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The laminar burning velocity (LBV) and cellular instability of ammonia/syngas/air were investigated using the spherically expanding flame method at an initial pressure of 3 atm and temperatures of 298–448 K. The impacts of equivalence ratio, temperature, and hydrogen ratio on LBV were scrutinized. The results demonstrate that the LBV varies non-monotonically with the equivalence ratio and increases with increasing temperature and hydrogen ratio. Flame instability was analyzed using flame uplift rate, Lewis number, thermal expansion ratio, flame thickness, critical radius, critical Peclet number and logarithmic growth rate of perturbation in combination with the schlieren images. Of these, the flame uplift rate is used to quantify buoyancy instability, a flame instability that has received little attention. At high pressures, lower LBV makes the flame susceptible to buoyancy instability. The flame uplift rate increases with increasing flame radius, suggesting that the buoyancy instability becomes increasingly significant as the spherical flame expands. The diffusional-thermal instability is weaker at the fuel-rich side and enhanced at the leaner side. As the hydrogen ratio increases, the flame instability increases. Hydrodynamic instability is not susceptible to temperature, which is only slightly weakened with increasing temperature. Additionally, the phenomenon of superadiabatic flame temperature (SAFT) in ammonia/syngas/air flames was first found and analyzed its temperature dependence. Increasing the initial temperature suppresses SAFT occurrence. [Display omitted] • LBVs of ammonia/syngas/air mixtures were measured at 298–448 K and 3 atm. • The buoyancy instability was studied in detail using flame uplift rates. • The effect of initial temperature on the flame instability was analyzed in detail. • The phenomenon of SAFT in ammonia/syngas/air flames was first found. [ABSTRACT FROM AUTHOR]

In urban pipelines, blending hydrogen into natural gas has been considered as an effective way of hydrogen usage to reduce carbon emission on household appliances. However, few studies, especially experimental ones are dedicated to address the characteristics of a typical domestic cooker due to the transition from natural gas to 20%hydrogen-enriched natural gas. This study experimentally investigated the changes in terms of the gas flow rate, flame temperature, heat transfer and emission characteristics of a domestic cooker as a result of such transition. Using a self-developed gas blending system, the flow rates of the both the mixed fuel and its components are obtained. The data shows that after blending hydrogen, the mixed gas flow rate becomes higher. Compared to the original cooker burning natural gas, hydrogen blending results in a decreased natural gas flow rate, leading to lower carbon emission. In addition, the thermal input to the cooker is lowered and hydrogen blending leads both the inner and outer combustion zones of the flame to shorten while the flame temperature to increase. As an attempt to optimize the performance of the cooker, the effects of wok stand height on heat transfer efficiency and NO/NO x /CO emissions are examined. It is found that the cooker fueled by 20%hydrogen-enriched natural gas exhibits lower heat transfer efficiency, higher NO/NO x emissions and lower CO emission. According to the fact that the heat transfer efficiency increases at lower wok stand height, the wok stand height is lowered from its original 7 cm–6 cm and 5 cm. The finding indicates that when the wok stand height is moderately decreased to 6 cm, NO/NO x emissions decrease and CO emission is only marginally increased. This study proposes that when natural gas is replaced by 20%hydrogen-enriched natural gas on a swirl flame cooker, the wok stand height can be slightly lowered to exploit the advantages of blended hydrogen combustion. • A systematic experimental study of the flow/temperature/emission/heat transfer of a cooker. • The changed flow rates are measured by using a self-developed device. • The height of the swirling flame shortens after blending hydrogen to natural gas. • The flame temperature/NOx emission increase while CO emission decrease. • Lowering the wok leads to higher heat transfer efficiency, lower NO x while only marginally higher CO. [ABSTRACT FROM AUTHOR]

To reduce carbon emissions, hydrogen is a clean energy as fuel to co-combustion with natural gas. This experimental work focuses on studying the effects of hydrogen addition to methane on combustion performance and emissions in non-premixed coaxial burners, establishing performance prediction models and optimizing operation conditions involving fuel velocity, hydrogen blending ratio and equivalence ratio. The global sensitivity and analysis of variance were adopted to quantify the contributions of independent variables on the output responses of temperature, O 2 , NO, CO and CO 2 emissions. The hydrogen blending ratio is the most influential parameter, whose total effects of NO and CO 2 emissions are 64.6% and 83.5%, respectively. The equivalence ratio is not significant to NO and CO 2 emissions, and the adjusted determination coefficient of the reduced prediction model is 0.9707 and 0.9360, demonstrating a better goodness of fit. Based on the response surface model and particle swarm optimization algorithm, a Pareto was solved showing NO and CO 2 emissions decrease by 42.0%–73.6% and 60.8%–89.5%, and peak temperature in the chamber centerline increases by 1.02%–3.61%. The research results provide a profound guide to predict and optimize combustion performance and emissions for methane-hydrogen non-premixed flame. [Display omitted] • Prediction models of CH 4 –H 2 non-premixed burner were built by response surface method. • Total effects of hydrogen blending ratio on NO and CO 2 emissions are 64.6% and 83.5%. • Equivalence ratio is not significant to flue gas temperature, NO and CO 2 emissions. • A Pareto set was obtained by optimizing flame temperature and pollutants via PSO. • Peak temperature increases by 2.30%, NO and CO 2 decrease by 59.4% and 78.3%. [ABSTRACT FROM AUTHOR]

AbstractThe flame temperature is a crucial parameter in combustion, indicating heat generation and transfer. However, determining the correct temperature becomes challenging when flame emissivity is unknown. This article presents a multispectral 2D temperature field reconstruction method using particle swarm optimization and the Broyden–Fletcher–Goldfarb–Shanno algorithm, combined with multivariate extreme-value optimization. This method establishes an objective function based on the correlation between the true temperature and spectral data. The objective function was minimized by adjusting the emissivity, enabling the reconstruction of 2D temperature and emissivity images without assuming an emissivity model. Calibration with a multispectral camera yielded the spectral response coefficients, and three-time spline interpolation was used to verify the calibration data. The reconstructed 2D temperature field showed a mean absolute error (MAE) of 4.61 and structural similarity (SSIM) of 0.995. The reconstructed emissivity image had an MAE range of 0.04 to 0.053 and an SSIM range of 0.897 to 0.915. The system, tested on a butane flame, showed a temperature range of 1001 K to 1356 K, with an average temperature of 1194 K and emissivity values ranging from 0.3166 to 0.8621. The results align with the expected combustion process and radiation characteristics distribution of the butane flame. [ABSTRACT FROM AUTHOR]

We present a linear stability analysis of the Richtmyer-Meshkov instability that develops when a shock wave reaches a sinusoidally perturbed premixed flame from behind. In the hydrodynamic regime, when acoustic contributions dominate the flame growth rate, the problem is analytically addressed by the direct integration of the sound wave equations at both sides of the flame, which are bounded by the reflected and transmitted shock waves and the flame front that acts as a contact surface in the hydrodynamic limit. The resolution involves: a hyperbolic change of variables to modify the triangular spatio-temporal domain, a transformation in the Laplace variable, the resolution of the functional equations in the frequency domain, and the final inverse Laplace transform. The latter involves a novel resolution method that is proven beneficial for long-time dynamics. Asymptotic analysis is also carried out to describe the early time and late time hydrodynamic response. The nonuniform flow field resulting from distorted oscillating shocks is characterized by acoustic, rotational, and entropic disturbances, each of which exerts a substantial influence on flame dynamics. These disturbances contribute to the intricate interplay of factors shaping the behavior of the flame in response to the nonuniform flow. In particular, the sensitivity of local flame propagation to temperature disturbances is investigated. This work contributes to a deeper understanding of Richtmyer-Meshkov instability dynamics and offers insights into instability reduction through the modulation of temperature disturbances generated by the transmitted shock. • Introduction of a self-consistent analytical model for Richtmyer-Meshkov instability within shock-flame interactions. • Development of an enhanced resolution method for the functional equation in the Laplace variable. • Introduction of a new resolution method for the transient evolution via the inverse Laplace transform. • Provision of a comprehensive mechanism regarding Richtmyer-Meshkov instability reduction. [ABSTRACT FROM AUTHOR]

