Flame Characteristics Research Articles

Effects of the cooling jets on the flame characteristics and wall temperature of air-cooled wall-strut flameholders

Air-cooled flameholder is a credible solution for restraining the increasingly raised inlet temperature and operation cycle of advanced afterburner/ramjet combustors. In previous study, the effects of cooling jets on the flow and cooling film characteristics of an air-cooled integrated flameholder (coupled with wall and strut parts) have been revealed by numerical analysis. Furthermore, this work aims to reveal the influence of jet cooling schemes and cooling jet conditions on the fuel spray, flame structure and wall temperature of air-cooled wall-strut flameholder. Experiments were performed to obtain the flame structures and wall temperature distributions. Numerical simulation with Discrete Phase Model was employed to analyze the distribution characteristics of vapor-phase fuel.The results suggest that the changes of cooling jet angle significantly affect both the vapor-phase fuel distribution in the backward-facing step region and the radial wake region. Moreover, as the mainstream velocity increases, the pilot flame temperature and area decrease, and its radial propagation capability worsen. An increase in the flow rate of radial cooling jet would lead to local extinction and deteriorate flame uniformity. Therefore, the cooling effectiveness of the air-cooled wall-strut flameholder is significantly influenced by the wall and radial cooling jet angles, as well as the aerodynamic conditions. Overall, when cooling hole angles on the wall-type step of α = 30°, β = 30°, and that on the radial strut of θ = 90°, the air-cooled wall-strut flameholder exhibits the best comprehensive performance.

Experimental and numerical investigations on NH3/H2 fueled combustion in the combustor with block for improved micro power generation

To advance the application of zero-carbon fuels in micro-combustion, enhance energy conversion, and reduce NOx emissions in NH3/H2-fueled micro-power generators, a micro-combustor with an insertion block is proposed and tested under various chamber configurations and operational conditions. Experimental and numerical tests are conducted in micro-combustors with varied block settings, burner dimensions, NH3 blended ratios (mN), and fuel flow rates (Vf). The results indicate that mN significantly impacts the generation and consumption of H, O, and OH radicals, as well as NO, affecting flame regime and heat transfer. Specifically, adding 5∼15% NH3 improves the operating performance of the burner, with the highest mean temperature achieved in combustor #24C3-0.4 at mN=15%. Block insertion alters flame characteristics and enhances gas-wall heat transfer, the combustor with thinner blocks at higher mN and thicker blocks at lower mN contributes to better thermal performance. Furthermore, combustors with thinner blocks exhibit lower NO emissions. The working performance of the micro-thermophotovoltaic system can be enhanced by selecting the appropriate burner length with block thickness W=0.4 mm and position Lb=7 mm based on Vf. The maximum electrical power of 3.7 W is achieved with a burner length of 28 mm for the system using InGaAsSb cells at Vf=1200 mL/min.

Experimental Study on Overpressure and Flame Characteristics of Hydrogen-methane mixture

In order to evaluate the consequences of hydrogen-methane mixture explosion accidents in open space and confined space, large-scale (8m3) open space and confined space (55m3) hydrogen-methane mixture explosion experiments were carried out to study the effects of hydrogen-doped ratio and equivalent ratio on hydrogen-methane mixture explosion characteristics. In the open space experiments, within the equivalence ratio range of 0.9 to 1.3, the overpressure measured at an equivalence ratio of 1.1 is the highest. When the equivalent ratio is 1.1, the higher the hydrogen blending ratio, the higher the overpressure peak and the farther the action distance. The overall overpressure increased significantly when the hydrogen blending ratio increased from 20% to 30%. When the hydrogen ratio is 30%, the flame propagation speed is as high as 20 m/s, which is about twice the flame propagation peak speed when the hydrogen ratio is 10%-20%. Therefore, from the angle of overpressure and flame development, the step point of overpressure harm can be obtained by a hydrogen mixing ratio of 20%. The overall trend of external overpressure change in confined and open spaces is consistent; both decrease with the increase in distance. However, the external overpressure in confined space is more significant than in open space, and the flame propagation speed is much higher than in open space. When the hydrogen mixing ratio is 5%, 10%, 15%, and 30%, the Outdoor flame propagation speed of 62.129/85.332/40.091/52.364 m/s, respectively. Compared with open space, the harm range of confined space is more extensive. This study provides an experimental basis for the safety assessment of hydrogen-methane mixture and the formulation of safety protection measures.

