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Achieving efficient and stable combustion of pure hydrogen fuel is the key to the development of gas turbine combustors to meet the goals of carbon peaking and carbon neutrality. The combustion characteristics of a novel multi-nozzle array fuel-staged combustor were investigated. The hydrogen content ranged from 0% to 100% by volume. The combustion characteristics investigated included combustion stability, NO x and CO emissions, and the structure of the flame. The model combustor demonstrated the capacity to achieve stable and low emissions combustion at hydrogen contents from 0% to 100%, without the occurrence of thermoacoustic or flashback phenomena throughout the course of the experiment. By using a fuel staging strategy, the lean blowout (LBO) of the model combustor methane-fueled had a global equivalent extension of 0.6 to 0.37. For the model combustor, NO x emissions were less than 15 ppm@15%O 2 in the adiabatic temperature range of 1300 K–2000 K. Furthermore, the lift-off height of the hydrogen flame remained essentially unchanged when the nozzle velocity was increased from 40 m/s to 87 m/s. In consideration of the safety concerns pertaining to the combustion of pure hydrogen fuel in close proximity to nozzles, further investigation is warranted. • The model combustor has excellent combustion stability for methane/hydrogen mixtures. • Lean blowout of the model combustor is effectively extended by fuel staging. • Central and local flue gas recirculation ensures combustion stability. [ABSTRACT FROM AUTHOR]

A thorough understanding of the D ifferential D iffusion (DD) effect is necessary for properly predicting combustion processes fueled by NH 3 /H 2 , especially because of the higher diffusivity of H 2 compared with thermal diffusivity and diffusivities of O 2 and NH 3. It is a common practice in turbulent combustion simulations to ignore the effects of DD by assuming that turbulent mixing overweighs the diffusion mixing, hence simplifying the modeling process. However, it is important to understand that, despite this assumption being valid for hydrocarbon fuels, it loses significance when it comes to the burning of H 2 because of the significant influence of DD. In this work, two direct numerical simulations (DNS) of a turbulent NH 3 /H 2 non-premixed flame in the mixing layer are conducted, one considers the DD and the other assumes the U nity L ewis N umber (ULN) to investigate the DD effect. It is found that DD allows more fuel to diffuse toward the flame front, significantly enhancing flame stability compared to the ULN assumption. It also keeps the scalar dissipation rate (SDR) at lower levels than in ULN due to smoother species distribution from enhanced diffusion. This supports the partially premixed and premixed combustion modes as well alongside non-premixed combustion, influenced by both ammonia's low reactivity and its higher diffusion flux. The tendency of ammonia to favor partially premixed and premixed modes offers insights into the causes of ammonia slip in emissions while burning in non-premixed mode. The fuel species diffusion angle measured from the flame front's normal direction is strongly influenced by the SDR, a higher SDR increases diffusion potential in the normal direction, resulting in a smaller diffusion angle, and vice versa. While the tangential diffusion magnitude is strongly influenced by the divergence of the diffusion flux, which is affected by the flame front curvature and reaction rates. • 3D DNS is performed to clarify the differential diffusion effect in a H2/NH3 flame. • The unity Lewis number model is compared with the multi-component diffusion model. • The unity Lewis number model underpredicted the diffusion magnitude of H2 and NH3. • The multi-component model can capture combustion modes unlike ULN model. • The flame curvature strongly affects reaction rates and fuel consumptions. [ABSTRACT FROM AUTHOR]

The BHM/5 separator is self-extinguishing after being separated from fire and has good flame retardancy and cycle stability. [Display omitted] • A fire-retardant separator (BHM/5) based on environment-friendly bacterial cellulose was developed. • The flame-retardant mechanism and combustion behavior of the BHM/5 were investigated, proving its superior fire safety. • Benefiting from the electrolyte affinity of the BHM/5, the assembled cell exhibited favorable electrochemical properties. Separators play a crucial role in enhancing the safety of lithium-ion batteries (LIBs); however, commercial polyolefin separators exhibit poor thermal stability and are flammable. This study investigates the use of green, environmentally friendly, and renewable bacterial cellulose as a substrate for developing a composite separator (BHM/5). The BHM/5 separator, comprising bacterial cellulose, an inorganic mineral nano-hydroxyapatite (HAP) and flame-retardant melamine polyphosphate (MPP), is fabricated via freeze drying and high-temperature pressing. The developed composite separator demonstrates superior thermal stability and excellent flame retardancy compared with commercial polyolefin separators while maintaining structural integrity at 200 °C and exhibiting self-extinguishing properties after ignition. Furthermore, the BHM/5 separator exhibits a high porosity of 74 % and a substantial electrolyte uptake of 459 %, achieving an ion conductivity of 1.44 mS/cm. As a result, the cell of the LiFePO 4 -Li system assembled demonstrates an initial discharge capacity of 131.35 mAh·g−1 at a current density of 1C and a capacity retention of 95.4 % after 150 cycles. [ABSTRACT FROM AUTHOR]

Ethane (C2) is the second largest component of natural gas, which exhibits superior combustion performance compared to methane (C1). The C2/NH 3 dual-fuel combustion strategy effectively mitigates the shortcomings of NH 3 flames. This study employed a spherical constant volume combustion chamber (CVCC) to measure the laminar burning velocity (S L) of C2/NH 3 across various equivalence (ϕ) and blending ratios (χ b). A chemical kinetics mechanism for C2/NH 3 is developed and optimized based on experimental data and existing models (GRI 3.0, SanDiego, CEU 1.1), achieving high fidelity in simulating S L for binary fuel flames. The concept of flame precursor waves is refined by analyzing the roles of concentration, temperature, and chemical waves in flame propagation. Unlike the absolute leading position of concentration waves, chemical and temperature waves closely couple, creating a positive feedback mechanism. An equation of sensitivity analysis is established to examine the effects of fluid dynamics, thermal diffusion, and Arrhenius effects on S L. Thermal expansion coefficient (σ) and laminar flame thickness (δ l) reflect fluid dynamic effects, with δ l significantly influenced by ϕ. At low χ b , NH 3 dominates thermal diffusion, limiting S L and enhancing instability. The Arrhenius effect remains the primary factor, particularly significant at low χ b , while C2 somewhat weakens the effects. Near the stoichiometric ratio, fluid dynamic effects become more pronounced, but excessive fluid density gradients inhibit flame propagation under rich fuel conditions. Nevertheless, the favorable thermal diffusion properties of C2 enhance the thermal diffusion effect, maintaining S L at a higher level. • The kinetics mechanism has been optimized for accurate prediction of S L. • The precursor waves at the flame front influence its propagation and development. • A relationship integrating physical and chemical effects is established. • C2 weakens the chemical effect but enhances the contribution of thermal diffusion. [ABSTRACT FROM AUTHOR]

