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Flame spray pyrolysis (FSP) is a process used to synthesize nanoparticles through the combustion of an atomized precursor solution; this process has applications in catalysts, battery materials, and pigments. Current limitations revolve around understanding how to consistently achieve a stable flame and the reliable production of nanoparticles. Machine learning and artificial intelligence algorithms that detect unstable flame conditions in real time may be a means of streamlining the synthesis process and improving FSP efficiency. In this study, the FSP flame stability is first quantified by analyzing the brightness of the flame’s anchor point. This analysis is then used to label data for both unsupervised and supervised machine learning approaches. The unsupervised learning approach allows for autonomous labeling and classification of new data by representing data in a reduced dimensional space and identifying combinations of features that most effectively cluster it. The supervised learning approach, on the other hand, requires human labeling of training and test data but is able to classify multiple objects of interest (such as the burner and pilot flames) within the video feed. The accuracy of each of these techniques is compared against the evaluations of human experts. Both the unsupervised and supervised approaches can track and classify FSP flame conditions in real time to alert users of unstable flame conditions. This research has the potential to autonomously track and manage flame spray pyrolysis as well as other flame technologies by monitoring and classifying the flame stability.

This paper presents a three dimensional numerical simulation of premixed methane-air low swirl stabilized flames. The computational domain has a simple geometry describing a LBS (low swirl burner) with 50mm of nozzle diameter. RANS Standard [kappa]- [varepsilom] model to treat turbulence coupled with partially premixed combustion model are used. The purpose is to show the applicability limits and their capacities to predict governing flame parameters by varying swirl intensity and CH4 mass fraction at the inlet, which shows the optimum operating area of the burner in terms of generated energy and flame stability with a particular interest to thermal NOx apparitions. This work is compared and validated with experimental and LES numerical simulation works available in the literature. Results offered good similarity for all flame studied parameters. Swirl number was varied from 0.5 to 1.0 to ensure a wide operating range of the burner. From S=0.6, we observed the onset of recirculation zones, while for the inert flow the appearance of recirculation zones was observed for S=0.9. CH4 equivalence ratio was increased from 0.6 to 1.4. That showed apparition of zones with important NOx mass fraction due to the existence of zones with high temperature. Otherwise, the flow field wasn't disturbed in terms of recirculation zones apparitions who remained absent for all cases. Actual investigation works to find equilibrium between the maximum of generated temperature and the minimum of NOx emissions for swirled burners. Used models haven't showed applicability limits, results were clear and precise and offered a significantly gain in computing time and means.

Hydrogen is considered to be the most promising clean energy of the 21st century, and its development and application are conformed to ‘carbon peaking and carbon neutrality goals’. Hydrogen-doped natural gas pipelines, as the main means of transporting hydrogen energy, are normally laid through low-pressure areas. The influence of the low-pressure hydrogen-doped environment on the flame propagation and explosion characteristics of hydrogen-doped natural gas is not yet clear. To solve this problem, this paper configures real multi-component natural gas and experimentally obtains flame propagation as well as explosion hazard parameters for natural gas/H 2 /air mixtures. The tensile flame propagation velocity changes from a gradual decrease to a gradual increase with increasing tensile rate for increasing hydrogen content. The laminar burning velocity increases from 0.44 m/s to 0.66 m/s at 0.75 bar and from 0.49 m/s to 0.69 m/s at 0.50 bar. The increase in laminar burning velocity becomes more and more significant after the hydrogen content exceeds 20%. As the hydrogen content increases, the flame surface goes from smooth to cracked and gradually increases. Lewis number, flame thickness, Markstein length and critical destabilisation radius decrease with increasing hydrogen and increase with decreasing pressure. The flame stability shows the same trend. The explosion hazard of natural gas/H 2 /air is reinforced as the hydrogen content rises, and the reduction in pressure reduces the explosion overpressure by 70% and the flame temperature by 10%. The results of the current research could provide a scientific reference for the safe delivery of hydrogen-doped natural gas.

