Results 1 - 10 of 261
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[en] To reveal the mechanisms of flame propagation through the hardly volatile metal dust clouds clearly, the flame propagating through zirconium particle clouds has been examined experimentally. A high-speed video camera was used to record the propagation process of the flame. Combustion zone temperature was detected by a fine thermocouple. Based on the experimental results, structure of flame and combustion courses of zirconium particles were analyzed, the combustion propagation in zirconium dust was investigated, and the velocity and temperature characteristics of the combustion zone were also elucidated. The combustion zone propagating through zirconium particle clouds consists of luminous particles. Particle concentration plays an important role in the combustion zone propagation process. With the increase of zirconium particle concentration, the maximum temperature of the combustion zone increases at the lower concentration, takes a maximum value, and then decreases at the higher concentration. It is also found that the propagation velocity of the combustion zone has a linear relationship with its maximum temperature.
[en] This paper examines the dynamics of unconfined hydrogen-air flames and the criterion for flame propagation between neighbouring pockets of reactive gas separated by air using the soap bubble technique. The combustion events were visualized using high-speed schlieren or large-scale shadowgraph systems. It was revealed that for sufficiently lean hydrogen-air mixtures characterized by low flame speeds, buoyancy effects become important at small scales. The critical radius of hemispherical flame that will rise due to buoyancy is highly sensitive to the hydrogen concentration. The test results demonstrate that for transition of a flame between neighbouring pockets, the separation distance between the bubbles is mainly determined by the expansion ratio for near stoichiometric mixture, but it becomes much smaller for leaner mixtures because the flame kernel rises due to buoyant effects before the flame can reach the second bubble, thus the separation distance is no longer governed by the expansion ratio. (author)
[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] In the present study, propagation of a gasification flame through a coal channel is considered. A simplified physical model incorporating all of the main physical factors determining the flame front propagation in a gasification reactor is suggested. It is demonstrated that the flame propagation is governed by the energy balance in the channel. The suggested model is in an agreement with experimental observations obtained in underground gasification of coal (UCG).
[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] This paper represents the first study of the effect of the duration of mechanical activation (MA) of pre-granulated Ni + Al mixtures with nickel powders of different types on the combustion rate and the change in the sample length after synthesis. The initial mixtures containing different types of nickel had different combustion rates. The mechanical activation leads to an equalization of the combustion rates for powder mixtures at an MA time of 3 to 5 min and for pre-granulated mixtures in the entire MA time interval. The rate of combustion increases with the increased MA time for both powdered and pre-granulated mixtures. An explanation of the observed dependences is proposed. A sudden elongation of the samples during combustion is shown to take place after preliminary granulation of the mixtures. This result is the consequence of a significant increase in gassing due to bundle decomposition at the combustion of granulated mixtures.
[en] In this study, the prediction capability of GOTHIC code for hydrogen combustion phenomena was validated with the results of two-dimensional premixed hydrogen combustion experiment executed by Seoul National University. In the experimental results, we could confirm the propagation characteristics of hydrogen flame such as buoyancy effect, flame front shape etc.. The combustion time of the tests was about 0.1 sec.. In the GOTHIC analyses results, the GOTHIC code could predict the overall hydrogen flame propagation characteristics but the buoyancy effect and flame shape did not compare well with the experimental results. Especially, in case of the flame propagate to the dead-end, GOTHIC predicted the flame did not affected by the flow and this cause quite different results in flame propagation from experimental results. Moreover the combustion time of the analyses was about 1 sec. which is ten times longer than the experimental result. To obtain more reasonable analysis results, it is necessary that combustion model parameters in GOTHIC code apply appropriately and hydrogen flame characteristics be reflected in solving governing equations
[en] Computer models of engine processes are valuable tools for predicting and analyzing engine performance and allow exploration of many engine design alternatives in an inexpensive fashion. At the present work, experimentally based burning rate sub-models for flame initiation and propagation periods were developed for a natural gas engine. The sub-models do not require any knowledge of the flame shape and propagation speed to calculate the burning rate. The flame initiation sub-model determines where the flame propagation period starts so that experimental spark timing can be used for the calculations. The flame initiation and propagation sub-models were used along with a Zero Dimensional (Zero-D) model to calculate cylinder pressure traces for various engine operating conditions. The Zero-D model is able to match the measured pressure data with less than 8% error in magnitudes if the computations are started at the experimental spark timing. If the flame initiation sub-model is tuned for a specific engine operating condition, then the model is able to match the measured pressure with less than 1% error in magnitudes
[en] It is shown that patterns of flame propagation and the spectral composition of emission depend strongly on the chemical composition of the contacting surfaces in a wide range of pressures. This reveals the important role of heterogeneous reactions between the active intermediate products in this mode of combustion.