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The influence of microstructure on the response of energetic structural materials (ESMs) under shock conditions remains inadequately quantified, and the energy release process is not thoroughly understood. In this work, taking the classical Ni/Al ESM as an example, the shock response was investigated by the shock compression theory with the microstructure-based chemical reaction kinetics model. This theory mainly refers to the equation of the state of multi-component materials with mixture rule, and the reaction at the particle contact interface is built to form the multiscale thermodynamics model. The physical states of material after shock, including relative volume, temperature, and extent of reaction, were analyzed. The results revealed the effect of the burn velocity, particle size and molar ratio on the shock response. Furthermore, the model facilitates a comprehensive understanding of energy release, the extent of the intermetallic reaction, and the oxidation reaction. Despite the involvement of only a small portion of materials in the oxidation reaction, the energy release proportion was comparable to that of the intermetallic reaction. Additionally, insights into the effect of the microstructure on the energy release revealed by the model matched the tests well. [ABSTRACT FROM AUTHOR]

Recently, there has been increased attention on mixtures of H 2 , NH 3 , CO, and CH 4 , leading to a higher demand for suitable global reaction mechanisms (GRMs). Although some GRMs have been proposed for binary mixtures such as H 2 +CH 4 and H 2 +NH 3 , a suitable GRM for the complex mixture of H 2 +NH 3 +CO + CH 4 has yet to be established. This study investigated GRMs for each pure gas (H 2 , NH 3 , CO, and CH 4) and their corresponding mixtures. Results from detailed reaction mechanisms (DRMs) and selected experiments were used as references. First, a 2-step GRM for H 2 was developed to improve the prediction in the fuel-lean conditions and was used to improve GRMs for H 2 +NH 3. A more reliable 5-step GRM for H 2 +NH 3 was also developed, including the 2-step GRM for H 2 and a modified 3-step GRM for NH 3. Second, GRMs for H 2 +CO + CH 4 were investigated. A 1-step GRM for CH 4 was improved to account for the pressure variations. More reliable GRMs that combine the water gas shift reaction (CO + H 2 O → CO 2 +H 2) and the modified 3-step reactions for CH 4 were also proposed. Thus, two GRMs could be suggested for H 2 +CO + CH 4 : a 5-step GRM including the 1-step GRM for H 2 and a 6-step GRM including the 2-step GRM for H 2. Finally, optimized 8-step and 9-step GRMs for H 2 +NH 3 +CO + CH 4 were proposed, and reasonable LBVs could be predicted across a wide range of temperatures (300–600 K) and pressures (1–5 atm). The number of reactions could be selectively reduced based on the fuel compositions. • Global reaction mechanisms (GRMs) for H 2 +NH 3 +CO + CH 4 mixtures were investigated. • Laminar burning velocities from reaction mechanisms and experiments were compared. • GRMs were improved, including 2-step for H 2 , 5-step for NH 3 , and 6-step for CH 4. • Results were valid in the temperature (300–600 K) and pressure (1–5 atm). [ABSTRACT FROM AUTHOR]

This study explores the complex mechanisms driving flame acceleration (FA) in hydrogen/air mixtures with transverse stratification, using high-fidelity 3-D Large Eddy Simulations (LES) in a confined, obstructed channel based on the GraVent explosion setup. A systematic methodology for LES of stratified hydrogen deflagrations is presented, showing reasonable agreement with experimental data. The impact of stratification on FA across different mixtures is analyzed, comparing each stratified mixture to an homogeneous counterpart for an equivalent amount of hydrogen leakage. A striking finding is that stratification does not always enhance FA. The analysis of the LES results reveals that FA in stratified mixtures is strongly influenced by channel geometry and obstructions, driven by two primary mechanisms: Flow Contraction (FC) and Flame-Vortex Interaction (FVI). These mechanisms show significant asymmetry, with greater amplification in regions of higher reactivity. Large gradients in burning velocity along the flame front also contribute to pronounced flame surface elongation, leading to larger flame surfaces that influence FA to varying degrees. Ultimately, stratified FA operates through two modes: a dominant small-surface mode in rich gas regions that strongly drives acceleration, and a large-surface mode in lean mixtures, which initially contributes less but becomes more significant as the flame expands. This highlights the need to perform both global and local analysis for understanding these flames. [Display omitted] • First 3D LES investigation of flame propagation in stratified hydrogen/air mixtures. • Excellent agreement between LES predictions and experimental data. • New insights on the role of mixture stratification on flame acceleration mechanisms. [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]

Methane (CH 4) serves as a significant hydrogen carrier and is the predominant component of natural gas. The comprehension of CH 4 combustion characteristics and chemical kinetics under unconventionally lean and rich conditions is essential for advanced industrial processes such as lean burn operations and syngas reforming. However, due to challenges in flame stabilization, corresponding experimental data on key CH 4 combustion characteristics such as laminar burning velocity are scarce, which in turn leaves existing kinetic models unvalidated. In this study, the laminar burning velocities of CH 4 +O 2 +N 2 , CH 4 +O 2 +Ar, and CH 4 +O 2 +CO 2 flames were measured using the heat flux method at 1 atm and 298 K. The equivalence ratio spanned from the very lean range of 0.3–0.6 to the very rich range of 1.5–1.8, through an oxy-fuel combustion approach, with most conditions being unexplored in existing literature. Simulations adopted six kinetic models that are widely-used for predicting CH 4 flames. These models exhibited mixed performance when predicting different diluent types and oxygen ratios, with none capable of accurately reproducing all experimental data within the uncertainty ranges. Analyses on A-factor reaction sensitivities were performed, along with rate constant uncertainty evaluations, based on which the model from the authors was updated. The updated model is compact, consisting of 91 species and 483 reactions, with shortened versions provided for different calculation purposes, and reproduce well the present experimental data. Furthermore, it maintained good predictability for previous validation targets of laminar burning velocities, ignition delay times, and NO speciation data in CH 4 , CH 3 OH, C 2 H 5 OH, and their blended flames, surpassing the capabilities of other literature models tested, thereby could help with the understanding and optimization of relevant applications. • New CH 4 S L data extend to extreme lean/rich conditions, expanding knowledge base. • Six kinetic models assessed against S L data, revealing model limitations. • Key CH 4 S L reactions identified through an innovative uncertainty analysis. • A new compact kinetic model offers improved predictability for extreme conditions. • The updated model also maintaining strong predictability against previous targets. [ABSTRACT FROM AUTHOR]