Turbulent diffusion flames are considered an active field of research used in many engineering applications of combustion theory. The basic properties of jet diffusion flames were obtained in the literature, and their confrontation with observations and experiments support the mathematical aspects of combustion theory founded by famous researchers throughout dozen of years. From the other side, fractal analysis was undertaken effectively in the literature based on recent experimental studies and observations supporting the idea that flame instability results in growth of fractal structures at a flame front. Besides, fractals were used successfully to model the effects of turbulence on flame propagation in heat engines and turbulent flows. In this study, we used the new concept of “product-like fractal measure” introduced recently in the literature by Li and Ostoja-Starzewski in their formulation of anisotropic continuum media to model combustion and turbulent jet diffusion flames in fractal dimensions. The basic equations for flames in fractal dimensions have been derived and applied to study laminar and turbulent non-premixed flame besides flame extinction due to heat volumetric heat loss. Several features have been obtained and discussed in particular the application of the theory at small combustion scales.

The powder scramjet engine is considered the best engine for hypersonic weapons because of its advantages of easy adjustment, flame stability, and high efficiency. However, due to the extremely short residence time of particle fuel in the combustion chamber under high Mach conditions, there is a risk of fuel mixing. Based on the existing combustion chamber models of scramjet engines, this paper proposes a new solid fuel blending enhancement structure by combining shock generator structure and transverse jet and compares the performance and mass transfer characteristics of different shock generators. The CFD method is used to solve the RANS formula to simulate the particle transfer process, and the SST k-ω model is used to calculate the complex turbulence. It was found that when the reverse shock generator was used, the mixing degree of solid particles was higher.

The paper addresses the prospects and challenges associated with the use of ammonia in gas turbine plants. The complexity of the chemical kinetic mechanisms of ammonia combustion and the insufficient amount of experimental data that can confirm the results still require a lot of scientific research. In this sense, this application is even less technologically mature than other sectors such as the marine engine one. From the point of view of combustion in gas turbines, the techniques in use and being perfected to deal with flame instability, low laminar burning velocity (about 20% of that of methane-air flames), the long ignition delay time and low volumetric heat release rate. In particular, the use of ammonia blended with other combustion enhancers such as hydrogen, methane and alcohols has been analyzed. Mild combustion is also being analyzed as a valid technique for dealing with the difficulties of ammonia combustion. The combustion of ammonia generates significant quantities of nitrogen oxides, both for the thermal mechanism and for the “fuel” one, which must therefore be mitigated, together with the emission of unburnt ammonia. Even in this case, blending with other fuels allows for improved emissions performance. The paper compares the different techniques and the relative advantages both in terms of combustion efficiency and emissions. Finally, the perspectives for the use of ammonia in gas turbines are outlined, highlighting the challenges still to be overcome, in a panorama of energy transition towards an increasingly decarbonized future, with the aim of mitigating climate change as much as possible.

This investigation presents experimental study on the synchronized fuel injection scheme of the upstream and downstream in cavity under the supersonic inflow condition of Mach 2.92, revealing the combustion organization mechanism of the synchronized injection in the scramjet. The results show that under the same global equivalence ratio, synchronized injection in the upstream and downstream of the cavity plays an important role in reducing ignition delay, combustion oscillation, and improving flame stability. The combustion of the downstream jet can promote the combustion inside the cavity, especially at the rear edge of the cavity, while the upstream jet can provide a large amount of high-temperature products and free radicals for the downstream jet, greatly promoting the combustion process of the downstream jet.

