Home – Home – Jornals – Combustion, Explosion and Shock Waves 2024 number 4

Aircraft engines are a source of significant greenhouse gas emissions, in particular CO₂. Due to the tightening of emission standards, ways to reduce CO₂ emissions from aviation are being sought. One of the most promising ways to achieve this goal is the use of fuels from renewable sources, such as plant materials. To simulate the working process of combustion chambers of aircraft engines when burning biofuels and their mixtures with petroleum fuels, knowledge of the physicochemical properties of such fuels is required. This paper provides a review of existing methods for calculating the physicochemical properties of oxygen-containing biofuels, including esters, alcohols and ketones. The presented methods are validated on substances acting as bioadditives to aviation fuel and analyzed in terms of calculation accuracy and ease of use for studying the working process in combustion chambers.

Results of a theoretical study of the reaction of 1-acenaphthylene oxidation by molecular oxygen are presented. The molecular parameters and relative energies are obtained with the use of the G3(MP2,CC)//B3LYP/6-311G(d,p) composite numerical scheme, which ensures chemical accuracy. The values of the rate constants and the relative yields of reaction products are calculated with kinetic accuracy for various conditions within the framework of the RRKM theory with the MESS package. The proposed mechanism includes competing reactions paths, where the channel leading to separation of atomic oxygen dominates at high temperatures and low pressures, while the channel leading to separation of carbon monoxide dominates at low temperatures and pressures.

The single-component propellants hydrazine and hydrogen peroxide are widely used in rocketry. Their use is associated with the development of catalysts that initiate ignition and combustion of propellants upon simple contact with the catalyst without prior heating. It is obvious that the initial step of ignition is the liquid-phase decomposition of a single-component fuel on a catalyst. Otherwise, the propellants simply could not ignite. Physicochemical and mathematical models of the liquid-phase catalytic decomposition and subsequent ignition of a single-component propellant in a granular catalyst layer are proposed.

Results of a theoretical study of the methine radical (CH) with acetonitrile (CH₃CN), which is a potentially important step in the formation of heterocyclic nitrogen-containing molecules in the interstellar space and planetary atmospheres, are presented. A profile of the potential energy surface is constructed, which describes the mechanism of the formation of both linear and cyclic products. The geometry, frequency of oscillations, and relative energy of the resultant structures are determined with the use of the explicitly correlated coupled cluster method and the density functional theory CCSD(T)-F12/cc-pVTZ-f12//ωB97xd/cc-pVTZ. Within the framework of the Rice-Ramsperger-Kassel-Marcus theory, rate constants and branching coefficients of reaction products are calculated under the conditions of deep space corresponding to the limit of zero pressure for various impact energies. It is found that the relative yields of reaction products depend on the initial adduct of the reaction.

The formation of nitrogen oxides during combustion of coal or biofuel containing fuel-coupled nitrogen is an important environmental problem. As the simplest model system used to describe coal combustion, one can use a pyridyl molecule, which, on the one hand, has an aromatic structure and, on the other hand, contains a nitrogen atom in its structure. This paper describes a theoretical study of the reaction of para-pyridyl interaction with molecular oxygen. A surface of potential energy interaction of para-pyridyl interaction with molecular oxygen is constructed. The para-pyridyl radical barrierlessly attaches an oxygen molecule with formation of the PyOO radical, and then the reaction can follow one of three paths, leading to four possible products: 3H-pyrrole, HCO + HCN, 1λ²-pyrrole, and 1λ³,4-oxazine.

The paper presents an experimental study of the lean and ultra-lean combustion modes of a multicomponent hydrogen-containing fuel in swirling flow under aerodynamic counterflow conditions. A counterflow burner unit was used to implement diffusion-kinetic combustion of a mixture of methane and a multicomponent hydrogen-containing gas in different concentration ratios. The experiments show that the addition of the multicomponent fuel to methane extends the range of stable combustion of lean mixtures and provides a reduction in the emission of polluting components in combustion products. These results can be used to increase the efficiency, safety, and service life of combustion chambers of gas turbine engines and power plants.

Subsonic turbulent combustion in a premixed methane--air mixture in a model channel with a backward step is considered (P. Magre et al., ONERA, 1975-1989). The main physical mechanisms characteristic of combustion in gas turbine combustors are reproduced in experiments. A brief overview of previous numerical simulations of these experiments is given. New results from a numerical study of the stabilized combustion regime in this combustor are described. Several partially stirred reactor (PaSR) models for describing turbulent combustion are compared with a quasi-laminar approach. A model of variable turbulent Prandtl and Schmidt numbers is presented, and its influence on the reproduction of this flow in calculations is considered.

