Combustion Zone Research Articles

A Method for Image-Based Interpretation of the Pulverized Coal Cloud in the Blast Furnace Tuyeres

The conditions in the combustion zones, i.e., the raceways, are crucial for the operation of the blast furnace. In recent years, advancements in tuyere cameras and image processing and interpretation techniques have provided a better means by which to obtain information from this region of the furnace. In this study, a comprehensive approach is proposed to visually monitor the status of the pulverized coal cloud at the tuyeres based on a carefully designed processing strategy. Firstly, tuyere images are preprocessed to remove noise and enhance image quality, applying the adaptive Otsu algorithm to detect the edges of the coal cloud, enabling precise delineation of the pulverized coal region. Next, a Swin–Unet model, which combines the strengths of Swin Transformer and U-Net architecture, is employed for accurate segmentation of the coal cloud area. The extracted pulverized coal cloud features are analyzed using RGB super-pixel weighting, which takes into account the variations in color within the cloud region. It is demonstrated that the pulverized coal injection rate shows a correlation with the state of the cloud detected based on the images. The effectiveness of this visual monitoring method is validated using real-world data obtained from a blast furnace of SSAB Europe. The experimental results align with earlier research findings and practical operational experience.

Influence of passive strut on the mixing and combustion performance enhancement

The scramjet engine is one of the possible means of reaching supersonic speed using airbreathing engines. As the inflow of air is at supersonic speed, proper mixing and combustion is a challenge. Researchers have used multi-strut arrangements to address the problem. However, the additional supply of fuel from multiple struts with inefficient mixing and combustion leads to losses in terms of fuel and efficiency. Alternatively, the multi-strut configuration could be used to improve the combustion and mixing efficiency passively. In the present investigation, two strut configurations, a fuel injection strut, and a passive strut, have been used. The computational study was done by solving steady Reynolds averaged Navier-Stokes (RANS) equations along with the Shear Stress Transport (SST) k-ω turbulence model, species, and ideal gas equation. Eddy dissipation model was used to solve reacting flow. The introduction of a passive strut in the wake of the fuel injection strut leads to vortices upstream and downstream of the passive strut. These vortices were observed to be responsible for enhancing the mixing and combustion. It was found that judicious placement of the passive strut in the wake of the combustion zone can enhance both the mixing as well as combustion efficiency with minimal loss in total pressure.

Measurement the 3D temperature distribution in the combustion zone using acoustic tomography and nolinear wavefont tracing

A non-invasive temperature measurement method in three dimensions is proposed to reconstruct the three-dimensional temperature. It relies on the use of nonlinear acoustic travel-time tomography, which incorporates acoustic path tracing, Gaussian kernel function, and modified Tikhonov regularization. Sound signals can be distorted due to large average temperature gradients and oscillatory release of heat in the combustion region. The effective acoustic signal is extracted based on spectral subtraction to evaluate the sound propagation time under distorted signals. The analysis of experimental errors indicates that the proposed acoustic pyrometry method has an average relative error of less than 15% compared to the time-averaged temperature measured by thermocouples. This result verifies the efficacy of the method when it comes to accurately reconstructing the temperature field in the combustion area. The reduction in error is attributed to the consideration of acoustic ray tracing within the proposed method.

EXTINGUISHING TIME OF OIL PRODUCT TANK FIRES WITH SELF-EXPANDING GAS-AEROSOL-FILLED FOAM

EXTINGUISHING TIME OF OIL PRODUCT TANK FIRES WITH SELF-EXPANDING GAS-AEROSOL-FILLED FOAM

Large eddy simulation of combustion characteristics during dual fuel switching process in gas turbine combustor

The present study aims to investigate the combustion characteristics, fuel switching strategy, and flame stability associated with fuel switching processes in a dual-fuel gas turbine combustor. Specifically, the Large Eddy Simulation method is employed in conjunction with a skeletal chemical reaction mechanism to simulate the fuel switching process. It is revealed that the presence of a local rich combustion zone, formed by an increased accumulation of fuel in the head region, leads to the displacement of the heat release position towards the downstream inner shear layer. Additionally, this condition causes a reduction in the recirculation zone area and a deterioration in the uniformity of fuel blending. Simultaneously, the combustor experiences low-frequency, high-amplitude pressure pulsations, as well as pulsations in the heat release rate. Furthermore, a comparative analysis is conducted to assess the discrepancies among three distinct fuel supply strategies employed during fuel switching. The fast-opening strategy is found to demonstrate superior performance indicators, as it accomplishes filling the combustor performance indicators within 80% of the allocated time due to its lower initial fuel changing rate.

