Search Results (61)

The performance of diffusion flame (DF) burners strongly depends on how effectively combustion gases mix and retain heat, yet the influence of exhaust nozzle geometry on these processes remains insufficiently characterized. This study examines how varying exhaust nozzle angle affects the thermal behavior and emissions of a methane (CH₄) diffusion flame under atmospheric conditions. A laboratory-scale burner with interchangeable exhaust nozzles (0°, 25°, and 50°) was operated at 1.8 kW using a fixed methane flow of 3 L/min and co-swirled air and fuel at 30°, across equivalence ratios (Φ) of 1.0, 0.7, and 0.5. Axial temperature measurements and exhaust gas analyses (Carbon dioxide (CO₂) and Carbon monoxide (CO)) were conducted to assess mixing, heat retention, and post-flame oxidation. Results show that exhaust nozzle geometry notably influences flame position and heat distribution, producing non-monotonic temperature trends with equivalence ratio. The 25° nozzle angle yielded the highest near-stoichiometric downstream and flue temperatures, reaching about 204 °C at x = 45 cm and 277 °C in the flue, compared with 72 °C and 177 °C for the 0° nozzle. In contrast, the 50° nozzle produced more uniform downstream temperatures (about 150–160 °C) and the lowest CO emissions, approaching zero near Φ ≈ 1.0. These findings demonstrate that coordinated control of swirl and exhaust nozzle angle can enhance thermal response and CO reduction in diffusion flame burners without significantly changing CO₂ levels. Full article

This study investigates the emission characteristics and flame behavior of an air-staged swirl burner operating on LPG. The burner is equipped with a 45° vane swirler and an adjustable secondary-air section. Experiments were conducted at air velocities ranging from 20 to 43 m/s using a Testo 350 gas analyzer, while temperature measurements were obtained with thermocouples positioned 90 mm downstream of the burner exit. The results show that increasing the secondary-air opening leads to a monotonic decrease in the mean exit temperature and NO_x formation over the entire velocity range. In contrast, CO concentrations increase at higher air velocities and larger secondary-air fractions due to reduced residence time and partial quenching of the reaction zone. The fully staged configuration (100%) achieved the lowest NO_x levels (≤3 ppm) at 20 m/s, whereas the non-staged case resulted in the highest temperatures and NO emissions. Overall, the experimental results demonstrate that a moderate secondary-air opening provides the best compromise between low NO_x emissions and acceptable CO levels for compact LPG-fired swirl combustors. Full article

Ammonia–coal co-firing is emerging as a promising technological pathway to reduce carbon production during coal-fired power generation. However, the coupling effects of the ammonia energy ratio (E_NH3) and equivalence ratio on the ignition mechanism and emission characteristics—particularly under staged injection conditions—remain insufficiently understood. This study investigates these characteristics in a laboratory-scale furnace. Spontaneous chemiluminescence imaging and flue gas analysis were employed to decouple the effects of aerodynamic interactions and chemical kinetics. The experimental results reveal that the ammonia injection strategy is the critical factor governing coal ignition performance. Compared to the premixed mode, staged injection—which establishes an independent, high-temperature ammonia flame zone—provides a superior thermal environment and circumvents oxygen competition between the fuels, thereby markedly promoting coal ignition. At an E_NH3 of 50%, the staged configuration reduces the ignition delay time of coal volatiles by a striking 60.93%. Within the staged configuration, increasing either the co-firing ratio or the overall equivalence ratio further enhances coal ignition. Analysis of pollutant emissions elucidates that the formation of NO, N₂O, and NH₃ is intimately linked to the local combustion conditions of ammonia. An excessively lean local equivalence ratio leads to incomplete ammonia combustion, thereby increasing N₂O and NH₃ slip. Full article

Recent progress in hydrogen combustion indicates that hydrogen could partially or fully replace traditional fuels in power plants, but maintaining stable flames remains a major challenge for many combustion systems. This study presents the effect of hydrogen enrichment of Liquid Petroleum Gas (LPG) on the low-swirl flame structure and flame temperature at different hydrogen mass fractions and equivalence ratios (φ = 0.501 and 1.04). The experimental observations for low-swirl flames under various conditions, including the effect of increasing hydrogen enrichment from 0% to ~20%, were discussed. Experiments were performed using a swirl burner, flame photography, and temperature measurements to evaluate the dynamic swirl flame, stability, and flame temperature distribution. The results show that moderate hydrogen enrichment (5–15%) improves flame stability and delays blow-off. In contrast, very high hydrogen concentrations may destabilize the flame due to higher reactivity and enhanced sensitivity to flow perturbations. Also, hydrogen enrichment up to ~20% enhances flame compactness, intensifies heat release, and reduces oscillatory instability without triggering blow-off or flashback, making hydrogen blending a promising strategy for stabilizing swirl flames at rich operating conditions. Finally, hydrogen enrichment consistently increases swirl flame temperature at both equivalence ratios. Full article

