Swirl Burner Research Articles

Flame stabilization and pollutant emissions of turbulent ammonia and blended ammonia flames: A review of the recent experimental and numerical advances

Compared to traditional hydrocarbon fuels, ammonia presents significant challenges as a fuel, including high ignition energy, low reactivity, slow flame propagation, and high NOx emissions, which hinder its use as a renewable fuel. Blending ammonia with fossil fuels like natural gas improves its combustion reactivity and helps mitigate CO2 emissions. However, there is still much to understand about the complex dynamics of ammonia and its blends with hydrocarbons. Key areas such as reaction kinetics mechanisms, ignition properties, flame propagation behaviors, and methods for controlling combustion performance under various conditions require further elucidation. This paper reviews recent advancements in experiments and numerical simulations aimed at developing stable, and low-emission combustors for ammonia-fired power generation. Recent burner and flame configurations, including non-swirling jets, single-stage swirl burners, two-stage burners, and newly developed double-swirl burners are analyzed for their flame stability and pollutant emission potential when firing ammonia and ammonia blends. Chemical kinetic modeling of ammonia and its blends plays a crucial role in understanding combustion behavior and pollutant emissions, particularly for NOx. However, there are challenges in predicting NOx emissions accurately, with significant disparities among different models. High-fidelity numerical simulations using detailed and skeletal mechanisms, direct numerical simulation, and large eddy simulation, have helped uncover crucial operational conditions affecting combustion and pollutant emissions, such as combustor pressure, air dilution, wall cooling, fuel/air mixing, and fuel blending. Nonetheless, the accuracy of chemical kinetic models and their integration into turbulent flow simulations remain critical limitations for numerical simulations of ammonia combustion.

Energy optimization of a steel slab reheating furnace through the use of swirl and diffusion burners using a new mathematical simulation methodology

This study proposed a new methodology to optimize the fuel use in a walking beam reheating furnace that uses swirl burners in the soaking zone through mathematical simulation. Likewise, the radiative effect of the WSGGM model over the heating and thermal gradient of the slab was analyzed, as well as its thermal implications of using swirl and diffusion burners. The model was validated with experimental temperatures obtained inside the furnace by using 16 thermocouples, and they were compared with those in the simulation, reaching an average error of 3.19%. This methodology has allowed the proposal of new operating conditions in fuel management, making the combustion process more efficient with an average saving of 5,067,360 kg of methane annually, representing 9% of the plant’s current use. This optimization process would mean substantial economic savings for the industry and would also be reflected in a significant decrease of greenhouse gases with adverse effects on the planet.

Sensitivity analysis of turbine stage aerothermal characteristics and blade cooling performance considering combustor swirl and hot spot

This paper investigates the global sensitivity of high-pressure-turbine (HPT) first stage cascades aerothermal characteristics and blade cooling performance under the influence of combustor swirl and hot spot. The combustor outflow conditions impact on turbine working performance and robustness. This paper is focused on the influence of uncertain combustor swirling flow and hot spot, rather than deterministic working conditions. A simplified combustor outflow simulation method is firstly proposed, and the effects of combustor outflow are quantified by combining chaos polynomial expansion with Sobol’ decomposition method. The results show that different rotating directions of the swirl lead to restricted influences on the averaged aerothermal performance of the turbine stage, but significantly affects its robustness. The positive swirl increases the total pressure loss generated by the lower passage vortex of the stator cascade, and the high uncertainty region of the stator cascade total pressure loss profile is the combined products of the residual swirl and the interaction between the passage vortex and mainstream. The total pressure loss of the rotor cascade due to leakage vortex has low sensitivity to the hot spot and swirl strength, while the total pressure loss generated by the passage vortex is affected by hot spot temperature. Temperature distribution affected by the passage vortex is sensitive to swirl strength. Generally, uncertainty variance of stage aerothermal parameters with positive swirl is about 30% larger than that of the negative case, since the positive swirl has stronger interactions with the blades, leading to more significant uncertainty. However, the averaged heat transfer coefficients with positive swirl are 37% less sensitive, compared to the negative swirl case. The results give better understanding on the influence mechanisms of turbine inflow conditions, emphasize the meaning of investigating uncertain characteristics of the turbine cascades. Investigations of this article provide reference for robust turbine blade cooling design.