CFD modeling of thermal processes in the firebox and heat load distribution on the screen surface firebox

Using ANSYS FLUENT numerical modeling and mathematical modeling, the main characteristics of combustion processes during the combustion of natural gas were determined. In this work, the combustion processes and NOx formation in the firebox were modeled at different loads of the GM- 50-14/250 boiler. The temperature distribution along the height of the firebox and the heat load on the screen panels were determined. The results of calculations by two types of models were compared with each other and with the data of measurements on the operating equipment. The environmental performance of the firebox, namely the formation of NOx at different heat loads, was determined. The maximum boiler capacity at which its operation meets European environmental standards was determined. The deviation of calculations on the formation of NOx in the GM-50-14/250 boiler at 40% of the rated power compared to the results of field tests using ANSYS FLUENT modeling was 8%, and using the mathematical model - 27%. When operating at rated power, the deviations of the results decreased to 2% and 8%, respectively. The deviation of the results of thermal calculations of the combustion in the firebox by different types of modeling in the active combustion zone and at the outlet of the firebox is up to 3% at different loads.

Numerical investigation on the exhaust gas combustion of an SOFC in a catalytic multichannel burner

The utilization of the exhaust gas of a solid oxide fuel cell is important to improve the energy efficiency and control pollutant emission. In this work, the combustion of solid oxide fuel cell exhaust gas (H2/CO) in a honeycomb ceramic catalytic burner is investigated numerically. A 2D numerical combustion model with 17 channels is built to analyze the influence of channel position on thermal performance and combustion characteristics. The high burnout of H2 and CO is obtained as 96.75% and 97.75%, respectively. The channels can be divided into three groups from the inside to the outside as follows: part 1, from the 9th channel to the 13th channel; part 2, from the 14th channel to the 16th channel; and part 3, the 17th channel. The channels in the same group presented the same results of flow, temperature, and combustion. Compared with the other channels, the outermost channel shows notable differences in depressing the temperature of the whole channel, moving the maximum temperature downstream, enlarging the temperature bias of the lower and upper walls, and enlarging the combustion zone. H2 and CO perform different combustion processes in the honeycomb ceramic catalytic burner. Compared with H2, the initial position of CO conversion is more affected by channel distribution. In the 17th channel, the CO oxidation rate is controlled mostly by the slower oxygen adsorption and the resulting low O(s) coverage. In the 9th channel, the CO oxidation rate is controlled mostly by the wall temperature and fuel-limited. The burnout rate of H2 changes from 95% to 99.9% with the channel position, but the burnout of CO varies little. The closer the channel to the outer wall, the higher the proportion of heterogeneous reaction and the more the generated heat. The generated heat by the channel can present a diversity of 4%.

Design and Analysis of Biomass Gasification Reactor

Abstract: Biomass can be utilized as a renewable source of energy through various processes, and its theory involves understanding the principles of biomass composition, conversion technologies, and environmental implications. The objective of current research is to evaluate the thermal and fluid flow characteristics of gasification reactor using CFD tool. From the CFD tool, the temperature distribution at the combustion zone, mixing zone and exit zone are evaluated. The effect of turbulent mixing in gasification is evaluated. The application of Computational Fluid Dynamics (CFD) analysis in the study of biomass gasification reactors has proven to be a valuable tool for understanding and optimizing the complex processes involved. CFD simulations provide insights into the intricate interactions between biomass particles and gasifying agents, offering a detailed understanding of fluid flow patterns, temperature distributions, and species concentrations within the reactor.