This study aims to provide laminar burning velocity measurements of lean, stoichiometric, and rich H 2 -air and CH 4 -air flames at cryogenic temperatures, as well as to determine the accuracy of the existing high-temperature modeling approach (i.e., empirical and kinetic models) to simulate them. The lowest temperatures reached experimentally are 100–120 K and 150–160 K (depending on the equivalence ratio) for H 2 -air and CH 4 -air mixtures, respectively. Simulations are conducted with Cantera down to 100 K in all conditions with several kinetic models. This study summarizes both critical aspects of the experimental procedures by comparing the present results with previous data and important numerical considerations by evidencing sensitive simulation parameters and addressing the 200 K temperature limit of Cantera's solver. Quantitative analyses revealed that both empirical power laws and kinetic models extrapolations are accurately predicting, within the experimental uncertainties, the laminar burning velocities of H 2 -air and CH 4 -air flames in almost all conditions. • Laminar burning velocities of H 2 -air and CH 4 -air flames at 100 K and 150 K. • The presented experimental procedure correct biases from previous literature. • Important aspects to simulate cryogenic flames down to 100 K are presented. • Usual kinetic and empirical models can be extrapolated to cryogenic temperature. [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]

During thermal runaway, high-capacity lithium iron phosphate (LFP) batteries can release substantial amounts of flammable thermal runaway gas (TRG), significantly increasing the explosion risk in battery energy storage systems (BESS). This study investigates the explosion characteristics of TRG from a 280 Ah LFP battery and compares the suppression effects of premixed 2H-Heptafluoropropane (HFC-227ea) and CO 2. Laminar burning velocities were calculated using experimentally measured pressure history data to validate a chemical kinetic model, facilitating the analysis of key parameters such as adiabatic flame temperature, adiabatic combustion pressure, heat release rate, and radical mole fractions. Results indicate that the explosion intensity is highest when the TRG-air equivalence ratio is 1.1, with a maximum explosion pressure (P max) of 0.475 MPa. 5% HFC-227ea can completely suppress the explosion, while CO 2 requires an addition of 25%. Under fuel-lean and stoichiometric conditions, HFC-227ea exhibits a combustion enhancement effect, increasing P max by up to 23.65%, with the effect becoming more pronounced as fuel-lean degree increase. Compared with CO 2 , HFC-227ea significantly reduces the thermal diffusivity of TRG-air, increases heat loss during flame propagation, and removes many chain reaction radicals. Its combustion enhancement effect is tied to its suppression mechanism, where the removal of chain reaction radicals releases significant heat, while producing flammable substances such as H 2 and CO, which sustain the chain reaction. These findings offer valuable insights for mitigating TRG explosion risks in BESS. • Evaluated the explosion intensity of thermal runaway gases in lithium-ion batteries. • Validation of reaction kinetic models using a cost-effective constant volume method. • HFC-227ea shows superior suppression effectiveness over CO 2 in fuel-rich conditions. • HFC-227ea leads to higher explosion intensity under lean-rich conditions. • Provide guidance on firefighting strategies for battery energy storage systems. [ABSTRACT FROM AUTHOR]

Some new, low-global warming potential refrigerants will be flammable, and the laminar burning velocity is a useful parameter for quantifying fire risk. Laminar burning velocity measurements have been made using a constant volume experiment with dry air and the refrigerant R-152a (CH3CHF2), pure and blended with R-134a (CH2FCF3), or R-1234yf (CF3CFCH2). The resulting burning velocity data deduced from the pressure rise in the chamber are presented for a range of fuel air equivalence ratio and loading of the less flammable refrigerant, for unburned gases at 298 K and 101 kPa as well as at 375 K and 253 kPa. For comparison, the 1-D, planar laminar burning velocity was numerically simulated using a recently developed kinetic mechanism that includes a wide range of refrigerants with air. The predicted burning velocities agree reasonably well with the experimental values, and the numerical results are used to understand the kinetic mechanism of the reaction of the refrigerants. Uncertainties in the experimental data from radiation heat losses as well as extrapolation to ambient conditions are explored. [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]

In the present study, the effect of hydrogen addition on turbulent flame propagation characteristics is investigated in a fan-stirred combustion chamber. The turbulent burning velocities of methane/hydrogen mixture are determined over a wide range of hydrogen fractions, and four classical unified scaling models (the Zimont model, Gulder model, Schmidt model, and Peters model) are evaluated by the experimental data. The acceleration onset, cellular structure, and acceleration exponent of turbulent expanding flames are determined, and an empirical model of turbulent flame acceleration is proposed. The results indicate that turbulent burning velocity increases nonlinearly with the hydrogen addition, which is similar to that of laminar burning velocity. Turbulent flame acceleration weakens with the hydrogen addition, which is different from that of laminar flame acceleration. Turbulent flame acceleration is dominated by turbulent stretch, and flame intrinsic instability is negligible. Turbulent stretch reduces with hydrogen addition, because the interaction duration between turbulent vortexes and flamelets is shortened. The relative data and conclusions can provide useful reference for the model optimization and risk assessment of hydrogen-enriched gas explosion. [ABSTRACT FROM AUTHOR]