In response to the carbon neutrality in internal combustion engines, this study investigates the effects of hydrogen addition on flame propagation dynamics for gasoline flames using a constant-volume chamber at an initial temperature of 400 K. The experiments span a wide range of equivalence ratios (0.7–1.6), pressures (0.1–0.2 MPa), and hydrogen mixing ratios (0%–100%). Results indicate that the normalized laminar burning velocity can exceed 20 at ϕ = 1.6. The influence of hydrogen addition on laminar burning velocity is primarily attributed to chemical effects, followed by dilution effects, and then thermal effects. Additionally, hydrogen addition increases flame instability under fuel-lean conditions but decreases it under fuel-rich conditions. As the equivalence ratio increases, the flame instability intensifies at low hydrogen mixing ratios whereas it diminishes for hydrogen mixing ratios larger than 75%. The measured acceleration exponents are 1.1–1.4, which are below the critical value of 1.5 for self-turbulization. • LBVs of gasoline/H 2 /air are measured with key reactions being revealed. • H 2 affects LBVs through chemical, dilution, and thermal effects in order. • H 2 increases flame instability in lean mixtures but reduces it in rich ones. • Diffusional-thermal and hydrodynamic instabilities have not led to self-turbulization. [ABSTRACT FROM AUTHOR]

Purpose: The swirl intensity imposed on the flow plays a vital role in aerodynamics, flame shape, flame stabilization and combustion intensity. In lean direct injection (LDI), the air and fuel are fed through separate channels, and the swirling air flows have a strong impact on fuel-air mixing and heat release. The literature indicates that the effects of swirling on helical axial LDI systems are limited to nonreacting flows studied through experimental methods, but not many studies have been reported on the reacting flows of a single swirler. The objectives of the paper are divided into two parts. The first part presents the role of swirl in nonreacting LDI systems and the second part describes spray combustion in LDI systems for low (swirl < 0.5) to high (swirl > 0.5) swirl numbers. Design/methodology/approach: The numerical model incorporates all the necessary features of the single helical axial swirler, starting from the hollow circular section to the outlet of a long mixing chamber. The commercial solver FLUENT is used to predict the flow field around the axial swirler. The first step is to establish a numerical procedure (based on computational fluid dynamics [CFD]) to predict the nonreacting flow behavior for different swirlers and the CFD results are validated against literature data. The spray atomization, droplet evaporation and the effects of interaction between the two phases are modeled by implementing various spray submodels in FLUENT. The large Eddy simulation (LES) reacting flow results for a vane tip angle of 60° are compared with test data and presented at multiple cross planes. Findings: The numerical simulations were carried out on a nonreacting single helical axial swirler for various vane tip angles, such as 40°, 50°, 55, and 60°, and the results were validated against test data. The centerline mean axial velocity and radial velocity profiles at several axial locations are in good agreement with the literature data. For reacting swirling flows, the experimental data is available only for a 60° vane tip angle. The S60 reacting flow LES mean predictions are compared at different cross planes. The axial momentum increases due to the liquid spray combustion in the gas phase and the reacting flow central recirculation zone is substantially shorter than the nonreacting flow. The impact of spray atomization due to interaction with the gas phase is verified, and the droplet mean diameter trends are consistent across different cross planes. The LES predictions of reacting flows for low to high swirls are investigated, and the effects on combustion performance are summarized. Originality/value: The novelty of the paper is highlighted in two key conclusions. First, the paper presents numerical methods for studying the role of swirl in a nonreacting LDI system and validates the results against experimental data. Second, the effects of combustion on the gas phase, spray combustion modeling and droplet atomization are numerically established and compared with literature data for a 60° vane tip angle. In addition, the role of swirl in the reacting flow field for vane tip angles of 40°, 50° and 60° is numerically investigated, and its effect on flame stability, pressure drop and NOx emissions is presented. The paper describes LES grid guidelines for the LDI swirler and presents a numerical modeling approach that helps to develop a robust swirler design through a parametric investigation of swirler geometry. The methodology can be extended to study multi-element swirler configurations, to understand the effect of swirl on droplet breakup, momentum exchange with adjacent swirlers, flame propagationand emissions. [ABSTRACT FROM AUTHOR]

The flame-retardant effect of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives in reducing the flammability of polymeric materials are well known. In this study, flame-retardant rigid polyurethane foams (FR-RPUF) were synthesized using a melamine-DOPO-based flame-retardant (MDFR). Additionally, MDFR was also used for preparation of a flame-retardant elastomeric polyurethane (FR-PUE). The chemical structure and thermal properties of the FR-RPUF and FR-PUE samples were studied with Fourier transform infrared (FTIR), field emission-scanning electron microscopy (FE-SEM), and thermogravimetric analysis (TGA). TGA results revealed that the incorporation of MDFR into the PU matrix significantly increased the char residue. The char residue of FR-RPUF with 0.5 wt% MDFR increased from 4.75% to 44.36%, as compared to the pure RPUF. Results from the microscale combustion calorimeter (MCC) test illustrated that the peak of heat release rate (pHRR), total heat release (THR), and heat release capacity (HRC) of the FR-RPUF and FR-PUE samples were reduced, as compared to the pure PU samples. The pHRR value of FR-RPUF with 3 wt% of MDFR decreased 12%, as compared to the pure RPUF, while the pHRR was obtained 34% lower than of the pure PUE. Furthermore, FR-RPUFs successfully passed the UL94 testing, achieving a V-0 grade. [ABSTRACT FROM AUTHOR]

An experimental study was performed to investigate the effects of flow swirl on flow/flame characteristics and stability of atmospheric premixed oxy-methane (CH4/O2/CO2) flames. The flames generated by two swirlers of 55° and 45° swirl angles were tested on a test stand for a dry low emission (DLE) model gas turbine combustor at constant inlet flow velocity of 5.2 m/s and over ranges of operating oxygen fraction (OF: 21% to 70% - by volume in the O2/CO2 mixture) and equivalence ratio ($\varphi $ φ : 0.2 to 1.0). Combustor static stability limits (flashback and blow-out) were determined experimentally in the $\varphi $ φ -OF domain to identify the operational ranges of the combustor while varying inlet flow swirl. To understand the mechanisms for flashback and blow-out, the lines representing the stability limits were displayed in the $\varphi $ φ -OF domain against the contours of combustor power density (PD: MW/m3/atm), adiabatic flame temperature (AFT), and inlet flow Reynolds (Re). Comparison of flame macrostructure and measurements of local flame temperatures were performed for the two swirlers over ranges of $\varphi $ φ , OF, and AFT to determine the effects of such operational parameters on flow/flame interactions and flame stability and to serve as a database for validating numerical models for such flames. The results show that, for both swirlers, the flames blow-out at a very similar AFT of ~1600 K indicating the dominant role of AFT in controlling premixed oxy-flame stability near the blow-out limit. Compared to the same combustor with a 55° swirler, the 45° swirler has a wider stable combustion zone. Comparing the flames of the same AFT, at fixed inlet flow velocity, shows almost identical flame macrostructure whatever the operating inlet flow swirl, OF and φ. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of different thermal conductivity flame holder materials with different blockage ratios to optimise flame stabilisation, blow-off limits and recirculation zone inside the combustor wall of a premixed LPG and air. The paper experimentally investigates the performance of flame holders are using three different materials such as ceramic flame holder, stainless steel flame holder and silicon carbide flame holder. The study aims to measure the blow-off limits, equivalence ratio, LPG mass flow rate, rich and lean flammability limits, and blow-off regions that impact flame stability and stable flames. The impact of disc-shaped materials having different blockage ratios such as 0.26, 0.36, 0.46, 0.56, respectively are investigated at an equivalence ratio of 1.80 and mass fuel flow rate of 0.61 g/s. The double-layered combustor having higher thermal conductivity for the inner wall and lower thermal conductivity material for the outer wall significantly reduces the heat loss to the surroundings. The study implies were the important implementation of wall material type, flame holder material type, optimal blockage ratio, flame stability of LPG and air-premixed flame, and mass fuel flow rate for attaining successful combustion. The results indicate that the lower thermal conductivity flame holder material along with the help of high and low double-layered wall material, optimal blockage ratio can induce a stable flame region and recirculation zone. The blockage ratio at 0.46 performed well in flame stabilisation, decreased flame length and also in flame shape. The flame species concentrations such as CO, NO, CO2, and O2 were analysed by using a Portable gas analyser. The results influence a better study of the performance of the different material-based flame holders. [ABSTRACT FROM AUTHOR]