A method of modeling turbulent combustion is implemented by an example of the diffusion flame of propane. A grid is generated, and tests are performed to verify that the grid element size is sufficient to satisfy criteria of the turbulence scale needed for large eddy simulation (LES). Results of numerical modeling of the temperature distribution during combustion of a diffusion flame of propane obtained by using the Reynolds-averaged Navier-Stokes (RANS) and LES approaches in a three-dimensional formulation are presented, and the numerical model is validated in terms of the main and intermediate combustion products. LES results for the temperature distribution in the combustion zone agree much better with experimental data than RANS predictions, and model validation based on the LES approach is confirmed by the analysis of numerical and experimental data on the main and intermediate combustion products. The averaged numerical parameters of turbulent combustion of the diffusion flame of propane can be used for determining the most complicated products of incomplete combustion of the fuel, e.g., polycyclic aromatic hydrocarbons by means of kinetic modeling with detailed chemical kinetics.

A review of the literature on the topic of soot formation during combustion of fuels from biocomponents is presented. The review contains brief information on the mechanisms of soot formation, the stages of its formation and the factors influencing this process. An analysis of representatives of various groups of oxygenated biofuels is carried out in terms of their influence on the level of soot formation. Generally accepted characteristics of the level of soot emissions for hydrocarbon fuels are given, their advantages and disadvantages are presented.

An economical calculation method for self-excitation of gas oscillations in low-emission combustion chambers of gas turbine units has been developed. The method is based on the SST SAS turbulence model and the turbulent combustion model with a modified equation for a variable degree of combustion completion. A multiplier associated with gas pressure oscillations is introduced into the source term of this equation. The tendency of the combustion chamber to excite gas oscillations is estimated by two parameters: the exponent of this multiplier (interaction index) and the logarithmic decrement of oscillation damping. When solving the problem of self-excitation of oscillations in the case of specifying a homogeneous methane-air mixture at the combustion chamber inlet, the first radial oscillation mode with a frequency of 2700 Hz appeared. In the case of separate air and fuel supply to the combustion chamber, the first longitudinal oscillation mode with a frequency of 300 Hz was excited. The use of resonant absorbers (small anti-vibration screens) made it possible to completely suppress radial oscillations.

This paper presents an analysis of trends in the development of combustion chambers for high- and medium-power gas turbine power units of advanced manufacturers pursuing a significant increase in the efficiency of the plants and fuel flexibility while maintaining environmental requirements. The experience in developing low-emission combustion chamber (LECC) in the All-Russian Thermal Engineering Institute is presented. The results of tests of the GT-16P LECC in a single-burner compartment with full parameters are presented. Its modification to a dual-zone configuration is shown, which made it possible to significantly extend the range of stable low-emission combustion over a wide temperature range of outside air. For acceptable values of NO_x , it was possible to reach a combustor exhaust gas temperature of 1700 °C. An analysis is made of the designs of gas turbine LECC burners allowing to avoid the main problems arising when burning fuel with a high content of hydrogen: flame breakthrough into the premixing zone, high pressure losses on burners, and combustion instability. It is shown that these designs do not contain a blade swirler and a pronounced premixing zone.

A comprehensive numerical and experimental study of NO_x formation during hydrogen combustion in a cylindrical combustor with a developed microflame burner is performed. Experimental data are obtained for various distributions of the fuel between the baseline and pilot contours of the burner. Numerical investigations of the combustion and NO_x formation processes in the combustor are performed for regimes corresponding to numerical studies. The computations are performed in a steady-state formulation with the use of the Reynolds-averaged Navier-Stokes equations for turbulence modeling. In hydrogen combustion simulations, the rate of fuel mixing with air is taken into account by using a similarity criterion related to diffusion (turbulent Schmidt number). The normal velocity of flame propagation is specified in accordance with the temperature and composition of the fuel-air mixture. The influence of the turbulent Schmidt number on the results calculated for nitrogen oxide emissions is studied.

