Stoichiometric Hydrogen-oxygen Research Articles

Measurement of Temperature and Concentration of OH Radicals in Combustion of Hydrogen and Ethanol by the Laser-Induced Fluorescence Technique

Diffusion combustion of ethanol and hydrogen and homogeneous combustion of hydrogen–oxygen mixtures are studied by the laser‐induced fluorescence technique in the linear regime and with signal saturation. Data on the flame temperature and OH concentration are obtained. The burning temperature of 3090 K for a stoichiometric O2–H2 mixture is in agreement with the known value. It is shown that the maximum concentrations of radicals in the hydrogen–air and stoichiometric hydrogen–oxygen flames are close to each other (4.4· 1016 cm-3).

Deflagrations of non-uniform mixtures: A first experimental approach

This paper is placed in a context of industrial safety. For that, we examine the more probable explosion which can be produced accidentally. In this work, we investigate the propagation behaviour of blast waves from deflagration in terms of concentration of explosive mixtures diluted into air. The dilution represents the non uniformity of the gaseous cloud versus time. Experimentally, the non uniform gaseous cloud is formed by the dispersion of a stoichiometric hydrogen-oxygen mixture initially confined in a hemispherical volume. The evolution of the blast wave is given by the pressure wave which is examined as a function of the time delay of dispersion (time between rupture of the confinement and the ignition), the position of the ignition source, and the volume of the confinement. The modelling of the dispersion of the gaseous cloud allows to control the flammability limit and correlate the blast wave propagation and the non uniformity gaseous cloud.

Chapman-Jouguet Oblique Detonation Structure Around Hypersonic Projectiles

How to generate a steady-state detonation around a hypersonic projectile in stoichiometric hydrogen-oxygen premixed gases is studied. The speed of the hypersonic projectiles was beyond the Chapman ‐Jouguet(C‐J) detonation speed. The e owe eld around the projectile was visualized by using a gate intensie ed charge-coupled device camera(single-frame schlieren picturesand OHradical self-emissionimages ). Threeparameters are varied:1 ) the projectile e ight length from diaphragm rupture location, 2 )the initial pressure of mixture below/above the critical pressureforsteady detonation initiation around a hypersonicprojectile, and3 )theprojectilespeed.Atthepressure condition below the criteria, the detonation structure is composed of three different shock and detonation waves, which appear just after a diaphragm rupture and evolve in time: an overdriven bow detonation wave, a strong detonation wave, and a diffracted shock wave. Their propagation after diaphragm rupture is investigated, and it is found that the C ‐J detonation wave moved away from the projectile and only a reactive bow shock wave remained around projectile far away from the diaphragm. At the pressure condition above the criteria, a steady oblique detonation wave was generated around the projectile as soon as the projectile broke the diaphragm. In this steady-state detonation-wave case, with respect to the e ow Mach number behind the wave front, the whole detonation wavewas divided into fourparts: 1 )strong overdriven detonation wave, 2 ) weak overdriven detonation wave, 3) quasi-C‐J detonation wave, and 4 ) C‐J detonation wave. It has been found that a rarefaction wave is generated at the projectile shoulder and that curvature of the wave has a signie cant effect on the structure of the detonation wave.

Experimental study of interaction between oblique detonation wave and rarefaction wave around a hypersonic free projectile

Hypersonic projectiles whose speed was beyond the Chapman-Jouguet (C-J) detonation speed, were fired into stoichiometric hydrogen-oxygen premixed gases. The flowfield around the projectile was visualized using a gated CCD camera. A steady-state detonation wave was generated around the projectile. With respect to the flow Mach number behind the wave front, the whole detonation-wave was partitioned into four parts; (i) strong overdriven detonation wave, (ii) weak overdriven detonation wave, (iii) quasi C-J detonation wave, and (iv) C-J detonation wave. It has been found that a rarefaction wave generated at the projectile shoulder has a significant effect on the structure of the detonation wave.

