D. A. Knyazkov

Terahertz free-electron laser radiation to determine water concentration in flames

The possibility of measuring the concentration of H2O molecules in flames based on the absorption of terahertz free-electron laser radiation was studied. These measurements were performed using the 177.32 cm−1 absorption line in the rotational spectrum of H2O. This line has a low intensity at room temperature, and at about 1000 K, its intensity is comparable to that of the strongest lines. The temperature dependence of the radiation absorption coefficient at a frequency of 77.32 cm−1 was studied theoretically and experimentally. It is shown that the method can be used for measurements in a sooty C2H4/O2/Ar flame, which strongly scatters visible and UV radiation.

Synthesis of mesoporous nanocrystalline TiO2 films in a premixed H2/O2/Ar flame

The synthesis of mesoporous nanocrystalline TiO2 films in a premixed (in vol %) 12.9/14.4/72.7 H2/O2/Ar flame doped with 0.1% titanium tetraisopropoxide [Ti(OC3H7)4] was studied. Stabilization of the flame and deposition of TiO2 nanoparticles were carried on the plane of a rotating disk. Spatial distributions of temperature and concentrations of major species in the flame were investigated. The applicability of the employed kinetic reaction scheme and the calculation method to the description of the structure of the investigated flame was tested. It was established that this method can be used to synthesize spherical crystalline nanoparticles of the anatase polymorphic form of TiO2 with an average diameter of 12 nm and a narrow size distribution (σ = 1.45), which can be used in the production of solar cells and gas analyzer sensors.

Effect of ethanol on the chemistry of formation of precursors of polyaromatic hydrocarbons in a fuel-rich ethylene flame at atmospheric pressure

The effect of the addition of ethanol (EtOH) to the initial combustible mixture on the concentration of various compounds, in particular, those preceding the formation of polyaromatic hydrocarbons in a fuel-rich (equivalence ratio of fuel ϕ = 1.7) flat premixed ethylene/oxygen/argon flame at atmospheric pressure was studied experimentally and by numerical modeling using a detailed mechanism of chemical reactions. Concentrations of various stable and labile species, including reactants, major combustion products, and intermediates in C2H4/O2/Ar and C2H4/EtOH/O2/Ar flames were measured along the height above the burner using molecular beam mass spectrometry. Experimental mole fraction profiles were compared with those calculated using the previously proposed mechanisms of chemical reactions. This mechanism was analyzed to determine the cause of the ethanol effect on the flame concentration of propargyl, the main precursor of polyaromatic hydrocarbons.

Dependence of the lower flammability limit on the initial temperature

The dependence of the lower flammability limit on the initial temperature is studied experimentally and numerically for upward flame propagation at a pressure of 0.1 MPa. It is shown that the Burgess and Wheeler rule, implying a linear dependence of the lower flammability limit on the initial temperature with the intersection of the temperature axis at the point 1300°C, does not hold for N2, CH3OH, CH2O, and CH4. For these substances, the intersection of the temperature axis is at the point 900 ± 20°C. The Burgess and Wheeler rule gives overestimated values of the limit which do not reflect the true conditions of explosion safety.

Inhibition of Methane–Oxygen Flames by Organophosphorus Compounds

For CH4/O2 flames doped with trimethyl phosphate (TMP), the flame structure is examined and the velocity of flame propagation is determined with the aim of studying the mechanism of inhibition of flames doped with organophosphorus compounds. The structure of a methane–oxygen flame doped with TMP stabilized on a flat burner at a pressure of 1 atm was studied. The dependence of flame propagation velocity on the concentration of TMP is measured using a Mache–Hebra burner to determine the effectiveness of a number of MP as a flame inhibitor. The mechanism of destruction of TMP in flames was used to model the flame structure and calculate the velocities of propagation of a methane–air flame as functions of the initial concentration of TMP. Calculation and experimental results are compared.

Comparative Analysis of the Chemical Structure of Ethyl Butanoate and Methyl Pentanoate Flames

The structure of premixed ethyl butanoate/O2/Ar flames stabilized on a flat burner at atmospheric pressure was studied by molecular beam mass spectrometry. Mole fraction profiles of the reactants, stable products, and major intermediates and temperature profiles were obtained in flames of stoichiometric (φ = 1) and rich (φ = 1.5) combustible mixtures. Experimental data are analyzed and compared with previously obtained experimental and numerical data for methyl pentanoate flames. The structure of ethyl butanoate flames is simulated using a detailed literature chemical-kinetic mechanism for the oxidation of fatty acid esters. The experimental profiles are compared with the simulated ones, and the conversion pathways of ethyl butanoate are analyzed. Based on a comparative analysis of experimental and simulated data, the main shortcomings of the model presented in the literature are identified and possible ways are proposed to improve the model. The decomposition of ethyl butanoate and methyl pentanoate are discussed based on an analysis of their conversion pathways; similarities and characteristic differences between their oxidation processes due to the structural differences of the molecules of the fuels are outlined.

Experimental and numerical investigation of the chemical reaction kinetics in H 2 /CO syngas flame at a pressure of 1–10 atm

The structure of a premixed stoichiometric flame of syngas (H2/CO/O2/Ar = 0.0667/0.0667/0.0667/0.8) stabilized on a flat burner at a pressure of 5 atm was studied experimentally and by numerical simulation. The mole fraction profiles of the reactants (H2, CO, and O2) and the major (H2O and CO2) and intermediate (O, OH, HO2, and H2O2) combustion products were measured by molecular beam mass spectrometry. The experimental data were compared with those calculated using three detailed chemical-kinetic mechanisms proposed in the literature for oxidation of a H2/CO mixture. Good agreement was found between the results of the experiment and simulation. Calculations of the structure of the flame of the same composition at a pressure of 1 and 10 atm were performed to establish the effect of the pressure on the chemical reaction kinetics in the syngas flame. The results were explained by kinetic analysis of the mechanisms.

Combustion chemistry of ternary blends of hydrogen and C1–C4 hydrocarbons at atmospheric pressure

Interest in the combustion chemistry of multifuel blends is motivated by the need to study the combustion of natural gas, which is known to be a mixture of alkanes. The present study performed using molecular beam mass spectrometry and numerical modeling has shown that the width of the zones of hydrogen and methane consumption in the H2/CH4/C3H8/O2/Ar flame and the width of the zones of methane and propane consumption in the CH4/C3H8/C4H10/O2/Ar flame differ significantly from each other. The causes of this phenomenon were determined by analyzing the modeling results. It has been found that in the presence of heavier compounds, lighter fuels, such as H2 and CH4, are formed, which reduces the total rate of their consumption and, hence expands the zone of their consumption in the flame. The influence of the presence of hydrogen in the fuel mixture on the concentration of C2 hydrocarbons has also been studied. It has been established that the addition of hydrogen reduces the maximum concentration of ethane, ethylene, and acetylene in the flame, and the fraction of unsaturated C2 hydrocarbons with respect to saturated ones also decreases.

Experimental and numerical study of the structure of a premixed methyl decanoate/oxygen/argon glame

The structure of a premixed methyl decanoate/oxygen/argon flame stabilized on a flatflame burner at atmospheric pressure was studied by molecular beam mass spectrometry. The results of the experiment are compared with the results of numerical simulations using two different mechanisms of chemical reactions proposed in the literature. The main intermediate combustion products of methyl decanoate were identified by gas chromatography-mass spectrometry. Analysis of the primary stages of decomposition of methyl decanoate shows that reactions involving free radicals play a decisive role in its oxidation, which agrees well with the results of the experiments.