This study combines high-speed shadowgraph imaging with numerical simulations to systematically examine the effect of the annular air gap area on the spray combustion characteristics of an alcohol-liquid-oxygen-air tripropellant coaxial direct-flow injector in an air heater operating under a low chamber pressure of 1.2 MPa. The underlying mechanisms of ignition, flame structure, injector atomization, and combustion stability are analyzed in detail. Results show that the annular air gap area has a significant impact on flame morphology and combustion performance. When the air gap area is relatively large (corresponding to an annular gap spacing of 1.95 mm), an elongated attached flame forms, and ignition is completed within 19 ms. Although the short ignition time and favorable flame stability are advantageous, the combustion efficiency is relatively low (91%), and the nozzle and throat are prone to ablation. When the air gap area is moderate (1.41 mm spacing), a conical flame develops, exhibiting the longest ignition time (997.4 ms) and a stratified structure consisting of fuel-rich combustion at the core and fuel-lean combustion at the periphery. This configuration demonstrates good stability. When the air gap area is small (1.10 mm spacing), a lifted flame forms. Although mixing and ignition occur relatively quickly (around 386.4 ms), stability is poor, with large chamber pressure fluctuations and a high risk of extinction once the air velocity exceeds the critical threshold. Reducing the air gap area effectively shortens the liquid oxygen atomization distance by 50% and significantly improves evaporation efficiency; however, excessive reduction promotes ignition-quenching-reignition cycles and worsens flame instability. Further analysis indicates that flame stability is primarily governed by the ratio of injection velocity to flame propagation velocity. When this ratio exceeds a critical value, shear-layer instability arises, increasing the amplitude of chamber pressure fluctuations by up to 200%. This research provides a theoretical foundation for optimizing injector design and improving combustion stability control in air heaters. The insights gained are essential for enhancing ignition reliability and thermal protection in hypersonic applications.

Lean premixed flame has lower nitrogen oxide emission for lower flame temperature. Whereas its poor flame stability, an annual rich pilot premixed flame was used to enhance flame stability and reduce emissions with lower ratio of pilot flame and main lean flame load. With the increasing of pilot flame load, air coefficient of main flame increases gradually. Increasing the main flame load, the air coefficient of stable main flame decreases, while the nitrogen oxide and carbon monoxide changes little. Under all main flame load, nitrogen oxide and carbon monoxide decrease sharply at first and then gets slowly. The ultralow Nitrogen Oxide of 18 mg/m³and carbon monoxide of 50 mg/m³can be reached, under the condition of main flame air coefficient from 1.3 to 1.5.

We investigate self-excited axisymmetric oscillations of a lean premixed methane–air V-flame in a laminar annular jet. The flame is anchored near the rim of the centrebody, forming an inverted cone, while the strongest vorticity is concentrated along the outer shear layer of the annular jet. Consequently, the reaction and vorticity dynamics are largely separated, except where they coalesce near the flame tip. The global eigenmodes corresponding to the linearised reacting flow equations around the steady base state are computed in an axisymmetric setting. We identify an arc branch of eigenmodes exhibiting strong oscillations at the flame tip. The associated eigenvalues are robust with respect to domain truncation and numerical discretisation, and they become destabilised as the Reynolds number increases. The frequency of the leading eigenmode is found to correspond to the Lagrangian disturbance advection time from the nozzle outlet to the flame tip. The essential role of this convective mechanism is also supported by resolvent analysis, which finds that the same flame-tip disturbance structure and frequency are optimally amplified when the flame is subjected to external white noise forcing. Strong non-modal effects in the form of pseudo-resonance are not found. Nonlinear time-resolved simulation further reveals notable hysteresis phenomena in the subcritical regime prior to instability. Hence, even when the flame is linearly stable, perturbations of sufficient amplitude can trigger limit-cycle oscillations and higher-dimensional dynamics sustained by nonlinear feedback. A Monte Carlo simulation of passive tracers in the unsteady flame suggests a nonlinear non-local instability mechanism. Notably, linear analysis of the subcritical time-averaged limit-cycle state yields eigenvalues that do not match the nonlinear periodic oscillation frequencies. This mismatch is attributed to the fundamentally nonlinear dynamics of the subcritical V-flame instability, where the dichromatic, non-local interaction between the heat release rate along the flame surface and the vortex dynamics in the jet shear layer cannot be approximated as a simple distortion of the mean flow.