Existing faulty coal-fired units generally achieve oil-free stable combustion only at loads over 30%, failing to meet low load regulation demands. To address the insufficient flexibility of boilers, a novel flame-stabilization theory was developed for retrofitting a 350 MW faulty coal-fired unit boiler. Based on the actual burner dimensions of the 350 MW unit boiler, a geometric scaling ratio of 1:7 between model and actual burners was established. Phase Doppler Anemometry (PDA) was employed to conduct gas particle flow experiments on the model burner, revealing the impact of different primary air velocities on the gas particle flow characteristics of the novel stabilized flow burner. The analysis of experimental results suggests that, When the primary air velocity is 9 m/s, a central recirculation zone forms at the burner outlet. At a primary air velocity of 10 m/s, an annular recirculation zone develops with a relatively large coverage area. When the primary air velocity increases to 11 m/s, the extent of the annular recirculation zone diminishes. At a primary air velocity of 10 m/s, an extensive annular recirculation zone forms at the burner outlet, which appears to provide sufficient energy for the ignition of pulverized coal. Elevated pulverized coal concentration near the burner centerline facilitates the formation of a high-temperature oxygen-lean reducing atmosphere, suppressing fuel-based NO_x generation. Therefore, it is recommended to set the actual operating parameters of the novel stabilized flow burner based on the 10 m/s primary air velocity condition in the gas particle flow experiments. Full article

The inherent residual swirl at the furnace outlet of tangentially fired boilers induces severe thermal deviations on high-temperature heating surfaces. To reveal the evolutionary patterns of thermal deviation during peak regulation operation, this study employed a numerical method to analyze the thermal deviation characteristics of high-temperature heating surfaces in a 350 MW tangentially fired boiler under 12 operating conditions (covering 100%, 72%, 50%, and 28% loads). As the load decreases, the average absolute vorticity at the platen bottom plane also decreases. However, its decreasing rate is pretty slow compared with that of the load, indicating that the velocity deviation increases relatively. In addition, the flow field becomes more sensitive to the mill group operation mode. Correspondingly, the thermal deviations of the division platen superheater, rear platen superheater, finishing reheater, and finishing superheater all show an upward trend. When the load decreases from 100% to 28%, the average heat absorption deviations of the four heating surfaces increase to 3.48, 2.06, 1.27, and 1.99 times their original values, respectively. A comparison of the internal operating conditions under four loads shows that activating the lower-layer burners helps to reduce thermal deviation. This study proposes indicators for characterizing and analyzing the thermal deviation of high-temperature heating surfaces and provides general suggestions for the operation of tangentially fired boilers. Full article

The operational optimization of industrial boilers utilizing hydrogen-enriched natural gas is constrained by two critical gaps: insufficient understanding of the coupled effects of hydrogen blending ratio, equivalence ratio, and boiler load on combustion performance—compounded by unresolved challenges of combustion instability, flashback, and elevated NO_x emissions—and a lack of systematic investigations combining these parameters in industrial-scale systems (prior studies often focus on single variables like hydrogen fraction). To address this, a comprehensive computational fluid dynamics (CFD) analysis was conducted on a 2.1 MW industrial boiler, employing the Steady Laminar Flamelet Model (SLFM) with a modified k-ε turbulence model and the GRI-Mech 3.0 mechanism. Simulations covered hydrogen fractions (f(H₂) = 0–25%), equivalence ratios (Φ = 0.8–1.2), and load conditions (15–100%). All NO_x emissions reported herein are normalized to 3.5% O₂ (mg/Nm³) for regulatory comparison. Results show that increasing the hydrogen content raises the flame temperature and NO_x emissions while reducing CO and unburned hydrocarbons; a higher equivalence ratio elevates temperature and NO_x, with Φ = 0.8 balancing efficiency and emission control; and reducing load significantly lowers furnace temperature and NO emissions. Notably, the boiler’s unique staged-combustion configuration (81% fuel supply to the central rich-combustion nozzle, 19% to the concentric lean-combustion nozzle) was found to mitigate NO_x formation by 15–20% compared to single-inlet burner designs, and its integrated cyclone blades (generating maximum swirling velocity of 14.2 m/s at full load) enhanced fuel–air mixing, which became particularly critical for maintaining combustion stability at low loads (≤20%) and high hydrogen blending ratios (≥20%). This study provides quantitative trade-off insights between combustion efficiency and pollutant formation, offering actionable guidance for the safe, efficient operation of hydrogen-enriched natural gas in industrial boilers. Full article