Self‐emulsification synthesis of epoxy phosphate ester and its flame‐retardant mechanism in flexible poly(vinyl chloride)/magnesium hydroxide composites

AbstractA trade‐off dilemma exists for simultaneously improving the mechanical properties and flame resistance of flexible polyvinyl chloride (fPVC)/magnesium hydroxide (MH) composites. In this study, epoxy phosphate ester (EPE), a hydrophobic surface modifier of MH, was synthesized using a self‐emulsification method. After modification, EPE was bonded to the surface of MH (MHEPE) without altering its morphology. The results of limiting oxygen index and cone calorimetry tests indicated that fPVC/MHEPE exhibited better flame retardancy and smoke suppression effects than did fPVC/MH. The peak of the heat release rate, total heat release, peak of the smoke production rate, and total smoke production of the fPVC/MHEPE composite were 206.0 kJ m−2, 45.90 MJ m−2, 0.0729 m2 s−1, and 9.88 m2, which were 8.64%, 14.00%, 27.61%, and 9.02% lower than those of the fPVC/MH composite, respectively. For the fPVC/MHEPE composite, a compact and continuous char residue formed, which could inhibit heat and flammable volatile migration between the matrix and burning zones. In the gas phase, the dilution effect of H2O vapor reduced the concentrations of O2 and flammable volatiles. The free‐radical quenching effect of ·PO and ·PO2 also played a vital role in extinguishing flame and terminating combustion. Further, the introduction of EPE improved the tensile and impact strengths of the fPVC/MH composites because of the excellent interfacial compatibility between MHEPE and the fPVC matrix. This study provides a simple and workable solution for the trade‐off dilemma, and the remarkable flame retardancy and mechanical properties of the fPVC/MHEPE composite render it a promising cable material.

Exploring the Impact of CO2 Atmosphere on Propane Moderate or Intense Low-Oxygen Dilution Combustion: A Numerical Simulation Study

Abstract Moderate or intense low-oxygen dilution (MILD) combustion is a promising combustion technology widely recognized by the international combustion community. In this study, numerical simulation was used to investigate the effects of CO2 atmosphere on MILD combustion of propane in a 20-KW furnace.The results show that the O2/CO2 atmosphere leads to a lower average temperature in the furnace, better temperature uniformity, and more uniform distribution of OH and CH2O compared to MILD combustion in the N2/O2 atmosphere. Propane MILD combustion is established well under the physical and chemical effects of CO2. An analytical approach is proposed to describe the physical and chemical effects of CO2 on MILD combustion. The physical effect of CO2 shortens the ignition delay time and advances the pyrolysis and ignition of propane, which causes a high-temperature zone in the front furnace and reduces the temperature uniformity in MILD combustion. However, the chemical effect of CO2 dominates the establishment of the MILD combustion by increasing the ignition delay time and reducing burning rates, with the help of the physical effects of CO2 by intensifying the entrainment in the furnace. Thus, the overall effects of CO2 lead to enhanced temperature uniformity by enlarging the area and evening the temperature of both the ignition zone and combustion zone. These findings provide valuable insights into the physical and chemical mechanisms of CO2 in MILD combustion and have important implications for optimizing combustion processes for improved efficiency and reduced emissions.

Effects of herbivory, fire, and vegetation type on soil compaction and aggregate stability in a semi-arid savanna

AbstractVegetation type is an important component of savannas contributing to changes in soil health. In savanna landscapes, the tree-grass balance is primarily governed by water, nutrients, fire, herbivory, and their interactions. Here we investigated the long-term effect of herbivores, fire, and vegetation type, and their interactions on selected physical properties (bulk density, penetration resistance, aggregate size fractions, and mean weight diameter (MWD)) of water stable aggregates within the crest and foot-slope of 20-year-old Nkuhlu exclosures located in Kruger National Park, South Africa. Burning, herbivory, and open grassland zones had a significant main and interactive ecological impact on all the soil physical properties under investigation. The interactions between fire, herbivores, and vegetation type within the crest and foot-slope of the Nkuhlu exclosure had a significant impact on soil bulk density, with areas under tree canopies having lower bulk density than open grassland zones in all the exclosures. In all the sampling sites, both burnt and unburnt plots of the full exclosure had lower penetration resistance than the control site and partial exclosure. Moreover, unburnt plots and canopy cover increased aggregate size distribution and mean weight diameter of water stable aggregates. Since fire and herbivory are closely linked and bring about changes in soil physical properties, the understanding of the dynamics of fire, herbivory, vegetation, and their interactions can then be used to help make effective management decisions that incorporate concerns of biodiversity in savanna ecosystems.