This paper presents a novel green combined heat and power generation system for industrial applications. It composes of a hydrogen-fueled combined cycle power plant and a battery energy storage. Firstly, the hydrogen-air rich mixture enters the combustion chamber of the gas turbine cycle for generating electricity, while recovering the heating energy from the exhausted flue gases for driving a steam turbine cycle. The heating energy extracted from the condenser heat exchanger is also used to supply the heating demand of the end-user. Moreover, a comprehensive thermodynamic model and analysis of H 2 combustion process is provided to estimate the adiabatic flame temperature based on enthalpies of reactants and products. The optimum operating point of the cogeneration system is found by solving a mixed-integer nonlinear problem using MATLAB and GAMS over a 24-h study horizon aiming to minimize its daily operation cost considering all technical constraints of system components and load-generation balance criterion. It is found that the energy efficiency of the hydrogen-fueled combined cycle changes from 46 to 58 % while generating 11.331–12.982 MW electricity and 4.436–4.984 MW heat. Two cases are studied without and with participation of battery in energy procurement strategy. It is demonstrated that the objective function of the optimization problem improves from 18 $ cost in case 1 to 29 $ revenue in case 2. • Thermodynamic model and analysis of a H 2 -fueled CHP plant is presented. • Adiabatic flame temperature is obtained based on enthalpies of reactants and products. • A high-temperature heat exchanger is used to produce steam from waste heat of gas turbine flue gases. • Optimal charge and discharge of battery is scheduled for higher cost savings. [ABSTRACT FROM AUTHOR]

Utilising ammonia, which is one of the most promising carbon-free fuels, comes with the challenge of stable combustion due to its low reactivity. Therefore, advanced strategies are needed, including blending ammonia with highly reactive fuels or implementing innovative combustion techniques. For this reason, the present study proposes an ammonia-methane dual-fuel co-firing combustion mode. The second focus is to analyse the effect of preheating the main swirl air on NO emissions and examine the chemical kinetic reactions. Experimentally, chemiluminescence imaging was conducted to analyse OH* and NH 2 * emissions to evaluate the flame structure and reaction zones. Numerically, simulations were performed using a chemical multi-reactor network model to examine kinetics. By comparing the fully premixed combustion to the dual-flame co-burning mode, the NO emissions decreased by 80% in the latter case at T = 473K and ϕ = 0.6. The NH 3 reaction pathway analysis shows a significantly higher percentage reduction of NO and NH 2 reactions in dual flame mode compared to premixed flames. Preheating the main air impacts NO reactions in the dual flame mode, allowing for lower NO emissions. • Pilot premixed NH 3 jet flame surrounded by swirl CH 4 flame is an alternative fuel injection strategy. • Lower emissions of NO can be attained with dual flame without compromising flame stability. • Higher NO x emissions are attained with increasing temperature for premixed flame. • NH 2 +NO ↔ NNH + OH is strengthened with increasing preheating temperature for dual flame. • Dual-fuel flame with preheating is a viable combustion method to lower NO x emissions. [ABSTRACT FROM AUTHOR]

The research has examined the effects of CO 2 dilution on ignition characteristics in H 2 /air mixtures. An ignition kernel was initiated by a laser-induced plasma in H 2 /air/CO 2 mixtures with a bulk velocity of 6.5 m/s. An infrared camera was used to measure radiation intensity emitted from H 2 O and ignition probabilities. A high-speed schlieren image system was utilized to measure ignition kernel areas and ignition time. High-speed chemiluminescence was performed to examine OH* intensities. Numerical simulations were conducted using GRI 3.0 mechanisms to calculate reaction rates and laminar flame speeds. The ignition probability is highest for the undiluted mixtures and decreases with increasing the CO 2 dilution fraction at constant adiabatic temperatures. A prolonged ignition time is observed at elevated CO 2 dilution concentrations. Increasing the CO 2 mole fraction decreases the ignition kernel growth, the integrated OH* intensity, and the integrated radiation intensity for each adiabatic temperature. CO 2 reacts with H radicals and decreases the production of OH*, OH, and H 2 O. The CO 2 dilution in the H 2 /air flames significantly contributes to the reduced reaction rate and flame speed, resulting in the low ignition probability. The high ignition probability is found at the large integrated OH* intensity in all cases. The ignition probability is high at the large integrated radiation intensity under the constant adiabatic flame temperatures. The OH* intensity is a critical parameter to estimate the ignition probability in the diluted lean hydrogen flames. • The effects of CO 2 dilution on the ignition process have been studied in lean premixed H 2 /Air flames. • The ignition probability decreases with increasing the CO 2 dilution fraction. • An increase in the CO 2 dilution fraction in the mixtures reduces OH* intensity and radiation intensity emitted from H 2 O. • The presence of CO 2 in the mixtures decreases reaction rates and flame speed. [ABSTRACT FROM AUTHOR]

The CH 4 -NH 3 (50%:50%) premixed flame with/without the wall effects are simulated and compared at the stoichiometric condition in this study. The effects of cold wall and local flame dynamics on the flame temperature, heat release rate (HRR), CH 4 /NH 3 oxidations and local CO/NO formations are analyzed quantitatively. Results show that the flame temperature and HRR are decreased and increased respectively along the flame front towards the axis of free flame, but they are both declined significantly towards the wall owing to suppressed chemical kinetics by the heat loss. The negative flame stretch and differential diffusion at the flame tip suppress the CH 4 oxidation and the fast path (NH 3 →NH 2 →NH→N 2) of NH 3 oxidation effectively, but affect the slow path (NH 3 →NH 2 →HNO→NO→N 2) of NH 3 oxidation moderately. This contributes to suppressed CH 4 /NH 3 oxidations and improved NO production at the flame tip of free flame. Based on NRR variations and ROP analysis, compared with CH 4 oxidation, wall heat loss exerts stronger suppressions on the fast path of NH 3 oxidation, while it decelerates the slow path of NH 3 oxidation less evidently. Since the fast path is the primary pathway of the NH 3 oxidation, the NH 3 oxidation suffers more effective suppression of the wall heat loss than the CH 4 oxidation. Furthermore, considering the significance of the slow path to the NO formation, the relatively enhanced importance of the slow path to the NH 3 oxidation in the near-wall region predominates the comparatively effective NO formation in the CH 4 -NH 3 flame compared with the pure CH 4 flame under the influence of wall heat loss. For the CO/NO formations, the local CO production/oxidation in the wall-impinging CH 4 -NH 3 flame are decelerated simultaneously due to the strong heat loss, while the local NO production/destruction are inhibited/improved by the wall heat loss. • The CH 4 /NH 3 oxidizations in the near-wall region are compared and investigated. • The individual/coupling effects of flame dynamics and cold wall are studied. • Different oxidization pathways of NH 3 suffer different influence near the wall. • Major oxidization pathway of NH 3 is weakened more effectively by the cold wall. • CO/NO formations are affected by flame dynamics, wall heat loss and burned gases flow. [ABSTRACT FROM AUTHOR]

We conducted a numerical study of the effects of a vortex generator (VG) on the combustion characteristics and physical fluid flow of LPG on a porous bluff-body slot burner (PBSB) model, validating the numerical and experimental results of the temperature distribution and mixture flow velocity. The VG position (fuel (F) and air (A) slots), direction (clockwise, CW, and counterclockwise, CCW), aspect ratio (AR), and distance (S) were investigated parametrically in our porous vortex generator slot burner (PVGSB) model. According to our results, the VGSB model with a VG angle of 60°, CW direction, aspect ratio of 0.4, and VG distance of 0 mm enhanced the flame temperature by 24.4% due to a greater vortex influence. Moreover, applying a reverse triangular bluff body to the VGSB model had a stronger effect on the vortices and swirl flow of the mixture compared to the cylindrical bluff body, achieving 34.9% higher combustion temperatures compared to the referenced PBSB model. This numerical study of using LPG combustion on a slot burner with VGs and a reverse triangular bluff body, which we refer to as the VGSB model, could be applied to enhancing physical air–fuel flow and the flame temperature as characteristics of combustion. [ABSTRACT FROM AUTHOR]