Comparison of critical conditions for DDT in regular and irregular cellular detonation systems

Abstract. The results of an experimental study of DDT in mixtures with regular and irregular detonation cellular structures are presented. Experiments were carried out in a tube 174 mm i. d. with obstacles (blockage ratios were 0.1, 0.3, and 0.6). Mixtures used were hydrogen–air and stoichiometric hydrogen–oxygen diluted with $\rm N_2$ , Ar, and He. The critical conditions for DDT are shown to depend on the regularity of the cellular structure of test mixtures. The critical values of the cell sizes in Ar- and He-diluted mixtures are shown to be significantly smaller than those in $\rm N_2$ -diluted mixtures. This means that systems with a highly regular detonation cellular structure have far less capacity for undergoing DDT compared to irregular ones with the same values of detonation cell sizes.

Review of investigations under way on the large-scale TsNIIMASH ballistic facility

The large-scale TsNIIMASH ballistic facility was built in 1992 through modernization of the large shock tunnel. Having 0.5 m caliber, the facility is 200 m long. Each experiment on the facility envisages an explosion of stoichiometric hydrogen-oxygen mixture, up to 300 cub. m by volume. In the air-evacuated ballistic channel 60 m long, the expanding explosion products of the detonating gas mixture boost gyrostabilized steel plates 0.5m in diam which travel along the channel on a magnetic suspension without a mechanical contact with the walls. The case is unique in combining the ballistic facility geometric dimensions with the plate high-precise motion. Results of experiments on graphite crystalline conversion into diamond are given. Investigations to use the shock tunnel for hypervelocity launch of compact projectiles are discussed.

Laminar flame structure in a low-pressure premixed H2/O2/Ar mixture

The chemical structure of a stoichiometric hydrogen-oxygen flame stabilized on a flat burner at a pressure of 47 torr is studied by molecular-beam mass spectrometry and computer simulation. Concentration profiles are measured for the stable flame components H2, O2, and H2O, as well as for the atoms and radicals H, O, and OH. The concentration profiles calculated using two different kinetic mechanisms are in acceptable agreement with experimental data. It is also shown that for sampling probes with thin walls (<-0.1 mm) at their tips, there is no need to perform the calculations using a specified temperature profile measured by thermocouples located near the aperture of the sampler, as recommended by a number of authors.

極超音速飛行体近傍に発生する定常斜めデトネーション波の構造

Hypersonic projectiles, whose speed was beyond the Chapman-Jouguet (C-J) detonation speed, were fired into stoichiometric hydrogen-oxygen premixed gases. The flowfield around the projectile was visualized using a gated CCD camera. Around the projectile, a steady-state detonation wave was generated. With respect to the flow Mach number behind the wave front, the whole detonation-wave was partitioned into four parts; (i) strong overdriven detonation wave, (ii) weak overdriven detonation wave, (iii) quasi C-J detonation wave, and (iv) C-J detonation wave, It has been found that a rarefaction wave delivered from the projectile shoulder has a significant effect on the structure of the detonation wave.

Experimental and numerical studies of the pressure field generated by DDT events

Results of experimental and numerical study of maximum pressures and impulses developed in closed vessel as a function of DDT location are presented. Experiments were carried out in the detonation tube with stoichiometric hydrogen-oxygen mixture diluted with nitrogen. The effect of two variables was investigated: distance between tube closed end and DDT origin, and the ratio of burned and unburned mixture volume prior to the DDT moment. It was found that impulse value is proportional to the total length of tube and does not depend significantly on DDT location. Results of numerical simulation are in good agreement with experimental data.

Reignition of detonations by reflected shocks

Numerical simulations are used to study the diffraction, decay, and reignition that occurs when a detonation propagates past an increase in cross-sectional area in a rectangular tube. The computations solve the time-dependent two-dimensional equations describing a reactive flow in an argon-diluted stoichiometric hydrogen-oxygen mixture at atmospheric pressure. Previous studies have shown that soon after transmission to a larger area, the reaction front decouples from the leading shock and forms a decaying blast wave (“bubble”) in the larger tube. Then, depending on the initial conditions, the detonation either continues to decay or is reignited as the bubble reflects off confining surfaces. For a strongly overdriven initiating detonation, reignition occurs through an interaction between the bubble and the original contact surface. For a more weakly driven system, reignition can occur in two ways: either in the slip line and Mach stem of the Mach reflection formed when the bubble reflects off the bottom surface of the tube, or by multiple shock interactions that occur when the reflected bubble overtakes the initial detonation front. The computations show the evolution and development of the cellular structure of the steady detonation front.