Atmospheric turbulence observed during a fuel-bed-scale low-intensity surface fire

Abstract. The ambient atmospheric environment affects the growth and spread of wildland fires, whereas heat and moisture released from the fires and the reduction of the surface drag in the burned areas can significantly alter local atmospheric conditions. Observational studies on fire–atmosphere interactions have used instrumented towers to collect data during prescribed fires, but a few towers in an operational-scale burn plot (usually > 103 m2) have made it extremely challenging to capture the myriad of factors controlling fire–atmosphere interactions, many of which exhibit strong spatial variability. Here, we present analyses of atmospheric turbulence data collected using a 4 × 4 array of fast-response sonic anemometers during a fire experiment on a 10 m × 10 m burn plot. In addition to confirming some of the previous findings on atmospheric turbulence associated with low-intensity surface fires, our results revealed substantial heterogeneity in turbulent intensity and heat and momentum fluxes just above the combustion zone. Despite the small plot (100 m2), fire-induced atmospheric turbulence exhibited strong dependence on the downwind distance from the initial line fire and the relative position specific to the fire front as the surface fire spread through the burn plot. This result highlights the necessity for coupled atmosphere–fire behavior models to have 1–2 m grid spacing to resolve heterogeneities in fire–atmosphere interactions that operate on spatiotemporal scales relevant to atmospheric turbulence. The findings here have important implications for modeling smoke dispersion, as atmospheric dispersion characteristics in the vicinity of a wildland fire are directly affected by fire-induced turbulence.

Research: influence of air classification ratio on low nitrogen performance of natural gas burner

ABSTRACT An innovative low-nitrogen natural gas burner was developed, leveraging air-staged combustion as the primary mechanism, supplemented by swirl combustion and flue gas recirculation technology. This design enables adaptation to a multitude of combustion conditions through the adjustment of the secondary air ratio. A prototype burner with a power output of 60 kW was constructed for experimental study. The velocity field, gas concentration field, temperature field, and NO x concentration within the combustion zone were analyzed under different load, and the impact of the secondary air ratio on the burner’s low-nitrogen combustion performance was explored. Experimental results showed that the burner can maintain stable combustion and low NO x emissions and had good load adaptability. The introduction of secondary air resulted in a “W”-shaped distribution characteristic within the combustion zone’s velocity and concentration fields, and effectively suppressed the formation of high-temperature zones, thereby reducing the generation of thermal NO x . A secondary air ratio of 27% significantly enhanced the gas atmosphere within the combustion zone, leading to more uniform gas distribution and improved mixing of the gas mixture. Furthermore, it had a better low-nitrogen performance. With an increase in burner load, the NO x concentration within the combustion zone also increased, reaching a peak value of 31 mg·m−3 at full-load, which still complied with low-nitrogen emission requirements.

Experimental studies of air ozonization influence on pollutants emission in vortex ignition-stabilizing modules of gas turbine combustion chambers

Reduction of pollutant emissions into the atmosphere is an urgent task of modern gas turbine engineering development. Such substances that have a negative impact on the environment include nitrogen oxides and carbon monoxide. The article provides a review of the existing methods for reducing the emissions of pollutants used in the combustion of hydrocarbon fuels in the combustion chambers of gas turbine units, as well as indicates promising technologies developed based on these methods. Justification is presented of the necessity to study the method of ozonization of air supplied to the fuel combustion zone to reduce the content of pollutants in its combustion products. The purpose of the study was to develop recommendations for reducing pollutant emissions within a given range of variations regime parameters. To perform the necessary set of experimental studies, a specialized laboratory stand was created, the combined circuit and measurement scheme of which is given in the article. A rather detailed description is given of the structural elements of the stand and, in particular, of the subject of research — a full-scale vortex ignitionstabilizing module of the combustion chamber of a gas turbine unit, an electric ozonator, air and combustible gas supply systems, an exhaust system with a central fan, control and measuring instruments and fittings. The tests were carried out in accordance with specially developed methods of controlling the stand operation in three modes: startup; transfer from one steady-state mode to another; stop. The influence of air ozonization on combustion processes in the vortex ignition-stabilizing module was determined by the content of nitrogen oxides and carbon monoxide in it. The factors that influence the decrease in the concentration of carbon monoxide in the combustion products during the combustion of air in ozonized air have been determined. The methods of calculation determination of combustible gas and air parameters — mass flow rates, flow velocities and dynamic heads — are described. The results of the performed experimental studies are presented in graphical interpretation, their detailed analysis is given, on the basis of which recommendations on practical use of the method of air ozonization are given.