Lubricating oil (LO) is an extensively applied fuel in industrial processes, often operating under high temperature and high-pressure conditions, which makes it prone to hot surface ignition. Hot surface ignition of LO is one of the potential sources of fire incidents in industrial processes and automotive lubrication systems. Taking LO as the object, a hot surface ignition experiment was conducted, using a self-developed test rig, image processing technology, and statistical analysis methods. The lowest ignition temperature of 311 °C was found. When the hot surface temperature exceeded 407 °C, the probability of ignition was prominent. Utilizing experimental probability data, a predictive model for ignition probability was established. In addition, the study discusses three stages of combustion and free radical generation, as well as the ignition delay time, flame duration, and flame height. Finally, the experimental results are compared with the measured distance of the automobile pipeline to quantify the fire risk of leaked LO. It is indicated that the dependence of ignition delay time on temperature is more substantial than oil volumes. As the volume of LO increased, the minor ignition temperature became smaller, and the probability of ignition decreased. The time when the flame height reached the measured distance accounted for 65–79% of the flame duration, and the average flame temperature was 1162–1347 °C. These results can quantify the danger of hot surface ignition resulting from leaked LO and guide the safety design for the automobiles. [ABSTRACT FROM AUTHOR]

AbstractAggregate drying is a crucial step in asphalt mixture production. Enhancing the model accuracy and controller performance of aggregate dryer burners is essential for consistent flame characteristics, reducing NOx emissions, and minimizing fuel consumption. This paper introduces a second-order nonlinear parametric model for coal powder burners that includes delay and noise. Model parameters were determined through experimental data using the Salp Swarm Algorithm, showing higher accuracy than models based on the least square method. A dual-layer model predictive control (MPC) based on this mathematical model was developed to improve the economic efficiency of the aggregate drying process. Simulation results showed that the dual-layer MPC saves 1.08 tons of coal every 10 h compared to a standard MPC. A full-scale prototype demonstrated average flame length, flame temperature, and NOx emissions of 4242.6 mm, 1729.4 °C, and 460.2 mg/m³, respectively, validating the accuracy of the proposed mathematical model and controller. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the auto-ignition process of hydrogen in a hot oxidizer stream composed of oxygen–nitrogen and oxygen–water vapor with nitrogen/water vapor mass fractions in a range of 0.1–0.9. The temperature of the oxidizer varies from 1100 K to 1500 K and the temperature of hydrogen is assumed to be 300 K. The research is performed in 1D mixture fraction space and in a forced homogeneous isotropic turbulent (HIT) flow field. In the latter case, the Large Eddy Simulation (LES) method combined with the Eulerian Stochastic Field (ESF) combustion model is applied. The results obtained in mixture fraction space aim to determine the most reactive mixture fraction, maximum flame temperature, and dependence on the scalar dissipation rate. Among others, we found that the ignition in H 2 - O 2 - H 2 O mixtures occurs later than in H 2 - O 2 - N 2 mixtures, especially at low oxidizer temperatures. On the other hand, for a high oxidizer temperature, the ignitability of H 2 - O 2 - H 2 O mixtures is extended, i.e., the ignition occurs for a larger content of H 2 O and takes place faster. The 3D LES-ESF results show that the ignition time is virtually independent of initial conditions, e.g., randomness of an initial flow field and turbulence intensity. The latter parameter, however, strongly affects the flame evolution. It is shown that the presence of water vapor decreases ignitability and makes flames more prone to extinction. [ABSTRACT FROM AUTHOR]

Providing NFPA 1403 compliant live-fire training can present thermal and chemical exposure risk to instructors and students. To reduce risk, training academies, fire departments, instructors, and standards setting technical committees need more information on how different training fuels used in common training structures can impact the environment in which firefighter training occurs. This study utilized a traditional concrete training structure with multiple compartments to characterize training environments with three different fuel package materials [i.e., low density wood fiberboard, oriented strand board (OSB), and wood pallets]. Exposure risks for a fire instructor located on either the first or second floor were characterized using measurements of heat flux, air temperature and airborne concentrations of several contaminants including known, probable, or possible carcinogens. It was hypothesized that utilizing a training fuel package with solid wood pallets would result in lower concentrations of these airborne contaminants [aldehydes, polycyclic aromatic hydrocarbons (PAHs) and volatile organic compounds (VOCs)] than wood-based sheet goods containing additional resins and/or waxes. Additionally, it was hypothesized that these concentrations would be lower than in the single compartment Fire Behavior Lab presented in a companion manuscript. For all measured compounds other than hydrochloric acid, airborne concentrations were 10 to 100 times lower than in the Fire Behavior Lab. OSB-fueled fires produced the highest median concentrations of total PAHs and VOCs such as benzene, while the pallet fuel package produced the lowest median concentrations of these compounds. These trends generally followed the qualitative visual obscuration created by each fuel. Additional tests were conducted on the OSB-fueled fires with increased ventilation and an alternate means of reducing visibility through smoldering smoke barrels. This OSB experiment with increased ventilation resulted in the highest temperatures in the fire room but the lowest impact on visibility throughout the structure, as well as the lowest overall concentrations of contaminants in this study. In contrast, the smoldering straw-filled smoke barrel created a highly obscured environment (with minimal impact on thermal environment) and some of the highest concentrations of the targeted contaminants of any test. These data may be useful in balancing obscuration for training with potential exposure to thermal stressors and contaminants. [ABSTRACT FROM AUTHOR]

The experimental investigation aimed to determine how the use of biodiesel derived from dill and cresson oil affected the performance of semi-industrial burners. Furthermore, an investigation will be conducted to assess the combustion properties of different blends of biodiesel, specifically B10, B20, B40, and B60. The study looks at biodiesel's chemical makeup, physical properties, and how it works in the system that moves it to the burner and the burner simulator's burning process. Biodiesel exhibits comparable qualities to conventional diesel oil, enabling the possibility of blending it to achieve the desired ratio. The results suggest that increasing the percentage of biodiesel leads to a reduction in flame distance and a rise in flame temperature. Furthermore, the complete combustion of the fuel is responsible for the brilliant and transparent flame. Additionally, using dill and Cresson fuels that come from biodiesel raises the average flame temperature by about 17% and 16.1%, respectively, compared to regular diesel fuel. [ABSTRACT FROM AUTHOR]

The determination of the characteristics and main combustion properties of fuels is necessary for post-implementation in different applications. Among the most important combustion properties of a fuel are the combustion products, flame temperature and laminar burning velocity. Therefore, this paper describes the step-by-step development and coding of a MATLAB application that can determine 12 combustion products, flame temperature and laminar burning velocity in order to understand the logic of calculus procedure, so any user would be able to make improvements of new functionalities (add more fuels, add more combustion products, etc.). The numerical procedure and methods (Gaussian elimination, Taylor Series and Newton–Raphson) parallel with their implementation as code lines for the development of the application are carried out using flow charts. In addition, simulations in Ansys Chemkin were performed and included in the application as part of the results comparison. It was found that: (1) The MATLAB Application codification and development were successfully explained in detail, (2) the functions and execution sequence are described by using flow charts and code extract, (3) the application is available to everyone for modifications, (4) the application can only be used for hydrocarbons fuels, (5) the application execution time registered was less than 8 s. [ABSTRACT FROM AUTHOR]

According to the control mechanism of surface arc discharge plasma actuation on the flow and combustion of flameholder, the applicability of the phenomenological model of surface arc discharge is verified. And, the effects of different actuation positions and actuation intensities on the flow field structure, fuel atomization, ignition delay and flame stability in the flameholder are systematically analyzed. The results show that different actuation positions have a significant impact on the flow field structure, especially when the actuation energy is effectively concentrated and a strong actuation region is formed, which leads to the expansion of the recirculation zone, which in turn promotes fuel atomization, slows down the ignition delay and increases the average flame temperature. At the same time, with the increase of actuation intensity, the length of the recirculation zone, the mixing efficiency and the combustion efficiency increased linearly. [ABSTRACT FROM AUTHOR]

