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[en] Possible physical mechanisms of the formation of the spin flame front in deflagrating gas mixtures are discussed. Conditions for the observation of a new physical phenomenon — the propagation of the spin flame front in a limiting propane-air mixture in an open narrow slot — are identified. Experimental techniques for investigating the spin mode of flame propagation in a gas mixture with low Reynolds numbers are suggested. The conditions where transport can affect the formation of a spin front in a gas-air mixture are formulated and prospects for future research are outlined.
[en] An experimental study on spherically expanding flames propagation of methane- air mixtures was conducted at constant pressure to measure unstretched laminar flame speeds, laminar burning velocity and flame stretch. The mixtures were ignited at equivalence ratios of 0.7, 0.9 and 1.0, under ambient pressure and temperature. It was found that the unstretched laminar burning velocity increased with the equivalence ratio. The flame propagation speed showed different trends at different equivalence ratio for tested mixtures.
[en] The mechanisms of the LaO molecules ionization in the low-temperature natural gas-air flame by single- and two-stage excitation are studied. It is shown that collision ionization is the basic mechanism
[ru]Изучены механизмы ионизации молекул LaO в низкотемпературном пламени природный газ - воздух при одно- и двухступенчатом возбуждении. Показано, что основным механизмом является столкновительная ионизация
[en] The effect of the excitation of oxygen molecules to the O2(a 1Δg) and O2(b1Σg+) electronic states in the electrical discharge on the velocity of laminar flame propagation in the H2-O2 mixture is analysed. The experimental data on the decay of the singlet delta oxygen in the post shock region in the H2-O2 mixture and the measurements of the laminar flame velocity are used to validate the developed kinetic model. The calculations show that the excitation of O2 molecules to the a 1Δg and b1Σg+ electronic states allows one to increase significantly (by a factor of 2.5) the velocity of flame propagation for the fuel lean hydrogen-oxygen mixture. For stoichiometric and fuel rich mixtures the increase in flame velocity due to an abundance of singlet oxygen molecules in the mixture is significantly smaller and attains a factor of 1.1
[en] In this paper the results of a series of tests on a spark-ignition engine using both gasoline and natural gas as fuels are reported. The engine used was a 4-cylinder Toyota model 3-TC with hemispherical combustion chamber and central ignition. (author)
[en] Nonchemical flame control using acoustic waves from a subwoofer and a lightweight carbon nanotube thermoacoustic projector was demonstrated. The intent was to manipulate flame intensity, direction and propagation. The mechanisms of flame suppression using low frequency acoustic waves were discussed. Laminar flame control and extinction were achieved using a thermoacoustic ‘butterfly’ projector based on freestanding carbon nanotube sheets. (letter)
[en] A model describing the propagation of buoyancy-driven flames and accelerated jet flames in a multicompartment building has been developed for lumped-parameter containment analysis codes. The model mimics the growth of flame fronts as observed from flame visualization experiments at Pisa University and captures the jet ignition phenomena observed in experiments at the Battelle Model Containment. The model establishes a complete scheme of flame propagation consisting of five flame modes, a fireball, a bubble, a prism, a spherical jet, and a planar jet. Through a flame transformation algorithm, flame propagation in a multicompartment system can be described by a birth and rebirth of these flame modes as many times as necessary until burning is complete. The model was implemented into the MAAP4 code. Comparison of the model prediction with Battelle's hydrogen test data (test H5) shows good agreement between the model and the experiment. The model correctly predicts the timing of jet ignition and the magnitude of pressure loads in the downstream compartment. The model was developed for the analysis of hydrogen deflagrations in any compartmentalized building including a reactor containment
[en] Full text: Laser induced breakdown of focused pulsed laser radiation, the subsequent plasma formation and thermalization offers a possibility of ignition of combustible gas mixtures free from electrode interferences, an arbitrary choice of the location within the medium and exact timing regardless of the degree of turbulence. The development and the decreasing costs of solid state laser technologies approach the pay-off for the higher complexity of such an ignition system due to several features unique to laser ignition. The feasability of laser ignition was demonstrated in an 1.5 MW(?) natural gas engine, and several investigations were performed to determine optimal ignition energies, focus shapes and laser wavelengths. The early flame kernel development was investigated by time resolved planar laser induced fluorescence of the OH-radical which occurs predominantly in the flame front. The flame front propagation showed typical features like toroidal initial flame development, flame front return and highly increased flame speed along the laser focus axis. (author)
[en] Conclusions and perspectives: Mild effect of initial temperature on the flame acceleration phenomenon (based on two experiments performed with 13% of H2 at 25ºC and 90ºC). Further experiments will enable a more detailed analysis • Higher initial temperatures and different hydrogen concentrations. • Effect of steam Simulations performed by IRSN, JSI and LEI show: • Capabilities/limits of numerical tools; • Strong influence of modeling choices. Data/knowledge gained from ENACEFF2 experiments can be used to: • Improve correlations for laminar/turbulent burning velocity; • Extend the validation domain of combustion models.
[en] A steady, one dimensional, low speed flame propagating in a dilute, monodisperse, sufficiently off stoichiometric and weakly heterogeneous spray with external heat recirculation is analyzed using activation energy asymptotics. A completely prevaporized mode and a partially prevaporized mode of flame propagation are identified. Heat recirculation is achieved by transferring heat through a tube wall within a given distance L. The external heat transfer results in either globally external heat loss or excess enthalpy burning (which is globally adiabatic) to the spray system with increasing wall temperature. The influences of external heat recirculation and liquid fuel spray on the combustion characteristics of the spray flames are examined with five parameters, namely the heat transfer length for excess enthalpy burning, the heat transfer coefficient, the amount of external heat transfer, the liquid fuel loading and the droplet size. It is found that the extent of flammability is enlarged with increasing heat transfer length and heat transfer coefficient or decreasing external heat loss. The range of flammability is also enlarged with increasing liquid loading or decreasing droplet size for lean sprays, while the opposite holds for rich sprays