Hydrogen has drawn great attention in recent years as a carbon-free fuel. The turbulent burning velocity ( S T ) is an important parameter for the design and modeling of hydrogen-fueled engines given the high propagation speed of hydrogen flames. It has been well documented that S T of hydrogen flames can be dramatically increased by thermo-diffusive effects which are sensitive to thermodynamic conditions. Previous studies have mainly focused on the pressure effect on S T of lean hydrogen flames, while the temperature effect has been largely ignored. In the present study, the turbulent burning velocity for a lean hydrogen/air mixture over a wide range of temperatures (300–641 K) and pressures (1–15 atm) is investigated through direct numerical simulations of statistically planar turbulent premixed flames. Results show that the variation of normalized turbulent burning velocity ( S T / S L , where S L is the laminar flame speed) with temperature and pressure is mainly controlled by the variation of the stretching factor I 0 . While S T / S L is only marginally dependent on temperature at the atmospheric pressure, it exhibits a decreasing trend with temperature at an elevated pressure (10 atm). This is associated with different temperature dependencies of flame surface area enlargement at the two different pressures, despite the monotonically decreasing trends of I 0 with temperature at both pressures. In addition, under engine-relevant conditions where the temperature and pressure increase simultaneously, the promotion effect of pressure is found to be largely canceled out by the suppression effect of temperature, leading to only a slight increase in I 0 and S T / S L . The observed trends are further explained through detailed flame dynamic analysis. Furthermore, I 0 at different temperatures and pressures is found to correlate very well with the enhancement of fuel consumption rate in the critically strained laminar flames. The present study elucidates the strong impact of temperature on S T of lean premixed hydrogen/air flames at elevated pressures and provides new insights into the modeling of S T , especially for engine-relevant conditions. [ABSTRACT FROM AUTHOR]

The flame-dynamic stability and internal mechanism in a stratified-rotation ethanol/air flame are investigated through the utilization of a stratified vortex-tube combustor based on an advanced numerical calculation method. The performance of flame-dynamic and combustion stability is examined by evaluating the stability limit, pressure fluctuation, and flame topology. Results demonstrate that the stratified vortex-tube combustor exhibits excellent combustion and flame-dynamic stabilities, with the lean stability limit consistently below 0.2 and pressure fluctuations within 2000 Pa, accompanied by a uniform flame topology without significant temporal variations over time. The burning velocity displays good adaptability to flow field disturbances, aligning well with the normal flow velocity on the flamelet throughout time. Slight variations in flame topology result in weak heat release fluctuations, effectively suppressing fluid disturbances in the post-flame zone. Decreased momentum flux and its alterations in the post-flame zone play a crucial role in achieving flame-dynamic stability due to intense momentum exchange within this highly rotating reactive flow environment. The Rayleigh parameter and flame transfer function are employed to quantify flame-dynamic stability, revealing that both weak thermo-acoustic coupling degree and limited response level of heat release rate fluctuations to fluid fluctuations significantly contribute to maintaining stable flames. These findings systematically elucidate underlying mechanisms responsible for achieving robust flame-dynamic stability observed within this highly rotating reactive environment. [ABSTRACT FROM AUTHOR]

Reactive burn models for heterogeneous energetic materials (EMs) must account for chemistry as well as microstructure to predict shock-to-detonation transition (SDT). Upon shock loading, the collapse of individual voids leads to ignition of hotspots, which then grow and interact to consume the surrounding material. The sub-grid dynamics of shock-void interactions and hotspot development are transmitted to macro-scale SDT calculations in the form of a global reactive "burn model." This paper presents a physically evocative model, called meso-informed sub-grid source terms for energy localization (MISSEL), to close the macro-scale governing equations for calculating SDT. The model parameters are explicitly related to four measurable physical quantities: two depending on the microstructure (the porosity ϕ and average pore size D ¯ v o i d ), one depending on shock–microstructure interaction (the fraction of critical voids ξ c r ), and the other depending on the chemistry (the burn front velocity V h s ). These quantities are individually quantifiable using a small number of rather inexpensive meso-scale simulations. As constructed, the model overcomes the following problems that hinder the development of meso-informed burn models: (1) the opacity of more sophisticated surrogate/machine-learning approaches for bridging meso- and macro-scales, (2) the rather large number of high-resolution mesoscale simulations necessary to train machine-learning algorithms, and (3) the need for calibration of many free parameters that appear in phenomenological burn models. The model is tested against experimental data on James curves for a specific class of pressed 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane materials. The simple, evocative, and fast-to-construct MISSEL model suggests a route to develop frameworks for physics-informed, simulation-derived meso-informed burn models. [ABSTRACT FROM AUTHOR]

Developing fuels without carbon, such as ammonia (NH 3), is crucial for achieving carbon reduction. Laminar burning velocity (LBV) is investigated, and distribution characteristics of OH and NH radicals are identified through planar laser-induced fluorescence. Rate of production of main free radicals and sensitivity analysis are also studied. The addition of NH 3 to CH 4 -air mixtures results in a decrease in the LBV, a rise in preheating zone height, a reduction in OH radical fluorescence intensity, and an enhancement in NH radical fluorescence intensity. Simulation reveals that the high NH 3 ratio enhance the negative impact of nitrogen-containing elementary reactions on LBV. The addition of NH 3 enhances the initial consumption of more OH via reaction R 248 : NH 2 + OH = NH + H 2 O , leading to increased NH production, and indicating a negative effect on LBV. The decrease in OH concentration is the main factor leading to a decrease in LBV. The reactions affecting the OH generation and consumption are R 39 : H + O 2 = O + OH and R 85 : OH + H 2 = H + H 2 O , respectively. The addition of NH 3 leads to a more significant reduction in R39. • The impact of NH 3 on the combustion characteristics of coal volatiles was studied. • The addition of NH 3 reduces the OH signal while increases the NH signal. • Primary reactions affecting LBV are H + O 2 = O + OH and H + CH 3 (+M) = CH 4 (+M). • H + O 2 = O + OH and OH + H 2 = H + H 2 O are the main reactions for OH generation and consumption. [ABSTRACT FROM AUTHOR]