Initiation of upstream-directed detonation induced by the venting of gaseous explosion

An experimental study to demonstrate the possibility of nontraditional trends of vented explosion hasbeen performed. The experiments have been carried out using a cylindrical horizontally placed 4-L explosion chamber. One of the end flanges of the explosion chamber was equipped with a centrally located opening. Initially, it was covered by a hermetically mounted diaphragm. Various configurations of short vent pipes were available for attachment to the opening. The explosion was initiated by an electrical spark at the closed end flange of the explosion chamber. Two mixtures under investigation were stoichiometric hydrogen-oxygen and acetone-oxygen mixtures diluted with nitrogen at initial pressures of 3 and 2 bar, respectively. Pressure and ionization measurements, streak camera photographs, and smoked plate records indicated that, under certain conditions, a detonation wave propagates upstream from the vent opening into the explosion vessel. The presence of at least a short duct is a necessary condition for the upstream-directed detonation event. The interpretation of the experimental results is based on the consideration of the intense mixing of the hot combustion products with the unburned gas in the vent duct. It was shown that a gradient of ignition delay of fresh mixture is set along the initial run of the vent pipe. As a result, upstream-directed detonation is initiated as a result of the shock wave amplification by coherent energy release (SWACER) mechanism.

Numerical simulation of the initiation of detonation in a gaseous layer of a stoichiometric hydrogen-oxygen mixture

Numerical simulation of the initiation of detonation in a gaseous layer of a stoichiometric hydrogen-oxygen mixture

Detonation cell widths in hydrogenoxygendiluent mixtures

Detonation cell widths have been measured for stoichiometric hydrogenoxygendiluent mixtures in a 15-cm diameter, 7.5-m-long, steel pipe with helium, carbon dioxide, steam, and argon as diluents. The range of investigation included initial temperatures from 20° to 100°C, initial pressures from 200 to 160 kPa, and hydrogen concentrations up to 60% by volume. Experiments conducted over a range of hydrogen concentrations indicated that detonation was possible down to flammability limits for certain mixtures. Over the range investigated, the initial temperature appeared to have no significant effect on the cell width. Empirical correlation to predict the cell width is presented.

Internal combustion steam turbine cycle with stoichiometric H2-O2 mixture.

A novel internal combustion steam turbine cycle suitable for an underwater power plant and a peak-cut electric power plant is proposed on various power levels. The feature of the cycle is the combustion of a stoichiometric hydrogen-oxygen mixture in the working fluid (water/steam), which allows higher initial steam temperature than that of the conventional steam turbine cycle. The combustion product which works in the turbine is extracted from the cycle in the liquid phase. This cycle has higher thermal efficiency than that in the case of external combustion. Thermodynamic performances of simple, regenerative and reheat-regenerative steam turbine cycle are compared. Effects of initial steam pressure, initial steam temperature, hydrogen excess ratio and power level on the thermal efficiency are discussed. The thermal efficiency of a 100MW reheat-regenerative cycle is 52 % on the basis of lower heating value.

Kinetics of OH recombination in the post combustion zone of an atmospheric pressure hydrogen-oxygen flame

The OH radical concentration and rotational temperature were measured in a stoichiometric hydrogen-oxygen flame under atmospheric pressure using infrared emission spectra. A highly non-equilibrium OH concentration was observed in the post flame gases and the OH decay profile was consistent with a second order dependence on the OH concentration. The associated OH decay rate constant was found to be substantially lower than the predicted values from some flame models. It appears that diffusional transport may be partly responsible for these discrepancies.