Flame temperature and spectral emissivity were the important parameters characterizing the sufficient degree of fuel combustion and the particle radiative characteristics in the Rocket Based Combined Cycle (RBCC) combustor. To investigate the combustion characteristics of the complex supersonic flame in the RBCC combustor, a new radiation thermometry combined with Levenberg-Marquardt (LM) algorithm and the least squares method was proposed to measure the temperature, emissivity and spectral radiative properties based on the flame emission spectrum. In-situ measurements of the flame temperature, emissivity and spectral radiative properties were carried out in the RBCC direct-connected test bench with laser-induced plasma combustion enhancement (LIPCE) and without LIPCE. The flame average temperatures at fuel global equivalence ratio (α) of 1.0b and 0.6 with LIPCE were 4.51% and 2.08% higher than those without LIPCE. The flame combustion oscillation of kerosene tended to be stable in the recirculation zone of cavity with the thermal and chemical effects of laser induced plasma. The differences of flame temperature at α = 1.0b and 0.6 were 503 K and 523 K with LIPCE, which were 20.07% and 42.64% lower than those without LIPCE. The flame emissivity with methane assisted ignition was 80.46% lower than that without methane assisted ignition, due to the carbon-hydrogen ratio of kerosene was higher than that of methane. The spectral emissivities at 600 nm with LIPCE were 1.25%, 22.2%, and 4.22% lower than those without LIPCE at α = 1.0a (with methane assisted ignition), 1.0b (without methane assisted ignition) and 0.6. The effect of concentration in the emissivity was removed by normalization to analyze the flame radiative properties in the RBCC combustor chamber. The maximum differences of flame normalized emissivity were 50.91% without LIPCE and 27.53% with LIPCE. The flame radiative properties were stabilized under the thermal and chemical effects of laser induced plasma at α = 0.6. [ABSTRACT FROM AUTHOR]

In the study, the secondary explosion characteristics of TiH 2 dust with different particle sizes induced by hydrogen-oxygen detonations were studied, using a shock tube with semi-open and seal conditions. The processes of dispersal and deflagration were analyzed by a high-speed camera, and the explosion temperature and pressure were measured with the two-color pyrometer technique and pressure sensors, respectively. The experiment results showed that the dust clouds of TiH 2 with smaller particle sizes were larger in volumes and more liable to combust. With the decrease of particle size, the deflagration processes of TiH 2 dust became more intense, while their average temperatures had reverse trends, that is, lager particle sizes had higher average deflagration temperatures. Compared with the semi-open condition of shock tube, the duration of combustion under the confined condition was prolonged and the shock waves were enhanced for the wall reflection, which made the ignition of TiH 2 dust more possible and the subsequent deflagration more violent. Furthermore, the effects of semi-open and seal conditions of shock tube on the peak pressures of secondary explosion were different, compared with no TiH 2 dust addition, the peak pressures of secondary explosion with TiH 2 powders decreased in semi-open condition but increased in seal condition. [Display omitted] • Secondary explosion of TiH 2 dust induced by hydrogen detonation were simulated. • Dust lifting characteristics of TiH 2 under the high-speed airflow were studied. • Dynamic flame temperature distributions of TiH 2 dust explosion were mapped. • Gas-solid two-phase interaction effects during TiH 2 dust explosion were analyzed. [ABSTRACT FROM AUTHOR]

Hydrogen-fueled gas turbines play one of the key roles in future carbon-neutral energy structure. Due to hydrogen's high flame speed and extreme flame temperature, design of burners applying hydrogen as fuel is of challenge. In this work, we conduct direct numerical simulations to investigate a non-premixed steam-diluted oxygen/hydrogen combustion, which is formed by inclined impinging fuel and oxidizer jets injected by sub-millimeter nozzles. This configuration inherently prevent flashback and has a higher mixing efficiency enhanced by jet impingement, thereby leveraging advantages of both conventional premixed and non-premixed configurations. The flame is lifted flame held at the jet impinging position far away from the wall boundary. The most intensive mixing process occurs at the outer sides of the two branches of hydrogen jet after impinging, forming the flame base and resulting in an edge-flame configuration. A larger jet inclination angle leads to more effective bulk turbulence mixing because of the increased mixing volume, thereby enhancing combustion completeness. Simultaneously, it results in lower wall heat flux due to gentler upstream recirculation of burnt products. Chemical explosive mode analysis is conducted to analyze the combustion procedure from ignition to burnt out. The flame is held by the recirculation of high-temperature burnt products upstream of the impingement position, and its structure is primarily formed by the simultaneous ignition of a widespread explosive mixture enhanced by intense turbulence. • DNSs are conducted to investigate the combustion of impinging fuel and oxidizer jets. • Edge-flame configuration is formed by impinging fuel and oxidizer jets. • Fuel and Oxidizer are intensively mixed near the oxidizer jet branches. • Inclination angle of jets affects the statistical thermophysical performance. • Flame is held by hot product recirculation. [ABSTRACT FROM AUTHOR]

Purpose: This study aims to numerically analyse a full-scale burner across a wide range of operating pressure conditions and determine the effect of swirl velocity on flame stabilization, flame holding and combustion performance. Design/methodology/approach: This study uses a numerical analysis approach to investigate a three-dimensional full-scale burner. Modified governing equations are used to determine the effect of swirl velocity on flame stabilization and flame holding. The GR-Mech 3.0 chemical reaction mechanism is used to predict the combustion process. To validate the model, a grid independence study is performed. Findings: The study reveals that swirl velocity enhances flame stability, resulting in better combustion rates. As the swirl velocity increases, higher flame temperatures are observed due to high convective heat recirculation. The heat transfer coefficient and high radiative extinction coefficient are found to vary based on fuel swirl velocity. The mass fraction of CH4 and CO emphasizes the role of swirl velocity on flame structure. Increasing velocity potentially improves combustion by delaying the process, leading to better combustion and lower emissions. Originality/value: The findings of this study contribute to the understanding of swirl-stabilized combustion and can guide the development of advanced combustion technologies, making it a valuable addition to the existing combustion field. [ABSTRACT FROM AUTHOR]

Biogas is a renewable and clean energy source that plays an important role in the current environment of lowcarbon transition. If high-content CO2 in biogas can be separated, transformed, and utilized, it not only realizes high-value utilization of biogas but also promotes carbon reduction in the biogas field. To improve the combustion stability of biogas, an inhomogeneous, partially premixed stratified (IPPS) combustion model was adopted in this study. The thermal flame structure and stability were investigated for a wide range of mixture inhomogeneities, turbulence levels, CO2 concentrations, air-to-fuel velocity ratios, and combustion energies in a concentric flow slot burner (CFSB). A fine-wire thermocouple is used to resolve the thermal flame structure. The flame size was reduced by increasing the CO2 concentration and the flames became lighter blue. The flame temperature also decreased with increase in CO2 concentration. Flame stability was reduced by increasing the CO2 concentration. However, at a certain level of mixture inhomogeneity, the concentration of CO2 in the IPPS mode did not affect the stability. Accordingly, the IPPS mode of combustion should be suitable for the combustion and stabilization of biogas. This should support the design of highly stabilized biogas turbulent flames independent of CO2 concentration. The data show that the lower stability conditions are partially due to the change in fuel combustion energy, which is characterized by the Wobbe index (WI). In addition, at a certain level of mixture inhomogeneity, the effect of the WI on flame stability becomes dominant. [ABSTRACT FROM AUTHOR]

Formic acid is a promising candidate fuel that can be produced by reacting renewable hydrogen with carbon dioxide. However, the burning safety characteristics of formic acid–air mixtures have not been fully studied. This paper presents an extensive theoretical study of the adiabatic explosion pressure of formic acid–air premixed laminar flames at various initial conditions (composition of formic acid: 17–38% volume; initial pressure: 0.1–1.5 bar; initial temperature: 333–500 K), using the GASEQ software package. GASEQ software calculates chemical equilibria based on ideal gas behavior and is based on the hypothesis of adiabatic expansion inside a closed containment that allows ideal expansion. The influence of the initial conditions (pressure, temperature, and concentration) of formic acid–air mixtures on the adiabatic explosion pressures, maximum flame temperature, and peak concentrations of the main reaction intermediates is investigated and discussed. It is found that the adiabatic peak explosion pressure (calculated equilibrium pressure) of the studied concentrations decreases with increasing initial temperature and increases linearly with increasing initial pressure. [ABSTRACT FROM AUTHOR]

