Showing papers by "Russian Ministry of the Emergency Situations published in 2010"

Promotion and inhibition of the combustion of methane in oxidative gases with various oxygen concentrations by fluorinated hydrocarbons

Abstract: Experimental data on the combustion characteristics of methane-oxidative gas (O2 + N2)-inhibitor (CHF3, C2HF5, and C4F10) mixtures and an analysis thereof show that fluorinated hydrocarbons (HFC and FC) exhibit the properties of both flame inhibitors and promoters. The flammability concentration limits, maximum explosion pressure ΔP max, maximum explosion pressure rise rate (dP/dt)max, and laminar flame speed S u are measured for near-limit methane-oxidative gas-fluorinated hydrocarbon mixtures. It is demonstrated that, when added to lean near-limit mixtures, HFC and FC behave as an additional fuel. Calculations of the thermodynamic characteristics of reactions involving fluorinated hydrocarbons capable of acting as both an inhibitor and oxidizer show that such reactions have significant heat effects, 150–700 kJ/mol, with the respective adiabatic temperatures being as high as 900–1800 K. The results of the present study suggest that the procedure of selecting fluorinated hydrocarbons for practical applications as fire and explosion suppressants should include careful tests of their promoting effect.

Specific features of the combustion of hydrogen-oxygen mixtures near the lower concentration flammability limit

Abstract: The combustion of hydrogen-air mixtures near the lower composition flammability limit in cylindrical reactors of various diameters is studied. The speed of flame propagation in the horizontal direction is lower than that in the upward direction. Chromatographic analysis showed that, during the combustion of these mixtures, hydrogen is consumed only partially. That the flame propagates despite a low adiabatic temperature can be explained by the formation of the well-known cellular structure.

Wide-line 1H NMR and DSC study of mesomorphic transformations of p-(alkoxybenzylidene)-p′-toluidines

Abstract: p-(Alkoxybenzylidene)-p′-toluidines (ABTs) with 7, 8, and 10 carbon atoms in the alkyl moiety have been studied by wide-line 1H NMR and DSC. The thermotropic properties of these compounds have been studied in the temperature range 20–80°C, including main mesomorphic transformations of ABTs. The 1H NMR line shapes, widths, and second moments, as well as specific features of their temperature-induced changes, are discussed. The DSC data are compared with the character of mesomorphic transformations and 1H NMR data. The formation limits and ranges and stabilities of liquid-crystalline states of the ABT structure emerging on heating are determined.