Articles in Press

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Summary:
Biogas and biomethane are renewable gases that should be strongly considered to accelerate decarbonization and reduce greenhouse gas emissions in many sectors. In addition, biomethane is important to provide renewable and more economical energy to consumers using the existing gas infrastructure. Moreover, biomethane can be easily stored and can be used as a balancer for intermittent renewable energy sources such as solar and wind. The EU considers bio-CNG (compressed), bio-LNG (liquefied) fuels to be an effective method in reducing emissions. Therefore, Europe leads the world in biogas and biomethane production. In this study, evaluations and general views were made about the definition of biogas and biomethane, production amounts in the world and purification methods (treatment) of biogas. The main purpose of the current study is to emphasize that biogas provides an important solution for decarbonization and that its usage areas can be expanded by purifying it as biomethane.

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Summary:
Buildings account for nearly 40% of global energy consumption, with heating, ventilation, and air conditioning (HVAC) systems representing a major share of this demand. As urbanization accelerates and energy insecurity intensifies, the integration of renewable energy technologies into building systems has become essential for achieving sustainability, energy independence, and carbon neutrality. Among these technologies, Stirling engines powered by concentrated solar thermal energy offer unique advantages, including high efficiency, fuel flexibility, and the ability to operate in tri-generation mode by simultaneously producing electricity, heating, and cooling. This review provides a comprehensive synthesis of research on solar-powered Stirling engines integrated with HVAC systems, emphasizing their role in sustainable building applications. The paper examines progress in four key domains: (i) solar powered HVAC technologies for building energy demand reduction, (ii) Stirling engines in combined heat and power (CHP) and combined cooling, heating, and power (CCHP) applications, (iii) modeling, simulation, and experimental advances in solar dish/Stirling systems, and (iv) multi-energy applications and optimization strategies. Special attention is given to the potential relevance for solar-rich but under-researched regions such as Afghanistan, where electricity shortages, high HVAC demand, and abundant solar resources intersect. The review identifies key research gaps, including the need for localized climate based studies, long term operational data, and system level integration strategies. Findings suggest that solar Stirling HVAC systems could provide a viable pathway for sustainable buildings in regions with high solar potential, supporting both environmental goals and energy security.

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Summary:
In this study, the production stages of biodiesel from olive stones and the equipment used in the production process are introduced. Furthermore, the engine performance and exhaust emissions of biodiesel blends obtained from olive stones (B20D80) and its nanoparticle-added derivatives in diesel engines were evaluated. Using test data provided by the PCS engine test system, experiments were conducted with pure diesel (D100), olive stones (BOS20D80), and various additives containing 50 ppm TiO₂ and 50 ppm activated carbon + 50 ppm TiO₂. The experiments revealed improvements in the thermal efficiency of the nanoparticle-added pure diesel and BOS20D80 fuels, while relatively higher NO emissions were observed.

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Summary:
In this study, six Savonius wind turbine models with different blade geometries were experimentally investigated in an open wind tunnel. The experimental analysis focused on torque, rotational speed, and aerodynamic efficiency. The results clearly indicate that blade geometry has a significant influence on turbine performance.

Among the classical semi-cylindrical designs, Model 2 demonstrated higher and more stable torque compared to Model 1. For the helical blade configurations, Model 4 produced approximately 40% higher torque than Model 3 under higher load conditions. Within the hybrid models, Model 6 consistently outperformed Model 5, generating nearly 50% higher torque across all load ranges and achieving the best overall efficiency.

In conclusion, hybrid and optimized blade geometries provide superior performance even under low wind speed conditions, highlighting their strong potential for small-scale wind energy applications.