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  • 1
    In: Eng, MDPI AG, Vol. 4, No. 1 ( 2023-03-01), p. 748-760
    Abstract: A technique alternative to the direct numerical simulation of turbulent combustion of gas mixtures is proposed. It is based on the solution of the three-dimensional transport equations for species concentrations and the energy conservation equation in the “synthetic” field of constant-pressure homogeneous, isotropic and statistically stationary (forced) turbulence using the detailed reaction mechanism. The synthetic turbulence with given spatial and temporal correlation functions is generated using the Monte Carlo method, assuming that the components of the vector of fluctuation velocity obey the normal Gaussian distribution. The technique is applied to the problem of turbulent combustion of fuel-lean and stoichiometric mixtures of hydrogen and methane with air at a turbulence intensity up to 10 m/s. The calculated turbulent flame propagation velocities agree satisfactorily with the values measured in the fan-stirred bomb. The predicted volume fractions of active reaction centers H, O, and OH in a turbulent flame are shown to be less than in a laminar flame up to an order of magnitude, which also agrees with the experiment. In general, calculations indicate that the “wrinkled flame” model is applicable to fuel-lean and stoichiometric mixtures of hydrogen and methane with air at turbulence intensities up to 10 m/s
    Type of Medium: Online Resource
    ISSN: 2673-4117
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 3041275-4
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  • 2
    In: Micromachines, MDPI AG, Vol. 13, No. 11 ( 2022-11-21), p. 2033-
    Abstract: Triethylaluminum Al(C2H5)3, TEA, and triethylborane, B(C2H5)3, TEB, are transparent, colorless, pyrophoric liquids with boiling points of approximately 190 °C and 95 °C, respectively. Upon contact with ambient air, TEA, TEB, as well as their mixtures and solutions, in hydrocarbon solvents, ignite. They can also violently react with water. TEA and TEB can be used as hypergolic rocket propellants and incendiary compositions. In this manuscript, a novel scheme of the heterogeneous interaction of gaseous oxygen with liquid TEA/TEB microdroplets accompanied by the release of light hydrocarbon radicals into the gas phase is used for calculating the self-ignition of a spatially homogeneous mixture of fuel microdroplets in ambient air at normal pressure and temperature (NPT) conditions. In the primary initiation step, TEA and TEB react with oxygen, producing an ethyl radical, which can initiate an autoxidation chain. The ignition delay is shown to decrease with the decrease in the droplet size. Preliminary experiments on the self-ignition of pulsed and continuous TEA–TEB sprays in ambient air at NPT conditions are used for estimating the Arrhenius parameters of the rate-limiting reaction. Experiments confirm that the self-ignition delay of TEA–TEB sprays decreases with the injection pressure and provide the data for estimating the activation energy of the rate-limiting reaction, which appears to be close to 2 kcal/mol.
    Type of Medium: Online Resource
    ISSN: 2072-666X
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2620864-7
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  • 3
    Online Resource
    Online Resource
    MDPI AG ; 2023
    In:  Fire Vol. 6, No. 2 ( 2023-02-15), p. 70-
    In: Fire, MDPI AG, Vol. 6, No. 2 ( 2023-02-15), p. 70-
    Abstract: Fires are considered among the most dangerous accidents on manned spacecraft. That is why several programs of combustion experiments were implemented at the International Space Station (ISS) since 2008. In the experiments with n-heptane and n-dodecane droplet combustion, a new phenomenon was discovered, namely, the phenomenon of the radiative extinction of a burning droplet with subsequent multiple flashes of flame. In this paper, n-dodecane droplet ignition, combustion, radiative extinction, and subsequent low-temperature oxidation with multiple flashes of cool, blue, and hot flames under microgravity conditions are studied computationally. The mathematical model takes into account multiple elementary chemical reactions in the vicinity of a droplet in combination with heat and mass transfer in liquid and gas, heat release, convection, soot formation, and heat removal by radiation. The model is based on the non-stationary one-dimensional differential equations of the conservation of mass and energy in liquid and gas phases with variable thermophysical properties within the multicomponent diffusion concept in the gas phase. Calculations confirm the important role of the soot shell formed around the droplet and low-temperature reactions in the phenomenon of droplet radiative extinction with multiple flame flashes in the space experiment at the ISS. Calculations reveal the decisive role of the blue flame, arising due to the decomposition of hydrogen peroxide, in the multiple flame flashes. Calculations with forced ignition of the droplet reveal the effect of the ignition procedure on droplet evolution in terms of the timing and the number of cool, blue, and hot flame flashes, as well as in terms of the combustion rate constant of the droplet. Calculations with droplet self-ignition reveal the possible existence of new modes of low-temperature oxidation of droplets with the main reaction zone located very close to the droplet surface and with only partial conversion of fuel vapor in it.
    Type of Medium: Online Resource
    ISSN: 2571-6255
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2924038-4
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  • 4
    In: Fuels, MDPI AG, Vol. 3, No. 4 ( 2022-11-14), p. 667-681
    Abstract: Hydrocarbon–hydrogen blends are often considered as perspective environmentally friendly fuels for power plants, piston engines, heating appliances, home stoves, etc. However, the addition of hydrogen to a hydrocarbon fuel poses a potential risk of accidental explosion due to the high reactivity of hydrogen. In this manuscript, the detonability of stoichiometric C3H8–H2–air mixtures is studied experimentally in terms of the run-up time and distance of deflagration to detonation transition (DDT). The hydrogen volume fraction in the mixtures varied from 0 to 1. Three different configurations of detonation tubes were used to ensure the DDT in the mixtures of the various compositions. The measured dependences of the DDT run-up time and distance on the hydrogen volume fraction were found to be nonlinear and, in some cases, nonmonotonic with local maxima. Blended fuel detonability is shown to increase sharply only at a relatively large hydrogen volume fraction (above 70%), i.e., the addition of hydrogen to propane in amounts less than 70% vol. does not affect the detonability of the blended fuel significantly. The observed nonlinear/nonmonotonic dependences are shown to be the manifestation of the physicochemical properties of hydrogen-containing mixtures. An increase in the hydrogen volume fraction is accompanied by effects leading to both an increase and a decrease in mixture sensitivity to the DDT. Thus, on the one hand, the increase in the hydrogen volume fraction increases the mixture sensitivity to DDT due to an increase in the laminar flame velocity and a decrease in the self-ignition delay at isotherms above 1000 K and pressures relevant to DDT. On the other hand, the mixture sensitivity to DDT decreases due to the increase in the speed of sound in the hydrogen-containing mixture, thus leading to a decrease in the Mach number of the lead shock wave propagating ahead of the flame, and to a corresponding increase in the self-ignition delay. Moreover, for C3H8–H2–air mixtures at isotherms below 1000 K and pressures relevant to DDT, the self-ignition delay increases with hydrogen volume fraction.
    Type of Medium: Online Resource
    ISSN: 2673-3994
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 3040987-1
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