Ksenia N. Osipova’s research while affiliated with Novosibirsk State University and other places

Understanding and controlling the combustion of clean and efficient fuel blends, like methane + hydrogen, is essential for optimizing energy production processes and minimizing environmental impacts. To extend the available experimental database on CH4 + H2 flame speciation, this paper reports novel measurement data on the chemical structure of laminar premixed burner-stabilized CH4/H2/O2/Ar flames. The experiments cover various equivalence ratios (φ = 0.8 and φ = 1.2), hydrogen content amounts in the CH4/H2 blend (XH2 = 25%, 50% and 75%), and different pressures (1, 3 and 5 atm). The flame-sampling molecular-beam mass spectrometry (MBMS) technique was used to detect reactants, major products, and several combustion intermediates, including major flame radicals. Starting with the detailed model AramcoMech 2.0, two reduced kinetic mechanisms with different levels of detail for the combustion of CH4/H2 blends are reported: RMech1 (30 species and 70 reactions) and RMech2 (21 species and 31 reactions). Validated against the literature data for laminar burning velocity and ignition delays, these mechanisms were demonstrated to reasonably predict the effect of pressure and hydrogen content in the mixture on the peak mole fractions of intermediates and adequately describe the new data for the structure of fuel-lean flames, which are relevant to gas turbine conditions.

Improving the fire resistance of polymeric materials is an important research problem, which is solved using various flame retardants. Organophosphorus compounds are among the most effective and environmentally friendly flame retardants. This paper reports an experimental, theoretical, and kinetic modeling study of the conversion of triphenyl phosphate (TPP) during thermal decomposition in an inert medium, i.e., under conditions typical of the flame zone near the polymer surface. Pyrolysis of TPP vapor was examined in a thermal reactor under argon flow at a pressure of 1 atm. The temperature dependence of the composition of TPP pyrolysis products leaving the thermal reactor was investigated by molecular beam mass spectrometry in the temperature range of 50 0-130 0 K. The geometry of all structures on the potential energy surfaces of TPP and primary and secondary decomposition products of TPP was optimized using density functional theory (DFT) (ωB97XD) with the 6-31G(d) basis set. The kinetic rate constants of the thermal decomposition reactions of TPP were calculated using the Rice-Ramsperger-Kassel-Marcus theory with the master kinetic equation (RRKM-ME) implemented in the MESS code, and thermochemical parameters were obtained for TPP and primary and secondary decomposition products of TPP in the temperature range of 20 0-60 0 0 K. A detailed chemical kinetic mechanism for TPP pyrolysis was developed by combining the primary TPP decomposition reaction pathways with the rate parameters derived from the theoretical calculations and submechanisms available in the literature for the conversion of the phenyl and phenoxy radicals and phosphorus containing products. The proposed kinetic mechanism quantitatively reproduces the measured temperature-resolved TPP mole fraction profile at the reactor outlet. The mechanism also provides a good fit to the experimentally observed trends in the conversion of major phosphorus-containing intermediates detected in this work.

1,2-Propylene oxide (PO, C3H6O) is considered as a promising agent for improving fuel. In this work, the effect of PO additives on the species pool in a premixed burner-stabilized fuel-rich (ϕ = 1.6) flame fueled by n-heptane/toluene mixture (7/3 by volume of liquids) at atmospheric pressure is studied by the flame-sampling molecular beam mass spectrometry and numerical modeling in order to get insight into the chemical aspects of the influence of oxygenates with an epoxy group on the formation of abundant intermediates (including PAH precursors) during combustion of fossil fuels. The flames with various loadings of PO in the fuel blend (from 0 to 16.3% in mole basis) are examined, and detailed kinetic mechanisms available in the literature are validated against the measurements of mole fraction profiles of reactants, major products, and many intermediate species. A higher reactivity of the fresh mixture and a reduction in the peak mole fractions of intermediates playing an important role in PAH formation (benzene, styrene, ethylbenzene, phenol, acetylene, diacetylene, etc.) are observed when PO is added. This was found to be due to simultaneously two factors: the partial replacement of "sooting" fuel (toluene, which is the main precursor of these species) with oxygenated additive, and the changes in the flame radical pool caused by PO addition. Propylene oxide additive was found to change the ratio between H, OH, O, and CH3 toward an increase in the proportion of O and CH3. The detailed kinetic mechanisms considered in the work are found to overpredict the peak mole fraction of acetylene, a key species playing a crucial role in PAH growth. Its chemistry is revisited in order to provide a better prediction of C2H2 and, as a result, PAHs.

Because it is a carbon free fuel with high volumetric and gravimetric hydrogen density, ammonia is considered to be a promising hydrogen carrier molecule; its combustion chemistry, consisting of ammonia and ammonia/hydrogen blends, are of great importance in engine and gas turbine systems. This paper presents experimental data and kinetic modeling of the structure of NH3/H2/O2/Ar premixed flames at elevated pressures. Equivalence ratios were maintained at 0.8, 1.0 and 1.2, and the NH3/H2 ratio was 1:1 (molar ratio). Experiments were performed at pressures of 4 and 6 atm. Eight recently published chemical-kinetic mechanisms of ammonia combustion and oxidation were applied to numerically simulate flame structure. Experimental and numerical data showed that the main nitrogen containing compounds in the post flame zone were N2 and NO, while the concentrations of N2O and NO2 were negligible. In terms of NO emissions reduction, it was revealed that rich conditions were more effective. At the same time, pressure increases resulted in decreasing NO concentration in the post flame zone, as well as lower maximum concentration of NO and N2O. Numerical analysis showed that N2O and NO2 were formed mainly from NO. To improve the agreement between experimental and numerical data, rate kinetic parameters of these reactions should be refined.

One of the most important problems of modern energy industry is the transition to carbon free fuels, which can mitigate the negative environmental effects. This paper presents experimental data on ammonia and ammonia/hydrogen blends oxidation in an isothermal jet-stirred reactor over the temperature of range 800–1300 K. Experiments were performed under atmospheric pressure, residence time of 1 s, various equivalence ratios, and with argon dilution at ≈0.99. It was revealed that hydrogen addition shifts the onset temperature of ammonia oxidation by about 250 K towards the lower region. A detailed chemical kinetic model which showed the best predictive capability was used to understand the effect of hydrogen addition on ammonia reactivity. It was shown that hydrogen presence results into higher concentrations of H, O and OH radicals. Moreover, these radicals start to form at lower temperatures when hydrogen is present. However, the change of the equivalence ratio has only slight effect on the temperature range of ammonia conversion.

This paper presents experimental data on the flame structure of laminar premixed ammonia and ammonia/hydrogen flames at different equivalence ratios (φ = 0.8, 1.0 and 1.2) and the laminar flame speed of ammonia/hydrogen flames (φ = 0.7–1.5) at 1 atm. Experimental data were compared with modeling results obtained using four detailed chemical-kinetic mechanisms of ammonia oxidation. In general, all models adequately predict the flame structure. However, for the laminar burning velocity, this is not so. The main nitrogen-containing species present in the post-flame zone in significant concentrations are N2 and NO. Experimental data and numerical simulations show that the transition to slightly rich conditions enables to reduce NO concentration. Numerical simulation indicate that increasing the pressure rise also results into reduction of NO formation. However, when using ammonia as a fuel, additional technologies should be employed to reduce NO formation.