Stability and Combustion/Emission Characteristics of Stratified Dual-Swirl Oxy-Methane Flames: Effects of Oxygen Fraction

Abstract The stability, combustion, and emission features of stratified oxy-methane (CH4/O2/CO2) flames stabilized over a dual annular counter-rotating swirl (DACRS) burner, developed for gas turbine combustion applications, were investigated experimentally. The experiments were performed at fixed velocity ratio (Vr = Vp/Vs = 3.0) in both the primary and secondary streams at a constant primary stream velocity, Vp of 5 m/s and at fixed primary stream equivalence ratio, φp = 0.9, and over ranges of oxygen fractions (OFp for the primary stream, OFs for the secondary stream) and secondary stream equivalence ratios. Measurements of flame macrostructure, temperature profiles, and exhaust emissions were recorded to characterize the flames and validate future numerical models. The testing findings revealed no flame flashback within the operational ranges of OFp and OFs and up to φs = 1.0. However, the near stoichiometric operation of the primary stream (φp = 0.9) at OFp = 0.38 permitted the main secondary flame to tolerate exceptionally lean conditions (φs = 0.397 at OFs = 0.34 and φs = 0.223 at OFs = 0.39), raising the thresholds for the flame blowout. Increasing OFp from 0.21 to 0.38 significantly reduced φS at blowout from 0.537 to 0.223, corresponding to a decrease in the combustor's global equivalence ratio (φg) at blowout from 0.554 to 0.254 at global oxygen fraction (OFg) from 0.38 to 0.39. Lower OFp values caused earlier flame lift-off, indicating the greater influence of OFp on flame macrostructures.

Dynamic evolution of flame and overpressure of leakage and explosion of hydrogen-blended natural gas in utility tunnels

In order to ascertain the true characteristics of the leakage explosion loads of hydrogen-blended natural gas (HBNG) in utility tunnels, the influence of leakage location on the concentration field distribution of HBNG leakage in utility tunnels was studied through the CFD technique. Furthermore, the characteristics of explosion flame and overpressure load distribution of HBNG of inhomogeneous distribution under effect of different ignition delay times and ignition positions were also investigated. The results show that the greater the distance between the leakage location and the air outlet, the more readily HBNG can propagate throughout the utility tunnel. This, in turn, leads to more prominent downstream gas cloud stratification. The development of explosion flame is primarily seen in the direction of low resistance and ample space within the utility tunnel. With the increase in ignition delay time (tid) and the backward shift of the leakage location (Llk), the average flame velocity generally exhibits a decreasing trend. Overall, the peak overpressure exhibits a concave trend. Under circumstances where the leakage source is in the front or middle section of the tunnel, the average peak overpressure demonstrates a general tendency of increase followed by decline with the increase in tid. In comparison, in the case of a leakage source located at the back end, it decreases gradually as tid increases. The most severe explosion overpressure load is readily induced when the leakage source is located at the front end. In the case of a leakage source located in the front section of the tunnel, the overpressure load at each measuring point decreases continuously and then rises as the ignition position moves backward. However, in the case of a leakage source located in the rear section of the tunnel, the average value of peak overpressure induced by ignition in the middle of the tunnel is the greatest, while the average value of peak overpressure induced by ignition at the back end is the smallest. The maximum explosion overpressure load is found at the front-most leakage source under front-end ignition conditions. The findings of this study offer scientific substantiation for the structure of the utility tunnel, which is designed for explosion withstanding, prevention, and control as well as risk assessment.