In response to environmental concerns, R1234yf is used in mobile air conditioning (MAC) systems, yet it can produce trifluoroacetic acid (TFA) in water bodies, a persistent pollutant with moderate phytotoxicity and high mobility. However, R152a, an alternative, faces challenges due to its flammability (classified as A2). To address this, we propose new R152a-R13I1 mixtures (M10–M50) as R1234yf replacements in MAC units. A Simscape/MATLAB model was developed to elucidate the thermodynamic performance of an MAC unit. Theoretical estimations showed a significant reduction in burning velocity (BV) and an increase in the lower flammability limit (LFL) when R13I1 was added to R152a. For instance, at 0.20 mole fraction of R13I1, BV decreased from 23.1 to 11.3 cm s−1; while, LFL increased from 4.9 to 6.28 vol. %. Hence, M20 emerged as the optimal choice due to its A2L flammability classification and superior thermal properties. Simscape/MATLAB results revealed M20's 11.5–35.4% higher coefficient of performance compared to R1234yf. The model was validated against R1234yf data, showing 3.8–13.8% error. Additionally, M20's impact on MAC CO2 emissions was evaluated, showing a potential 34.1% reduction compared to R1234yf. This highlights the environmental benefits of transitioning to R152a-R13I1 blends in MAC systems. [ABSTRACT FROM AUTHOR]

The aim of this work is to provide new experimental data on laminar burning velocities for a new synthetic mixture composed of Camisea natural gas and CO2. It was found that the relevant published experimental background data are limited to mixtures composed of methane and CO2; considering the fact that Camisea natural gas is widely used in Peru, this experimental research will serve as a supportive resource for further experimental and industrial implementations in this country, such as the design and modeling of new engines or industrial burners that are designed to be fueled by this mixture. An experimental setup for analyzing three types of flame geometry, which is feasible to implement for a wide range of conditions, was built in PUCP PI0735 laboratory and all the measurements were obtained for a range of mixtures (0%, 21.2%, 28.5%, 38.9%, 50% CO2) and ratios from around 0.55 to 0.95 at atmospheric conditions. The laminar burning velocities results obtained were analyzed in groups based on %CO2. In addition, the experimental margin error was determined by considering all the sources. The following conclusions were reached: (1) The laminar burning velocity decreases with the increase in CO2 percentage in the mixture due to the CO2 decreasing the flame temperature effect. (2) The flat flame type provided the highest value of burning velocity for each group of CO2 percentage in which it appears. (3) The highest obtained laminar burning velocity value was 22.64 ± 0.15 cm/s, for a flat flame with a ratio of 0.72 and 29.98% of CO2, while the lowest obtained value was 6.78 ± 0.15 cm/s for a conical trunk flame with a ratio of 0.59 and 49.83% of CO2. (4) The highest evaluated CO2 percentage was 50.97% for a conical trunk flame with a ratio of 0.69 and a burning velocity value of 11.04. [ABSTRACT FROM AUTHOR]

Values of laminar burning velocity obtained by the constant volume method suffer from the inaccuracies introduced by the semi-analytical burned gas mass fraction model and flame stretch. A cylindrical combustion chamber with full optical access was developed in the present study, enabling the photography of the flame until the flame touches the inner wall of the combustion chamber. This enables direct visualization of the flame, thus eliminating the dependency on burned gas mass fraction models. The values of laminar burning velocity obtained by simultaneous measurement of flame radius and pressure-time data using the constant volume method are not stretch-free. This paper also develops a methodology for stretch correction based on the determined laminar burning velocity. Experiments were performed on mixtures of methane and air at initial pressures (0.8–1.05 bar), initial temperatures (293–320 K) and equivalence ratios (0.8–1.2). Stretch-corrected laminar burning velocity for lean, stoichiometric, and rich methane-air flames has been obtained in the present study, and the results obtained are validated against available experimental data and 1-D flame computations. It is expected that the proposed method significantly reduces the inaccuracies in laminar burning velocity obtained by the constant volume method. [ABSTRACT FROM AUTHOR]

In the present work, the laminar burning velocities of NH3 + hydrous C2H5OH + air flames were measured using the heat flux method at 1 atm with varied equivalence ratios and mixing ratios (with hydrous ethanol molar fractions of 45%–75%). The measurements were carried out at unburned temperatures of 358 and 378 K. The results show that the laminar burning velocities increase with the increase of hydrous ethanol mixing ratio and temperature, indicating that hydrous ethanol contributes to the combustion of NH3 flames. Based on Wang et al.'s CEU‐NH3 mechanism, sensitivity, reaction pathways, and product formation rate analyses were conducted. The results show that the addition of water reduces the laminar burning velocities of mixed fuel. Intermediate radicals such as NH and HNO are crucial for the formation of NO. After adding water, in the preheating zone, the total production rates of key species such as NH3, H, O, and OH radicals and intermediate species like NH2, NH, HNO, and N decrease, leading to a reduction in the total NO generation rate and the peak mole fraction of NO in the reaction zone. [ABSTRACT FROM AUTHOR]

The fundamental combustion field of ammonia-hydrogen fuel is being extensively researched. However, studies on the laminar burning velocity (LBV) under high pressure with varying hydrogen concentration conditions are relatively scarce. This study innovatively used the constant volume method (CVM) to measure LBV of ammonia-hydrogen fuels with various hydrogen concentrations X H2 = 15%–30%, initial temperatures T i = 298–428 K, initial pressures P i = 1–3 bar, and equivalence ratios ϕ = 0.8–1.4. The LBV of the fuel mixture up to the temperature and pressure of 540 K and 7 bar under isentropic adiabatic assumption was determined with the CVM method. The results illustrate that the enhancing effect of hydrogen concentration on LBV is suppressed under high pressures, supporting the argument that the equivalence ratio associated with the maximum LBV is solely determined by the initial fuel composition. Chemical kinetics simulations were also analyzed including flame structure, sensitivity analysis, and reaction pathways. It indicated that the elementary reaction H + O 2 <=>O + OH predominantly governs the LBV of ammonia-hydrogen. An increase in hydrogen concentration intensifies this process by boosting the concentration of free radical hydrogen, albeit with a concomitant rise in NO emissions due to nitrogen-containing radical oxidation. Conversely, an increase in initial pressure diminishes NO emissions by strengthening the pathway from NO to NNH. The findings of this study enhance the LBV database of ammonia-hydrogen fuel at high pressures and high temperatures, and can further act as a reference for other experiments. • Investigated NH 3 /H 2 /Air laminar burning velocity via the constant volume method. • Provided the laminar burning velocity data under continuously elevating temperature and pressure. • Analyzed the impact of elevated hydrogen concentration and pressure on NO emissions. • Findings show that increased pressure aids in reducing NO emissions by promoting its consumption. [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]