A comprehensive numerical and experimental study of the flame flashback boundaries in combustion of a premixed methane-hydrogen flame in a vortex burner with flow swirling and also in a model combustor, which is a prototype of low-emission combustors with fuel premixing is performed. Based on the results of the study, recommendations are given, which allow the flame flashback to be determined with an error smaller than ±5%. These results can be used to increase the accuracy of determining the flame flashback in combustion of the methane-hydrogen fuel at the stage of preliminary design of combustors for aviation gas-turbine engines and propulsion facilities.

The results of using the developed multichannel panoramic flow imaging system with combustion in a model channel on a test rig. The main emphasis is on the principles of operation of imaging system components, features of their choice, and requirements to the system and parameters of its components. The advantages and disadvantages of the developed multi-channel imaging system are discussed. Possible ways to modify its components in order to more accurately describe combustion are presented.

The conducted research relates to the works on obtaining consolidated materials by the method of self-propagating high-temperature synthesis (SHS) with subsequent compaction of hot products (SHS compaction). By the method of SHS compaction of mechanically activated mixtures of Ni and Ti powders, pore-free samples of titanium nickelide with a diameter of 70 mm and a thickness of 8 mm were obtained. The combustion of the Ni + Ti mixture was carried out in a reaction mold without preliminary heating and a protective environment. The effect of mechanical activation in a ball mill on the characteristics of the mixtures and the combustion parameters was studied. The analysis of the microstructural characteristics showed that an increase in the reactivity of Ni + Ti MA mixtures and the implementation of exothermic interaction in the SHS mode are due to a decrease in the crystallite size in Ni particles, an increase in the dislocation density in them and the formation of composite Ti-Ni particles. The maximum combustion temperature of the reaction mixture is 1150 °C, the average combustion velocity is 3.5 cm/s. The main phases of the synthesized alloy are Ti₂Ni, NiTi and Ni₃Ti. The compressive strength of the samples is 1350 MPa, the Vickers microhardness is 11.1±1.2 GPa.

The influence of mechanical activation and amount of Fe + Co + Cr binder on the combustion rate and maximum temperature, sample elongation during combustion, composite particle size and mixture yield after activation, phase composition and morphology of synthesis products in the Ni-Al-(Fe-Co-Cr) system was studied. Mechanical activation of the Ni + Al + x(Fe + Co + Cr) mixture allowed the samples to burn at room temperature with a Fe + Co + Cr binder content of up to 40%. Activation of the mixtures increased the combustion rate and temperature, sample elongation and porosity, and decreased their strength. An increase in the Fe + Co + Cr binder content in the activated Ni + Al + x(Fe + Co + Cr) mixture led to an increase in the mixture yield after mechanical activation, a decrease in the composite particle size and an elongation of the synthesis product samples. The dependence of the combustion rate of activated mixtures on the content of the Fe + Co + Cr binder is non-monotonic, and has a maximum at a binder content of 10%. High-entropy alloys - solid solutions based on intermetallic compounds NiAl and Ni₃Al - were synthesized by the SHS method.

The paper describes the production of aluminum matrix composite materials containing metallic glass particles of the composition Fe₆₆Cr₁₀Nb₅B₁₉ by successively applying mechanical activation of the initial powders in a planetary mill and spark sintering. During sintering at 540 °C, the metallic glass particles are completely or partially converted into the intermetallic compound Fe₄Al₁₃. Composite materials sintered from a mixture of Al + 20 (vol.) % Fe₆₆Cr₁₀Nb₅B₁₉ are characterized by anisotropy of mechanical properties: the yield strength in compression, microhardness and deformation at failure in the pressing direction during sintering are 550 MPa, 200 HV and 14.2%, respectively, while in the direction perpendicular to the pressing direction, these characteristics are 740 MPa, 250 HV and 2.2%

The composition of combustion products of calcium hypophosphite Ca(H₂PO₂)₂ with sodium or potassium nitrates or nitrites as oxidizers in air at atmospheric pressure has been studied. Synthesis was carried out to obtain double phosphate of the composition Na(K) CaPO₄. Mixtures of powders with zero oxygen balance were prepared using, if necessary, an additional amount of ammonium nitrate. The phase composition of condensed combustion products was studied by X-ray powder analysis. The mixtures burned stably at atmospheric pressure releasing P₄O₁₀ aerosol. The combustion products were melted white particles up to 1 mm in size. In condensed combustion products were found to contain the double phosphates NaCaPO₄, Na₂CaP₂O₇, K₂CaP₂O₇, and KCaPO₄ and calcium pyrophosphates Ca₂P₂O₇.