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is one of the high-energy oxidants, but has limited application due to its high sensitivity. In this work, polyvinylidene fluoride (PVDF) was used as a co-oxidizer, which is expected to increase the safety of CL-20. One kind of novel graphene-based carbohydrazide complex (GCCo and GCNi) was employed to modify the properties of dual-oxidant CL-20@PVDF composites by the spray drying method and compared with traditional nanocarbon materials (CNTs and GO). The properties of these composites were investigated using the TGA/DSC technique and impact test. The results show that GCCo and GCNi could increase the activation energy (Ea) of CL-20@PVDF composites, and change the physical model of CL-20@PVDF, which followed the random chain scission model and then the first-order reaction model. In addition, these nanocarbon materials could reduce the impact sensitivity of CL-20@PVDF by their unique structure. Besides that, a dual-oxidant CL-20@PVDF system was used to improve the combustion property of Boron. GCCo and GCNi with the synergetic effect could increase the flame temperature and control the burn rate of CL-20@PVDF@B compared with CNTs and GO. The energetic nanocarbon catalyst-modified oxidant provides a facile method for stabilizing high-energy but sensitive materials to broaden their application. [ABSTRACT FROM AUTHOR]

A self-sustained burner was built for diesel oil without an atomizer using metal fiber felt as an evaporator. The effects of firing rate, excess air coefficient, and altitude on the temperature distribution, NOx emission, and CO emission were studied. The results indicated that fuel evaporation and combustion inside the burner are significantly influenced by the altitude. The overall temperature distribution inside the burner first decreased and then increased with the increase in altitude. The main reasons for the formation of NOx are the local high temperature during start-up and the high temperature after flame stabilization. The NOx emission initially decreased and then increased with the increase in altitude. The NOx emission is the lowest at an altitude of 1700 m and reaches its maximum value at an altitude of 4780 m. The main cause of CO generation is incomplete combustion during the start-up process. The CO emission decreased with the increase in the excess air coefficient at the same altitude. Less CO is produced with the increase in altitude at the same firing rate and excess air coefficient. [ABSTRACT FROM AUTHOR]

Present computational simulation studied H2-CH4 combustion characteristics in a specific gas turbine combustor used for power generation. Across four thermal loads (1.1-4.4 bar) and varying hydrogen fraction (0-50% by volume), changes in flame temperature, reaction zone stability, and flow field are scrutinized. Results show coherent thermal patterns and stable flame fronts across all conditions, indicating hydrogen addition does not deteriorate combustion when blended with methane. Flame temperatures increase by approximately 40 K with increasing hydrogen fraction. Acceptable NOx emissions are observed, peaking at 6.20 ppm with 50 % H2 at 168 kW. The combustor enables reliable operation for blends up to 50% hydrogen. These results suggest potential for increasing legislated hydrogen blending limits for more sustainable gas turbine power generation. By expanding the viable envelope for hydrogen-methane mixtures, this work contributes to understanding combustion of decarbonized fuels in gas turbines. However, as results are limited to the investigated combustor geometry, generalized conclusions cannot be drawn at this stage. Nonetheless, this study represents an incremental advancement in knowledge that may inform future research on sustainable power generation and decarbonization efforts. [ABSTRACT FROM AUTHOR]

Rice husks are not readily biodegradable making their disposal challenging due to the common disposal method of open burning which has negative environmental effects. Additionally, banana, sweet potato and cassava peelings form a large percentage of organic municipal solid waste. Therefore, this study developed rice husk biochar briquettes with organic municipal peelings waste as binders. Rice husks biochar was formed via carbonization processes in a step-down kiln at temperatures ranging between 400 and 500 °C. Organic binders were mixed with the rice husk biochar at different ratios of 10% and 15% before being compacted at a pressure ≤ 7 MPa into briquettes. Thermogravimetric results showed that the developed briquettes had high ash contents ranging from 44% to 47%. Rice husk biochar briquettes with the highest particle density were observed for briquettes with 15% cassava peel binder at 427.1 kg/m3. The highest HHV and maximum attainable flame temperature of 21.75 MJ/kg and 828.7 °C were obtained for rice husk biochar briquettes with 15% matooke peeling organic binder. For all rice husk biochar briquettes, increasing the organic peeling binder had a positive impact of reducing the ash content, while at the same time increasing the peak temperatures, thus contributing to their enhanced thermal stability. [ABSTRACT FROM AUTHOR]

Azodicarbonamide (ADC) based airbag gas generants with various potential oxidizers, including (1) C2H4O2N4/KNO3 (2) C2H4O2N4/NaNO3 (3) C2H4O2N4/Sr(NO3)2 (4) C2H4O2N4/Ba(NO3)2 (5) C2H4O2N4/KIO4 and (6) C2H4O2N4/NaIO4 were thoroughly tested to identify the best mixture for a real-time ballistic application. The evaluation of the gas generant mixtures is carried out based on the performance properties such as quantity of oxidizer decomposed (in g) to give 1 g of O2, residual mass % of the mixture, density of the oxidizer, oxygen balance percentage for the oxidizer, adiabatic flame temperature, onset temperature, activation energy, pre-exponential factor, critical ignition temperature, change in enthalpy, change in entropy, impact sensitivity and friction sensitivity of the gas generant mixtures. Using the TOPSIS methodology, a systematic approach was developed for the first time to determine the best suitable airbag gas generant for real-time ballistic application by taking into account all of these properties. TOPSIS findings revealed that the preferred order of the airbag gas generant mixture is C2H4O2N4/KIO4 > C2H4O2N4/NaIO4 > C2H4O2N4/KNO3 > C2H4O2N4/NaNO3 > C2H4O2N4/Sr(NO3)2 > C2H4O2N4/Ba(NO3)2. A similar methodology can also be used to discover the best fuel/oxidizer mixture for any other composition. [ABSTRACT FROM AUTHOR]

Large hydrocarbon fuels are used for ground and air transportation and will be for the foreseeable future. A key parameter when burning these fuels is the turbulent consumption speed, which is the velocity at which fuel and air are consumed through a turbulent flame front. Such information can be useful as a model input parameter and for validation of modeled results. In this study, turbulent consumption speeds were measured for three jet-like fuels using a premixed turbulent Bunsen burner. The burner was used to independently control turbulence intensity, unburned temperature, and equivalence ratio. Each fuel had similar heat releases (within 2%), laminar flame speeds (within 5–15%), and adiabatic flame temperatures. Despite this similarity, for constant ReD and turbulence intensity, A2 fuel (i.e. jet-A) has the highest turbulent flame speeds and remains stable (i.e. without tip quenching) at lower ϕ than the other fuels. In contrast the C1 fuel, which consists of heavily-branched alkanes, contains no aromatics and has a relatively high average molecular weight, has the slowest turbulent flame speeds and is the most prone to tip quenching. The C1 fuel has the highest stretch sensitivity, in general, as indicated by calculated Markstein numbers. This work shows that turbulent flame speeds and tip stability of multi-component large hydrocarbon fuels can be sensitive to the chemical class of its components. [ABSTRACT FROM AUTHOR]