Visualization of ammonia-methanol solution combustion under spark and passive jet ignition mode in an optically-accessible engine

Ammonia-methanol (A-M) solution is a promising carbon-neutral fuel for internal combustion engines. In this paper, the in-cylinder flame imaging and measurements of A-M solution under spark ignition (SI) and passive jet ignition (JI) mode were conducted, based on an optically-accessible engine. For 7 mol/L A-M solution combustion, the flame shows brown to purple color under stoichiometric condition and orange color under lean conditions. An increased burning rate is obtained under JI mode, with higher flame speed, shorter ignition delay and combustion duration at different excess air ratios (λ = 1∼1.6) than that in SI mode. It also allows a retarded spark timing for higher power output and thermal efficiency. As ammonia energy ratio increases from 13.7 % to 50 %, the flame development becomes slower under SI mode, while JI mode shows limited improvement of combustion. For pre-chamber nozzle designs, an area-to-volume ratio larger than 0.025 cm−1 is conducive to ignition and combustion for 7 mol/L A-M solution. Besides, the effects of slot, unequal and jet-crossing nozzle were also evaluated. Overall, this work provides the basic insights of flame characteristics and demonstrates the combustion accelerating effect of JI method for ammonia-methanol fueled engines.

The combustion of lemon peel oil/gasoline blends in spark ignition engine with high-insulation piston crown coating

This study explored the recovery of oil from lemon peel biomass and then tested it in a spark ignition as a substitute for gasoline. The study adopted the micro-arc oxidation coating technique, intending to improve the engine performance of the lemon peel oil-gasoline blends. The oil was recovered from discarded lemon peel biomass using steam distillation and then tested in the engine as a fuel by blending it with gasoline at volume ratios of 10, 20, and 30%. An endoscopic visualization approach was employed in this research work to assess the combustion initiation and flame characteristics of gasoline and lemon peel oil blends under different test conditions. Compared to gasoline and blends comprising 20 and 30% lemon peel oil, the 10% lemon peel oil mix produced higher thermal efficiency and lower emissions. The optical analysis demonstrated that premixed combustion with the 10% blend was found to be the highest, resulting in improved combustion and subsequently increased cylinder pressure. To improve the engine performance of the lemon peel oil blends with higher substitution (20 and 30%), the piston was coated with a ceramic coating. A novel technique, namely the micro-arc oxidation technique, was utilized for the coating. The coated piston engine fueled with a 20% lemon peel oil blend showed a 3% and 4.69% increase in thermal efficiency compared to the uncoated piston fueled with a 20% blend and sole gasoline, respectively. The hydrocarbon and carbon monoxide emissions of the engine with a coated piston fueled by the 20% lemon peel oil blend were reduced by 12.7% and 12%, respectively, as compared to gasoline operation in the engine with an uncoated piston.

Flame Combustion State Detection Method of Cement Rotary Furnace Based on Improved RE-DDPM and DAF-FasterNet

It is of great significance to effectively identify the flame-burning state of cement rotary kilns to optimize the calcination process and ensure the quality of cement. However, high-temperature and smoke-filled environments bring about difficulties with respect to accurate feature extraction and data acquisition. To address these challenges, this paper proposes a novel approach. First, an improved denoising diffusion probability model (RE-DDPM) is proposed. By applying a mask to the burning area and mixing it with the actual image in the denoising process, local diversity generation in the image was realized, and the problem of limited and uneven data was solved. Secondly, this article proposes the DAF-FasterNet model, which incorporates a deformable attention mechanism (DAS) and replaces the ReLU activation function with FReLU so that it can better focus on key flame features and extract finer spatial details. The RE-DDPM method exhibits faster convergence and lower FID scores, indicating that the generated images are more realistic. DAF-FasterNet achieves 98.9% training accuracy, 98.1% test accuracy, and a 22.3 ms delay, making it superior to existing methods in flame state recognition.