Compared with pure NH 3 fuel, the lower NO emission conditions of NH 3 –H 2 mixtures under the oxygen-enriched combustion mode have been identified quantitatively. Furthermore, the effects of the H 2 addition on the NO productions of premixed oxygen-enriched NH 3 –H 2 flames are studied numerically, while the major reactions responsible for the variation of total NO are identified. Results show that the H 2 addition is eligible to reduce the NO emissions of the oxygen-enriched NH 3 combustion if the laminar burning velocity is fixed to a larger value (>23 cm/s). The quantitative equations are obtained to determine the optimum oxygen-enriched conditions of the NH 3 –H 2 mixture, aiming to achieve lower NO emission and similar or improved combustion stability compared to pure NH 3 fuel by restricting the minimum and maximum O 2 percentages for the NH 3 –H 2 mixtures. Based on the rate of production (ROP) analysis, for the oxygen-enriched NH 3 –H 2 combustion, R144 (HNO + H<=>H 2 +NO) is consistently the most significant NO production reaction, while R85 (NH + NO<=>N 2 O + H) and R91 (N + NO<=>O + N 2) play significant roles in the NO consumption. When the laminar burning velocity (S L) is kept to a lower value, the increased total NO of the oxygen-enriched NH 3 flames with the H 2 addition is ascribed to more efficient suppressions on the NO consumption reactions of R85, R91 and R77 (NH 2 +NO<=>NNH + OH). In contrast, thanks to the extra impact of the higher O 2 percentage on the H/O/OH radical pool at larger S L , the NO production reactions begin to suffer stronger suppressions of the H 2 addition, resulting in the reduced total NO of NH 3 –H 2 mixtures. Furthermore, R144 is identified as the key reaction influencing the variation trend of total NO at both lower and higher S L values. • NO emissions of oxygen-enriched NH 3 –H 2 combustion are investigated. • Lower NO emission conditions of NH 3 –H 2 mixture than NH 3 are identified. • H 2 addition leads to opposite change of NO emission at small and large S L. • Effects of H 2 addition on NO formations are analyzed at different S L. • R144 plays a decisive role in determining the opposite change of NO emission. [ABSTRACT FROM AUTHOR]

The global rise in carbon emissions presents a rising challenge for current and future generations. In the pursuit of zero carbon emissions, ammonia (NH3) has emerged as an attractive alternative energy source. Ammonia offers a carbon-free fuel option with a higher energy density than liquid hydrogen while maintaining ease of transport and storage. However, ammonia still has its drawbacks, such as a high autoignition temperature, slow burning velocity, and low heating value, that demand further investigation of its combustion characteristics. This experiment was done to study the effect of nozzle shape and equivalence ratio (ϕ) on the combustion of an ammonia/oxygen/argon mixture using a constant volume combustor equipped with a sub-chamber. The fuels were premixed for 10 minutes and conditioned to an initial pressure of 0.2 MPa and an initial mixture temperature of 423 K. The results show that the different nozzle shapes each have their advantages in terms of pressure and jet speed. Overall, the lean mixtures (ϕ0.6 and ϕ0.8) consistently performed better compared to the stoichiometric mixtures (ϕ1.0) in all categories investigated in this study. The round nozzle generates higher pressure, while the special shape nozzle enhances jet speed, highlighting trade-offs between the two. [ABSTRACT FROM AUTHOR]

Due to the carbon dioxide (CO2) content in biogas, using biogas is relatively limited in many industrial applications. Hydrogen (H2) is a highly reactive gas that is used extensively to enhance the burning rate of biogas, on the other hand, nitrous oxide (N2O) is a powerful oxidizer that can improve the burning rate of biogas. The laminar burning velocities of biogas-hydrogen-air and biogas-N2O mixtures at various equivalence ratios were investigated experimentally using the spherical flame methodology. It was found that the laminar burning velocities were enhanced in biogas-hydrogen-air and biogas-N2O mixtures. However, the enhanced laminar burning velocities of biogas-N2O showed a more significant increase than biogas-hydrogen-air due to the significant energy released by the N2O decomposition reaction. The flame thickness of the biogas-N2O mixture indicated lower values than biogas-hydrogen-air mixtures, suggesting a higher flame instability of the biogas-N2O mixture than biogas-hydrogen-air mixtures. The Lewis number of biogas-N2O mixture showed lower values than all biogas-hydrogen mixtures, indicating higher diffusive-thermal instability influence on biogas' flame. The reactions of H + O2⇔ OH + O and H + CH3(+M) ⇔ CH4(+M) represented the most significant reactions influencing the laminar burning velocities of biogas-hydrogen mixtures, while the N2O + H⇔N2 + OH, and N2O(+M) ⇔ N2 + O(+M) reactions represented the most important reactions in biogas-N2O combustion. [ABSTRACT FROM AUTHOR]

Ammonia is a promising hydrogen carrier and carbon-free fuel. In this work, new laminar burning velocity data of ammonia under intensified preheating (773K–848K) and N 2 diluted condition is provided. Temperature coefficient that reflects the exponentially positive effect of preheating is reevaluated and compared with literature data at lower preheating temperatures, which is in the range of 2.08–2.30 with an improved accuracy. In contrast, dilution is of a linearly negative effect. The laminar burning velocity decreases by more than 20% as the O 2 content drops from 21% to 19%. Besides, 11 recently published kinetic models are evaluated based on the experimental data. The Otomo18 model makes the best prediction with a small relative difference (≤±5%). Accordingly, the effects of radiation heat loss and dilution are analyzed in detail. The former is found insignificant, and the latter is mainly attributed to the adiabatic flame temperature drop. [Display omitted] • New S l data of NH 3 flame over 773K is provided. • Temperature coefficient is still close to 2.0. • Thermal effect dominates the negative dilution effect. • Radiation heat loss is no more significant under preheated condition. • Otomo mechanism performs better in S l prediction. [ABSTRACT FROM AUTHOR]

