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    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, Ahmet
    The 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.
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    Exergy and NOx Emission-Based Ecological Performance Analysis of the Scimitar Engine
    (Asme, 2020) Tanbay, Tayfun; Durmayaz, Ahmet
    Scimitar 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.
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    Fully meshless solution of the one-dimensional multigroup neutron transport equation with the radial basis function collocation method
    (Pergamon-Elsevier Science Ltd, 2020) Tanbay, Tayfun; Ozgener, B.
    In this paper a fully meshless method is proposed for the numerical solution of the one-dimensional multigroup neutron transport equation with anisotropic scattering. Both first-order and even-parity forms of the transport equation are studied. The radial basis function collocation method is chosen for the spatial treatment, and Legendre polynomials are used to approximate the angular variable. The selection of the Legendre polynomials instead of discrete ordinates approach resulted with a fully meshless algorithm in both independent variables. Multiquadric is utilized as the radial function. Seven problems are considered to evaluate the performance of the method. The results show that the method converges exponentially, and it is possible to obtain high levels of accuracies for the multiplication factor and neutron flux with a good stability in both spatial and angular domains. For the one-group isotropic benchmark problem, discrete ordinates solutions employing discontinuous linear finite elements for the spatial variable are also provided, and a comparison of the methods revealed that the fully meshless method produced more accurate results than the discrete ordinates-finite element scheme when the shape parameter is properly chosen. (C) 2019 Elsevier Ltd. All rights reserved.
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    A Meshless Method Based on Symmetric RBF Collocation for Neutron Diffusion Problems
    (Polish Acad Sciences Inst Physics, 2019) Tanbay, Tayfun; Ozgener, B.
    In this study we have worked on the numerical solution of the multigroup neutron diffusion equation with the symmetric radial basis function collocation method. For the spatial approximation of the neutron flux, multiquadric, inverse multiquadric, and Gaussian basis functions are used as the interpolation functions. To test the performance of the method, both external and fission source problems are considered in two-dimensional Cartesian geometry. The effect of the shape parameter on the convergence and stability of the numerical algorithm is also investigated. The results have shown that, when the multiquadric is chosen, the symmetric RBF collocation method converges exponentially, and it is possible to obtain highly accurate multiplication factors and neutron flux distributions with this algorithm.