Flame inhibition using nanotechnology

Flame inhibition is significant as it directly contributes to fire safety and prevention. Effective flame inhibition can reduce the spread and intensity of fires, protecting lives, property, and the environment. The research focused on the significant role of nanomaterials, specifically aluminum oxide (Al₂O₃), in improving fire retardation and enhancing fire inhibition performance. Nanoparticles can be used in flame inhibition, as they might merge two flame inhibition techniques: cooling and physical barriers. They offer unique properties due to their small size and high surface area, which can enhance their effectiveness in disrupting the combustion process. Nanoparticles can act as heat sinks, absorbing heat and reducing the temperature of the combustion zone (cooling method). They can also catalyze the formation of non-combustible gases or form a protective layer on the material's surface (physical method). Due to these properties, nanoparticles are increasingly studied and utilized for advanced flame retardant systems. Experimental work was carried out to accomplish the goal of the research. The fire inhibition test was performed within a pressure range between 3.2 and 5.3 cm of Hg, corresponding to a fuel-oxygen ratio of 9.3 % to 14.8 %, respectively. A novel nanoparticle material was involved in this analysis, including Al₂O₃. Based on the research analysis, the critical research results revealed that Al₂O₃ employment as a fire inhibitor provided a more enhanced impact of fire retardance and flame inhibition compared with conventional retardation materials, reflected in more sustainability and less adverse environmental effects.Furthermore, the experimental findings indicated that the flammability limits range between a lower flammability limit of approximately 9.3 % and an upper one of 14.8 % under specified amounts of pressure and temperature. In addition, increasing the inhibitor quantity could raise the lean flammability limit. Raising the nanomaterial mass would extend the flammability limits, altering the concentration of these nanoparticles to increase inhibitory effectiveness and change the lower and upper flammability limits.The study concluded that adjusting nanoparticle concentrations can significantly alter inhibitory effectiveness. The novelty lies in the use of a novel nanoparticle material, demonstrating improved sustainability and effectiveness in fire retardation of a highly flammable gaseous mixture.

Influence of velocity on the transient auto-ignition of ethylene jet in a hot coflow

The difficulty of ignition is one of the main problems in the combustion chamber of the air-breathing combined engine. Based on this, the transient auto-ignition in the turbulent non-premixed flames of ethylene in a high-speed jet in hot coflow was studied using a newly developed burner. High-speed hydroxyl (OH) planar laser-induced fluorescence (up to 10 kHz) and large eddy simulations (LES) were performed to investigate the auto-ignition process. The experimental conditions included injection velocities of 334–491 m/s, and the effect of jet velocity on the mixing process, ignition process, and flame stabilization mechanisms were investigated. The results showed that the numerical simulation results were consistent with the experimental data. The velocity could affect the auto-ignition position, whereas it had no effect on the auto-ignition time. The increase in fuel jet velocity is beneficial to the mixing of fuel and high-temperature gas and helps to increase the premixed combustion zone during the formation of fire kernels. Moreover, as the velocity increased, the flame status changed from a transitional flame to a lifted flame, the growth rates of the flame volume and total heat release increased, and the flame stabilization mechanism changed from flame propagation to auto-ignition.

Investigation of the parameters influence of the oxy-fuel burner and the test bench parameters on the deviation of the model similarity criterions from the full-scale values

The article presents the results of a study of the workflow parameters influence in the full-scale and model burners of the combustion chamber oxy-fuel combined cycle on the deviation of similarity criteria from full-scale values. The variable parameters are the pressure and velocity of the fluid under model conditions, as well as the power of model and full-scale burners. The supercritical parameters of the working fluid in the cylindrical sections of the combustion zone at a pressure of 30 MPa and a temperature of 1570 ℃ were taken as full-scale conditions. In this paper, the dependences of the deviations of hydrodynamic and thermophysical similarity criteria on the speed and pressure of the combustion products of an oxygen-fuel mixture with carbon dioxide in the working zone of the test bench for burners are obtained. The parameters of the working fluid and the power of model burners are obtained, at which the values of the criteria deviations are minimal.

