The impact of changing obstacle sizes on shock wave generation for various fuel types in detonation engines

In this master's thesis, the focus is on the theoretical investigation of detonation engines, which have been proven to have higher efficiency, and supporting these theoretical findings with CFD (Computational Fluid Dynamics) analyses. The study examines two main components of detonation engines: the pre-detonator and the main-detonator. The pre-detonator plays the role of a shock initiator for the detonation engine, comprising two sections: the driver region characterized by high pressure, temperature, and the driven region containing unburned fuel and air. In this thesis, gaseous fuels such as acetylene, ethylene, ethane, methane, kerosene, and hydrogen were used to generate a shockwave in a pre-detonator under three different equivalence ratios and five different blockage ratios. The shock wave resulting from combustion within the geometry leads to elevated pressures and temperatures, thereby increasing viscosity. As the viscosity of the gas increases, it reduces the Reynolds number and, consequently, the velocity. Turbulence-enhancing obstacles were placed within the geometry at different heights and widths (0.5-0.75-1-1.25-1.5) to increase the reduced velocity due to the gas's viscosity in the pre-detonator. It was observed that this turbulent structure enhances the homogeneity of the gas mixture, thus shortening the time required for shock wave formation due to the obstacles. The effects of geometries with different blockage ratios on parameters such as pressure, temperature, velocity, and the formation time of the shock wave were investigated within the scope of the thesis. The analyses were performed using computer-aided calculation software, automatically varying the blockage ratios. The obtained data were then interpreted using graphs and contours. Based on the conducted studies, the design of the pre-detonator was facilitated. An approach has been developed to ensure the continuity of the shock wave by feeding the pre-detonator output to the main detonator. As part of this thesis, preliminary design work on the injector design, the number of injectors, and the injection positioning related to the fuel spraying process has also been carried out. These studies were calculated taking into account the two-phase flow. The two-phase flow would be advantageous in cooling the engine, given the high heat flow and temperature of the detonation engine. The analyses of the designed injectors were conducted using User-Defined Functions (UDF) in the CFD program under both 2D and 3D conditions. In the context of this thesis, an approach for designing pre-detonators and main detonators in accordance with the requirements was established and contributed to the scientific literature for use in research and development activities in the field. By using these data, our country's aerospace sector will be supported in the chassis of research and development activities for detonation engines that can be produced using this knowledge. The data reported in the chassis of the study, in light of the effects of physical and chemical parameters in the transition stages from deflagration waves to detonation waves, are significant for the advancement of flame-based research.