Biodiesel is one of the most important alternative fuels due to limited conventional resources. Methyl octanoate with long alkyl chain and mono-alkyl ester is one of the surrogate fuels of actual biodiesel. In order to clarify distinctive combustion characteristics of methyl octanoate, comparison with alkane in traditional diesel is necessary. Therefore, this work chose n-nonane with same carbon number as methyl octanoate. The laminar flame speeds of two fuels were measured at different conditions (T = 423 K, P = 1 and 3 atm, and φ = 0.7–1.5) in a constant volume combustion bomb. Results show that laminar flame speed of n-nonane is higher than that of methyl octanoate in most conditions, but lower in fuel-rich conditions. The combined chemical kinetic model of methyl octanoate and n-nonane was developed through eliminating unnecessary reactions, which can well predict the experimental results of laminar flame speed and ignition delay time. The adiabatic flame temperature results from the updated kinetic model show that the temperatures of n-nonane are higher than methyl octanoate in whole conditions, which is unexpectedly opposite to their laminar flame speeds order in fuel-rich conditions. In overall conditions, the intermediates of methyl octanoate tend to produce CH3, which consumes H radicals, thereby reducing the laminar flame speed, which can explain the higher laminar flame speed of n-nonane in most conditions. Meanwhile, the oxidation reactions with oxygen molecules of intermediates of n-nonane are suppressed due to low combustion temperature at φ = 1.5 unlike at φ = 0.7 and 1.0. On the contrary, those of methyl octanoate have similar reactions between φ = 0.7, 1.0, and φ = 1.5. It means that the laminar flame speed of n-nonane decreases more significantly than methyl octanoate as the equivalence ratio increases from φ = 1.0 to φ = 1.5. [ABSTRACT FROM AUTHOR]

Hydrogen and ammonia are playing an increasingly vital role in combustion technologies. Recently, some detailed reaction mechanisms (DRMs) can predict reliable laminar burning velocities (LBVs). Meanwhile, despite their broad applicability in practical combustion engineering, global reaction mechanisms (GRMs) suitable for ammonia and its mixtures with hydrogen or nitrogen have yet to be reported. This study aims to address this gap by investigating new GRMs. Five DRMs were used to calculate the LBVs, and their average values were employed as a reference. First, a single-step GRM was developed for hydrogen (H 2 + 0.5O 2 → H 2 O), and another single-step GRM was developed for ammonia (NH 3 + 0.75O 2 → 0.5N 2 + 1.5H 2 O). However, their combined GRM did not provide reasonable predictions of LBVs for the H 2 +NH 3 mixtures. Therefore, a 4-step GRM was developed consisting of the single-step hydrogen and three additional reactions, i.e., an endothermic ammonia decomposition (NH 3 + 0.5O 2 → NO + 3H), an exothermic NO reduction (NO + 2H → 0.5N 2 + H 2 O), and an exothermic H recombination (H + H → H 2). In conclusion, this 4-step GRM and its revisions could predict reasonable LBVs, flame temperatures, and primary product compositions for mixtures of hydrogen, ammonia, and cracked ammonia gas over a wide range of temperatures (300–600 K) and pressures (1–5 atm). • Global reaction mechanisms (GRMs) were investigated for H 2 +NH 3 +N 2 mixtures. • Laminar burning velocities (LBVs) from the detailed reaction mechanisms were compared. • Single-step GRMs were improved for the individual fuels H 2 and NH 3. • Available ranges were extended in temperatures (300–600 K) and pressures (1–5 atm). [ABSTRACT FROM AUTHOR]

The effects of hydrogen (H 2) addition on the freely-propagating acetylene-oxygen (C 2 H 2 –O 2) flames in a doubly-infinite domain are investigated, considering separate and coupled chemical and transport phenomena. Results show that increasing proportions of H 2 enhance the laminar flame speeds of C 2 H 2 –O 2 mixtures. Moreover, H 2 promotes the C 2 H 2 –O 2 flame to contain both light (H, H 2) and heavy (C 2 H 2) species. Compared with the Soret diffusion and radiation effect, the unity Lewis number assumption can induce substantial inaccuracies. Sensitivity analysis indicates that the key elementary reaction H + O 2 O + OH exerts stronger influences on the laminar flame speed. Additionally, due to the effective enthalpy of C 2 H 2 being greater than H 2 , adding H 2 decreases both adiabatic flame temperature and enthalpy of C 2 H 2 –O 2 flames. Notably, reactions C 2 H 2 + O H + HCCO and C 2 H + H 2 H + C 2 H 2 in the C 2 H 2 sub-mechanism are identified as important exothermic- and endothermic-reactions respectively. Furthermore, it is demonstrated that dilution effects from CO 2 have a larger impact compared to those from H 2 O and Ar. Finally, the effects of initial pressure and temperature on the laminar flame speeds are also discussed. The results of the present work provide guidance for the effective use of binary fuel and risk control as well as fire suppression. • The effects of hydrogen additions on acetylene-oxygen flames are numerically studied. • Different flame diffusion models are characterized. • Chemical and thermal structures are revealed separately. • The effects of different dilution gases and initial conditions are considered. [ABSTRACT FROM AUTHOR]

Ammonia, being a carbon-free fuel, is garnering increasing attention in the combustion community. However, its application is still impeded by its limited stability range and significantly NOx emissions. This study delves into the impact of primary and overall equivalence ratios (ϕ pri and ϕ ovr) on emissions production in ammonia–hydrogen co-firing flames, utilizing a two-stage swirling model gas turbine combustor. The emissions concentration is measured using Fourier Transform Infrared Spectroscopy (FTIR). The physical and chemical processes influencing emissions production are comprehensively analyzed through a combination of Large Eddy Simulation (LES) and Flamelet-Generated Manifold (FGM) method. The reliability of the simulation is validated by the experimental data, showing a good capability in predicting the combustion. Results indicate that the two-stage combustion strategy exhibits significantly controlling effects on NOx and unburned NH 3 emission. The NO emission exhibits a non-monotonic variation with ϕ pri , reaching its lowest value at ϕ pri ≈ 1.2. Further analysis shows that ϕ pri plays a crucial role in determining the temperature and OH concentration in the primary combustion zone, thereby influencing NOx production in this area. When the primary zone is operated at lean condition, the reduction on NO in secondary zone is primarily attributed to dilution effect by the secondary air. In contrast, when ϕ pri > 1, the concentrations of the main emissions in secondary zone are dominated by chemical effects. In this scenario, unburned NH 3 and H 2 from the primary zone are consumed, resulting in a substantial production of NO in the secondary combustion zone. Additionally, with an increase in ϕ pri , the secondary NO production also increases. The ϕ ovr exhibits two considerable effects. On one hand, an increase in ϕ ovr results in a higher local equivalence ratio in the secondary zone, thereby promoting local NOx production. Simultaneously, the elevated flame temperature enhances the consumption of N 2 O. On the other hand, the rise in ϕ ovr results in a reduction in vortex scale and residence time in the secondary combustion zone, leading to a decrease in local NO production. • The NOx mitigation of NH 3 /H 2 /air co-firing flames have been achieved through the secondary staged air. • The proposed LES-FGM method was validated adequate predicting the flow field and emission characters. • The impact of primary and overall equivalence ratio on emissions have been revealed in-depth. • The optimal operating condition for emission control in the current combustor has been proposed. [ABSTRACT FROM AUTHOR]

This article explores the feasibility of generating velocity maps for a flame and its plume from a burning candle using Schlieren Image Velocimetry (SIV). Currently, SIV is predominantly employed in the literature to track highly turbulent flows by using the developing eddies as flow markers. The novelty of this study lies in evaluating the quality of a nearly laminar flame, which exhibits significant background density variation due to its own plume. In addition to the SIV technique, a brief assessment is conducted using a segmented color filter, specially designed and manufactured to evaluate the potential for measuring the temperature range of the flame. [ABSTRACT FROM AUTHOR]

A model of opposed flame spread along thin electric wires is developed to estimate the variation of flame spread rate ( $ {V_\textrm{f}} $ V f ) with oxygen concentrations and oxidiser flow velocity. The length of pyrolysis zone ( $ {L_{\textrm{py}}} $ L py ) and $ {V_\textrm{f}} $ V f are treated as eigenvalues of the problem, and one-dimensional energy balance equations for the wire core and insulation are formulated to derive their solutions. To obtain a set of steady solutions for $ {L_{\textrm{py}}} $ L py and $ {V_\textrm{f}} $ V f , the macroscopic energy balance equation for the entire system is calculated from the one-dimensional energy balance equations with appropriate boundary conditions. Since the equations are nonlinear function of $ {L_{\textrm{py}}} $ L py and $ {V_\textrm{f}} $ V f , multiple solutions appear. The physical meaning of each solution is evaluated based on the deviation of energy from the equilibrium. Comparison of the temperature distribution along the wire with experimental data confirms that the model reproduces well the actual flame spread process. The variation of $ {V_\textrm{f}} $ V f with oxygen concentration shows a C-shaped curve. The upper branch is the stable solution, and the lower branch is the unstable solution and the merging point of two branches correspond to the limit condition for flame spread. Therefore, the model can be used to estimate the limiting oxygen concentration based on the existence of a solution for $ {V_\textrm{f}} $ V f . Furthermore, the variation of $ {V_\textrm{f}} $ V f with oxidiser flow velocity shows O-shaped curve, and it is confirmed that radiative extinction under low flow velocity and blow-off under high flow velocity can also be estimated with the model. Mapping of variations of radiative extinction and blow-off extinction with oxygen concentration reveals the U-shaped flammability diagram. The predicted flame spread limits are in good agreement with the limiting oxygen concentrations measured in both microgravity and normal gravity, demonstrating the validity of using this model to predict flammability characteristics of electric wires under various oxidiser flow velocity. [ABSTRACT FROM AUTHOR]