The flame macrostructure and thermoacoustic instability in a centrally staged burner operating in different pilot stage equivalence ratios

The main focus of this paper is to discover the link between flame macrostructure and thermoacoustic instability in a centrally staged swirl burner. In practical combustors, the flow rate in the pilot stage is much smaller than that in the main stage. However, the modification in the pilot stage could alter the flame macrostructure while maintaining a similar total flow rate. Therefore, the thermoacoustic instability was examined at different flame macrostructures by varying the pilot stage equivalence ratio under identical main stage inlet conditions. High-frequency planar laser measurements and chemiluminescence measurement were conducted to enhance spatial and temporal accuracy, providing a more comprehensive understanding of thermoacoustic instability. Two different flame macrostructures, S-type and I-type flames, were identified based on the preheating zone distribution. They exhibit distinct thermoacoustic instabilities, with the I-type flames demonstrating more intense instability than S-type flames. The results indicate that the variation of flame macrostructure influences the coupling of flame heat release and flow field. Specifically, the preheating zone and heat release of I-type flames exhibit greater sensitivity to flow field fluctuations, resulting in a more intense and complex fluctuation of the flame. This discrepancy leads to variations in thermoacoustic instability intensity, as well as the changes in the phase coupling between heat release and acoustic pressure, which in turn impact the total Rayleigh index. Meanwhile, significant differences exist in the distribution pattern and range of flow field fluctuations between I-type and S-type flames.

CFD modeling and industry application of a self-preheating pulverized coal burner of high coal concentration and enhanced combustion stability under ultra-low load

Deep participation in peak regulation is a fundamental issue in flexible peak regulation. The ability to operate coal-fired power units under ultra-low load plays a crucial role in China’s pursuit of its energy goals. This study focuses on the performance analysis of a self-preheating pulverized coal burner with high coal concentration under ultra-low load conditions through simulations and experiments. A numerical comparison between the performance of a traditional swirl burner and a self-preheating burner is conducted using a 5 MW combustion test furnace. The results demonstrate that the self-preheating burner exhibits superior combustion stability and can maintain stable combustion even at an ultra-low load of 15 %. Additionally, the air distribution of the self-preheating burner under ultra-low load conditions is investigated numerically. The results reveal that under 15 % load, primary air rate of 12.0 % and internal secondary air rate of 54.2 % enable the self-preheating burner to achieve stable combustion performance with a char burnout rate of 98.6 %. Furthermore, in the absence of separated over fire air (SOFA) conditions, the NOx emission level ranges from 150 to 165 mg/m3. Based on numerical results, the self-preheating burner is implemented in an industrial setting, specifically a 29 MW coal-fired industrial boiler demonstration project. The results indicate that the self-preheating burner can achieve stable combustion at approximately 13 % load, with an average combustion efficiency of 93.24 %. The research validates the excellent performance of the designed self-preheating burner under ultra-low load conditions, which contributes to addressing the challenge of deep participation in peak regulation.

A novel swirl burner with coal co-firing ammonia: Effect of extension length of the dual-channel ammonia pipe on combustion and NOx formation

