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Öğe Assessment of NOx emissions of the Scimitar engine at Mach 5 based on a thermodynamic cycle analysis(Pergamon-Elsevier Science Ltd, 2020) Tanbay, Tayfun; Uca, Muhammed Biqar; Durmayaz, AhmetThe Scimitar engine is a new advanced propulsion system designed to propel the aircraft A2 of the LAPCAT project. It is a hybrid system that utilizes the features of turbofan, ramjet and air-turborocket. Hydrogen and air are used as the fuel and oxidant, respectively, while helium is used to transfer heat from the hot incoming air to the hydrogen in the engine. In this study, we present a thermodynamic cycle analysis of the Scimitar engine for the assessment of NOx emissions. The combustion of fuel is studied in detail with an equilibrium model taking into account various dissociation and formation reactions since high levels of temperatures are achieved in its combustion chamber. The NOx emissions of the engine at Mach 5 and the effects of fuel and air flow rates, cruise speed and altitude on these emissions are presented by solving a nonlinear system of equations formed through our novel thermodynamic model. The results show that the NO emissions of the engine can be diminished significantly by decreasing air flow rate, cruise speed and altitude and by increasing the fuel flow rate. The variations of NO2 emissions with these parameters are similar except the variation with altitude which has an inverse effect as compared to the variation of NO. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Energy, exergy and ecological analysis and multiobjective optimization of the hydrogen-fueled Scimitar engine with fixed nozzle geometry(Pergamon-Elsevier Science Ltd, 2022) Tanbay, Tayfun; Durmayaz, AhmetIn this study, an energy, exergy and ecological analysis and multiobjective optimization of the Scimitar engine with fixed core nozzle outlet geometry are carried out at hypersonic cruise conditions. A single-objective optimization is performed first, which revealed that overall efficiency and coefficient of ecological performance are maximized with different optimum nozzle outlet areas, and it propounded the need for a multiobjective optimization. The single objective optimization also showed that decreasing the hydrogen fuel mass flow rate and cruise altitude together with increasing the air mass flow rate and cruise speed improve the performance of the engine. Then, the multiobjective optimization is performed with the utopia point method. It is concluded that for fuel and air mass flow rates of 3.99 kg/s and 178.6 kg/s, respectively, and cruise speed and altitude of Ma = 5.2 and 22 km, respectively, the optimum core nozzle outlet area is 4.00 m(2), when equal weight factors are used for overall efficiency and coefficient of ecological performance. A comparison with the base scenario results showed that the overall efficiency has increased from 55.1% to 57.3%, and the engine size is reduced from 5.38 m(2) to 4.00 m(2) with the multiobjective optimization. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Exergy and NOx Emission-Based Ecological Performance Analysis of the Scimitar Engine(Asme, 2020) Tanbay, Tayfun; Durmayaz, AhmetScimitar engine is a hypersonic hybrid engine designed to propel the LAPCAT A2 aircraft. In this study, a novel exergy and NO(x)emission-based ecological performance analysis of the engine is performed. For this purpose, first, a component-based exergy analysis for the cruise phase of the Scimitar engine in air-turborocket mode is performed and the exergy destruction rates of engine components are determined at Mach 5 by the thermodynamic model developed. Then, a novel objective function, the coefficient of emission-based ecological performance (CEEP) is defined as "the propulsive power produced per unit environmentally harmful exhaust gas emission rate," which can be utilized to assess the ecological impact of any jet engine. Finally, the impacts of cruise speed, altitude, and air and fuel mass flow rates on the exergetic and NO(x)emission-based ecological performance of the engine are investigated by the aid of the newly defined CEEP, together with the exergy efficiency and the coefficient of ecological performance. It is found that the combustion chamber is responsible for 57.36% of the overall exergy destruction rate of 123.80 MW at the cruise conditions, and CEEP relatively increases by 13.8% when the hydrogen fuel consumption rate is increased from 3.96 kg/s to 4.17 kg/s. Increasing the cruise speed from Ma = 4.88 to Ma = 5.2 and decreasing the altitude from 25 km to 23 km cause a relative degradation of 12.75% in CEEP.