Both NH3 and H2 are considered to be carbon-free fuels, and their mixed combustion has excellent performance. Considering the laminar burning velocity as a key characteristic of fuels, accurately predicting the laminar burning velocity of NH3/H2/Air is crucial for its combustion applications. The study made improvements to the XGBoost model and developed NH3/H2/Air Laminar Burning Velocity Net (NHLBVNet), which adopts a composite hierarchical structure to connect the functions of feature extraction, feature combination, and model prediction. The dataset consists of 487 sets of experimental data after the exclusion of outliers. The correlation coefficient ( R 2 > 0.99) of NHLBVNet is higher than that of the XGBoost model ( R 2 > 0.93). Robustness experiment results indicate that this model can obtain more accurate prediction results than other models even under small sample datasets. [ABSTRACT FROM AUTHOR]

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]

Ammonia (NH 3), as an ideal zero-carbon fuel, plays a positive role in mitigating global warming. By cofiring NH 3 with highly reactive small molecule fuels such as hydrogen (H 2), carbon monoxide (CO) and methane (CH 4), the reactivity of NH 3 combustion can be significantly enhanced. In this work, a detailed kinetic mechanism for NH 3 /CH 4 /H 2 /CO containing 146 species and 1099 reactions was developed and extensively validated with selected experimental data from the literature on laminar burning velocity (LBV), ignition delay time (IDT), and species concentrations measured in burner-stabilized flames (BSF), plug flow reactors (PFR) and jet-stirred reactors (JSR), covering temperatures of 273–2000 K, pressures of 0.053–40 atm and equivalence ratios of 0.1–2. In addition, the detailed mechanism was simplified to include 53 species and 353 reactions using three simplification methods. Kinetic modeling analysis showed that the chemical and transport effects of H 2 , CO and CH 4 are the main factors enhancing NH 3 combustion, which rising with the increasing initial temperature and decreasing ammonia blending ratio. Among the four reactants, H 2 is consumed first, followed by CH 4 and NH 3 , with CO reacting last. By modifying the Metghalchi-Kech power law equation, it was found that a clear linear relationship exists between LBV and the sum of the maximum mole fractions of O, H, OH, and NH 2 radicals. [Display omitted] • A kinetic mechanism for NH 3 /CH 4 /H 2 /CO was proposed and simplified. • Validation range includes T 0 of 273–2000 K, P 0 of 0.053–40 atm and Ф of 0.1–2. • Chemical kinetics of LBV for NH 3 /H 2 , NH 3 /CO and NH 3 /CH 4 blends were studied. • The correlation between LBV and free radicals was investigated. [ABSTRACT FROM AUTHOR]

For net‐zero carbon emissions, hydrogen/ammonia blends have drawn considerable attention for the application in industrial combustion devices. Various chemical mechanisms have been developed to describe the oxidation and combustion of hydrogen/ammonia mixtures at certain conditions. A comprehensive evaluation and comparison of the performance of these mechanisms is thus of high interest, especially in terms of their application for particular computational studies. Thus, this work aims to compare the existing chemical mechanisms in terms of their performance for the combustion of hydrogen/ammonia mixtures over a wide range of experimental conditions. In addition to previous literature studies, the model performance is evaluated by using two different methods for the assessment of prediction accuracy. Besides the conventional measure of point‐wise differences between model and data, the curve‐matching method is also applied, which quantifies the dependence of model response on physical conditions additionally, by comparing the similarity between the curve shapes of the predicted and measured results. Extensive experimental data are taken into account in the model evaluation, including 136 datasets obtained from various facilities in the past 10 years. Nineteen mechanisms are compared, which were published in recent five years. It is revealed that these models give strongly different numerical results for combustion targets, such as laminar burning velocities, ignition delay times, and species concentrations. The chemical mechanisms of Zhang et al. (2021), Han et al. (2023), Mei et al. (2019), Li et al. (2019), and Stagni et al. (2020) show relatively satisfactory performance over the entire investigated domain. Moreover, it is found that the estimated prediction accuracy of chemical mechanisms is highly sensitive to model evaluation methods. [ABSTRACT FROM AUTHOR]

Ammonia is carbon-free and is a very promising renewable fuel. The ammonia/diesel dual-fuel combustion strategy is an important combustion strategy for ammonia internal combustion engines. To achieve clean and efficient combustion with a high ammonia blending ratio in ammonia engines, it is important to thoroughly investigate the combustion characteristics and chemical reaction mechanisms of ammonia/diesel fuel blends. Based on the constant volume combustion vessel experiments, the laminar burning velocities (LBVs) of ammonia/n-heptane blends were measured at the conditions of an ammonia–energy ratio of 60–100%, at initial pressures of 0.1–0.5 MPa and initial temperatures of 338–408 K, and under an equivalence ratio regime of 0.8–1.3. The experimental results indicate that the laminar burning velocities of ammonia/n-heptane fuel blends increase with a decreasing ammonia–energy ratio. Specifically, with an ammonia–energy ratio of 60%, an initial temperature of 373 K, an initial pressure of 0.1 MPa, and an equivalence ratio of 1.1, the measured LBV is approximately 20 cm/s, which is about 61% faster than that of pure ammonia flames under the same conditions. A previously developed chemical kinetic mechanism is employed to simulate the new experimental data, and the model exhibits overall good performance. The sensitivity analyses have been conducted to highlight the important reaction pathways. The elementary reaction O2 + Ḣ<=>Ö + ȮH demonstrates the most significant promotional effect on the laminar burning velocities, while the interaction reaction pathways of via H-abstraction from n-heptane by ṄH2 radicals are not showing obvious effects on the simulation results under the studied conditions. [ABSTRACT FROM AUTHOR]