The coal/ammonia co-firing technology for thermal power generation is a feasible method to effectively reduce CO2 emissions. However, the easy formation of NOx is one of the challenges faced by this technology owing to the high nitrogen content in ammonia. This study proposes a novel swirl burner with a scalable dual-channel ammonia pipe, and evaluates the combustion and NOx formation under different extension lengths of the dual-channel ammonia pipe (i.e., 0 m, 0.4 m, 0.8 m, 1.0 m, 1.2 m). The results show that the extension length of the dual-channel ammonia pipe significantly affects the flow, combustion, and NOx formation. When the extension length of the dual-channel ammonia pipe is above 0.8 m, the ammonia stream can completely penetrate the internal recirculation zone into the high CO environment, which contributes to promoting the ammonia pyrolysis and inhibiting the ammonia oxidation to form NOx. NOx emissions significantly decrease from 846 ppm to 146 ppm as the extension length of the dual-channel ammonia pipe from 0 m to 0.8 m, but change slightly as further increases from 0.8 m to 1.2 m. The carbon content in fly ash decreases from 4.53% to 3.40% as the extension length of the dual-channel ammonia pipe increases from 0 m to 1.0 m. Still, it increases from 3.40% to 3.70% as the extension length of the dual-channel ammonia pipe rises to 1.2 m. Overall, it is reasonable to set the extension length of the dual-channel ammonia pipe at 1.0 m in this studied condition, which can obtain low NOx and low carbon content in fly ash.

Evaluating potential of increasing flow intensity and reducing crevice volume to improve thermal efficiency and hydrocarbon emission in spark-ignition natural gas engines

Low thermal efficiency and high hydrocarbon emissions caused by slow combustion rates and high methane emissions hinder the development of natural gas (NG) engines. Engine structure modifications have always been an important means of improving the combustion effects of engines. This study investigates the effects of combustion chamber improvements on the thermal efficiency and hydrocarbon emissions of stoichiometric spark-ignition NG engines through numerical simulations. The improvements aimed to enhance squish flow, organize high tumble flow, and reduce crevice volume. The results indicate that strengthening the squish intensity by increasing the squish area of the piston can accelerate flame propagation and reduce exhaust loss. However, this improvement is hindered by a significant rise in heat transfer loss, which limits further gains in thermal efficiency. Compared to the traditional high swirl combustion chamber, a high tumble combustion chamber (dual straight intake port combined with a hemispherical piston) can promote flame propagation in the early stages of combustion and increase thermal efficiency by 1.43%. However, the accelerated flame propagation rate resulting from increased flow intensity has little potential to reduce hydrocarbon emissions due to the small contribution of flame quenching to unburned hydrocarbon production. The primary source of hydrocarbon emissions from NG engines is unburned methane in the piston crevice. Therefore, when addressing hydrocarbon emissions from NG engines, the first consideration should be to minimize the volume of the piston crevice, which will significantly reduce methane emissions and incomplete combustion loss.

Effects of wall confinement on flame topologies and lean blowout characteristics of partially premixed DME/air flames in a gas turbine model combustor

Dimethyl ether (DME) is a promising alternative fuel for gas turbines, considering its renewable nature and potential for large-scale synthesis from CO2 feedstock. However, there are limited studies on the swirl combustion characteristics of DME, particularly regarding the stability performance. This work investigates the effects of wall confinement on flow, mixing, and lean blowout (LBO) characteristics of partially premixed DME/air swirl flames in a gas turbine model combustor. Flow and flame macrostructures are captured using particle image velocimetry and planar laser-induced fluorescence (PLIF) measurements, respectively. The results show remarkable differences in flame topologies between unconfined and confined flames, especially the formation of inner recirculation zone and outer recirculation zone. The LBO limits are measured over various Reynolds numbers and flame dynamics approaching LBO are captured using 10 kHz OH* chemiluminescence imaging. Unconfined flames have unexpectively lower LBO limits (∼0.4) than the LBO limits of confined flames (over 0.5). Approaching LBO, unconfined flames display a quiet blowout mode featuring swirling spiral blow-off behaviors. In contrast, confined flames exhibit a violent blowout mode featuring large-scale quasi-instability behaviors, including periodic events of local extinction, flame lift-off, and re-ignition. Based on the numerical simulations and simultaneous OH- and CH2O-PLIF measurements, the large discrepancy in the measured LBO limits between the two configurations is found to result from different re-ignition processes related to the low-temperature ignition before the final blowout. These findings highlight the crucial roles of wall confinement in determining the stable flame topologies, LBO characteristics, and mechanisms driving the LBO physics for partially premixed DME/air swirl flames.

