Supersonic Combustion Mode Analysis of a Cavity Based Scramjet

This study numerically investigated the combustion instability and characteristics of a laboratory-scale gaseous hydrogen-fueled scramjet combustor. For this purpose, a numerical simulation with an improved detached eddy simulation and a detailed hydrogen/oxygen reaction mechanism was performed. The numerical framework used high-resolution schemes with high-order accuracy to ensure high resolution and fidelity. A total of five fuel injection pressures were considered to characterize the combustion instability as a function of the equivalence ratio. A sampling time of up to 100 ms was considered to sufficiently accumulate several cycles of low-frequency combustion instability dynamics with a period in the order of 100 Hz. Numerical results revealed the repetitive formation/dissipation dynamics of the upstream-traveling shock wave, and it acts as a key factor of combustion instability. The period and derived principal frequency of these upstream-traveling shock waves is several ms. The frequency analysis showed that the instability frequency increased in the low-frequency range as the combustion mode transitioned from the cavity shear-layer to the jet-wake type. This characteristic was derived from the transition in combustion mode at the same equivalence ratio. Therefore, it suggests that the instability frequency shifting is governed by the combustion mode rather than the equivalence ratio. These comprehensive numerical results demonstrated not only the effect of the equivalence ratio but also the important role of the combustion mode on the low-frequency combustion instability.

Section: Characteristics Of the Combustion Instabilitymentioning

confidence: 97%

Reactive Flow Dynamics of Low-Frequency Instability in a Scramjet Combustor

Jeong,

Han,

Sung

et al. 2023

“…Scramjet, as a new type of high-speed propulsion, has become the focus of research. Currently, most of the research is based on liquid fuels such as liquid hydrogen and kerosene [1][2][3][4]. However, the inherent deficiencies of liquid fuel in storage, maintenance, acceleration, stable combustion, rapid response, and technical complexity also bring restrictions to the application of liquid scramjet [5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Solid Rocket Scramjet Based on Central Strut

Zeng,

Wang,

Huang

et al. 2024

Scramjet based on solid propellant has become a potential choice for the development of future hypersonic vehicles. In this paper, a boron-containing solid rocket scramjet based on the central strut injection was proposed, and the ground direct-connect experiment with the equivalence ratios of 0.43 to 2.4 under the flight condition of Mach 6, 25 km was carried out. The pressure and flow rate over time were measured in the experiment. The results show that the engine can realize stable supersonic mode or subsonic mode combustion by changing the gas flow rate. The engine can effectively increase the combustor pressure, reduce the unstable combustion time, and advance the strong combustion position by increasing the gas flow rate. The engine achieved high combustion efficiency when the equivalence ratio was about 1, with a maximum of 88.28%. A numerical simulation analysis was also carried out in this paper. Compared to the experimental results, the pressure error obtained by numerical simulation was less than 4%, and the typical position error was less than 3%, suggesting that the simulation model can be used to predict the behavior of scramjet.

“…Currently, the cavity flame-holding structure has become one of the most common flame stabilization structures in scramjet combustion chambers. In addition to the cavity, baffles and rear steps are also commonly used flame stabilization structures in scramjet combustion chambers [6,7].…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of Combustion Mechanism with Multi-Position Injection in a Dual-Mode Combustor

Dong³

et al. 2023

To improve the flame propagation, combustion stability, and uniformity of the temperature field, multi-position injection is applied in a dual-mode combustor by controlling heat release in different locations. Using the chemical reaction of the finite rate combustion model and the detailed reaction mechanism of hydrogen combustion as described by Jachimowski, the influence of different multi-position injection patterns in a dual-mode combustor is analyzed. The one-equation Large Eddy Simulation (LES) turbulence model was chosen to define the sublattice turbulent viscous terms in a three-dimensional scramjet model. Based on a combustion chamber, the effect of the injection equivalent ratio (0.35–0.70), the relative position of the nozzle holes, and the injection pressure on the combustion process and flow field characteristics are analyzed with multi-position injection. The combustion efficiency, total pressure recovery coefficients, and pressure distribution under different operation conditions are compared. We observed that the combustion intensity increases and the upstream combustion shock string distance becomes greater with increased equivalent ratios. When the global equivalent ratio of multi-position injection remains unchanged, the arrangement of nozzles with the small injection spacing, i.e., two injection holes arranged face to face on the upper and lower walls, or the setting of multiple injection holes with the same pressure, can effectively increase the stability rate of the combustion flow field. In addition, the combustion efficiency at the outlet and the internal pressure of the combustion chamber in the stable state are also improved, relative to the increased total pressure loss.