Öğe Impact of combustion chamber wall heat loss on the energy, exergy, ecology, NOx emission based performance and multiobjective optimization of the precooled scimitar engine(Pergamon-Elsevier Science Ltd, 2023) Tanbay, Tayfun; Durmayaz, AhmetIn this paper, the impact of the combustion chamber wall heat loss on the performance of the hydrogen-fueled precooled combined cycle Scimitar engine is investigated. Overall and exergy efficiencies, coefficient of ecological performance and coefficient of emission based ecological performance (CEEP) are considered as the performance indicators to analyze the effects of wall heat loss flux, chamber length, chamber contraction area ratio, throat area and nozzle convergent half angle. A multiobjective optimization is carried out to find the optimum values of hydrogen and air mass flow rates, cruise speed and altitude and core nozzle outlet area. It is found that a wall heat loss flux of 10 MW/m2 decreases the overall efficiency by 1.1% and causes an increase of 2 kJ/gNOx in CEEP. Multiobjective optimization revealed that increasing the hydrogen mass flow rate, decreasing the cruise speed and air mass flow rate improve the overall performance while the optimum values of cruise altitude and core nozzle outlet area are 23 km and 4.94 m2, respectively. The optimized design has a 20.35% better emission performance than the base design with a compromise of a 3.38% reduction in the overall efficiency.& COPY; 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.Öğe Multiobjective optimization of a pressurized water reactor cogeneration plant for nuclear hydrogen production(Elsevier Ltd, 2024) Tanbay, Tayfun; Durmayaz, AhmetIn this paper, energy, exergy, economic analysis and multiobjective optimization of a pressurized water reactor (PWR) nuclear cogeneration plant for hydrogen production through high-temperature steam electrolysis (HTSE) are carried out. HTSE requires energy in the form of both heat and electrical work. A novel parameter, namely the heat/total energy ratio, is defined, and used as a decision variable in optimization. In addition to energy ratio, hydrogen production capacity, reactor thermal power, live steam temperature, reheating mass flow rate ratio, reheating temperature and steam extraction location are considered as the decision variables to simultaneously optimize the thermal efficiency, thermal-to-hydrogen efficiency, utilization factor, exergy efficiency and total revenue of the cogeneration plant. The analysis and optimization focus on the secondary cycle of the PWR and the effects of hydrogen and electricity prices and ambient conditions are also taken into account since these prices have a significant impact on the optimum design. For a hydrogen price of 4 $/kg and an electricity price of 0.1 $/kWh, when equal preference is given to all objective functions, the optimum production capacity is 6.778 kg/s. The energy ratio has an optimum value if the optimization focuses exclusively on the thermal efficiency and total revenue. © 2023 Hydrogen Energy Publications LLCÖğe MULTIOBJECTIVE OPTIMIZATION OF A PWR NUCLEAR COGENERATION PLANT FOR HYDROGEN PRODUCTION(International Association for Hydrogen Energy, IAHE, 2022) Tanbay, Tayfun; Durmayaz, AhmetIn this paper, the multiobjective optimization of a nuclear cogeneration plant for hydrogen production is carried out. The analysis focuses on the secondary cycle of a pressurized water reactor nuclear cogeneration plant providing process heat and electrical energy to a high-temperature steam electrolysis facility. The utopia point method is used to determine the values of heat/electricity energy ratio, hydrogen production capacity, live steam temperature and steam extraction node that yield a compromise optimum solution between thermal efficiency, thermal-to-hydrogen production efficiency, exergy efficiency and utilization factor. For a hydrogen production capacity of 7 kg/s, an energy ratio of 0.0561 results with the best overall performance, while an energy ratio of 0.10 gives the best performance for a capacity of 0.1 kg/s. © 2022 Proceedings of WHEC 2022 - 23rd World Hydrogen Energy Conference: Bridging Continents by H2. All rights reserved.Öğe Numerical modelling of groundwater radionuclide transport with finite difference-based method of lines(Springer, 2023) Tanbay, Tayfun; Durmayaz, AhmetIn this study, the advection-dispersion equation with decay is numerically solved by the finite difference-based method of lines (FD-MOL) to simulate groundwater radionuclide transport. Finite difference orders of 1,2,.,8 are used for spatial approximation, while the linearly implicit Euler scheme is employed adaptively for temporal discretization. Four different problems are investigated, and results show that FD-MOL provides accurate and stable numerical solutions. Coarse temporal grids can be utilized implicitly, for instance, a maximum step of 1000 years with 400 spatial nodes yields RMS errors of 7.508 x 10(-6), 7.395 x10(-5) and 7.705 x10(-6) in (234) (92) U, (230) (90) Th and (226) (88) Ra normalized concentrations, respectively, for the decay chain problem.