A novel approach to the characteristic splitting scheme for mildly compressible flows based on the weighted averaged flux method

In the present work we improve the characteristic splitting approach for computing mildly compressible flows. This splitting approach is consisted of two separate steps namely an advective step and a purely hyperbolic, acoustic step. Typically, a pressure correction method is used for solving the acoustic step which may lead to overly dispersive, incorrect results. As a remedy to this issue, a novel solution approach on the basis of the weighted averaged flux method (WAF) is proposed, which solves the non-conservative, hyperbolic equations of the acoustic step directly. The stability and accuracy of this novel WAF method is demonstrated and an implicit, monotone formulation for three-dimensional unstructured grids is given. The simulation of the non-reacting flow in a swirl burner proves the applicability of the method.

Combustion and emission characteristics for various swirler geometries and fuel heating values in a premixed low swirl combustor system

This study investigated combustion and emission characteristics with various swirler parameters (i.e., swirl angle and perforated screen blockage) and fuel heating values (4,000 kcal/Nm3∼9,560 kcal/Nm3, 16.3 MJ/kg∼55.5 MJ/kg in SI unit) using the premixed low swirl combustor system. Flashback limits were evaluated as a flame stability and flame structures were analyzed by acquiring chemiluminescence (OH* and CH*) and OH-Planar Laser Induced Fluorescence (PLIF) signals. NOx and CO emissions were evaluated by calculating emission indices (EINOx and EICO). As a result, the swirl angle did not affect flame stability, whereas screen blockage increased flashback limits. The highest screen blockage (β = 0.8) showed the flashback limit of 5.6 kW, around 1.5 times higher than the lowest screen blockage (β = 0.6). Also, the blockage affected the radical distributed position due to the ratio between swirling and non-swirling flow. The lower heating value fuel showed reduced flashback limits, decreased radical intensities, and lower emissions (EINOx and EICO). The lowest heating value gas (HV 4000) had an EINOx of less than 0.5 g/kg and an EICO of less than 5 g/kg, respectively. In conclusion, these findings would be helpful databases for optimizing heating values to solve environmental pollution issues.

Physics-guided fuel-switching neural networks for stable combustion of low calorific industrial gas

Dual fuel combustion of low calorific industrial gas has been widely used in various types of burners for industrial production needs. Fuel switching rule is purely empirical lacking theoretic basis, potentially leading to flame extinction or excessive waste of ignition fuel. This study focuses on exploring physics-guided fuel-switching strategy for stable combustion of coke oven gas (COG) and blast furnace gas (BFG) in representative swirl burner. Stable operating regimes for COG and BFG are firstly identified with chemical eigen-analysis. The intrinsic propensity of flame extinction during fuel switching is revealed by positive chemical eigenvalues, and the key species and elementary reactions are identified. A clustered neural network with flag controller (CNNF) is then constructed to achieve stable combustion during fuel switching from COG to BFG as early as possible to reduce the use of COG. Results show that COG must be used to ignite and increase the ambient temperature to at least 673 K to avoid flame extinction. The chemical eigen-guided CNNF controller can adjust the switch speed to advance the fuel switching time by 14 % and can be further expanded to other fuel switching applications.

Prediction of flame transfer function and combustion instability on a partially premixed swirling combustor by the system identification and CFD methods

Combustion instability can lead to high amplitude oscillations of pressure in the combustion chamber, which would seriously affect the normal operation of the combustion system. In order to reduce the cost and time of combustion chamber design and testing, combustion instability of the partially premixed swirl combustor was predicted, by solving the Helmholtz equation coupled the flame transfer unction (FTF). In the experimental study, by changing the equivalence ratio, the pressure in the combustion chamber appeared to oscillate in different forms including combustion noise, intermittent oscillation and limit cycle oscillation, while the frequency of the self-excited oscillations was obtained to be 165 Hz at the equivalence ratio of 0.7. In Computational Fluid Dynamics (CFD) Simulations, by applying Discrete Random Binary Signal (DRBS) excitation at the inlet, the FTF has been calculated by system identification method, where the excitation results of perturbation signals with different magnitudes were studied. And the result was basically consistent with the FTF calculated by the single-frequency excitation method, which means that the system identification method is suitable for calculating the FTF of the partially premixed swirl combustor. The pulse excitation method has been proposed to determine the selection of the filtering order, and the accuracy of the method has been validated through comparing the FTF results obtained by using different filter orders for discrimination. Moreover, coupling the FTF into the Helmholtz equation, the oscillation frequency of the system was predicted as 159.7 Hz, compared with the experimentally measured oscillation frequency of 165 Hz, which verified that the model could be effectively used for the prediction of oscillation frequency in the partially premixed combustion systems.

