Ignition Of Hydrogen-oxygen Mixtures Research Articles

Analysis of the Effect of Mathematical Models of Chemical Transformations on the Ignition of Hydrogen-Oxygen Mixtures

Analysis of the Effect of Mathematical Models of Chemical Transformations on the Ignition of Hydrogen-Oxygen Mixtures

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

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.

Metal Hydride Technology of Hydrogen Activation

The effect of hydrogen activation by metal hydrides is considered. It is established that activated hydrogen exists in different forms: in the form of excited H2 molecules, excited hydrogen atoms and positive ions. To study the activation of hydrogen, various methods of mass spectrometry were used. The reasons for the formation of activated hydrogen in interaction with hydride-forming materials are discussed. For hydride-forming materials, one of the possible factors leading to the activation of hydrogen followed by desorption into the gas phase is isobaric hysteresis. Hysteresis in metal-hydrogen systems occurs when the pressure of hydride formation is higher than the pressure of its decomposition. The use of the phenomenon of metal hydride activation can improve the energy characteristics of virtually all types of energy-converting devices using hydrogen as a working fluid. This effect can be used in reactions of heterogeneous catalysis, in particular, in the ignition of hydrogen-oxygen mixtures, in devices using hydrogen as a working medium, as an environmentally friendly energy carrier in engines or in power and electro-physical facilities. It is shown both experimentally and theoretically that the use of atoms and excited hydrogen molecules as an activation ionic additive to traditional fuels leads not only to saving the latter but also to reducing the content of toxic products in the exhaust gases. A small (0.5 %) admixture of atomic hydrogen in the combustion zone is just as effective as the addition of 10 – 12 % of ordinary molecular hydrogen. The use of excitation energy for nonequilibrium states of hydrogen appears to be one of the most promising ways to solve the problem of increasing the efficiency of energy equipment and improving its environmental characteristics.

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.

The effect of metal hydride activation and use of energy nonequilibrium hydrogen

The means of production and fields of application of energy nonequilibrium hydrogen states in processes of energy conversion are briefly reviewed. The effect of metal hydride hydrogen activation is considered, which can be applied to reactions of heterogeneous catalysis, ignition of hydrogen-oxygen mixtures, devices using hydrogen as a working medium with energy supplied from an external source, as well as to electrophysical units. The probability of the thermodynamically nonequilibrium concentration of excited particles near the surface of hydride-forming materials is quantitatively estimated.

Numerical study of two-dimensional effects associated with laser-induced ignition in hydrogen-oxygen mixtures

Numerical simulation of reacting flows (combustion processes, chemical vapour deposition, hypersonics etc.) is a demanding task due to the strong interaction of flow field, chemistry and molecular transport. Mathematical modelling is performed by solving the set of Navier-Stokes equations (i.e., conservation of mass, energy, momentum, and species mass) which involves an enormous numerical and computational effort due to the large number of equations, the strong coupling and the non-linearity of the partial differential equation system. A numerical method for the solution of the stiff partial differential equation systems is described allowing the globally implicit simulation of unsteady chemically reacting laminar flows in up to two space dimensions. Spatial discretization on structured grids that are adapted statically leads to large differential-algebraic equation systems which are solved numerically by implicit extrapolation or BDF (backward differentiation formula) methods. Due to the large dimension of the differential-algebraic equation system, the sparse structure of the Jacobian (which is needed for the implicit solvers) has to be used for the evaluation of the Jacobian as well as for the solution of the linear equation systems. Results are presented for the one- and two-dimensional simulation of laser-induced ignition of hydrogen-oxygen mixtures in a finite cylinder. It is shown that the reduction of the problem to one spatial dimension is not appropriate for a description of the physical phenomenon considered. Additionally, results of a successful numerical simulation of the ignition by a physically realistic tailled shape of the igniting laser beam are presented. This is a truly two-dimensional physical phenomenon, and cannot be described by a one-dimensional approach.

Ignition of hydrogen-oxygen mixtures in reflected shock waves

The ignition anomaly that has been known to occur behind reflected shock waves in oxy-hydrogen systems below the temperature corresponding to the extrapolated value of the second explosion limit was studied. During the study particular attention was given to the effects of exothermic energy release due to chemical reaction. Average translational temperatures were determined by measuring both pressure and density in a thermoneutral gas system of different specific heat ratios, γ's. In this case the experiments did not show the gradual increase of temperature which was considered to be due to the boundary layer effects. Also measurements of the temperature rise in the course of the induction period, as manifested by the absorption hydroxyl radical, were performed under conditions of various amounts of exothermic energy release per unit mass of the medium and for different values of γ. On this basis it was found that when the exothermic effects are relatively small, the temperature rise of the substance can be evaluated from gasdynamic and chemical kinetic analysis of a homogeneous gas system, but when the exothermic effects are large this calculation was shown to be invalid. It is suggested that the main reason for this invalidity is associated with the significant amount of inhomogenity caused by exothermic processes.

Study of the reaction of atomic hydrogen with ethane

1. The rate constant of the reaction of atomic hydrogen with ethane was determined by measuring the first limits of ignition of hydrogen-oxygen mixtures, containing small additions of ethane. 2. From the same data we determined the rate constant of the reaction H+O2=OH+O, the value of which is in good agreement with the literature data.

The Ignition of Hydrogen-Oxygen Mixture by Shock Wave. I. The Condition for Shock Ignition for Hydrogen-Oxygen Mixture

Abstract Using the shock tube, the authors measured the minimum ignition pressure P1 of the reservoir for the hydrogen-oxygen mixture of various pressures (P0) and various compositions, and obtained the following results. 1) The higher the value of P0, the easier the ignition. 2) The concentration range of hydrogen in the gaseous mixture for shock ignition is 4∼94%, and the minimum value of P1⁄P0 was found in the gaseous mixture of about 40∼50% hydrogen, when P0 is over 200 mmHg. 3) The ignition is easier by the use of a shock tube with a conical end rather than that with a plane end.

The Ignition of Hydrogen-Oxygen Mixture by Shock Wave. II. Measurement of the Pressure and the Volocity of Shock or Detonation Wave

Abstract We have carried on a series of experiments on the shock ignition of a gaseous mixture 2H2+O2 by using a shock tube equipped with pick-ups, which can be used for measuring the pressure and the velocity of shock or detonation waves. The results are summarized as follows: 1) When the pressure P0 of a gaseous mixture is higher than 200 mmHg, the ignition starts between the membrane and the first pick-up along the test chamber and the detonation becomes stable before the detonation wave arrives at the first pick-up. 2) In case P0 is lOO mmHg, the detonation is initiated by an incident shock wave in some cases and by a reflected one in other cases. 3) When P0 is higher than 200 mmHg, the pressure of the detonation wave initiated by shock ignition increases along with the increase of P0 but its velocity decreases with a similar increase.

The lower limit of ignition of hydrogen-oxygen mixtures

The lower limit of ignition of hydrogen-oxygen mixtures