The hydrogen–oxygen reaction on lanthanum oxide and europium oxide

The stoichiometric hydrogen–oxygen reaction has been studied in a static system over lanthanum oxide and europium oxide at an initial hydrogen pressure of approximately 200 N m−2 from 480 to 775 K, and at different initial hydrogen pressures from 70 to 750 N m−2 over the same temperature range. Nonstoichiometric reactions were conducted at five different temperatures over lanthanum oxide and four different temperatures over europium oxide, at hydrogen–oxygen ratios in the range 0.1 to 10. After detailed kinetic analysis it is shown that the results fit an equation of the form:[Formula: see text]where k is a proportionality constant, [Formula: see text] and [Formula: see text] are the adsorption coefficients for hydrogen and oxygen, respectively, PT is the total pressure of hydrogen plus oxygen, [Formula: see text] and [Formula: see text] are the partial pressures of hydrogen and oxygen, respectively, and x equals 2 for lanthanum oxide and 1 for europium oxide. The mechanism involves the competitive adsorption of molecular hydrogen and oxygen, with the rate-determining step involving the interaction between adsorbed hydrogen molecules and adsorbed oxygen or hydrogen peroxide (double hydroxide groups).

Parameters of the equilibrium gas flow in a detonation equipment

The detonation method of depositing coatings is widely used. However, detonation equipment has been designed from empirical data without a detailed understanding of the process dynamics. Gas flow calculations made using the simplified assumption that the detonation products are an inert gas with a constant adiabatic parameter have resulted in theoretical product temperatures 24% higher than actual. This results in a substantial overestimate of the metal particle temperatures. Here, the detonation products are considered as a reacting medium having an equilibrium chemical composition at each point, and the parameters of the gas flow are calculated for a detonation wave propagating in a tube, while a comparison is made with experimental data for a stoichiometric hydrogen-oxygen mixture. Calculations were made for a C/sub 2/H/sub 2/+2.5 O/sub 2/ mixture and for a 2H/sub 2/+O/sub 2/ mixture, and were found to be in agreement with the experimental data. An algorithm has been devised that enables one to solve the problem for a series of detonating gas mixtures that are promising for detonation deposition.

Coal gasification in steam at very high temperatures

Gasification of pulverized coal in steam has been investigated at heating rates of 10 6 K/s and peak gas temperatures of 3300 K. These severe conditions were achieved in a batch process reactor by igniting a stoichiometric hydrogen-oxygen mixture in which the coal had been blown into turbulent suspension. Subsequent gas-phase combustion was followed by heat conduction from the nascent steam to the coal. Variable solids/gas mass ratios were investigated. Stabilized carbon gasification yields as high as 80% were achieved.

The hydrogen-oxygen reaction on lanthanide oxides: VII. The hydrogen-oxygen reaction on samarium oxide

The stoichiometric hydrogen-oxygen reaction has been studied over samarium oxide at an approximately constant initial hydrogen pressure of 220 N m −1 over the temperature range 323 to 558 K and at varying initial hydrogen pressures at six different temperatures. The nonstoichiometric reaction has been studied at hydrogen-oxygen ratios from 0.14 to 10.2, at initial hydrogen pressures up to about 1 × 10 3 N m −2, and at 423, 500, 589, and 650 K. After detailed kinetic analysis it appears that the results best fit an equation of the form: −dP T dt = kb H 2 2P H 2 2b O 2 P O 2 (1 + b H 2 P H 2 + b O 2 P O 2 ) 3 , where k is a proportionality constant, b H 2 and b O 2 are the adsorption coefficients for hydrogen and oxygen, respectively, p t is the total pressure of hydrogen plus oxygen, and P H 2 and P O 2 are the partial pressures for hydrogen and oxygen, respectively. The most likely mechanism is one involving the competitive adsorption of molecular hydrogen and oxygen, with the ratedetermining step involving the interaction between H 2O 2(ads) and H 2(ads).

The hydrogen-oxygen reaction on lanthanide oxides: VI. The stoichiometric hydrogen-oxygen reaction on dysprosium oxide pretreated with hydrogen or oxygen

The stoichiometric hydrogen-oxygen reaction on dysprosium oxide pretreated with hydrogen or oxygen has been studied at 398, 418, and 473 K at an approximate initial hydrogen pressure of 200 N m −2, together with some lower pressures. The contact time and pressure of the pretreating gas has been varied. The results support the general mechanism already proposed, with a rate-determining step involving the interaction between H 2O 2(ads) and H 2(ads). The change in activity and effects of pretreatment with temperature have been related to the change in oxygen adsorption and the strength of the hydroxyl bond.