Impacts of Fuel Stage Ratio on the Morphological and Nanostructural Characteristics of Soot Emissions from a Twin Annular Premixing Swirler Combustor.

Soot particles emitted from aircraft engines constitute a major anthropogenic source of pollution in the vicinity of airports and at cruising altitudes. This emission poses a significant threat to human health and may alter the global climate. Understanding the characteristics of soot particles, particularly those generated from Twin Annular Premixing Swirler (TAPS) combustors, a mainstream combustor in civil aviation engines, is crucial for aviation environmental protection. In this study, a comprehensive characterization of soot particles emitted from TAPS combustors was conducted using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The morphology and nanostructure of soot particles were examined across three distinct fuel stage ratios (FSR), at 10%, 15%, and 20%. The SEM analysis of soot particle morphology revealed that coated particles constitute over 90% of the total particle sample, with coating content increasing proportionally to the fuel stage ratio. The results obtained from HRTEM indicated that average primary particle sizes increase with the fuel stage ratio. The results of HRTEM and Raman spectroscopy suggest that the nanostructure of soot particles becomes more ordered and graphitized with an increasing fuel stage ratio, resulting in lower oxidation activity. Specifically, soot fringe length increased with the fuel stage ratio, while soot fringe tortuosity and separation distance decreased. In addition, there is a prevalent occurrence of defects in the graphitic lattice structure of soot particles, suggesting a high degree of elemental carbon disorder.

Experimental study on combustion flow field characteristics of swirl combustor

The impact of the swirl number on the flow field of a single-stage swirl combustor is investigated using the particle image velocimetry technology. The variations in recirculation zone size, pulsating region, turbulent distribution, vorticity, and Reynolds stress within the combustor are summarized through quantitative analysis of the flow field. Experimental results indicate the following: (1) Under the same air mass flow rate, the length of the recirculation zone in the combustion state is shorter than that in the cold state. (2) The length of the recirculation zone and the axial vortex spacing display a decreasing trend as the swirl number increases, while the width of the recirculation zone demonstrates an increasing trend. (3) For the single-stage swirl combustor, the primary pulsating region is at the swirling jet area at the exit of the swirl. As the swirl number increases, the standard deviation of radial velocity fluctuations and turbulent kinetic energy also increase. (4) The strong shear region of the single-stage swirl combustor can be divided into inner and outer shear layers based on the vorticity distribution and the Q criterion. The vortices in the inner and outer shear layers exhibit opposite orientations according to the vorticity distribution. Overall, the research results can provide basic experimental data for numerical simulation of swirl combustion.

Numerical simulation study on hydrogen ammonia mixed combustion in a swirl combustion chamber

Abstract The NO x emissions and combustion performance of pure ammonia and hydrogen-doped combustion (90% NH3 volume fraction and 10% H2 volume fraction) in the cyclone combustion chamber were comprehensively analyzed through numerical simulations under varying thermal operating conditions. The findings reveal that the flame characteristic length in hydrogen-doped combustion surpasses that in pure ammonia combustion, indicating an extended migration of the high-temperature zone after hydrogen doping. Furthermore, the addition of hydrogen results in an elevated exhaust temperature within the combustion chamber, while the Outlet Temperature Distribution Function (OTDF) decreases, signifies an enhancement in the uniformity of temperature distribution at the outlet. Moreover, the reflux zone experiences less impact, and the mixed gas velocity increases following hydrogen doping. Notably, NO x emissions demonstrate a significant decrease after the addition of hydrogen. The average NO emission concentration in pure ammonia combustion, under various operating conditions, is measured at 212.47 mg/m3, representing a 3.51-fold increase compared to hydrogen-doped combustion.

