The present study analyzes the combustion process of mixed biomass pellets in a domestic boiler. For the purposes of the research, experimental measurements of flue gases are combined with numerical simulations based on computational fluid dynamics (CFD). Special attention is given to the impact of the ratio between primary and secondary air on the combustion process, emission characteristics, and thermal balance. The results show that an air distribution ratio of 60/40 (primary/secondary) leads to more complete combustion, reducing emissions of carbon monoxide (CO) and nitrogen oxides (NOx), while also improving the efficiency of the boiler. The analysis of the numerical modeling results shows that CO emissions decrease by 12% and NOx emissions by 27%. The calculated model is validated using experimental data on flue gas temperature, oxygen (O₂) and carbon dioxide (CO₂) concentrations, and combustion efficiency, and a high degree of correspondence between theoretical and actual measurements is established. The simulations reveal the dynamics of the temperature field, the movement of flue gases, and the role of turbulence in the combustion chamber. Optimization of the air distribution is proven to improve the combustion process and reduce the harmful emissions generated. The obtained results highlight the potential of mixed biomass pellets as a sustainable alternative to conventional fuels, provided that combustion parameters are precisely regulated. They can serve as a foundation for the enhancement of biomass-based heating systems in order to achieve higher efficiency and environmental sustainability. A market research study is also conducted, revealing that mixed pellets are preferred due to their high calorific value, low cost, and low ash content.

An algorithm for numerical analysis of the transient thermal processes in high temperature gas chamber furnaces for ceramic firing is developed. It is based on mathematical models of the conjugate heat transfer, including combustion, turbulent flows of the torch and gas mixtures, heat transfer through radiation, conduction and convection. The algorithm is used for analysis and improvement of the efficiency of a furnace for firing of technical ceramics.

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 (NO_x). The results indicate that SH pellets generate the highest emissions (CO: 1095.3 mg/m³, NO_x: 679.3 mg/m³), while W pellets achieve the lowest (CO: 0.3 mg/m³, NO_x: 194.1 mg/m³). The mixed W/SH pellets produce intermediate values (CO: 148.7 mg/m³, NO_x: 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.

This study analyses the potential of using sunflower husks as an energy source by producing bio-pellets and evaluating their combustion process in residential settings. As one of the leading sunflower producers in the European Union, Bulgaria generates significant agricultural residues with high, yet underutilized, energy potential. This study employs a combination of experimental data and numerical modelling aided by ANSYS 2024 R1 to analyse the combustion of sunflower husk pellets in a hot water boiler. The importance of balanced air distribution for achieving optimal combustion, reduced emissions, and enhanced thermal efficiency is emphasized by the results of a comparison of two air supply regimes. It was found that a secondary air-dominated air supply regime results in a more uniform temperature field and a higher degree of oxidation of combustible components. These findings not only confirm the technical feasibility of sunflower husk pellets but also highlight their commercial potential as a sustainable, low-cost energy solution for agricultural enterprises and rural heating providers. The research indicates that there are business-to-business (B2B) market opportunities for biomass producers, boiler manufacturers, and energy distributors who wish to align themselves with EU green energy policies and the growing demand for solutions that support the circular economy.

Plasma nitriding is an advanced method to increase the hardness and wear resistance of different metal parts with complex shapes and geometries. The modelling is an appropriate approach for better understanding and improving such technologies based on multi-physical processes. Mathematical models of the coupled electromagnetic, fluid flow, and thermal processes in vacuum chambers for the low-temperature plasma treatment of metal parts have been developed. They were solved numerically via ANSYS/CFX software for a discretized solid and gas space of a plasma nitriding chamber. The specific electrical conductivity of the gas mixture, containing plasma, has been calibrated on the basis of an electrical model of the chamber and in situ measurements. The three-dimensional fields of pressure, temperature, velocity, turbulent characteristics, electric current density, and voltage in the chamber have been simulated and analysed. Methods for further development and application of the models and for technological and constructive enhancement of the plasma treatment technologies are discussed.

An assessment of the possibilities of replacing the widely used cotton fibre as a natural raw material in the production of nitrocellulose with waste cotton fabrics was performed. The impact of the key factors on the properties of the resulting materials was analyzed through comparative evaluation of the processing conditions and the obtained material characteristics. Based on the obtained results, including the evaluation of the resulting material properties, an initial selection of potential waste materials to be nitrated was made. This will lead to an increase in the environmental and technological efficiency of the nitrocellulose production process.