Comparative CFD Analysis of Air–Fuel Ratio Effects on the Performance of a Non-Premixed Combustion Burner

Effect of Fuel Type on Flow-Thermal Field Evolution and Preheating Performance of Scrap in Molten Iron Ladle

Against global carbon neutrality targets, the carbon-intensive steel industry bears severe decarbonization stress, wherein advanced low-carbon smelting technologies dominate its green transition. Scrap preheating boosts scrap ratio and cuts steelmaking carbon emissions; optimized fuel-scrap matching and fuel grading by scrap type significantly improve thermal efficiency and reduce preheating energy demand. This work establishes a 3D numerical model for randomly stacked scrap within a 100-t hot metal ladle to compare natural gas, coke oven gas and converter gas regarding flow field, flame structure, thermal distribution, scrap heating performance and energy efficiency under equal total heat input. Numerical simulations with the k-ε turbulence, EDC combustion and P-1 radiation models are performed to couple flow, heat transfer and combustion. Fuel composition strongly governs flame morphology and thermal behaviors. Natural gas and converter gas form intact, stiff flames, while coke oven gas produces discontinuous unstable flames. Flow intensity decreases in the sequence converter gas, coke oven gas and natural gas, and high-speed turbulent fluctuation of converter gas facilitates heat diffusion. Under the same heating duration, the average surface temperatures of scrap are 695 K, 782 K and 411 K for natural gas, converter gas and coke oven gas, respectively. Converter gas achieves the highest preheating efficiency of 11.2 %, followed by natural gas (5.9 %), and coke oven gas is the lowest (2.4 %) due to its low calorific value. Moreover, fuel-scrap matching characteristics reveal that natural gas is suitable for light and thin scrap to avoid overheating, while converter gas is more favorable for medium and heavy scrap with improved heat penetration. This work reveals the influence mechanism of gas type on ladle scrap preheating and provides theoretical support for fuel selection and process optimization in high-efficiency and low-carbon scrap preheating applications.

Impact of refractory elements design on heat transfer in the combustion chamber of wood-log gasification boilers

Combustion of wood logs continues to improve despite the diversification and standardization of wood-derived fuels. Gasification boilers— featuring separate gasification and combustion chambers—are widely used to meet stringent environmental requirements, yet they remain underrepresented in the engineering and scientific literature. To bridge this gap, 146 simulations were conducted to assess how refractory size, position, inclination angle, producer gas quality, and gas-inlet location affect flue-gas residence time, temperature fields, and heat transfer to boiler water. An 18-kW boiler is experimentally characterized with respect to producer-gas composition and temperature under varying gasification conditions. These data are used as boundary conditions for a CFD model that features non-premixed combustion and is described using the standard k–ε turbulence model, the Discrete Ordinates radiation model, and a domain-based weighted-sum-of-gray-gases model for radiative properties. Refractories not only protect metal surfaces, enable complete combustion, and aid particulate removal, but also enhance heat transfer. In total, 8 different combustion chamber designs are analyzed. Compared to the best refractory-free case, a combustion chamber with a U-shaped flue-gas flow path and two additional refractory-coated surfaces achieves 22% higher heat transfer despite a 17% smaller heat-exchange area. Refractories that create a U-shaped flow path extend flue-gas residence time, span at least half the chamber length, and feature an asymmetric channel height that favors a smaller flue-gas cross-section at the exit. Finally, combustion chamber design depends on upstream gasification performance—specifically, producer-gas composition and temperature, and air-preheating temperature.

Numerical Study of the Effects of the Primary Air/Secondary Air Ratio and Coal Quality on Combustion Characteristics and Emissions in a 115 MW CFB Power Plant