Experimental and theoretical investigations were performed on the propagation behavior of ammonia/hydrogen premixed flames, and an in-depth theoretical analysis of flame instability was carried out. The laminar burning velocity (LBV), burning flux, and net heat release rate (HRR net) were calculated. The instability was measured by flame thickness, thermal expansion ratio, effective Lewis number, and perturbation dimensionless growth rate. The effects of equivalence ratios (0.8, 1.0, 1.2, and 1.4), initial pressures (1, 2, and 3 bar), and hydrogen additions (15, 20, 25, and 30%) on ammonia/hydrogen premixed flames were determined. The findings indicated that as the hydrogen addition rises, both the LBV and burning flux increase, and the peak HRR net rises and shifts towards the low-temperature reaction zone, indicating that the diffusivity and reactivity of hydrogen can enhance the combustion intensity. The increment in the equivalence ratio improves the flame stability. Hydrodynamic instability effect always destabilizes the flame during the combustion process. In rich mixtures, the hydrogen addition improves thermal-diffusion stability, delaying the occurrence of flame instability whereas in lean mixtures, the hydrogen addition thermal-diffusionally destabilizes the flame. • Laminar burning velocity and burning flux of NH 3 /H 2 mixtures were measured. • The intrinsic instability of NH 3 /H 2 flame was investigated. • H 2 promotes the NH 3 /H 2 flame propagation and increases the heat release rate. • The hydrogen addition stabilizes the flame at high equivalence ratio. [ABSTRACT FROM AUTHOR]

To understand the effect of flame instability on the formation of the tulip flame, this paper modified the multi-phenomena combustion model and used the CFD code GASFLOW-MPI system to perform a numerical simulation of premixed stoichiometric hydrogen/air deflagration without considering the influence of flame stretch rate, Darrieus-Landau (DL) instability and thermal-diffusive (TD) instability based on the consideration of the heat transfer mechanism. The influence of different control factors on the formation of the tulip flame was compared and analyzed, and the accuracy of the numerical simulation was verified by combining it with experimental results. The research results showed that the coupling effect of DL instability and TD instability was the main reason for the formation of tulip flames, and DL instability played a dominant role. Furthermore, the DL instability determined the growth rate of the deflagration pressure amplitude and its fluctuation frequency. Finally, DL instability and TD instability had a more significant effect on flame propagation than heat loss. When either effect of DL instability and TD instability was ignored as a factor, the pressure gradient near the flame front decreased sharply and no vortex was generated. • The reason for the formation of tulip flames was obtained. • The Darius-Landau instability played a dominant role in the instability coupling. • Flame instability have a greater effect on flame propagation than heat loss. [ABSTRACT FROM AUTHOR]

Mixtures of hydrogen with common hydrocarbon fuels are considered viable for reducing carbon footprint in modern industry, power production, and transportation. The addition of hydrogen alters the kinetics and thermophysical properties of the mixtures, as well as the composition and properties of combustion products, requiring detailed research into the features of flame propagation in hydrogen-enriched hydrocarbon–air mixtures. Of particular interest are also the safety aspects of such fuels. In this paper, experimental results are presented on the premixed laminar flame propagation in channels formed by two closely spaced plates (Hele-Shaw cell), with the internal straight walls forming a diverging (diffuser) channel with the opening angles between 5 and 25 degrees. Methane–hydrogen–air mixtures with the hydrogen relative contents of 0%, 25%, and 50% and global equivalence ratio of unity were ignited by a spark near the closed narrow end of the channel. Experiments were performed with the gap width of 3.5 mm; video recordings were processed in order to determine the quantitative features of the flame front propagation (leading and trailing point coordinate, coordinates of the cusps, cell sizes and shapes). The main features of flame propagation (fast initial expansion, development of cellular flame, self-induced longitudinal oscillations) are obtained and compared to clarify the effect of hydrogen contents in the fuel and channel geometry (gap width, opening angle). [ABSTRACT FROM AUTHOR]

In the European Union, coal consumption in the power industry has been declining over time. Energy sources such as renewable energy, nuclear energy, and natural gas are being used on an increasing scale. Despite this, fossil fuels continue to be an important pillar of the energy industry in many countries around the world. There are various methods for diagnosing the combustion process, and one of them is based on a fibre-optic system for monitoring changes in flame intensity. Thanks to its innovative design, it allows information to be extracted from the flame under conditions of high temperatures and high dusting. The article presents an analysis of measurement signals for the recognition of states of flame intensity resulting from changes in the operating point of a power boiler. Trends in the flame that occur during the combustion process, which exceed the ranges specified by experts, can cause disturbances in combustion stability. The measurement data after preprocessing were classified using artificial neural networks to determine the conditions for flame stability. Based on the recurrent neural network models used, a classification accuracy of more than 99% was achieved. This allowed for the recognition of flame states in the combustion process. [ABSTRACT FROM AUTHOR]

This study focuses on C 2 H 2 as an industrial gas for boiler soot-blowing, aiming to investigate the combustion characteristics of mixed fuels with H 2 and syngas as additives. Using a constant-volume combustion bomb at 300 K and 1 atm, the laminar burning velocity (S L) of C 2 H 2 /H 2 /air and C 2 H 2 /syngas/air premixed flames is measured. Flame stability, pressure variations, sensitivity, combustion reaction characteristics, and product composition is comprehensively analyzed. Results show that increasing H 2 and syngas content significantly enhances S L , with H 2 addition yielding a greater increase. In fuel-rich regions, this improves flame stability, while in fuel-lean areas, stability decreases. Furthermore, H 2 and syngas enhance the net reaction and heat release rates of key chain reactions, while significantly increasing concentrations of key radicals like H and OH, positively influencing combustion mechanisms. This study provides experimental and theoretical support for optimizing C 2 H 2 combustion in soot-blowing, enhancing cleanliness and stability with broad industrial applications. • Analysis of combustion characteristics based on C 2 H 2 with H 2 /syngas addition. • The effects of H 2 /syngas content on flame instability is analyzed. • The chain reaction is evaluated by sensitivity and net reaction rate analysis. • The impact of H 2 /syngas content on the mole fraction of key radicals is analyzed. [ABSTRACT FROM AUTHOR]

