Xiangyu Zeng

Numerical simulations were performed to investigate the effects of chamber geometry and ignition sequence on pre-mixed H ₂ /O ₂ flame propagation and deflagration-to-detonation transition (DDT) under high-pressure conditions. Based on the OpenFOAM platform and utilizing a detailed H ₂ /O ₂ chemical kinetic mechanism consisting of 8 species and 19 elementary reactions, high-resolution simulations were conducted on flame development in two-dimensional axially symmetric combustion chambers. By altering geometric parameters such as chamber length and contraction angle, as well as implementing different multi-point ignition sequences, the study analyzed flame acceleration mechanisms, turbulent evolution patterns, and DDT (deflagration-to-detonation transition) triggering mechanisms. The results show that chamber contraction geometry modifies flame development by changing the available propagation space and reflected-shock trajectories. In the elongated contraction channel, the rightward-propagating flame is stretched into a finger-like structure and accelerates to approximately 1000 m/s before DDT initiation. The ignition sequence determines the shock-wave interference pattern; later-ignited flames experience pronounced deflection and compression due to pre-existing shock waves. Two dominant DDT triggering mechanisms are identified: hotspot-induced DDT caused by reflected-shock focusing and flame-stagnation-induced DDT caused by sustained shock–flame coupling in confined regions. Ultimately, detonation wave evolution is governed by both high acoustic impedance ratios and intense interface instability. This study clarifies the roles of contraction geometry and ignition sequence in controlling flame–shock coupling and DDT initiation in confined high-pressure hydrogen–oxygen combustion systems.

To investigate the early-stage flame propagation and pressure response of premixed H₂-O₂ combustion under ultra-high-pressure constant-volume conditions, a transient CFD model was developed for a large-volume confined chamber. The numerical framework combines a density-based solver, the Peng–Robinson real equation of state, large eddy simulation, and a reduced H₂-O₂ chemical kinetic mechanism. Simulations were conducted at initial pressures of 30 and 40 MPa, H₂/O₂ molar ratios of 8:1 and 12:1, and three-, four-, and five-point ignition configurations. The results show that increasing the initial pressure from 30 MPa to 40 MPa advances the pressure rise onset from approximately 1.65 ms to 1.28 ms and increases the maximum pressure rise rate from 18.6 MPa·ms⁻¹ to 27.4 MPa·ms⁻¹ under the H₂/O₂ = 8:1 and three-point ignition condition. Under the investigated fuel-rich conditions, increasing the H₂/O₂ molar ratio from 8:1 to 12:1 delays the pressure rise onset from approximately 1.28 ms to 1.46 ms and reduces the maximum pressure rise rate from 27.4 MPa·ms⁻¹ to 21.1 MPa·ms⁻¹. For the 30 MPa and H₂/O₂ = 8:1 cases, the four-point ignition case produces the largest pressure rise rate of approximately 23.5 MPa·ms⁻¹, whereas the five-point ignition case shows a lower pressure fluctuation amplitude of approximately 3.6 MPa. The present conclusions are based on CFD quantitative engineering predictions and should be further validated using quantitative experimental measurements.

In response to the current limitation where conventional constant volume combustion apparatuses are generally confined to pressure ratings of 5–20 MPa, insufficient for the demands of ultra-high-pressure combustion fundamental research, this study designs and verifies a high-pressure-resistant constant volume combustion apparatus with a rated working pressure of 250 MPa. The strength design and safety factor calculation for the combustion chamber main body were conducted based on the Lame thick-walled cylinder elastic theory. A finite element numerical simulation method was systematically employed to perform static analysis, transient impact response analysis, and high-cycle fatigue-life assessment of the key components of the apparatus. The results indicate that under a 250 MPa design internal pressure load, the maximum circumferential stress at the inner wall of the combustion chamber main body is 328.0 MPa, with a safety factor greater than 1.5, complying with relevant safety codes for high-pressure vessels. Under transient loading simulating combustion impact, the maximum equivalent stress of all structural components is below the material yield strength, with a maximum elastic deformation of less than 0.06 mm, demonstrating excellent structural stiffness and impact resistance. Fatigue assessment with a design-life target of 1.0 × 10⁶ pressure cycles shows that the cumulative damage values for all components are significantly less than 1.0, meeting the reliability requirements for long-term cyclic service. This apparatus integrates functional modules such as high-pressure precision gas mixing, high-energy reliable ignition, high-speed transient parameter acquisition, and safe product collection, providing a stable, controllable, and safe experimental platform for in-depth research on the combustion mechanisms of gaseous fuels under ultra-high-pressure conditions.