The distribution of combustion air in a Circulating Fluidized Bed (CFB) boiler plays an important role in determining combustion performance and emission formation. Variations in coal quality result in differences in combustion characteristics, making it necessary to optimize the Primary Air/Secondary Air (PA/SA) ratio. This study aimed to analyze the effects of PA/SA ratio variations and coal quality on temperature distribution and exhaust gas composition in a 115 MW CFB power plant. The simulation was conducted using Computational Fluid Dynamics (CFD) with Ansys Fluent 2024 R2 software, incorporating PA/SA ratio variations of 40/60, 50/50, 60/40, and 70/30 for two coal types: Low-Rank Coal (LRC) and Medium-Rank Coal (MRC). The analyzed parameters included temperature distribution and mass fractions of CO₂, O₂, and NOx. The simulation results showed that PA/SA ratios of 40/60 and 50/50 produced more homogeneous temperature distributions compared with the 60/40 and 70/30 ratios. MRC produced higher furnace temperatures than LRC but also resulted in increased NOx emissions. The highest CO₂ mass fractions were obtained at PA/SA ratios of 40/60 and 50/50, with values of approximately 0.16–0.17, indicating more effective carbon conversion. An increase in the primary air ratio increased the concentrations of O₂ and NOx in the furnace. Overall, the 50/50 PA/SA ratio provided the optimal combustion performance, characterized by a more homogeneous temperature distribution, high carbon conversion efficiency, and controlled NOx emissions.

Impact of ammonia energy ratio on combustion characteristics, energy efficiency, and emissions in a dual-fuel ammonia/diesel engine

Experimental Study on Laminar Burning Velocity and Flame Instability of Liquefied Petroleum Gas/Dimethyl Ether Blended Gas: Effects of Equivalence Ratio and Blended Ratio

Liquefied petroleum gas/dimethyl ether (LPG/DME) blended gas is a promising clean alternative fuel, characterized by high efficiency and clean combustion properties. To reveal the combustion characteristic mechanism and evolutionary process under multi‐factor coupling conditions, this study investigates the propagation and instability characteristics of spherically expanding flames of LPG/DME blended gas at different equivalence ratios ( φ  = 0.7–2.0) and blending ratios ( X  = 0–1.0) using a constant volume combustion bomb and high‐speed schlieren technique. Combined with CHEMKIN chemical kinetic calculations (mainly including reaction pathway and sensitivity analyses), the evolution and competition laws of diffusive‐thermal and hydrodynamic instabilities under different φ and X conditions are explored, as well as the significant influence of buoyancy instability on flame morphology and propagation under highly fuel‐rich conditions. Results show that the laminar burning velocity ( S L ) first increases and then decreases with φ , with a peak value of 0.47811 m/s occurring at φ  = 1.0–1.2. In contrast, S L decreases with increasing X , reaching a minimum of 0.04262 m/s. Under lean conditions, the effective Lewis number Le eff  ≫ 1, and the flame remains stable under the dominant effect of diffusive‐thermal instability. Under rich conditions, increasing X enhances diffusive‐thermal instability, raises the flame thickness ( δ ) to a maximum of 0.624 mm, and decreases the thermal expansion ratio ( σ ) to a minimum of 6.595, thereby weakening hydrodynamic instability and causing flame instability. At a highly rich condition of φ  = 2.0, the dominant instability mechanism shifts from the combined effect of diffusive‐thermal and hydrodynamic instabilities to buoyancy instability, further increasing the tendency toward flame instability. Through reaction path and sensitivity analysis, the mechanism that LPG addition influences combustion rate by controlling OH radical fraction is clarified.

Effect of Burner-Hole Variation on Airflow, Flame Characteristics, and Thermal Performance of a Waste Cooking Oil Stove

This study investigated the effect of burner hole variation on the flame behavior thermal performance of a waste cooking oil stove. Three cylindrical burner configurations with 25, 28, and 31 holes. The methods included measurement of fuel consumption, flame temperature at the flame core and outer flame zones, visual flame appearance analysis. The results showed that increasing number of burner holes improved the effective air supply to the combustion zone, as indicated by the increase in air output mass from 0.00075kg/s (25 hole burner) to 0.00093kg/s (31 hole burner) while obstructed air mass decreased from 0.00225 to 0.00207kg/s. This improvement intensified flame behavior and accelerated water heating. The estimated boiling times for the hole burner 28 and 31 showed no significant difference, with a variance of only 0.10 minutes. Fuel consumption increased only slightly from 0.040 to 0.047kg. Flame temperature and flame height also increased consistently with burner hole number. Overall, the 31 hole burner provided the maximum combustion intensity, whereas the 28 hole burner offered the best practical balance between fuel consumption and heating performance. These findings demonstrate that burner hole optimization is an effective strategy for improving the practical thermal performance of household waste cooking oil stoves.