Waterborne novolac epoxy based thermal resistant and fire‐retardant thermal insulation coatings were developed in this work. Novolac (phenolic) epoxy emulsion (PEE) was prepared by the phase inversion method based on formulation optimization by orthogonal array testing. The prepared emulsions have similar particle size, viscosity, and stability to commercial bisphenol a glycidyl ether epoxy emulsion (PZ). DSC results showed that the varnish film based on PEE had a higher glass transition temperature and initial thermal decomposition temperature compared with PZ cured by the same curing agent. Waterborne thermal insulation coating with PEE and PZ as binders and hollow glass microspheres (HGMs) as thermal insulation fillers were studied. The results indicated that the thermal conductivity of the coating decreased with an increase in HGMs content. Specifically, the thermal conductivity of the PEE coating containing 20 wt% HGMs is as low as 0.093 W/(m·K). It reduces the exterior temperature of the hot tank from approximately 200 °C to approximately 106 °C. Furthermore, the HGMs/PEE waterborne thermal insulation coating exhibits good thermal stability and flame retardance. [ABSTRACT FROM AUTHOR]

Considering the requirements for developing hydrogen combustion chambers and the application potential of micro-mix combustion, the flame macrostructure and evolution of hydrogen-air multi-microjet flames have been investigated to discover the relationship between flame macrostructure and thermoacoustic instability. A novel burner has been tested under different combustor liner lengths to simultaneously produce stable and unstable combustion under the same operation conditions. A compact conical flame shape without adjacent flame front interference is observed. In comparison with the combustor liner length, the flame temperature variation shows an insignificant effect on the thermoacoustic instability but triggers an oscillation mode transition from low-frequency (∼210–240Hz) to high-frequency (∼400–440Hz) under unstable combustion. Different flame evolutions are revealed for these oscillation modes. DMD analysis and LES simulation show that the high-frequency oscillation mode is mainly controlled by flame front oscillation and flame pinch-off process. However, the low-frequency oscillation mode is characterized by flame extinction on a large scale. Both equivalent ratio and velocity fluctuations contributed to flame and heat release oscillations under low and high flame temperatures. These findings help understand the mechanisms, driving hydrogen-air flame dynamics, and designing hydrogen combustors. • A novel hydrogen micro-mix combustion burner was investigated. • A change in the liner length significantly impacted the combustion instability. • An increase in the flame temperature induced a transition of the oscillation mode. • The relationship between flame evolution and combustion instability was revealed. [ABSTRACT FROM AUTHOR]

Swirl-stabilized auto-igniting spray flames are essential for designing efficient and clean combustion systems. The present study performs large eddy simulations of the dilute auto-igniting methanol flame in a vitiated, hot coflow of varying swirl intensities. The six-dimensional Flamelet Generated Manifold technique is used to solve the reactive flow accurately and economically. The swirl numbers (SN), i.e., 0.2, 0.6, 1.0, and 1.4, are used to assess their effect on auto-ignition and flame stability. At lower to moderate swirl numbers (SN = 0.2, 0.6), the increase in swirl is found to increase the liftoff height. Beyond the critical swirl number (SN = 0.6), the liftoff height drops. Also, the time-averaged flame structure transitions from a tubular-like flame into a uniformly distributed combustion region at these high swirl numbers. It also results in a more compact flame for the higher swirl numbers. These effects on flame dynamics are analyzed in detail using the mean gas-phase flow field distribution, particle statistics, and proper orthogonal decomposition. [ABSTRACT FROM AUTHOR]

To enhance the performance of combustors in micro thermophotovoltaic systems, this study employs numerical simulations to investigate a planar microscale combustor featuring a counter-flow flame configuration. The analysis begins with an evaluation of the effects of (1) equivalence ratio Φ and (2) inlet flow rate Vi on key thermal and combustion parameters, including the average temperature of the combustor main wall ( T ¯ w ), wall temperature non-uniformity ( R ¯ T w ) and radiation efficiency ( η r ). The findings indicate that increasing Φ causes these parameters to initially increase and subsequently decrease. Similarly, increasing the inlet flow rate leads to a monotonic decline in η r , while the T ¯ w and R ¯ T w exhibit a rise-then-fall trend. A comparative study between the proposed combustor and a conventional planar combustor reveals that, under identical inlet flow rate and equivalence ratio conditions, the use of the counterflow flame configuration can increase the T ¯ w while reducing the R ¯ T w . The Nusselt number analysis shows that the counter-flow flame configuration micro-combustor achieves a larger area with positive Nusselt numbers and higher average Nusselt numbers, which highlights improved heat transfer from the fluid to the solid. Furthermore, the comparison of blow-off limits shows that the combustor with counter-flow flame configuration exhibits superior flame stability and a broader flammability range. Overall, this study provides a preliminary investigation into the use of counter-flow flame configurations in microscale combustors. [ABSTRACT FROM AUTHOR]

Manganese phytate (MnPa) was prepared and synergistically combined with expandable graphite (EG) flame retardant modified polyurethane foam (PUF). Utilizing thermogravimetric (TG), pyrolysis kinetic analysis, CONE analysis, smoke toxicity analysis, limiting oxygen index (LOI), and UL-94 horizontal combustion test procedures, the thermal stability and combustion parameters of the modified PUFs were examined. The flame retardancy and smoke suppression of the modified PUFs were analyzed based on the heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and total smoke release (TSR). The results showed that MEPUF3 had the highest thermal decomposition rate temperature, initial thermogravimetric temperature, and activation energy (E). It was shown that MEPUF3 had the lowest HRR of 17.68 kW/m2, the lowest THR of 1.15 MJ/m2, the lowest SPR of 0.0046 m2/s, the lowest TSR of 19.58 m2/m2, the lowest Ds of 32.1, the highest transmittance of 57.7%, and the highest LOI of 23.0%. The present study showed that MEPUF3 possessed good thermal stability and flame retardant properties, which provided useful references for subsequent phytate and EG-modified PUFs. [ABSTRACT FROM AUTHOR]