Slim-floor-type of steel-timber hybrid floor systems which use steel beams contained within the depth of the cross-laminated timber (CLT) floor slab offer many benefits, but there is still very little research available on the fire resistance performance of these systems. In the study presented in this paper two furnace tests and numerical simulations have been conducted to investigate the thermal profiles of the steel member and CLT slabs and to obtain information on the temperature development and charring of the hybrid beam section when it is exposed to standard fire conditions. Also, the effects of intumescent fire protection on temperatures and charring performance were investigated. Numerical 2D thermal simulations for unprotected and protected cases were conducted using SAFIR software, and the agreement between experiments and numerical-analysis predictions were in general very good. The results show that intumescent protection reduces the temperatures of the steel and CLT components as well as charring depth significantly, and the start of charring at CLT slab support may be delayed if intumescent paint protection thicker than that required for the load bearing steel member is used. The result also showed that CLT temperatures exceed 100°C already in the early stages of the fire which decrease the strength and stiffness properties of CLT much before the start of charring. Therefore, the fire design of the CLT slab support should not only consider the char depth and residual cross-section analysis but also the reduction in strength. [ABSTRACT FROM AUTHOR]

The physical characteristics of solid biofuel under combustion in a Rijke tube installation have been studied. A decrease in the flame temperature and an increase in the heat flux density on the tube wall on the occurrence of vibrating combustion were detected. To study vibrating combustion under conditions close to practical use in power plants, experiments were carried out on a "container–tube" type installation. The optimal parameters of the installation for the implementation of vibrating combustion of solid biofuels were obtained. A theoretical model of the development of sound disturbances of a combustion wave has been developed and its influence on heat transfer characteristics has been elucidated. An empirical-theoretical relationship has been obtained for calculating heat transfer in a Rijke tube during vibrating combustion. A model is proposed for calculating the amplitude of disturbances for instabilities in "container–tube" installations. [ABSTRACT FROM AUTHOR]

Thermal runaway (TR) is a serious thermal disaster that occurs in lithium-ion batteries (LIBs) under extreme conditions and has long been an obstacle to their further development. Water mist (WM) is considered to have excellent cooling capacity and is widely used in the field of fire protection. When used in TR suppression, WM also exhibits strong fire-extinguishing and anti-re-ignition abilities. Therefore, it has received widespread attention and research interest among scholars. However, most studies have focused on the cooling rate and suppression effect of TR propagation, and few have mentioned the effect of WM on flame heat transfer, which is a significant index in TR propagation suppression. This study has explored the suppression effect of WM released at different TR stages and has analyzed flame temperature, heat release, and heat radiation under WM conditions. Results show that the flame extinguishing duration for WM under different TR stages was different. WM could directly put out the flame within several seconds of being released when SV opened, 3 min after SV opening and when TR ended, and 3 min for WM when TR was triggered. Moreover, the heat radiation of the flame in relation to the battery QE could be calculated, and the case of WM released 3 min after SV opening exhibited the greatest proportion of heat radiation cooling η (with a value of 88.4%), which was same for the specific cooling capacity of WM Qm with a value of 1.7 × 10−3 kJ/kg. This is expected to provide a novel focus for TR suppression in LIBs. [ABSTRACT FROM AUTHOR]

Tailoring the energy release performance of the thermites is crucial for their application in various fields. In this article, dual‐oxidant Al/MnO2/CuO ternary thermites with varying compositions were prepared and systematically evaluated. The ignition delay time, heat of reaction, self‐sustained burning rate, and pressure performance of the thermites were evaluated. As the Al/CuO content increased, the ignition delay time and heat of reaction decreased, while the reaction efficiency, burning rate, pressure peak, and pressurization rate increased. Furthermore, the synergistic addition of the MnO2 and CuO led to enhanced relative flame intensity and maximum flame temperature in the ternary thermite. Our work demonstrates an effective strategy for regulating the energy performance of the thermites by co‐adding of metal oxides. This approach opens avenues for tailoring thermite properties to meet the diverse requirements of various applications. [ABSTRACT FROM AUTHOR]

The combustion of hydrogen and carbon-monoxide mixtures, so-called syngas, plays an increasingly important role in the safety context of non-fossil energy generation, more specifically in the risk management of incidents in process engineering plants for ammonia synthesis and in nuclear power plants. In order to characterize and simulate syngas/air combustion on industrially relevant scales, subgrid modelling is required, which is often based on a reaction progress variable. To understand the influence of different fuel compositions, turbulence intensities and flame topologies on different possible definitions of reaction progress variable, detailed chemistry direct numerical simulations data of premixed, lean hydrogen/air and syngas/air flames has been considered. A reaction progress variable based on normalized molecular oxygen mass fraction has been found not to capture the augmentation of the normalized burning rate per unit flame surface area in comparison to the corresponding 1D unstretched premixed flame due to preferential diffusion effects. By contrast, reaction progress variables based on other individual species, such as hydrogen, can capture the augmentation of the rate of burning well, but exhibit a pronounced sensitivity to preferential diffusion effects, especially in response to flame curvatures. However, a reaction progress variable based on the linear combination of the main products can accurately represent the temperature evolution of the flame for different mixtures, turbulence intensities and varying local flame topology, while effectively capturing the augmentation of burning rate due to preferential diffusion effects. However, its tendency to assume values larger than 1.0 in the regions of super-adiabatic temperatures poses challenges for future modeling approaches, whereas the reaction progress variable based on hydrogen mass fraction remains bound between 0.0 and 1.0 despite showing deviations in comparison to corresponding variations obtained from the unstretched laminar flame depending on flame curvature variations. [ABSTRACT FROM AUTHOR]

Excessive NO x and CO 2 emissions pose a significant challenge in the clean combustion of natural gas, which is expected to be solved through the combination of exhaust gas recirculation and hydrogen enrichment. In this study, the pollutant emission and temperature distribution of a laminar diffusion flame during the combustion of CH 4 mixed with CO 2 /N 2 /H 2 are experimentally investigated. The NO emission reduction effect of CO 2 dilution on hydrogen-enriched methane is evaluated as well. The experimental results show that CO 2 dilution has a deeper NO emission reduction and flame temperature attenuation than N 2 dilution. At a given blending ratio of 50%, CO 2 dilution effectively reduces NO emissions by approximately 50%, whereas N 2 dilution decreases NO emissions by about 10%. Compared with N 2 dilution, the peak flame temperatures of CO 2 dilution cases are reduced by 15.3 K, 45.1 K, 31.7 K, 32.6 K, and 44.3 K, respectively, when the blending ratios increase from 10% to 50% with an interval of 10%. The difference caused by the CO 2 /N 2 dilutions between the inhibition effect from the inherent attributes and the enhanced mixing effect on the flame temperature, results in a significant peak temperature gap of 45.1 K at a 20% blending ratio. H 2 enrichment enhances the flame temperature and promotes the combustion reaction process, resulting in a more compact flame structure. NO emission factors for H 2 blending ratio of 0% and 50% are 1953 mg·(kg Fuel)−1 to 2544 mg (kg Fuel)−1, respectively, which is due to the excessive NO generation because of the temperature rise in the combustion zone. CO 2 dilution demonstrates an excellent NO emission reduction effect on hydrogen-enriched methane gas. This paper may provide some references for the development and application of exhaust gas recirculation and hydrogen enrichment. • The combustion characteristics of CH 4 mixed with CO 2 /N 2 /H 2 are investigated. • CO 2 is better than N 2 in NO emissions reduction and flame temperature attenuation. • H 2 enrichment increases the NO emissions and decreases the CO emissions. • H 2 enrichment increases the flame temperature and promotes combustion reaction. • CO 2 shows an excellent NO emissions reduction for hydrogen-enriched methane. [ABSTRACT FROM AUTHOR]