Addressing climate change and reducing greenhouse gas emissions are critical priorities. Utilizing hydrogen-rich methane or pure hydrogen as fuels within gas turbines, facilitated by array micro-tube premixed combustion technology, is anticipated to markedly accelerate the decarbonization process of the energy sector. In this study, the flame structure of the array micro-tube premixed burner under various fuel compositions was examined using OH-Planar Laser-Induced Fluorescence and Particle Image Velocimetry measurement techniques. The effects of the equivalence ratio (φ) and the hydrogen power ratio (HPR) on the characteristics of the flame front, including its curvature, density, volume, and the associated flow field properties, were discussed. As φ and HPR increase, the wrinkled structure of the flame front is significantly enhanced, with a more pronounced effect on smaller scales. This enhancement leads to the separation of the unburned pockets from the main flame. Concurrently, both the flame length and the flame area decrease with the augmentation of φ and HPR, indicating a more concentrated combustion process and increased combustion intensity under hydrogen-enriched and pure hydrogen conditions. The study also observed a slight increase in both the negative and positive curvatures of the flame front, with a more notable increase in the negative curvature. The increased negative curvature results in an elevated degree of wrinkling and a higher value of Σ (flame surface density), reaching a maximum of 0.876 mm−1 under the conditions where φ is 0.8 and ⟨c⟩ (mean progress variable) is 0.5, resulting in the smallest observed flame volume of 100.6 mm3. Upon coupling the flame with the flow field, it was discovered that the exit flow field of the array micro-tube exhibits symmetry and a characteristic conical flame shape. The burning velocity of the side flame brushes increases, and the velocity peak shifts upstream. The aforementioned findings confirm that the addition of hydrogen increases the laminar flame velocity, enabling the flame to stably anchor to the microtube outlet and thereby enhance the flame's robustness and stability. [ABSTRACT FROM AUTHOR]

In this work, combustion characteristics of premixed n-dodecane/air mixtures are investigated at elevated mixture temperatures through laminar burning velocity measurements at atmospheric pressure and elevated temperatures using an externally heated diverging channel method. The experiments were conducted up to high-temperature conditions of 610 K at varying equivalence ratios (ϕ = 0.7–1.3) to mimic the conditions of practical application devices. With an increase in the mixture temperature, the laminar burning velocity increases because of the rise in reactant enthalpy. The peak laminar burning velocity is observed at ϕ = 1.1 for all the mixture temperatures, except at 600 K, where the maximum laminar burning velocity is observed for stoichiometric conditions. The minimum temperature exponent exists for a slightly rich mixture condition (ϕ = 1.1). Out of all mechanisms, the laminar burning velocity predictions using the Lawrence Livermore National Laboratory model are consistent with the present data at all mixture temperatures. Normalized sensitivity analysis is analyzed using the Lawrence Livermore National Laboratory mechanism to understand the key reactions affecting the laminar burning velocity of the n-dodecane/air mixture. The chain branching reaction R16: H + O2 <=> O + OH has a major influence on the enhancement of the laminar burning velocity. Reaction pathway analysis is carried out at stoichiometric conditions for mixture temperatures of 400 K and 600 K, where it is observed that the elemental flux of the reaction, converting CO to CO2, gets reduced by 42.91% at the high-temperature condition. [ABSTRACT FROM AUTHOR]

This study employs Cantera code to investigate the laminar burning velocity of different ammonia–hydrogen mixtures. Suitable models were selected from recent literature, and the one with the lowest root mean square error (RMSE) against experimental data was identified through the error function method. Bao mechanism shows an RMSE value of 4.71 at atmospheric pressure for ammonia–hydrogen mixtures, while the Otomo mechanism exhibits an RMSE of 2.11 under high‐pressure conditions. Additionally, sensitivity analysis was conducted to highlight critical reactions within each mechanism, emphasizing distinctions between different pressures. This approach aims to choose the proper mechanism to reduce computational and experimental costs in the early stages of ammonia–hydrogen research. [ABSTRACT FROM AUTHOR]

As a carbon-free hydrogen-carrying fuel, ammonia can effectively alleviate the problem of CO 2 emissions and has great application potential in marine engines. The low laminar burning velocity and calorific value, and the narrow flammability limit range make the combustion of pure ammonia difficult. Ammonia/methanol mixed combustion is a feasible method to improve ammonia combustion and mitigate CO 2 emissions. It is difficult to accurately predict the laminar burning velocity (LBV) and ignition delay time (IDT) of ammonia/methanol combustion simultaneously by the existing chemical kinetic mechanisms. This study aims to develop a detailed chemical kinetic mechanism that can simultaneously predict the LBV and IDT. The new-developed mechanism was fully validated based on experimental data. Furthermore, it was employed to investigate the effects of methanol blending ratios and equivalence ratios on the LBV and IDT in NH 3 /CH 3 OH mixed flames. Besides, chemical kinetic analyses were conducted to elucidate the influence of methanol mixing ratios and equivalence ratios on LBV and IDT. Reaction pathway analysis revealed that the NH 3 and CH 3 OH chemistry interacted by the sharing of H, OH and O radicals in fuels' decomposition, and chemical interactions of N-containing radicals with the C 1 species. The reactions involving C-containing species can notably improve the LBV of NH 3 /CH 3 OH mixed combustion. At low equivalence ratio, LBV increases in proportion to the fuel proportion. Conversely, at high equivalence ratio, the effect of oxygen concentration on LBV becomes the dominant factor. • A chemical kinetic mechanism of NH 3 /CH 3 OH was developed. • CH 3 O, CH 2 OH, H and OH radicals facilitate the NH 3 oxidation. • C-containing species notably improved LBV. • The effect of equivalence ratio on IDT is smaller than methanol blending ratio. [ABSTRACT FROM AUTHOR]