Two potential decarbonization pathways for natural gas (NG)-fueled gas turbine engines include blending hydrogen (H2) into NG and postcombustion carbon capture. H2 blending changes several combustion properties, including flame speed and stretch sensitivity. The use of post-combustion carbon capture systems is typically facilitated by the implementation of exhaust gas recirculation (EGR), where exhaust gases are injected into the inlet of the engine, increasing carbon dioxide (CO2) concentration at the outlet and, hence, increasing the efficiency of carbon capture technologies. In this work, we explore the impact of H2 blending and EGR on the stability of a swirl-stabilized, central-piloted flame. Mixtures of NG and H2 are tested at a range of different diluent compositions, with oxygen varied from 21% to 15% by volume in the oxidizer. In all cases, a constant adiabatic flame temperature is maintained to mimic the operation of a gas turbine at a given turbine inlet temperature. A variable-length combustor is used for testing, where combustor length is varied to understand the dynamic stability characteristics of the system. Results show that EGR and H2 work in opposition to each other, where higher levels of EGR result in poor flame holding and higher levels of H2 result in better flame holding. Increasing H2 generally increases the amplitude of thermoacoustic instability at each condition, a result of the change in flame position in this particular combustor. Importantly, H2 can be added to NG to improve flame holding without significantly decreasing CO2 levels in the products, showing that H2 blending can be a method for counteracting combustor operability issues that arise from high levels of EGR necessary to improve the efficiency of typical carbon capture systems. [ABSTRACT FROM AUTHOR]

In this article, the effect of different boundary conditions and different thermal and physical properties of walls and gas on flame characteristics and stability of hydrogen–air mixture are investigated using an analytical method. This method solves the gas–wall energy equation, and the hydrogen mass conservation equations. The jump conditions are obtained by integrating the energy and mass equation into a small control volume around the flame. For validation of this model, the temperature distribution on the outer surface of the wall is compared with experimental data that show the maximum relative error of 3.5% for Q = 400 mL/min and 4.9% for Q = 200 mL/min. The maximum variation of gas temperature is nearly 6.5 times of wall temperature variation. The wall can be considered one‐dimensional for conventional wall materials with K > 10. For the existence of combustion inside the chamber, when the value of K is greater than 10, the Péclet number should also be considered greater than 10. In a constant equivalence ratio, increasing the medium temperature increases flame stability. [ABSTRACT FROM AUTHOR]

This paper presents a detailed comparative analysis and discussion of two typical predictive methods for combustion instability in long flame combustion chambers: the coupled method and the decoupled method. Using large eddy simulation (LES), the coupled method directly predicts stability in typical long flame combustion chambers. In the decoupled method, stability in the combustion chamber is predicted by combining a low-order acoustic network for long flames with flame responses and mean parameters from numerical simulations. The research results indicate that the coupled method provides full-field information, while the decoupled method neglects certain factors, such as the coupling between combustion and acoustics. However, the decoupled method can directly determine combustion instability based on the growth rate of oscillation modes. The flow field undergoes periodic changes, with the region of fluctuation in the combustion heat release rate gradually increasing, resembling vortex development, which ruptures upon encountering the wall due to radial constraints. Furthermore, in the decoupled method, the periodic changes in the flow field are controlled by the frequency of incoming flow disturbances, whereas in the coupled method, they are controlled by the acoustic frequency of the combustion chamber. In the coupled method, the coupling among disturbances and the acoustic disturbances at the boundaries amplifies the disturbances, causing the radial scale of the fluctuation region in the combustion heat release rate to increase along the axial direction and approach a fixed value faster than in the decoupled method. • A detailed comparative analysis and discussion of two typical predictive methods for combustion instability in long flame combustion chambers: the coupled method and the decoupled method are investigated. • The coupled method directly predicts stability in typical long flame combustion chambers. • In the decoupled method, stability in the combustion chamber is predicted by combining a low-order acoustic network for long flames with flame responses and mean parameters from numerical simulations. [ABSTRACT FROM AUTHOR]

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The influence degree of structural parameters and operating parameters on the low NOx performance of burners was studied by numerical simulation and orthogonal experiment. Excess air coefficient (factor A) and flue gas circulation rate (factor B) were used as operating factors, fuel nozzle diameter (factor C), cyclone blade end deflection angle (factor D), flame-stabilizer inclination angle (factor E), and internal circulation tube diameter (factor F) were used as structural factors, the average temperature (Tav), maximum temperature (Tmax) of the combustion chamber, and NO emission value at the combustion chamber outlet (MNO) were used as indicators. Range analysis and variance analysis were used to analyze the specific influence of the above factors on the indicators. In the studied cases, the most significant factor affecting Tav and MNO is the factor B, followed by the factor C. The more significant factor affecting Tmax is the factor A, followed by the factor C. The coupling of multiple parameters has a significant effect on the distribution of flow field in the combustion chamber. Vortices are produced in all the cases studied. The vortices are basically symmetrical, but the number of vortices varies from 2 to 6. The results show that the burner has good flame stability. [ABSTRACT FROM AUTHOR]

Autoignition widely exists in combustion devices that feature hot air. The unsteady autoignited flames caused by autoignition are potential hazards to the stable operation of combustion systems, often causing flameout or damage to the combustion devices. In this paper, we present our recent work in understanding the key factors determining the instability of autoignited turbulent jet flames and a novel method to suppress flame instability. Firstly, we studied the flame using a jet-in-hot-coflow burner. The instability behaviors were characterized using a pressure probe and a high-speed camera. When the fuel mole fraction was below a critical value, the amplitude spectrums of the unsteady autoignited flame had low-frequency and high-frequency peaks. The experimental results show that the low-frequency peak is related to the autoignition intermittency and can be eliminated by enhancing chemical reactions. The high-frequency peak is related to the autoignition frequency, and the peak amplitude can be reduced by improving reactants mixing. Considering that the heating rod can enhance the reaction as a heat source and improve mixing as a bluff body, we inserted an electric heating rod into the autoignition spatial region to suppress the flame instability. The suppression of flame instability by heating rod at different temperatures and locations were experimentally studied. The heating rod insertion can significantly reduce low-frequency and high-frequency instability. Moreover, increasing the rod temperature can also effectively reduce the amplitude of high-frequency pressure pulsation. The results show that the electric heating rod is an efficient method to suppress the instability of autoignited flame. [ABSTRACT FROM AUTHOR]

Metal–organic frameworks (MOFs) have garnered significant attention in recent years due to their potential application in flame‐retardant polymeric materials. In this work, Fe2O3/ZnFe2O4/g‐C3N4@ZIF‐8 flame retardants were synthesized via solvothermal and calcination techniques, and their elemental composition and morphologies were thoroughly characterized. The flame retardancy of polyurea (PUA) composites incorporating varying dosages of these flame retardants was evaluated using cone calorimetry tests (CCT). The findings demonstrate that the incorporation of Fe2O3/ZnFe2O4/g‐C3N4@ZIF‐8 significantly enhanced the flame retardant properties of PUA composites. With the addition of 3 wt% of the flame retardant, the peak heat release rate (PHRR), total heat release (THR), total smoke production (TSP), and total CO yield (TCO) of the PUA composites decreased to 890.82 kW/m2, 131.34 MJ/m2, 12.30 m2, and 2.39 g, respectively, reflecting reductions of 33.59%, 18.59%, 29.40%, and 47.93% compared with pure PUA. The flame‐retardant mechanism was systematically analyzed in both the condensed and gas phases. This study provides a robust experimental foundation and novel insights that contribute to the development of advanced flame‐retardant coating materials. [ABSTRACT FROM AUTHOR]

