Browsing by Author "Mileva N."

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    CFD-based analysis of wood pellet combustion in a domestic boiler (small-scale)
    (2025-01-01) Krumov K.; Zlateva P.; Mileva N.
    This study presents a numerical analysis of the wood pellet combustion process in a domestic hot water boiler using computational fluid dynamics (CFD) methods. The aim is to assess the impact of primary and secondary air distribution on the temperature field, flow behavior, and pollutant formation. A three-dimensional model of the combustion chamber in code ANSYS CFX was developed. Two air supply configurations were analyzed: 40% primary / 60% secondary air and 60% primary/40% secondary air. The solid fuel was represented by an equivalent gas mixture to simulate the volatile components released during combustion. The simulation results demonstrate that the air distribution ratio substantially influences flame morphology, thermal field uniformity, and the generation of pollutants. The 40/60 air ratio supply configuration promotes improved air-fuel mixing, enhanced combustion stability, and reduced emissions of carbon monoxide (CO) and methane (CH4). In contrast, the 60/40 air ratio configuration yields higher flame temperatures but favors incomplete oxidation, leading to increased emission levels. The proposed numerical model represents a useful basis for optimizing air supply regimes in domestic pellet-fired boilers to achieve improved combustion efficiency and reduced environmental impact.
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    Numerical and Experimental Analyses of Flue Gas Emissions, from Biomass Pellet Combustion in a Domestic Boiler
    (2025-10-01) Mileva N.; Zlateva P.; Ivanov M.; Krumov K.; Terziev A.; Comarla A.
    This study explores the combustion behavior of three biomass pellet types—wood (W), sunflower husk (SH), and a mixture of wood and sunflower husks (W/SH)—in a residential hot water boiler. Experiments were carried out under two air supply regimes (40%/60% and 60%/40% primary to secondary air) to measure flue gas concentrations of oxygen (O2), carbon monoxide (CO), and nitrogen oxides (NOx). The results indicate that SH pellets generate the highest emissions (CO: 1095.3 mg/m3, NOx: 679.3 mg/m3), while W pellets achieve the lowest (CO: 0.3 mg/m3, NOx: 194.1 mg/m3). The mixed W/SH pellets produce intermediate values (CO: 148.7 mg/m3, NOx: 201.8 mg/m3). Overall boiler efficiency for all tested fuels ranged from 90.3% to 91.4%. Numerical simulations using ANSYS CFX (2024 R2 (24.2)) were performed to analyze temperature distribution, flue gas composition, and flow fields, showing good agreement with experimental outlet temperature and emission trends. These findings emphasize that both pellet composition and air distribution significantly influence efficiency and emissions, offering guidance for optimizing small-scale biomass boiler operation.