The use of additive manufacturing (AM) has seen increased utilization over the last decade, thanks to well-documented advantages such as lower startup costs, reduced wastage, and the ability to rapidly prototype. The poor surface finish of unprocessed AM components is one of the major drawbacks of this technology, with the research literature suggesting a measurable impact on flow characteristics and burner operability. For instance, surface roughness has been shown to potentially increase resistance to boundary layer flashback—an area of high concern, particularly when utilizing fuels with high hydrogen content. A more detailed understanding of the underlying thermophysical mechanisms is, therefore, required. Computational fluid dynamics can help elucidate the impact of these roughness effects by enabling detailed data interrogation in locations not easily accessible experimentally. In this study, roughness effects on a generic gas turbine swirler were numerically modeled using a low-y+ detached eddy simulation (DES) approach. Three DES models were investigated utilizing a smooth reference case and two rough cases, the latter employing a literature-based and novel equivalent sand-grain roughness (k_s) correlation developed for this work. Existing experimental isothermal and CH₄ data were used to validate the numerical simulations. Detailed investigations into the effects of roughness on flow characteristics, such as swirl number and recirculation zone position, were subsequently performed. The results show that literature-based k_s correlations are unsuitable for the current application. The novel correlation yields more promising outcomes, though its effectiveness depends on the chosen turbulence model. Moreover, it was demonstrated that, for identical k_s values, while trends remained consistent, the extent to which they manifested differed under reacting and isothermal conditions. Full article

Reducing the anthropogenic impact on the environment is an increasingly urgent challenge, particularly in the energy and heat generation sectors. This study presents the results of an experimental investigation into the combustion characteristics of four nozzle types in a burner system. The experiments focused on emissions of NOx and CO under varying equivalence ratios. This study presents an experimental investigation of combustion with one swirl-stabilized nozzle and two multihole plates under varying equivalence ratios (φ). The swirl-stabilized configuration produced the highest NOx, reaching 54.4 ppm at φ = 0.9, which we attribute to higher flame temperatures and longer effective residence. In contrast, the multihole plates—122 holes of 1.0 mm and 36 holes of 4.0 mm in a 100 mm insert—exhibited lower NOx and lower temperatures owing to more effective fuel–air mixing. CO showed a strong dependence on both geometry and φ; the lowest levels occurred near φ ≈ 0.9, consistent with optimal combustion. The findings underscore the importance of nozzle geometry and air–fuel ratio in optimizing combustion efficiency and minimizing harmful emissions, providing valuable insights for the development of low-emission combustion systems in modern energy applications. Full article

Hydrogen is a promising fuel in the current transition to zero-net CO₂ emissions. However, most practical combustion equipment is not yet ready to burn pure hydrogen without adaptation. In the meantime, blending hydrogen with natural gas is an interesting option. This work reports a computational study of the performance of swirl-stabilized natural gas/hydrogen flames in a novel combustion chamber design. The combustor employs an air-staging strategy, introducing secondary air through a top-mounted plenum in a direction opposite to the fuel jet. The thermal load is fixed at 5 kW, and the effects of fuel composition (hydrogen molar fraction ranging from zero to one), excess air coefficient (λ = 1.3, 1.5 or 1.7), and primary air fraction (α = 50–100%) on the velocity, temperature, and emissions are analysed. The results show that secondary air changes the flow pattern, reducing the central recirculation zone and lowering the temperature in the primary reaction zone while increasing it further downstream. Secondary air improves the performance of the combustor for pure hydrogen flames, reducing NO emissions to less than 50 ppm for λ = 1.3 and 50% primary air. For natural gas/hydrogen blends, a sufficiently high excess air level is required to keep CO emissions within acceptable limits. Full article

Ammonia (NH₃) and hydrogen (H₂) are considered promising fuels for the power sector’s decarbonization. Their combustion is capable of producing energy with zero direct CO₂ emissions, and ammonia can act as a stable energy H₂ carrier. This study numerically investigates the design and implementation of staged combustion of a mixture of NH₃/H₂ by means of CFD simulations. The investigation employed the single-phase flow RANS governing equations and the eddy dissipation concept (EDC) combustion model, with the incorporation of a detailed kinetic mechanism. The combustion chamber operates under the RQL (rich–quench–lean) combustion regime. The first stage operates under rich conditions, firing mixtures of ammonia in air, enriched by hydrogen (H₂) to enhance combustion properties in a swirl and bluff-body stabilized burner. The secondary stage injects additional air and hydrogen to mitigate unburnt ammonia and NO_x emissions. Simulations of the first stage were performed for a thermal input ranging from 4 kW to 8 kW and flames with an equivalence ratio of 1.2. In the second stage, additional hydrogen is injected with a thermal input of either 1 kW or 2 KW, and air is added to adjust the global equivalence ratio to 0.6. Full article