This paper investigates the laminar burning velocity (S L) and instability of NH 3 /bio-syngas under different bio-syngas contents, oxygen enrichment factors (Ω), and the cracking ratio of NH 3 (ζ) using a constant-volume combustion bomb. The results show that increasing bio-syngas, Ω , and ζ effectively enhance the S L of the fuel. Around ζ = 60%, the relationship between S L and the NH 3 content before cracking is reversed. Increasing the bio-syngas and ζ enhance S L through the chemical effect, while Ω primarily enhances S L through the thermal effect. When Ω = 50%, the contribution of thermal effect can reach up to 94.53%. Linear stability analysis indicates that increasing the bio-syngas content and ζ reduces the critical Peclet number (Pe c), while Ω increases Pe c. As the bio-syngas content and ζ increase, the growth rate of perturbation (∑) monotonically increases, indicating instability. Ω , on the other hand, decreases ∑ , making it negative. • Bio-syngas, O 2 enrichment, and pre-cracking increase the S L of NH 3 /bio-syngas. • Virtual gas method to analyze transport, thermal, and chemical effects. • Linear stability theory to analyze flame instability. • Definition of flame stabilization range based on the Peclet number. [ABSTRACT FROM AUTHOR]

Moderate or intense low-oxygen dilution (MILD) combustion has the potential to enhance flame stability and control NOx emissions when using ammonia (NH 3) as fuel. However, the effects of a wide range of ammonia ratios on the combustion characteristics and NOx emissions of jet in a hot co-flow (JHC) ammonia-doped MILD combustion have not been thoroughly investigated. In this study, the combustion and NOx production characteristics of CH 4 /NH 3 hot co-flow combustion jets with a wide range of NH 3 contents (i.e. , ammonia ratios) are investigated systematically. The results indicate that all the simulated cases fall within the MILD combustion regime. The autoignition temperature increases, while the maximum temperature rise decreases monotonically with the increase of ammonia ratio. This suggests that the MILD combustion regime is more easily achieved with the addition of ammonia. The maximum temperature rise shows only slight changes when the ammonia ratio is less than 60%. This phenomenon occurs because the adiabatic flame temperature decreases with the blending of ammonia; however, the heat loss due to radiation is also reduced. Under most conditions, the emission index of NO (EINO) initially increases with the ammonia ratio when it is below 50%, but gradually decreases when it exceeds 50%. Additionally, the EINO decreases with an increase in hot co-flow temperature for a given ammonia ratio, indicating that the overall NO emission levels are suppressed by raising the hot co-flow temperature, despite the peaks of the NO rise. Changes in key chemical reaction pathways are also analyzed. It is found that hydroxyl (OH) radicals play a significant role during the dehydrogenation of NH 3 into NH 2 radicals. In ammonia-rich combustion, a higher ammonia ratio suppresses the conversion of NH i to HNO, while promoting the conversions of NH i to N 2 H 2 , NN, and N 2 O. This shift is advantageous for the conversion of NH 3 into N 2. [Display omitted] • Jets in hot co-flow combustion are simulated with a wide range of ammonia ratios. • Combustion regime and temperature variation are analyzed. • Emission index of NO (EINO) under different conditions are calculated. • Reaction pathways of NH 3 into NO with low and high ammonia ratios are compared. • Effects on NH i radical conversion to N-containing species are also discussed. [ABSTRACT FROM AUTHOR]

Due to the high costs associated to experimental testing of hydrogen (H 2) explosions, numerical simulations play an essential role in the design of safe industrial systems. In this work, we investigate the use of the Thickened Flame Model (TFM) to perform simulations of H 2 deflagrations. Specific issues arise when considering hydrogen: (i) due to differential diffusion, the flame is very sensitive to stretch; (ii) instabilities of the flame front are generated and lead to an increased flame propagation speed. Both of these phenomena are affected by flame thickening. First, the flame sensitivity to stretch is artificially increased by the thickening. The recently developed Ma-TFM model proposes a correction of diffusive fluxes to reach the correct Markstein length and is selected in this work. Secondly, thermo-diffusive and hydrodynamic flame instabilities are also altered by thickening. By computing the dispersion relationship for a hydrogen/air mixture, we show that the instability scales are proportional to the thickening factor F. A simple subgrid scale (SGS) model, based on the computations of laminar unstable 2-D and 3-D flames, is then considered to take into account the effect of instabilities. The Ma-TFM and SGS instability models are applied together for the first time on a semi-industrial vented lean hydrogen deflagration, leading to promising results. In particular, it is found that considering 3-D unstable flames is necessary to accurately predict the experimental pressure peaks. [Display omitted] • Stretch corrected Thickened Flame Model coupled to a model for flame instabilities. • Thermodiffusive instability scales are proportional to the thickening factor. • Successful simulation of a semi-industrial vented hydrogen deflagration. • 3-D nature of thermo-diffusive instabilities needs to be considered. [ABSTRACT FROM AUTHOR]

A laminar stagnation flow flame stabilized at a plane wall is theoretically analyzed, coupled with a thermo‐elasticity model in the wall. Mathematical models for both the flame and the wall will be proposed, and corresponding analytical solutions based on their dimensionless forms will be obtained. The mathematical analysis of this flame‐solid interaction primarily focuses on the effect of the flame on combustion‐induced thermo‐mechanical stresses and the influence of wall material on flame properties such as flame temperature and stability against extinction. A sensitivity analysis is further performed to examine how thermo‐mechanical stress inside the wall is affected by changes in other combustion conditions (e.g., mixture composition, flame stretch rate). This study offers valuable insights into understanding the interaction between flames and solids, a relationship crucial in engineering applications such as the interaction between combustion processes and blades within gas turbine machinery. [ABSTRACT FROM AUTHOR]

This study utilizes numerical simulations to investigate combustion efficiency in a Double Cavity Trapped Vortex Combustor (DCTVC). The DCTVC, employing a double cavity design and a cavity stabilization concept, enhances flame stability and minimizes pressure drop, achieving optimal performance by injecting an appropriate mix of fuel and air into the first cavity. Vortices and eddies are utilized to achieve the greatest turbulent mixing in the DCTVC combustion chamber. Because turbulence is precisely contained inside the two chambers where reactants are introduced and effectively blended, this enhances the efficiency of the fuel and air blending process. The momentum flux ratio between the cavities and mainstream flow significantly impacts the flow structure in the cavity region under under-reacting flow circumstances. Studying NOx emissions in combustors is imperative due to their relationship with turbulence intensity, recirculation zones, and trapped vortex zones, which directly impact combustion efficiency and emission levels. Staged combustion systems, commonly associated with DCTVCs, exhibit the potential for a substantial 30% to 60% reduction in NOx emissions. A parametric study, varying parameter such as the cavity's geometry provides valuable insights in flow and flame structure, demonstrating the adaptability and efficiency of combustion in the DCTVC. [ABSTRACT FROM AUTHOR]

