while all elevated-pressure experiments were diluted with a He:O2 ratio of 7:1 to minimize instabilities. The laminar flame speed measurements of hydrogen and syngas are compared to available literature data over a wide range of equivalence ratios, where good agreement can be seen with several data sets. Additionally, an improved chemical kinetics model is shown for all conditions within the current study. The model and the data presented herein agree well, which demonstrates the continual, improved accuracy of the chemical kinetics model. A high-pressure shock tube was used to measure ignition delay times for several baseline compositions of syngas at three pressures across a wide range of temperatures. The compositions of syngas (H2/CO) by volume presented in this study included 80/20, 50/50, 40/60, 20/80, and 10/90, all of which are compared to previously published ignition delay times from a hydrogen-oxygen mixture to demonstrate the effect of carbon monoxide addition. Generally, an increase in carbon monoxide increases the ignition delay time, but there does seem to be a pressure dependency. At low temperatures and pressures higher than about 12 atm, the ignition delay times appear to be indistinguishable with an increase in carbon monoxide. However, at high temperatures the relative composition of H2 and CO has a strong influence on ignition delay times. Model agreement is good across the range of the study, particularly at the elevated pressures.