The last decades have offered new challenges to researchers worldwide through the problems our planet is facing both in the environmental protection field and the need to replace fossil fuels with new environmentally friendly alternatives. Bioenergy, as a form of renewable energy, is an acceptable option from all points of view, and biofuels, due to their biological origin, have the ability to satisfy the new needs of humanity. As they release non-polluting combustion products into the atmosphere, biofuels have already been adopted as additives in traditional liquid fuels, intended mainly for the internal combustion engines of automobiles. The current work proposes an extension of the biofuel application in combustion processes specific to industrial furnaces. This technical concern has not been found in the literature, except for the achievements of the research team involved in this work, who performed the previous investigations. A 51.5 kW burner was designed to operate with glycerin originating from the triglycerides of plants and animals, mixed with ethanol, an alcohol produced by the chemical industry recently used as an additive in gasoline for automobile engines. Industrial oxygen was chosen as the oxidizing agent necessary for the liquid mixture combustion, allowing us to obtain much higher flame temperatures compared with the usual combustion processes using air. Mixing glycerin with ethanol in an 8.8 ratio allowed for growing flame stability, also accentuated by creating swirl currents in the flame through the speed regime of fluids at the exit from the burner body. Results were excellent in both the flame stability and low level of polluting emissions. Full article

Biogas, derived from human waste or industrial byproducts, is considered one of the most environmentally acceptable fuels. However, such fuels often exhibit relatively low efficiency, making it essential to develop technologies that facilitate their effective combustion. This article investigates the combustion of biogas with the addition of hydrogen at varying degrees of flow swirling. For this purpose, a burner was used in which methane, hydrogen and CO₂ were mixed in a mixer. The studies revealed that increasing the proportion of hydrogen in biogas leads to an average 15% rise in the NO_x concentration. Additionally, an increase in the degree of swirling has a positive effect on NO_x generation. On the other hand, a higher proportion of hydrogen reduces the concentration of CO in the exhaust gases. The presence of ballast gases, such as CO₂, generally results in relatively low NO_x levels when combined with a high swirling number. The analysis of combustion products for CO₂ indicates a 14% increase in CO₂ proportion. The highest concentrations of CO₂ were observed in biogas with the highest CO₂ ballast content. In terms of reducing NO_x and CO, SW = 1.3 is the most successful. On the other hand, this angle leads to an increase in the CO₂ concentration. Full article

Large-scale industrial burners are essential components in various industries including power generation and chemical processing. Enhancing their energy efficiency and reducing emissions, particularly nitrogen oxides (NOx), requires a combination of experimental research and computational fluid dynamics (CFD) simulations. While there exist numerous emission control techniques, the main focus of the present review study was the passive control technique. The result of this review indicates that biodiesel fuel crude palm oil (CPO) was found to reduce emission components, particularly carbon components and particulate matter (PM). Moreover, it also mitigates cavitation within the injector’s orifice, reducing wear and tear. Although cavitation enhances spray atomization and creates finer droplets for improved combustion, it can damage injector orifices. Optimizing the orifice design, such as by adopting conical orifices over cylindrical ones, can significantly reduce cavitation and its adverse effects. Furthermore, innovations such as swirling fuel–air premixing within injectors enhance combustion efficiency and lower emissions by improving fuel–air mixing. However, spray characteristics, particularly the Sauter mean diameter (SMD), remain critical for predicting combustion performance. Further investigations into spray fineness and its impact on combustion dynamics are essential for advancing emission control and performance optimization. Full article

The global shift toward renewable fuels and the reduction in anthropogenic environmental impact have become increasingly critical. However, the current challenges in fully transitioning to environmentally friendly fuels necessitate the use of transitional fuel mixtures. While many alternatives have been explored, the combination of hydrogen and LPG appears to be the most practical under the conditions specific to Kazakhstan. This study presents experimental findings on a novel burner system that utilizes the airflow swirl and hydrogen enrichment of LPG. It evaluates the effects of hydrogen addition, fuel supply methods, and swirl intensity—achieved by adjusting the outlet vanes—on flame stabilization as well as NO_x and CO emissions. The results show that the minimum NO_x concentration achieved was 12.08 ppm, while the minimum CO concentration was 101 ppm. Flame stabilization studies indicate that supplying the fuel at the center of the burner, rather than at the base, improves stabilization by 23%. Additionally, increasing the proportion of hydrogen positively affects stabilization. However, the analysis also reveals that, as the hydrogen content in the fuel rises, NO_x concentrations increase. These findings highlight the importance of balancing the hydrogen enrichment, airflow swirl, and fuel supply methods to achieve optimal combustion performance. While hydrogen-enriched LPG offers enhanced flame stabilization, the associated rise in NO_x emissions presents a challenge that requires careful management to maintain both efficiency and environmental compliance. Full article