On the effects of oxygen fraction on stability and combustion characteristics of dual-swirl oxy-methane flames: An experimental and numerical study

The effects of oxygen fractions of primary and secondary streams on flow/flame interactions, flame stability and macrostructure, and combustion and emissions characteristics of premixed oxy-methane (CH4/CO2/O2) flames were studied experimentally and numerically in a dual annular counter-rotating swirl (DACRS) burner for applications of clean power production in gas turbines. The primary stream oxygen fractions (OFp) of 34 % and 25 % were paired with secondary stream oxygen fractions (OFs) ranging from 25 % to 39 % at fixed primary stream equivalence ratio (φp = 0.9), fixed velocity ratio of 3.0 by the primary (of 5 m/s) and secondary (of 1.667 m/s) streams, and over ranges of secondary stream equivalence ratios (φs). The results showed that at OFp = 34 % and OFS = 39 %, the pilot flame supports a lean secondary flame down to φs = 0.434 at combustor global equivalence ratio (φg) of 0.467. Flame flashback concerns were not seen in the operative OFs zone until the secondary stream reached stoichiometric operation (φs = 1.0). The widths and forms of the inner and outer recirculation zones (IRZ and ORZ) are not significantly affected by changes in OF. Reducing φg and OFg resulted in decreases in Damköhler number (Da), laminar flame speed, and CO emissions.

Flame Speed Measurements of Ammonia–Hydrogen Mixtures for Gas-Turbines

Abstract Recent findings from the U.S. Energy Information Administration project an increase in domestic fossil fuel consumption (e.g., petroleum and natural gas) and global greenhouse gas emissions through 2050 (Nalley, S., 2021, “International Energy Outlook 2021 (IEO2021),” IEO2021 Release, CSIS, Center for Strategic and International Studies, Washington, DC, Technical Presentation, pp. 2–12). Consequently, advanced combustion research aims to identify fuels to mitigate fossil fuel consumption while minimizing exhaust emissions. Ammonia (NH3) is one of these candidates, as it has historically been shown to provide high energy potential and zero-carbon emission (CO and CO2) (Hayakawa, A., Goto, T., Mimoto, R., Arakawa, Y., Kudo, T., and Kobayashi, H., 2015, “Laminar Burning Velocity and Markstein Length of Ammonia/Air Premixed Flames at Various Pressures,” Fuel, 159, pp. 98–106). As a hydrogen (H2) carrier, NH3 serves as a possible solution to the U.S. Department of Energy's Hydrogen Program Plan by providing efficient H2 storage and conservation capabilities (U.S. Department of Energy, 2020, “Department of Energy Hydrogen Program Plan,” U.S. Department of Energy, Washington, DC, Report No. DOE/EE-2128). As a result, applied turbine-combustion research of NH3 and H2 fuel has been conducted to identify combustion performance parameters that aid in the design of sustainable turbomachinery (Chiong, M.-C., Chong, C., Ng, J., Mashruk, S., Chong, W., Samiran, N., Mong, G., and Medina, A., 2021, “Advancements of Combustion Technologies in the Ammonia-Fuelled Engines,” Energy Convers. Manage., 244, p. 114460). One of these key combustion parameters is the laminar burning speed (LBS). While abundant literature exists on the combustion of NH3 and H2 fuels, there is not sufficient evidence in high-pressure environments to provide a comprehensive understanding of NH3 and H2 combustion phenomena in turbine-combustor settings. To advance the state of the knowledge, NH3 and H2 mixtures were ignited in a spherical chamber across a range of equivalence ratios at 296 K and 5 atm to understand their flame characteristics and LBS which was determined using a multizone constant volume method. The experimental conditions were selected according to primary turbine-combustor conditions, as much research is needed to support NH3–H2 applicability in turbomachinery for power generation. The effect of H2 addition to NH3 fuel was observed by comparing the LBS for various NH3–H2 mixture compositions. Experimental results revealed increased LBS values for H2 enriched NH3, with the maximum LBS occurring at stoichiometry. The experimental data were accurately predicted by the University of Central Florida (UCF) NH3–H2 mechanism developed for this investigation, while NUI 1.1 simulations overestimated recorded LBS data by a significant margin. This study demonstrates and quantifies the enhancing effect of H2 addition to NH3 fuels via LBS and strengthens the literature surrounding NH3–H2 combustion reactions for future work.