Determination of the optimal total oxygen concentration and oxygen partitioning ratio based on the heat transfer characteristics of oxy-coal combustion in a swirl burner

Oxy-coal combustion is an attractive option for CO2 capture from coal-fired power plants due to high carbon capture efficiency and favorable economic performance. It is critical for the operation of the power plants to maintain similar heat transfer characteristics by rationalizing the partitioning strategy of the oxidant streams when retrofitting coal-fired power plants with oxy-fuel combustion technology. In the present work, the oxy-coal combustion characteristics under various total oxygen concentrations XO2,total of 21 %–32 % and oxygen partitioning ratio conditions in a 100 kW vertical swirl burner were numerically investigated by using computational fluid dynamics (CFD) models. And the effects of the XO2,total and oxygen partitioning ratio on the heat transfer characteristics of oxy-coal combustion were numerically simulated to quantitatively obtain the optimal oxygen supply partitioning strategy for the retrofitting of coal-fired power plants. Then the flame structure, heat transfer flux, and char burnout rate at different oxygen partitioning ratios between the primary and secondary streams were systematically analyzed to further determine the optimal oxygen partitioning ratio. The results showed that the maximum flue gas temperature Tmax increased by 220 K and the total heat transfer flux on the furnace wall increased by 42 % when the XO2,total was increased from 21 % to 32 %, respectively. Under oxy-coal combustion conditions, the Tmax at the XO2,total of 32.4 % was consistent with that under air combustion condition, while the total heat transfer flux at the XO2,total of 29.4 % matched with that under air combustion condition. Moreover, the total heat transfer flux and the flame length were increased by 17.3 % and 46.3 %, respectively, as the oxygen concentration of the primary stream XO2,Pri was increased from 6.5 % to 45 % at the XO2,total of 29 %. More importantly, the total heat transfer flux at the XO2,Pri of 31.9 % under oxy-coal combustion condition matched with that under air combustion condition. The optimal total oxygen concentration and oxygen partitioning ratio of oxy-coal combustion based on the heat transfer characteristics were quantitatively determined, which gave an important reference for the oxy-coal combustion retrofitting of traditional coal-fired power plants.

Investigation of differential diffusion in lean, premixed, hydrogen-enriched swirl flames

Hydrogen combustion is a promising alternative to fossil fuel combustion in an effort to reduce our carbon footprint. However, hydrogen combustion is prone to thermodiffusive instabilities largely dependent on differential diffusion, a phenomenon that can lead to higher probabilities of flashback in industrial burners, given hydrogen’s high reactivity and diffusivity. This paper evaluates low-swirl flames of methane and air enriched with hydrogen to highlight the onset of differential diffusion. Testing was conducted in a fully controllable swirl burner, where bulk velocity Uav = 13 m/s and swirl number S = 0.6 were kept constant for each hydrogen–methane blend to isolate increases in flame surface area from increases in turbulence intensity. Furthermore, each fuel blend of hydrogen and methane is evaluated at the same laminar flame speed of SLo = 0.267 m/s to isolate flame stretch effects on the turbulent burning rate. Combined hydroxyl (OH) PLIF and stereoscopic PIV at the National Research Council of Canada were used to analyze the OH fluorescence in a 2D-3C velocity field for each flame condition. High-speed PIV at McGill University was used to resolve local flame phenomena, such as local flame displacement velocity and flame stretch rate. Using these techniques, it can be observed that the flame displaces axially in response to turbulent flame speed while exhibiting increases in flamefront wrinkling. This increased corrugation due to flame stretch is highlighted in the PDFs of local curvature and κSf and is further evidenced by a shift towards positive curvatures (κ> 0) for increasing H2 volume fraction. This trend suggests that there is a strong correlation with increases in turbulent burning rate and positive curvature as a result of differential diffusion, but it is not necessarily a control mechanism of the most forward propagating points proposed by the theory of leading points.