Numerical Study on Effect of Flue Gas Recirculation and Co-Firing with Biomass on Combustion Characteristics in Octagonal Tangentially Lignite-Fired Boiler

The octagonal tangentially fired boiler can be utilized for burning lignite with high moisture. Co-firing biomass in an octagonal tangential boiler is considered a promising approach. A numerical simulation is carried out in this study to analyze the impact of flue gas recirculation (FGR) and the biomass blending ratio on heat and mass transfer in an octagonal tangentially fired boiler. When the FGR rate increases from 0 to 30%, the maximum temperature in the boiler decreases from 2162.8 to 2106.5 K. Simultaneously, the average temperature of the center longitudinal section decreases from 1589.0 to 1531.9 K. The maximum fluctuation of the outlet flue gas temperature remains within 10.9 K for the four calculated working conditions. Consequently, the efficiency of the boiler is basically unchanged. However, the flue gas temperature at the furnace outlet decreases significantly from 1605.9 to 1491.9 K. When the biomass blending ratio increases from 0 to 20%, the mean temperature of the primary combustion zone decreases from 1600.5 to 1571.2 K.

Investigation on unsteady formation and evolution of high-temperature zone in a staged swirl combustor

The high-temperature zone of a laboratory staged swirl gas turbine combustor was studied under different Stratification Ratios (SR) based on experimentally validated Large Eddy Simulation (LES). CH4/air mixtures were adopted with a constant global equivalence ratio of 0.5. Three flame conditions with SR = 1, 2 and 3 were chosen for Particle Image Velocimetry (PIV) and OH Planar Laser-Induced Fluorescence (OH-PLIF) measurements. The LES was performed with the Flamelet-Generated Manifold (FGM) combustion model and validated against the experimental velocity fields and flame structures. Then, a detailed analysis of the formation, evolution, and dissipation of the high-temperature zone was conducted. It is observed that a larger SR deteriorates the uniformity of the exit temperature distribution. One major reason is that with increased SR, rich-burn region is observed to be more dominant. This leads to enhanced non-premixed combustion and an extended heat release region towards downstream, which intensively contribute to the high-temperature zone formation. Additionally, vortices along the shear layers are found to enhance the mixing between fluids of different temperatures, which plays a crucial role in dissipating the high-temperature zone. Higher SR leads to a larger Primary Recirculation Zone (PRZ), and the partially dissipated high-temperature fluid can be recirculated into the PRZ, thus increasing the dissipation distance. With lower SR, however, the high-temperature parcels can be broken and even completely dissipated. This accounts for lower temperature gradients and a more uniform exit temperature distribution. The findings from this study offer new perspectives on understanding the effect of temperature in the primary combustion zone on the exit temperature distribution.

Experimental and numerical study on a cavity-swirler-based combustion strategy for advanced gas turbine engine

A cavity-swirler-based combustor has been found to possess the capability of achieving robust stability, high combustion efficiency, low emissions, and a short flame length. However, the effect of cavity air-injection mode on the combustion and emission performances of the cavity-swirler-based combustor was not well understood to date. In this work, numerical and experimental investigations were conducted to analyze the flowfield, combustion efficiency, combustion stability, pollutant emissions, temperature distribution, and flame characteristics of the combustor under two different cavity air-injection modes, namely case-1 and case-2. The air-injection hole of case 1 was designed on the cavity inner-wall, while the air-injection hole of case 2 was designed on the cavity outer-wall. The results indicate that the combustion performance of the combustor is significantly influenced by the air-injection mode, leading to different flow fields within the combustor. Case 1 demonstrates notable advantages in terms of lean blowout limit compared to case 2. However, case 2 achieves a much more uniform distribution of outlet temperature. Higher combustion efficiency was achieved by case-1 under low fuel equivalence conditions, whereas case-2 exhibited greater combustion efficiency under high fuel equivalence conditions. Both case-1 and case-2 displayed distinct combustion zones that were separate from each other.