Advanced image processing techniques for multi-level characterization of significant flame features in carbon-neutral combustion

This research presents an advanced image processing framework designed for the multi-level characterization of significant flame features in carbon-neutral combustion systems. The study introduces an optimized neural network based on a brainstorming algorithm and an enhanced support vector machine (SVM) algorithm, which utilizes an improved particle swarm optimization (PSO) technique. The framework is capable of accurately processing complex flame image data, achieving flame classification accuracy rates of up to 100 %. The proposed system combines detailed analysis of flame brightness, texture, and morphological features, contributing to the comprehensive monitoring of combustion states. Additionally, the paper describes the design of a clean burner that promotes the full combustion of zero-carbon gases. The integration of this burner with the advanced monitoring system significantly enhances safety and efficiency in industrial applications. This work addresses the challenges associated with the transition to renewable gases and provides a robust solution for maintaining stable and efficient combustion processes.

Study on the acoustic disturbance characteristics of the spray flame

The axial sound field was added to the ethanol spray flame as a perturbation element to study the dynamic response and combustion characteristics. A forced acoustic field is applied to a small oscillating flame. In cases where the frequency of the external sound field matches the eigenfrequency, even small amplitude self-excited flames demonstrate significant instability. As the intensity of the sound field increases, the amplitude of pressure oscillations sharply rises, and the pressure and flame heat release oscillations are in-phase. When the sound field operates at frequencies other than the eigenfrequency, it has an inhibitory effect on the evaporation and combustion process of ethanol droplets. Consequently, intensifying the sound field leads to a reduction in both the area of the evaporation combustion zone and the axial temperature of the flame. The CO formation is influenced by both temperature and the sound field, showing a pattern of increasing and then decreasing with the increase of sound intensity. Additionally, NOx generation exhibits higher emission concentrations in low-temperature and short flames, which is more likely to prompt NOx and is not closely related to frequency.

Research on flame characteristics and coating growth process of titanium alloy in HVAF spraying

AbstractIn this work, a flow field model of WC–12Co powder sprayed by high‐velocity air fuel (HVAF) was established based on the computational fluid dynamics (CFD) method. The macro–micro coupled thermodynamic model of coating multilayer growth process was established based on the birth and death element method. The temperature and velocity of the particles in the combustion flame were applied to the coating growth model, and the transient evolution of the coating temperature and thermal stress was revealed. The results show the temperature and thermal stress of coatings increase with the increasing the number of spraying layers, and their incremental gradient gradually decreases with the increasing the number of deposition layers. The peak temperature of the coating surface reaches 1494 K, and the peak thermal stress of the first coating reaches 2693 MPa. The maximum stress of spraying particles appears at the contact edge of particles. Further preparation of WC coating, through the hardness, friction, and wear, corrosion tests verify that WC–12Co coating can effectively provide the TC18 substrate performance. The microhardness of WC–12Co coating was approximately three times that of TC18 substrate. The average friction coefficient and corrosion rate of the coating are 0.15 and 0.06 mg/cm2/h lower than that of the substrate, respectively.

Effects of internal intervention in tubes on shock wave attenuation, formation and propagation of flame during high-pressure hydrogen release

Experiments on the impacts of the combination of fin structure and expansion chamber on shock wave attenuation, hydrogen ignition, and flame characteristics during high-pressure hydrogen release were carried out. The fin is a four-edged platform hollowed out on all sides. The inflated upper and lower tube walls are located 85, 95, and 105 mm away from the nickel burst disk. With the incident shock wave traveling through the fin, the reflected shock and the superposition of multiple reflected shock waves appear, and the reflected shock wave intensity can equal that of the release pressure. The decrease of the incident shock wave intensity behind the fin leads to the decrease of the non-uniformity of the mixed layer temperature, further causing the decrease of the flame propagation velocity. The presence of fins increases the probability of ignition in the fin region and the critical release pressure for ignition is significantly lower than that in the barrier free tube, mainly because the fin inside intensifies the hydrogen/air mixture, resulting in a lower minimum ignition energy required for self-ignition. Furthermore, the decrease of flame propagation velocity leads to the increase of hydrogen consumption inside the tube and the decrease of shock overpressure outside.