Experimental combustion characteristics and NOx emissions for a 600‐MWe utility boiler after the retrofitted: Effects of load variation

AbstractTo enhance the rapid switching ability of the boiler load and reduce NOx emissions, a new combustion system was implemented in a 600‐MWe wall‐fired boiler with swirl burners. This system included two levels of overfire air (OFA) and low NOx combustion technology. Industrial tests were conducted at 300‐, 450‐, and 600‐MWe loads before and after the retrofitted. These tests included measuring flue gas and furnace temperatures with thermocouples and analyzing local gas concentrations using a gas analyzer. The research results indicate that under conditions where the OFA ratio exceeds 30%, the burner exhibits good ignition performance at different loads. At the 600‐MWe load, the nitrogen oxides (NOx) emissions were reduced by 55% compared to before the retrofit. After the retrofit, the flame center inside the furnace of different loads was located at the height of 33.36 m, the first and second‐stage cooling water quantities were slightly higher, the reheat cooling water quantity was greatly reduced after the retrofit, and contributes to the boiler's safe operation. Under different load conditions after the retrofit, the gas temperature near the sidewall was below 850°C, and the O2 concentration near the sidewall was above 5%, effectively suppressing sidewall high‐temperature corrosion and slagging.

Investigation on self-excited thermoacoustic instability and emission characteristics of premixed CH4/NH3/air flame

Ammonia is one of the promising carbon-free alternative fuels for low-carbon power generation. This study investigated the self-excited thermoacoustic instability of premixed CH4/NH3/air flame in a swirl burner. The work aims to determine the effects of ammonia mole fraction (χNH3), equivalence ratio (Ф) and combustion chamber length (CL) on flame morphology and self-excited flame dynamics. In addition, the emission characteristics of CH4/NH3/air flame were also investigated. Results show that the thermoacoustic instability of the 1/4 wave mode is excited when 0.8≤Ф≤1.2 and χNH3 ≤ 0.3. There are apparent pressure fluctuations and heat release fluctuations in the combustion chamber. The fluctuating frequency decreases with increasing CL. The maximum fluctuating frequency and oscillation intensity appear near Ф=1.0. When χNH3 increases, the amplitude of fluctuating pressure and heat release rate decrease obviously, and the instability range narrows to Ф=1.0–1.1 simultaneously. The low-order acoustic network model successfully predicted the instability transition and frequency decreasing trend caused by increasing ammonia. The increase in the convective time delay is responsible for this transition. Emission analysis indicates that NOx emission can be controlled within 100 ppm under fuel-rich conditions, but the CO emission increases sharply. Thermoacoustic instability and nitrogen oxides can be simultaneously controlled under fuel-rich conditions when χNH3>0.3. However, this will be limited by unburned reactants.

Modeling effects of swirl burners on the heating quality of slabs and flame morphology in a walking-beam reheating furnace

This paper developed a model of zone segment swirl burners to realize individual separation of swirl burners within a CFD model of an industrial-scale walking-beam reheating furnace. Numerical results are validated against the experimental measurements, demonstrating good agreement and credibility. Leveraging this model, a comprehensive investigation on the effect of swirl angle on the flame morphology and the slab heating quality has been conducted. Comparing various swirl angles (0°, 25°, 45°, and 65°) provides valuable insights into their impact on flame morphology, and slab heating quality. A swirl angle of 25° has been identified as optimal, yielding the maximum flame area within the furnace, measuring 326.09 m2. Furthermore, it reduces the maximum absolute temperature deviation of the discharged slab’s top surface centerline to 7.64 K, marking a substantial 25.83 % reduction compared to the 0° angle. These results highlight the critical role swirl burners play in the reheating furnace and identify the optimal swirl angle for effectively enhancing both the economic benefits and product quality in industrial processes.