This paper investigates the theoretical implications of applying Darcy's law to premixed flames, a topic of growing interest in research on flame propagation in porous media and confined geometries. A multiple-scale analysis is carried out treating the flame as a hydrodynamic discontinuity in density, viscosity, and permeability. The analysis accounts in particular for the inner structure of the flame. A simple model is derived allowing the original conservation equations to be replaced by Laplace's equation for pressure, applicable on both sides of the flame front, subject to specific conditions across the front. Such model is useful for investigating general problems under confinement including flame instabilities in porous media or Hele-Shaw channels. In this context, two Markstein numbers are identified, for which explicit expressions are provided. In particular, our analysis reveals novel contributions to the local propagation speed arising from discontinuities in the tangential components of velocity and gravitational force, which are permissible in Darcy's flows to leading order, but not in flows obeying Euler or Navier–Stokes equations. [ABSTRACT FROM AUTHOR]

Flame stability and pollutant emission performances of a porous burner fueled with ammonia/hydrogen blend were investigated numerically in this study. In this regard, a 2D solver based on finite volume method was developed in order to simulate reacting flow and heat transfer modes through a porous medium. Combustion characteristics in terms of porous structure, equivalence ratio and fuel component were studied and the pollutant emission trends were discussed. Flame stability limit was observed to be extended with increasing equivalence ratio regardless to ammonia fraction. Results proved that addition of ammonia in the fuel blend reduced the flame stability limits and thermal flame thickness but led to the enhanced NO emission. Increasing equivalence ratio led to a decrease in thermal flame thickness under fuel-lean conditions while it caused that the thickness of flame zone to be increased slightly under fuel-rich conditions. It was found that flame stability limits were extended as the mean pore diameter of the porous medium increased. The maximum amounts of NO concentration were achieved at stoichiometric conditions while, NO emission increased as equivalence ratio increased at fuel-lean conditions and it decreased as equivalence ratio increased at rich combustion regimes. [ABSTRACT FROM AUTHOR]

To ensure the safe utilization of hydrogen-enriched natural gas (HENG), it is essential to explore effective explosion suppressants to prevent and mitigate potential explosions. This study experimentally investigates the impact of ultrafine water mist containing K2CO3 additives on the explosion characteristics of methane/hydrogen/air premixed combustion. The influence of varying K2CO3 concentrations on pressure rise rates and flame propagation was analyzed across different hydrogen blending ratios. The results demonstrate that the addition of K2CO3 to ultrafine water mist significantly enhances its suppression effects. The peak overpressure decreased by 41.60%, 56.15%, 64.94%, and 72.98%, the flame speed decreased by 30.66%, 70.56%, 46.72%, and 65.65%, and the flame propagation time was prolonged by 25%, 20.83%, 22.92%, and 18.75%, respectively, for different hydrogen blending ratios, showing a similar trend. However, the suppression effectiveness diminishes under high hydrogen blending ratios and low K2CO3 concentrations. Further analysis using thermogravimetric infrared spectroscopy and chemical kinetics simulations revealed that the heat release rate and the generation rate of active free radicals significantly decrease after the addition of K2CO3 to the ultrafine water mist. The recombination cycle of KOH → K → KOH, formed by reactions (R211: K + OH + M = KOH + M) and (R259: H + KOH = K + H2O), continuously combines active free radicals (·O, ·OH) into stable product molecules, such as H2O. However, at low K2CO3 concentrations, reaction R211, which suppresses laminar combustion sensitivity and consumes a larger quantity of active free radicals, does not dominate, leading to a reduced suppression effect of K2CO3 ultrafine water mist. Several factors during the reaction process also adversely affect the performance of K2CO3-containing ultrafine water mist. These factors include the premature onset of laminar flame instability at low K2CO3 concentrations, the increased flame-front propagation speed due to the addition of hydrogen to methane, which shortens the residence time of K2CO3 in the reaction zone, and the turbulence caused by unvaporized droplets. [ABSTRACT FROM AUTHOR]

Polymer nanofibers exhibit unique nanoscale effects, high specific strength and modulus, exceptional design flexibility, large aspect ratios, and substantial specific surface areas. These characteristics have drawn significant attention in emerging fields such as flexible electronics, 5G communications, and new energy vehicles. Notably, poly(p‐phenylene benzobisoxazole) nanofibers (PNFs) present the best thermal stability and flame retardancy among all known polymer nanofibers. Furthermore, due to the highly oriented molecular chains and orderly structure, PNFs demonstrate superior thermal conductivity compared to conventional polymer nanofibers, thus garnering significant attention and favor from researchers. This paper summarizes the latest research progress of PNFs, detailing three preparation methods (electrospinning, mechanical dissociation, and protonation) along with their respective advantages and disadvantages. It also elucidates the current development status of PNFs in applications such as flame retardancy, thermal conduction, electrical insulation, electromagnetic shielding, and battery separators, and discusses the challenges and prospects faced by PNFs. This paper aims to provide theoretical guidance for the preparation and application of PNFs, enhancing their potential in advanced applications, and further expanding their application scope. [ABSTRACT FROM AUTHOR]

This study presents a novel proof‐of‐concept method for synthesizing aerogel on ceramic insulation blankets using a vacuum infusion sol–gel process with subsequent drying at ambient pressure, enhancing adhesion and durability and enabling coating on complex geometries. Scanning electron microscopy (SEM) analysis revealed a porous microstructure in the ceramic blankets, while the polymethylsilsesquioxane (PMSQ) aerogel exhibited a well‐defined and interconnected network. Fourier transform infrared (FTIR) spectroscopy and solid‐state nuclear magnetic resonance (NMR) analyses confirmed the presence of silica and carbon, respectively. Among the various compositions, the 10 wt.% PMSQ aerogel blanket establishes highly effective thermal stability in thermogravimetric analysis (TGA) results. Pristine ceramic and aerogel blankets were subjected to a 1300°C butane flame for high‐temperature stability tests that indicated the 10% PMSQ aerogel composite blanket presented better insulation properties and back surface temperature of approximately 170°C, the lowest among the other surface back temperatures of the other samples. Water contact angle measurements confirmed the hydrophobic properties and surface free energy (SFE) of PMSQ aerogel ceramic blankets. Optimizing surface‐free energy and surface tension is crucial for enhancing these materials’ hydrophobicity, thermal insulation, and structural integrity. The surface energy ranged from 11.19 to 0.96 mJ/m2, while the surface tension ranged from 48.47 to 64.97 mN/m for 10%–30% PMSQ aerogel ceramic blankets. [ABSTRACT FROM AUTHOR]