Analysis of Biomass Briquette Mixed Bagasse and Sugarcane Peel on the Performance of Forced Top-Lit Updraft Gasifier Stove

The population growth in Indonesia from 270 million in 2020 to 279 million in 2024 has increased LPG consumption, potentially leading to future fuel shortages. The top-lit updraft (TLUD) gasifier stove using renewable biomass materials, offers a sustainable alternative. Biomass such as bagasse and sugarcane peel can be optimized into charcoal briquettes with high calorific value and low emissions. The calorific value of briquettes can be further enhanced by blending other high–calorific biomass materials. This experimental research focuses on testing the calorific value of raw bagasse and sugarcane peel before carbonization, as well as briquette mixtures (70:30, 50:50, 30:70) using a bomb calorimeter. The fuel briquettes are tested by operating the TLUD gasifier stove, measuring performance in terms of water boiling time (WBT) and flame characteristics. Results show that the 30:70 bagasse-to-sugarcane peel composition has the highest calorific value (6,242.292 cal/gram), followed by the 70:30 composition (6,094.753 cal/gram) and the 50:50 composition (5,657.935 cal/gram). The 30:70 ratio also achieved the longest flame duration (119 minutes 32 seconds), the highest combustion chamber temperature (570.2°C), and the greatest flame height (11.468 cm). The TLUD stove demonstrated an efficiency of 56.41%, with a char weight of 61 grams and a water temperature increase from 28.4°C to 90.4°C in 10 minutes 45 seconds. These briquettes met the SNI 01-6235-2000 standard, which requires a minimum calorific value of 5000 cal/g.

EMG-YOLO: An efficient fire detection model for embedded devices

The number of edge embedded devices has been increasing with the development of Internet of Things (IoT) technology. In urban fire detection, improving the accuracy of fire detection based on embedded devices requires substantial computational resources, which exacerbates the conflict between the high precision needed for fire detection and the low computational capabilities of many embedded devices. To address this issue, this paper introduces a fire detection algorithm named EMG-YOLO. The goal is to improve the accuracy and efficiency of fire detection on embedded devices with limited computational resources. Initially, a Multi-scale Attention Module (MAM) is proposed, which effectively integrates multi-scale information to enhance feature representation. Subsequently, a novel Efficient Multi-scale Convolution Module (EMCM) is incorporated into the C2f structure to enhance the extraction of flame and smoke features, thereby providing additional feature information without increasing computational complexity. Moreover, a Global Feature Pyramid Network (GFPN) is integrated into the model neck to further enhance computational efficiency and mitigate information loss. Finally, the model undergoes pruning via a slimming algorithm to meet the deployment constraints of mobile embedded devices. Experimental results on customized flame and smoke datasets demonstrate that EMG-YOLO increases mAP@50 by 3.2%, decreases the number of parameters by 53.5%, and lowers GFLOPs to 49.8% of those in YOLOv8-n. These results show that EMG-YOLO significantly reduces the computational requirements while improving the accuracy of fire detection, and has a wide range of practical applications, especially for resource-constrained embedded devices.

Evaluation of Current and Future Aviation Fuels at High-Pressure Rich-Quench-Lean-Type Combustor Conditions

Abstract Decarbonizing the aviation sector is one of the biggest challenges to minimize climate change effects associated with carbon dioxide emission. Sustainable aviation fuels will play a major role in this context especially for long-distance flights where hydrogen or all-electric propulsion systems do not present a feasible alternative. In addition, aromatic-free sustainable aviation fuels offer a promising solution to lower soot emissions of aeroengines. Jet A-1 as reference fuel, two blends, and two neat synthesized paraffinic kerosenes (SPKs) from hydroprocessed esters and fatty acids (HEFA) were tested to characterize the combustion behavior of drop-in/near drop-in fuels. Experiments in an optically accessible high-pressure rich-quench-lean (RQL)-type combustor at typical aeroengine conditions were performed using optical diagnostics, exhaust gas, and particle sampling measurements to delineate the fuel effects on spray, flame, and emission characteristics. Measurements were performed at pressures up to 10 bar, air preheating temperatures up to 773 K and primary zone equivalence ratios up to 1.66. Liquid fuel distribution and fuel placement were found to be sensitive to fuel properties. By contrast, no pronounced influence on flame position and shape were observed. As a consequence, NOx and CO emissions of the tested fuels differed only moderately. However, particulate matter measurements at the fuel richest operating condition showed a clear fuel ranking with the lowest particle emissions evident for the two neat HEFA-SPK samples. Moreover, the particle volume concentration at the fuel richest condition followed the expected trend with fuel H-content.