Coupling the San Diego gas phase reaction mechanism and the Moss Brookes soot model using FLUENT14.0 software, the effect of adding H2/CO on the fuel side on soot formation in an ethylene/air laminar diffusion flame was studied. A specific analysis was conducted on the effects of H2, CO and its chemical effects on flame temperature, soot volume fraction, mole fractions of important intermediate products OH, H, and C2H2, as well as rate of soot mass nucleation, surface growth, and oxidation. In the numerical calculation, the virtual substances FH2 and FCO are set to separate the chemical effect of H2 and CO and to analyze the chemical effect of adding H2 and CO on soot formation. The results show that the flame temperature increases slightly, and the soot volume fraction decreases monotonically with adding H2 and CO. The chemical effect of H2 increases the temperature, the mole fraction of C2H2 and H, the soot nucleation rate, and the surface growth rate, and finally, it promotes soot formation. The chemical effect of CO increases the temperature and H mole fraction, reduces the OH mole fraction, and then increases the soot surface growth rate and reduces the soot oxidation rate. The higher soot nucleation, surface growth rate, and lower oxidation rate jointly promote soot formation. [ABSTRACT FROM AUTHOR]

Microwave plasma sources are used in various applications, but inefficiency can limit their usefulness. Researchers have investigated a new approach with which to improve efficiency by using a waveguide with a special tuner. A standard waveguide was compared to one equipped with a stub tuner, which allows for the fine-tuning of the electrical properties. The experiment used a frequency of 2.45 GHz and tested input powers of 1 kW and 1.5 kW. Experiments showed that waveguides with tuners transferred power more efficiently, with fewer reflected and more transmitted microwaves. While peak temperatures remained similar, the tuned waveguide produced a hotter plasma flame (30–60 °C) at the same distance. Notably, increasing the input power further boosted the flame temperature by 300 °C. These findings suggest that stub tuners can significantly improve the efficiency of microwave plasma sources. This paves the way for more efficient plasma generation technologies and potentially allows for applications requiring even higher power. [ABSTRACT FROM AUTHOR]

The behavior of technical nanoparticles at high temperatures was measured systematically to detect morphology changes under conditions relevant to the thermal treatment of end-of-life products containing engineered nanomaterials. The focus of this paper is on laboratory experiments, where we used a Bunsen-type burner to add titania and ceria particles to a laminar premixed flame. To evaluate the influence of temperature on particle size distributions, we used SMPS, ELPI and TEM analyses. To measure the temperature profile of the flame, we used coherent anti-Stokes Raman spectroscopy (CARS). The comprehensible data records show high temperatures by measurement and equilibrium calculation for different stoichiometries and argon admixtures. With this, we show that all technical metal oxide nanoparticle agglomerates investigated reform in flames at high temperatures. The originally large agglomerates of titania and ceria build very small nanoparticles (<10 nm/"peak 2") at starting temperatures of <2200 K and <1475 K, respectively (ceria: Tmelt = 2773 K, Tboil = 3873 K/titania: Tmelt = 2116 K, Tboil = 3245 K). Since the maximum flame temperatures are below the evaporation temperature of titania and ceria, enhanced vaporization of titania and ceria in the chemically reacting flame is assumed. [ABSTRACT FROM AUTHOR]

Ceramizable silicone rubber (CSR) composed of silicone rubber matrix and inorganic fillers can be transformed into a dense flame-retardant ceramic upon encountering high temperatures or flames. Conventionally, CSR can be sintered into a dense ceramic at temperatures above 1000 °C, which is higher than the melting point of a copper conductor used in a power cable. In this study, the vulcanization process and mass ratio of inorganic fillers of CSR were studied to lower its ceramization temperature to 950 °C. The electrical and mechanical properties of CSRs and their ceramic bulks were studied with various ratios of wollastonite and muscovite. It was found that the CSR samples could be successfully fabricated using a two-step vulcanization technique (at 120 °C and 150 °C, respectively). As a high ratio of muscovite filler was introduced into the CSR, the sample presented a high dc electrical resistivity of 6.713 × 1014 Ω·cm, and a low dielectric constant of 4.3 and dielectric loss of 0.025 at 50 Hz. After the thermal sintering (at 950 °C for 1 h) of the CSR sample with a high ratio of muscovite, the ceramic sample exhibits a dense microstructure without any pores. The ceramic also demonstrates excellent insulating properties, with a volume resistivity of 8.69 × 1011 Ω·cm, and a low dielectric loss of 0.01 at 50 Hz. Meanwhile, the three-point bending strength of the ceramic sample reaches a value of 110.03 MPa. This study provides a potential route to fabricate CSR used for fire-resistant cables. [ABSTRACT FROM AUTHOR]

DAP-4(C6H18N3Cl3O12) is a novel molecular perovskite energetic materials compound that is characterized by high energy, high thermal stability and high oxidation stability. The properties of DAP-4 were enhanced by preparing mixtures of 5%, 10%, 15%, 20%, and 30%SnO2/Al/DAP-4 using the solvent evaporation method. The morphology and structure of the samples were characterized using scanning electron microscopy and energy dispersive spectroscopy. The thermal decomposition characteristics of the samples were analyzed using differential scanning calorimetry and thermal reconnection techniques. The combustion performance test device was used to comparatively analyze the burning pressure, flame temperature, and heat of combustion of the samples. The optimal preparation ratio was determined, and the thermal decomposition mechanism of the SnO2/Al/DAP-4 mixture was deduced. The findings suggest that: The SnO2 and Al powders can be uniformly mixed with DAP-4, leading to the creation of a SnO2/Al/DAP-4 composite that displays outstanding dispersion properties. At the optimal preparation ratio of 20%SnO2/Al, the activation energy required for the thermal decomposition of SnO2/Al/DAP-4 is the lowest, at 106 kJ mol−1. This leads to a significant decrease in the peak temperature of the exothermic decomposition of DAP-4. During the combustion process, the addition of 20%SnO2/Al significantly increased the combustion intensity of DAP-4. This resulted in an increase in the combustion pressure up to 1.1 MPa and a rise in the flame temperature up to 3136 ℃, releasing more combustion heat compared to the feedstock and other proportions of the SnO2/Al/DAP-4 mixtures. [ABSTRACT FROM AUTHOR]

Performing pyrolysis studies on polymer matrix composites, at rates that match the elevation of temperature met during a fire exposure, is of primary interest for the aeronautics field. In this study, one aspect of the material response under flame is investigated, which is the thermal degradation of the polymer matrix. Thermogravimetric analyses (TGA), up to five hundred Kelvins per minute, are performed on polyphenylene sulfide (PPS) and carbon fiber-reinforced polyphenylene sulfide (CF/PPS), to mimic the heating rate conditions commonly met during a fire. The influence of the heating rate regarding the PPS decomposition signature is discussed from both the residual mass and the characteristic temperature corresponding to the maximum rate of degradation. Then, the PPS thermal decomposition features are compared with those of several thermoplastic polymers and thermoplastic–based composites. It is observed that PPS stands out when subjected to fast elevation of temperature. Indeed, its amount of «char», obtained after thermal degradation, increases with the heating rate. To investigate possible mechanistic causes behind this singular behavior, the influence of the heating rate on the degradation mechanisms occurring into PPS and CF/PPS is investigated. TGA coupled with Fourier transform infrared spectroscopy (FTIR) is used to obtain the decomposition products. The results plaid for the coexistence of two main degradation mechanisms, being the random chain–scission and the depolymerization. Nevertheless, when the heating rate increases, the random chain–scission seemingly becomes the predominant mechanism along the whole process. [ABSTRACT FROM AUTHOR]