Three clean gases (shale gas, biomass gas, and coalbed gas) are simulated by using Chemkin-Pro software. The GRI 3.0 mechanism, which exhibits superior predictive performance overall, is chosen for numerical simulation based on comparative analysis. The comprehensive analysis of the effects of fuel components on flame speed and temperature in the three mixtures. Based on the laminar burning velocity, the numerical decoupling method is used to separate the chemical and physical effects of CH4, as well as the dilution, thermal, and chemical effects of CO2. At the same time, verification and analysis are carried out by sensitivity analysis and flame structure analysis. Sensitivity analysis is employed to evaluate the impact of key fundamental reactions on laminar burning velocity and temperature, while flame structure analysis is utilized to ascertain variations in crucial species and temperatures during flame combustion. [ABSTRACT FROM AUTHOR]

The deflagration-to-detonation transition (DDT) poses significant risks in the oil, gas, and nuclear industries, capable of causing catastrophic explosions and extensive damage. This study addresses a critical knowledge gap in understanding the DDT of ethane–air mixtures on a large scale, amid increasing industrial utilization and production of ethane. A novel computational framework is introduced, utilizing the finite-volume code named Morris Garages, which incorporates reactive compressible Navier–Stokes equations, adaptive mesh refinement, and correlations of turbulent burning velocities. This model integrates the most recent data on laminar and turbulent burning velocities for premixed ethane–air mixtures, simulating flame acceleration and DDT within a two-dimensional large-scale setting, measuring 21 m in length and 3 m in height, with obstacles mimicking pipe congestion. Two mixture scenarios, lean and near-stoichiometric, are analyzed to evaluate the effects of equivalence ratios on flame propagation and DDT. The simulations, validated against large-scale experimental data from Shell, show reasonable agreement and provide critical insights into the onset conditions of DDT, such as temperature, pressure, flame speed, and turbulent kinetic energy. Furthermore, the ξ–ε detonation peninsula diagram is utilized to explore autoignition and detonation behaviors in ethane–air mixtures. [ABSTRACT FROM AUTHOR]

This study evaluates the laminar burning velocity of oxyfuel syngas mixtures. Experimental measurements were performed in standard conditions (298 K and 1 atm), varying the oxyfuel syngas composition (H2/CO/CO2/O2) and equivalence ratio for lean mixtures. The experimental setup uses the heat flux method, validated with CH4/air and H2/CO/air measurements. The results were compared with six chemical kinetic mechanisms developed for syngas, aiming at evaluating their predictive capabilities. The mixtures presented a tendency to the appearance of cellular instability in the flame front that was prevented to a certain extent. The CO2 effects on the flames were explored through numerical analysis, isolating the thermodynamic properties, transport properties, thermal radiation, and chemical effects. The CO2 or N2 effect as bath gas in the oxidizer is also evaluated in terms of the laminar burning velocity and mixture's effective Lewis number. Limitations due to cellular instability were studied, analyzing the influence of fuel dilution and composition on the onset of cellular instability at the flames. The results showed a good prediction of the experimental data by the evaluated kinetic mechanisms. The expected reduction in the laminar burning velocity with CO2 dilution is primarily due to the effect of carbon dioxide's thermodynamic properties, followed by its transport properties (when compared to N2 dilution), chemical effects, and heat losses by radiation. Cellular instability is attenuated with high dilution levels due to the reduction of hydrodynamic instability. At the same time, the increase of the H2 concentration in the mixture leads to more unstable flames due to both hydrodynamic and thermal-diffusive instability. A laminar burning velocity threshold above which the measurements were not possible due to the effects of cellular instabilities was identified and analyzed in detail. [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]

Biogas is an efficient and environmentally friendly gaseous fuel. To ensure the safety of biogas applications, highly effective extinguishing technologies for suppressing biogas flames should be developed. In this paper, the extinguishing performance and kinetic mechanism of 2-BTP were studied experimentally and numerically. The results indicate that 2-BTP has excellent inhibition effect on biogas flames, but it depends on the ratio of hydrogen and oxygen in the reactants. For hydrogen-rich and oxygen-poor flames, 2-BTP shows efficient inhibition effect. However, it shows a little combustion promotion effect for hydrogen-poor and oxygen-rich flames at the addition of certain concentrations. The H and OH radical concentration variation and their production/consumption reactions are analyzed subsequently, and the simulation computation shows that some competing reactions involving Br-containing species lead to these results. The purpose of this research is to gain an in-depth understanding of the potential and effectiveness of 2-BTP in suppressing biogas fires, which can lead to better forecasting and optimization of its application, with the goal of enhancing the efficiency of fire extinguishment and minimizing possible adverse effects. • 2-BTP is particularly effective to slow the burning velocities of stoichiometric and fuel-rich biogas flames. • The effect of 2-BTP on combustion promotion or inhibition depends on the amount of hydrogen and oxygen in the flame. • The hydrogen contained in 2-BTP and the reaction HBr + O → Br + OH support the combustion of lean flame to some extent. [ABSTRACT FROM AUTHOR]

In this paper, the effects of equivalence ratio (0.8-2.0) and temperature (30°C-120°C) on ethanol, acetone, and, ethyl acetate vapors explosion characteristics through experimental and numerical studies were investigated. The explosion overpressure and flame propagation velocity were recorded through the pressure transducer and high-speed camera. The results showed that the flame propagation velocity, peak explosion overpressure, and peak growth rate of explosion overpressure increased first and then decreased with the increase of equivalence ratio. The cracks on the flame surface enhanced with the increase of the equivalence ratio. As the initial temperature increased, peak explosion overpressure, the flame propagation velocity, and peak growth rate of explosion overpressure gradually increased. The sensitivity analysis of laminar burning velocity indicated that with the change of equivalence ratio and initial temperature, the shared elementary reactions that increased the reactivity were H + O2 < = > O + OH, HCO + M < = > H + CO + M, and CO + OH < = > CO2 + H, and the shared elementary reaction that reduced the reactivity was H + OH + M < = > H2O + M. The main factor affecting laminar burning velocity was the mole fraction of H and OH radicals. [ABSTRACT FROM AUTHOR]