To guide the nozzle design for a novel oxy-fuel combustion facilitated pyrolysis technology, oxy-fuel rich combustion of pyrolysis gas is investigated experimentally and numerically. Two numerical models are compared and validated by experimental observations, among which the Eddy Dissipation Concept model performs better in prediction of flame length, maximum temperature, species conversion and flame stability with the modified fine scale constant. Flame length is found to be inversely proportional to the mixing rate of fuel and oxidizer. For non-premixed nozzles, the mixing rate increases with the increase in difference between the inner and annular velocity. For partially premixed nozzles, higher annular velocity promotes the mixing. The selective combustion molar ratio of three fuel components in practical nozzles are between those in premixed flame and at thermodynamic equilibrium assumption. CH 4 is consumed the most, while H 2 consumption molar ratio to CH 4 is 56%–69% and CO is net produced after the combustion. • The modified EDC model reasonably predicts flame appearance and blow-off limits. • Flame length is inversely proportional to the mixing rate of fuel and oxidizer. • For partially premixed nozzles, higher annular velocity promotes the mixing. • H 2 consumption molar ratio to CH 4 is 56%–69%, while CO is net produced. • For oxy-fuel rich combustion, yellow flame occurs at better premixed conditions. [ABSTRACT FROM AUTHOR]

Large Eddy Simulation (LES) coupled with the Linear Eddy Model (LEM) provides a robust method for studying turbulent combustion, but it is computationally expensive due to the need for highly resolved sub-grid LEM domains. These domains simulate sub-grid stirring through stochastic rearrangements of scalar fields, while large-scale transport is modelled using a Lagrangian ‘splicing’ scheme. To address the computational cost of LES-LEM, a super-grid (SG) framework for LEM closure was developed by the authors (Comb. Theor. Model. 28, 2024), which uses coarse-graining, on-the-fly chemistry tabulation and a presumed PDF approach to reconstruct thermochemical fields at LES resolution. This study applies SG-LEM to a challenging setup, Case 1 of the Volvo Validation Rig, which involves a bluff-body-stabilised turbulent premixed propane-air flame, as a stress test to identify limitations that were not revealed by the previous application, in particular that of the coarse-graining parameters used to generate the super-grid. The intent is to yield a more realistically constrained assessment of the current capabilities of the method, and insight into possible ways for improving it. Four simulations were conducted using three SG cluster sizes. The finest resolution was tested with a global 2-step mechanism, showing good agreement with experimental data for temperature and velocity, particularly near the bluff body. The two larger cluster sizes used a 66-step skeletal mechanism for more detailed chemical closure but led to unphysical quenching due to splicing inaccuracies. To mitigate these issues, two novel additions were introduced: an intra-cluster-stirring routine and a method to control SG cluster shapes to reduce numerical dissipation. These methods improved flame stability with coarser SG clusters and more detailed mechanisms. Comparison with experiments showed good agreement for temperature and velocity, though elevated CO levels were observed in the recirculation region. Potential methods for further improving SG-LEM's capabilities are discussed. [ABSTRACT FROM AUTHOR]

Ammonia, regarded as a zero-carbon fuel, presents significant challenges due to its notable combustion and chemical inertness. To mitigate these challenges, blending liquid ammonia with carbon-neutral methanol offers a promising avenue for creating an innovative, stable, and large-scale producible carbon-neutral fuel. This study investigates the impacts of xCH 3 OH (methanol mole ratio in methanol-ammonia mixture) and v (mean jet velocity at nozzle outlet) on forming stable flames of a premixed methanol-ammonia argon-oxygen (MA-AO) gaseous jet in the atmospheric surrounding. Results indicate that the pure ammonia argon-oxygen (A-AO) mixture can be ignited by an electrical spark with the energy of about 52.1 mJ, but it cannot grow to be a stable jet flame although the fire nucleus can form. Blending methanol is very helpful in forming a stable jet flame of the MA-AO mixture. When xCH 3 OH is lower than 49% at λ = 1.0, only the fire nucleus could be formed without a stable jet flame. When xCH 3 OH is more than 49%, there is a certain mean jet velocity range for different xCH 3 OH to form a stable flame. At the low-velocity limit, the flame would be quenching. While the flame would be blown off at the high-velocity limit. The velocity limits of quenching and blow-off become higher with higher xCH 3 OH , and the blow-off velocity limit increases more evident. • The ammonia combustion could be triggered with spark energy of 52.1 mJ. • There is a threshold of methanol-ammonia ratio to form a stable methanol-ammonia flame. • The methanol-ammonia flame stability has a close relationship with mean jet velocity. [ABSTRACT FROM AUTHOR]

A constant volume combustion chamber is employed to investigate the laminar burning characteristics of syngas. The effects of changes in diluent gas composition (CO 2 /N 2) and H 2 /CO ratio on the laminar burning velocity (S L) of syngas are decoupled and analyzed. The instability of laminar flames is analyzed using effective Lewis number, flame thickness, thermal expansion ratio, and linear stability theory. The results indicate that as the amount of diluent gas increases, thermal diffusion instability (TD) increases, while hydrodynamic instability (DL) gradually decreases. With a decrease in the H 2 /CO ratio, TD gradually decreases, and DL increases. When the diluent content is below 45%, the critical flame radius under N 2 dilution conditions exceeds that under CO 2 dilution conditions. Above 45%, the situation reverses. As the H 2 /CO ratio decreases, the critical flame radius gradually increases. When the H 2 content is high, the critical flame radius under N 2 dilution conditions is larger. • Comprehensive analysis of the impact of diluent content and H 2 /CO ratio. • Decoupling analyzes the dilution, thermal, and chemical effects of CO 2. • Decoupling analyzes the chemical and physical effects of changing the H 2 /CO ratio. • The spherical flame instability is analyzed with linear stability theory. • Analyzing the instability range of flames by incorporating critical radius. [ABSTRACT FROM AUTHOR]

To achieve stable combustion within supersonic combustors, the strut-based mixing augmentation techniques are commonly employed. Large Eddy Simulations (LES) are employed to capture the intricate details of the combustion process in this study, focusing on the influence of shock waves induced by the leading edge of the strut and recirculation zones formed at the trailing edge on flame structure and stability. The effects of five struts with different leading edge angles on the stabilization characteristics of lifted jet flames were investigated, and a novel wedge-shaped strut was proposed. The results reveal that variations on the leading-edge angle of the struts lead to significant differences in the morphology of the jet flames. Under conditions permitting stable combustion, a strut with a 5° leading edge half-angle exhibits the highest combustion efficiency, though the combined effects of shock waves and recirculation zones in the 7° leading edge half-angle strut are also noteworthy. Based on these findings, a novel wedge-shaped strut design is introduced, which combines the characteristics of both strut types. The novel wedge-shaped strut achieves a combustion efficiency of 97 % at the slight cost of additional total pressure loss, providing a foundation for further optimization. • The stabilization properties of lifted jet flames induced by struts were investigated numerically. • A wedge-shaped strut combustor was proposed based on the parametric study. • A combustion efficiency level of 97 % was achieved with a 3 % increase in total pressure loss. [ABSTRACT FROM AUTHOR]