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    Combustion characteristics and performance of a Wankel engine for unmanned aerial vehicles at various altitudes
    (Elsevier Ltd, 2024) Kucuk, Merve; Sürmen, Ali; Şener, Ramazan
    This study investigates the effects of altitude on the combustion, emissions, and performance of a Wankel engine for unmanned aerial vehicles (UAVs). The main motivation behind the presented study is to contribute to the Wankel engine designs used as a power source in UAVs by revealing the operating conditions at various altitudes. For these purposes, a gasoline fueled Wankel engine was simulated at sea level conditions for different equivalence ratios and results were validated with their experimental counterparts. Then, CFD simulations were carried out at various altitudes (6000 ft, 10,000 ft, and 15,000 ft). The simulation results show that decreasing ambient air temperature, and pressure at higher altitudes reduces the fresh charge density, hence combustion efficiency and heat release rate (HRR). As a result, the performance characteristics such as the indicated mean effective pressure (IMEP), the indicated torque, and indicated power decrease and exhaust emissions increase. For 6000 rpm, IMEP decreases by 39.11%, 53.79%, and 69.22%, and the indicated power reduces by 35.51%, 52.47%, and 65.05% at the altitudes of 6000 ft, 10,000 ft, and 15,000 ft, respectively, compared to those obtained at the sea level conditions. As for exhaust emissions, CO and CO2 are lowest at sea level conditions and increase with altitude. © 2023 Elsevier Ltd
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    Cryogenic milling-based keratin microparticle production from Anatolian goat fibers and their structural, chemical and thermal properties
    (Sage Publications Ltd, 2023) Duman, Seyma; Kucuk, Merve
    Fibers procured from Anatolian goat (Capra aegagrus hircus) furs were converted into keratin microparticles by the cryogenic milling method. Single-stage mechanical milling with a 2.5 h optimal grinding time was sufficient enough to generate the desired high-quality microparticles. No chemical solvents were utilized during the production process of keratin microparticles. Structural, chemical and thermal properties of keratin microparticles were assessed using particle size analyzer, stereo microscope, Brunauer-Emmett-Teller (TM) surface analyzer, field emission scanning electron microscope, X-ray diffractometer, attenuated total reflection Fourier transform infrared spectroscopy, thermogravimetric analyzer and differential scanning calorimetry methods. According to the characterization results, microparticles with amorphous structure in micro size could be produced without any agglomeration during the milling process. Goat farming is usually for dairy products and their fibers have very limited use in the textile industry because of their flat structure. Therefore, the conversion of goat fibers into another product that can be used in other industrial areas is expected to contribute significantly to a sustainable economy.
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    Effectiveness of hydrogen enrichment strategy for Wankel engines in unmanned aerial vehicle applications at various altitudes
    (Elsevier Ltd, 2024) Kucuk, Merve; Şener, Ramazan; Sürmen, Ali
    This study investigates the effectiveness of the hydrogen-enrichment strategy on a Wankel engine for unmanned aerial vehicles (UAVs). The primary motivation behind this study is to contribute to the Wankel-type rotary engine designs by revealing the influences of the hydrogen enrichment method on the Wankel engine performance at various altitudes. To achieve these objectives, CFD simulations were conducted by applying a hydrogen enrichment method to a neat gasoline Wankel engine model at sea level, 5000 ft and 15,000 ft altitudes. The hydrogen energy fraction at the intake was gradually increased from 0% to 10%. The decrease in ambient air temperature, pressure, density, and insufficient fresh charge with the increase in altitude leads to the reduced reference chamber temperature and pressure of the Wankel engine. Thus, the combustion worsens, the heat release rate (HRR) and performance decrease, also emissions deteriorate in these colder operating conditions. On the other hand, the unique physicochemical properties of hydrogen such as wide flammability limits, high homogeneity, relatively small quenching distance and high flame speed allow hydrogen-enriched mixture flames to propagate toward the narrower gaps in the combustion chamber and make up for some drawbacks of Wankel engines. As a result, flame propagation is accelerated and fuel burning rate, peak pressure and temperature values in the reference chamber are increased by hydrogen addition. For the cases at sea level with 5% and 10% hydrogen energy fraction, IMEP is increased by 6.59%, 8.50%, and the indicated power is increased by 35.51% and 52.47%. In the cases with the same energy fraction at 15,000 ft, IMEP is increased by 26.61% and 48.75%, and the indicated power is reduced by 26.61% and 48.75%, respectively. It has been proven that a small amount of hydrogen by energy fraction improves combustion efficiency and performance. The findings show that hydrogen has excellent compatibility with Wankel engines and hydrogen enrichment is a very practical concept for the improvement of the performance of these engines for UAVs. Thus, Wankel engines, which are already a very favorable power source for UAVs, become even more favorable by the hydrogen-blending strategy. © 2023 Hydrogen Energy Publications LLC
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    Effects of thermodynamic pressure on laminar spray flame propagation into monodisperse fuel droplet-mists
    (Elsevier, 2025) Ozel-Erol, Gulcan; Kucuk, Merve; Chakraborty, Nilanjan
    The effects of droplet diameter, overall equivalence ratio (0.8-1.5), and primary evaporation zone length (2-10 mm) on the burning velocity and thermal flame thickness in laminar n-heptane monodisperse spray flames under varying pressures (1.0-2.0 bar) have been analysed using 1D numerical simulations. It is observed that for gaseous premixed flames, both flame speed and thickness decrease with increasing pressure. However, in spray flames, flame thickness increases while burning velocity decreases as pressure rises, primarily due to reduced evaporation rates that limit fuel vapor availability. Larger droplet sizes further diminish evaporation rates, which lowers burning velocity and increases flame thickness, regardless of pressure. The finite evaporation rate also results in local equivalence ratios that are lower than the overall equivalence ratio in the heat release zone within the flame, especially at high pressures and with large droplets. In overall fuel-rich mixtures (e.g., for an overall equivalence ratio of 1.5), this can lead to more reactive gaseous mixtures and higher burning velocities than corresponding gaseous premixed flames, particularly for small droplets. Notably, the burning velocity in some spray flames can exceed the burning velocity of the corresponding premixed flames at the same gaseous-phase equivalence ratio at the heat release rate location. Enhanced burning velocity is also attributed to the generation of reactive species (e.g., H-2, C2H2, C2H4) from droplet evaporation and pyrolysis behind the flame front, which diffuse back into the reaction zone and accelerate the combustion process. However, the formation of these species diminishes at higher pressures, reducing this enhancement effect.
