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Ramjet propulsion is often favored for powering supersonic vehicles cruising at speeds exceeding Mach 3. Despite the relatively simple geometric design of these engines compared to turbo-based alternatives, the complex flow physics involved makes their design and optimization challenging. Hence, the design and performance analysis of ramjet engines are crucial to ensure that the propulsion system meets the demands of the flight trajectory. To address this, a design and analysis methodology using zero-and-one dimensional models, Busemann intakes, and detailed chemistry approach is applied to explore the design space of ramjet engines. By investigating design parameters across a wide range of operational conditions, a multi-dimensional data matrix is generated. Employing a sensitivity analysis technique referred to as Shapley Additive Explanations (SHAP) framework, the propulsive performance characteristics under various operational and design conditions are discussed. • Airbreathing propulsion is favorable for powering high-speed vehicles. • A reduced-order method is proposed to explore the design space of ramjet engines. • Sensitivity analysis is performed via Shapley Additive Explanations (SHAP) framework. • The thrust generation efficiency of ramjet is preserved for varying operational conditions. • Intake design dictates the fuel consumption and uninstalled thrust generation. [ABSTRACT FROM AUTHOR]

It is of great significance to study the hysteresis phenomenon in the unstart/restart process of supersonic inlets for restart control in the practical operation of ramjet engines. In this paper, the unsteady numerical simulations are conducted for the unstart/restart processes of a ramjet engine with a two-dimensional twin-duct inlet configuration under asymmetric incoming-flow conditions (M a 0 = 2.6,β = 2°), and the unstart/restart characteristics of the inlet caused by the plug throttling and the thermal choking are compared and analyzed. The results show that from the perspective of source incentives, the hysteresis loop of the restart process of the leeward inlet caused by the thermal choking is larger than that of the restart process of the leeward inlet caused by the plug throttling, which indicates that it is difficult to verify the restart performance of the ramjet with the two-dimensional twin-duct inlet configuration in the actual operating process by the inlet's plug-throttling experiment in the conventional wind tunnel. In addition, in the practical operations, the increase of fuel gas causes the transition of the leeward inlet to the unstart state, and part of the fuel gas reacts and combusts stably on the external compression surface of the leeward inlet, which easily leads to the burning of the inlet if there is without any special thermal protection. [ABSTRACT FROM AUTHOR]

In this study, a rocket-aided ramjet engine (RARE) configuration is proposed that is aimed at improving the thrust gap and enhancing the engine thrust stability in the ramjet-to-scramjet mode transition of dual-mode scramjet (DMSJ) engines. The combustion mode and relevant heat release characteristics in the kerosene-fueled combustor during the mode transition are analyzed in detail through numerical simulations and ground direct-connect tests at the simulated flight condition of Mach 6. In the ramjet mode, the combustion mode distribution is dominated by diffusion and supersonic combustion, whereas the heat release comes mainly from diffusion and subsonic combustion. The subsonic combustion mode is that which has the highest heat release efficiency, accounting for 28.6% of the total combustion volume, and contributing 67.9% of the total heat release. The combustion heat release level in the rocket-aided scramjet mode is higher than the simple sum of the pure rocket and scramjet modes. The RARE combustor effectively maintains the heat release level and stabilizes the distribution of several different combustion modes from the ramjet to the scramjet mode using the embedded rocket. Furthermore, a robust method for a smooth ramjet-to-scramjet mode transition is provided for ramjet engines. Compared with the engine operation without embedded rocket, the engine thrust variation is reduced from 50.77% to 1.33% with the aid of the embedded rocket, which enhances the operational stability of the engine considerably during the mode transition. [ABSTRACT FROM AUTHOR]

The fuel injection system is the main process in supersonic vehicles. In this article, injection of fuel jet through a trapezoidal strut in the coaxial supersonic air stream is investigated. The numerical method is applied for the simulation of three-dimensional trapezoidal lobe strut in supersonic flow. Hydrogen gas is injected from the end of the trapezoidal strut injector to augment fuel mixing and diffusion downstream by intensifying vortices inside the domain. The power of the vortices varies by the injector velocity and free stream condition. To simulate our model, RANS equations with the SST turbulence model are solved. Effects of free-stream velocity and fuel jet total pressure on fuel distribution and mixing are also investigated. Our results indicate that fuel mixing enhances about 18% when a rectangular strut is replaced by a trapezoidal one. An achieved finding disclosed that the strength of vortices is amplified by the presence of a trapezoidal strut injector. [ABSTRACT FROM AUTHOR]