Prediction of the Flame Characteristics of an Industrial Gas Turbine Operated With CO2-Diluted Air Through a High-Fidelity Numerical Analysis: A Comparison Between Flamelet Generated Manifolds and Artificially Thickened Flame

Abstract In light of the global commitment to decarbonize industrial processes, carbon capture and storage (CCS) plays a pivotal role in mitigating greenhouse gas emissions from gas turbine (GT) power generation processes. Achieving an efficient GT–CCS coupling requires the employment of high percentages of exhaust gas recirculation (EGR) to maximize the CO2 content at the CCS inlet. Nevertheless, such operating conditions pose critical challenges for conventional combustion systems due to reduced oxygen levels associated with higher EGR, limiting engine operability. To address this challenge, the development of innovative technical solutions is essential to extend the combustor operational capabilities at high EGR rates. For this goal, a significant number of computational fluid dynamics (CFD) simulations are required to identify the flame stability limits across various EGR levels and burner designs. It is imperative, in this context, to minimize computational costs while maintaining high accuracy. In this work, a comprehensive comparative study of an extended version of the flamelet generated manifolds (FGM) and the artificially thickened flame (ATF) model is performed through a large eddy simulation (LES)-based CFD analysis. The investigation is performed within the context of an industrial lean-premixed burner manufactured by Baker Hughes, operating with natural gas and CO2-diluted air at atmospheric pressure. While the extended-FGM has been previously presented by the authors in a study on the same test rig under standard air conditions, the current work aims to extend its application to critical oxygen-depleted conditions, where near-blowout phenomena such as flame liftoff and length elongation may become significantly pronounced. Numerical validation is carried out through a direct comparison of the computed averaged heat release, representing the flame topology, with detailed OH* chemiluminescence images from a test campaign conducted by the technology for high temperature (THT) Lab of the University of Florence. The experimental data will serve as the primary benchmark for assessing the models’ effectiveness in capturing the main dynamics of such critical operating conditions. Furthermore, potential disparities in both thermal and flow fields at the burner exit region between the two models will be discussed.

The analytical model of flame characteristics of hydrogen–air through wall and gas interaction analysis

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

Fire and smoke transport dynamics in a dead-end tunnel under heavy rainfall

Fire is one of the most common major accidents during tunnel construction and operation. This work conducted scale-model experiments to investigate the pool burning progress and flame characteristics in a dead-end tunnel with one end closed and the other open under heavy rainfall. The results show that, compared to opening both ends, the global burning time of fires is significantly decreased, and the quasi-stable burning phase is advanced under the combined effects of the closed end and heavy rainfall. The reason is that the increase in ceiling temperature, resulting from the accumulation of hot smoke, leads to an increase in radiative feedback of the fuel from the environment and an acceleration in the pool's burning rate. A coefficient (denoted by γ) is defined to evaluate the increase in the burning rate resulting from the dead-end. The enhancement ratio is found to be related to rainfall intensity, raindrop size, and pool size, and a correlation has been established based on the experimental results. The fire has an increased flame height and a reduced tilt angle under the impact of the dead-end. The changes in flame geometry parameters are mainly influenced by thermal buoyancy and the restriction of the dead-end. Prediction formulas for flame height and tilt angle under the combined effects of the dead-end and heavy rainfall have been proposed based on theoretical analysis. Under these combined effects, the tunnel space becomes eroded by dirty air.