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    Influence of Hydrogen Enrichment Strategy on Performance Characteristics, Combustion and Emissions of a Rotary Engine for Unmanned Aerial Vehicles (UAVs)
    (Mdpi, 2022) Kucuk, Merve; Surmen, Ali; Sener, Ramazan
    In recent years, there has been great interest in Wankel-type rotary engines, which are one of the most suitable power sources for unmanned aerial vehicle (UAV) applications due to their high power-to-size and power-to-weight ratios. The purpose of the present study was to investigate the potential of a hydrogen enrichment strategy for the improvement of the performance and reduction of the emissions of Wankel engines. The main motivation behind this study was to make Wankel engines, which are already very advantageous for UAV applications, even more advantageous by applying the hydrogen enrichment technique. In this study, hydrogen addition was implemented in a spark-ignition rotary engine model operating at a constant engine speed of 6000 rpm. The mass fraction of hydrogen in the intake gradually increased from 0% to 10%. Simulation results revealed that addition of hydrogen to the fuel accelerated the flame propagation and increased the burning speed of the fuel, the combustion temperature and the peak pressure in the working chamber. These phenomena had a very positive effect on the performance and emissions of the Wankel engine. The indicated mean effective pressure (IMEP) increased by 8.18% and 9.68% and the indicated torque increased by 6.15% and 7.99% for the 5% and 10% hydrogen mass fraction cases, respectively, compared to those obtained with neat gasoline. In contrast, CO emissions were reduced by 33.35% and 46.21% and soot emissions by 11.92% and 20.06% for 5% and 10% hydrogen additions, respectively. NOx emissions increased with the application of the hydrogen enrichment strategy for the Wankel engine.
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    Production and characterization of keratin microparticles obtained from wool fibers by cryogenic milling method
    (Taylor & Francis Inc, 2022) Duman, Seyma; Kucuk, Merve
    In this study, keratin particles were obtained from wool fibers by the cryogenic milling method without utilizing any chemical solvent. The optimal milling period and low energy expenditures are the predominant advantages of the proposed method as the first attempt to incorporate cryogenic milling into the process of keratin production from a wool resource. The configuration, size distribution, surface area, crystallinity, chemical composition, and thermal properties of keratin particles were assessed by a particle size analyzer, stereo microscope, Brunauer-Emmett-Teller (TM) surface analyzer, scanning electron microscope, x-ray diffractometer, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analyzer measurements. The characterization results indicate no alteration in the structural and chemical properties of keratin microparticles after cryogenic milling. The procurement of waste fibers from wool, one of the main raw materials of the textile industry, and processing them into keratin particles by an environment-friendly and innovative method can be considered the pioneering aspects of this study.
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    THE EFFECT OF PRESSURE INCREASE ON DROPLET EVAPORATION IN TWO-PHASE COMBUSTION ENVIRONMENT
    (Begell House Inc., 2022) Kucuk, Merve; Sürmen, Ali
    The effects of pressure increase on combustion quality due to the droplet evaporation in dropletladen mixtures have been analyzed with the emphasis on the importance of detailed chemistry. A one-dimensional (1D) code with detailed chemistry and transport has been utilized in order to investigate the evaporation process of fuel droplets of different diameters at a high ambient pressure. Steady-state parametric analyses are performed using n-heptane fuel droplets. It has been found that the initial droplet diameter and the stoichiometry have significant effects on droplet evaporation, thus on flame propagation and combustion quality under high-pressure conditions. The findings regarding the effects of droplet diameter on combustion indicate that evaporation rate of the droplets is directly related to the gaseous fuel mass fraction. Small droplets evaporate before the flame front, but larger droplets cannot complete their evaporation before they reach the flame front, causing a lower gaseous fuel mass fraction. Findings regarding the stoichiometry effects are that the gaseous fuel mass fraction reaches its highest value after the flame front under rich mixture conditions. While the droplets in the lean mixture evaporate completely before the flame front, the droplets in the rich mixture can penetrate towards the flame. Increase in the equivalence ratio and decrease in the droplet diameter increase the evaporation rate and flame spread. It should be noted that this is only a theoretical study on combustion phenomena using detailed chemistry. However, pressure levels used in the analyses are similar to operating pressure of various combustors. For this reason, findings are believed to give researchers insight into the design of many combustors with spray combustion. © 2022 Begell House Inc.. All rights reserved.