V. Yu. Navtsenya

Bio: V. Yu. Navtsenya is an academic researcher from Russian Ministry of the Emergency Situations. The author has contributed to research in topics: Combustion & Flammability. The author has an hindex of 4, co-authored 18 publications receiving 53 citations.

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.

Influence on fluorocarbons flammability limits in the mixtures of H2-N2O and CH4-N2O

Abstract: The flammability limits for combustible gas (methane, hydrogen)-nitrous oxide-fluorinated hydrocarbon (trifluoromethane CHF3, pentafluoroethane C2HF5, perfluorobutane C4F10) mixtures are experimentally determined The upper and lower flammability limits turned out to be, respectively, significantly higher and lower as compared to those characteristic of the combustion in air The compositions of the mixtures at the peaks of the flammability curves are characterized by lower values of the fuel equivalence ratio φ (in most cases, φ 05) It was established that the inhibiting concentrations of fluorinated hydrocarbons for the combustion of methane and hydrogen in nitrous oxide are similar, in contrast to the combustion in oxygen- nitrogen oxidative media A qualitative interpretation of the results is given

Effect of diluents of various chemical nature on the flammability limits of gas mixtures

Abstract: The effect of diluents of various chemical nature [halogenated hydrocarbons, inhibitors developed at the Institute of Structural Macrokinetics and Problems of Materials Science (ISMAN), superheated water aerosol] on the flammability limits of hydrogen-methane mixtures in air was investigated experimentally. It was found that ISMAN inhibitors, which are aliphatic hydrocarbons, reduce the upper flammability limit of hydrogen even more effectively than the well-known inhibitor 1,2-dibromotetrafluoroethane. Flammability curves for hydrogen and methane in mixtures with the above-mentioned diluents were obtained. The results are interpreted qualitatively by considering various kinetic regimes of nonisothermal chain branching reactions.

The predominant role of the competition between the chain-branching and chain-terminating reactions in the formation of concentration limits of flamepropagation

Abstract: For the combustion of hydrogen and methane in air, as examples, it was demonstrated that the competition between the chain-branching and chain-terminating steps, the main factor determining the inflammation and combustionintensity, as well as the transfer of heat evolved in the chain combustion to adjacent layers of the gas mixture, provide an explanation for all features of critical conditions for flame propagation. The thermal theory, which ignores the avalanche-like chain propagation in combustion at atmospheric pressure, fails to explain many of these regularities. The consideration of the competition between the chain-branching and chain-terminating steps makes it possible to estimate the self-heating at the lower concentration limit.

Propagation indices of methane-nitrous oxide flames in the presence of inert additives

Abstract: The propagation indices (explosion pressures, rates of pressure rise, severity factors and explosion times) of CH4-N2O flames in the presence of inert gases (He, Ar, N2 and CO2) were determined by experiments performed in a spherical vessel with central ignition. Lean-and stoichiometric mixtures (φ = 0.8 and 1.0) with a variable inert gas concentration between 40 and 60% were studied, at variable initial pressures within 0.50 and 1.75 bar. Inert gas addition to each of the studied CH4−N2O mixtures results in the decrease of both experimental and adiabatic explosion pressure and of the maximum rate of pressure rise, along with the increase of the explosion time. CO2 was found to be the most efficient inert additive, followed by N2, Ar and He. The measured and computed propagation properties are examined as functions of the total initial pressure and the inert gas concentration. The correlation of peak explosion pressures with the initial pressures, derived from the heat balance of the isochoric combustion of a fuel-oxidizer mixture under non-adiabatic conditions, is used to evaluate the heat losses during the closed vessel combustion, dependent on the initial CH4/N2O ratio and on inert concentration of the flammable mixtures.