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In the study of self-ignition during pressurized hydrogen release, the morphology of the rupture disk alters the flow and mixing processes of the gas jet, as well as the development of shock waves, thereby affecting the occurrence of self-ignition. This study employs the LES method based on the RNG-SGS model, EDC model, and NUIMech1.1 H 2 combustion mechanism to investigate the flow mixing, shock wave development, and self-ignition phenomena under three different the rupture disk morphologies. The research findings indicate that as the growth trend of the rupture disk rupture ratio increases, the propagation speed of shock waves within the tube and the compression speed of the air and hydrogen-air mixing region accelerate, resulting in an earlier occurrence of self-ignition. A more complex rupture morphology leads to higher mixing rates between hydrogen and air and increased complexity of shock waves. Self-ignition initially occurs in the fuel-lean region of the boundary layer, followed by ignition at the center of the tube. The characteristic number of rupture disk is proposed to describe its impact on the self-ignition time. The competitive relationship between the two elementary reaction pathways of oxygen influences the development of the flame. • A CFD model for hydrogen release and self-ignition is established and validated. • The development process of multidimensional shock waves is described in detail. • The process of self-ignition and entire flame development is fully captured. • The reaction mechanism and HRR of self-ignition are analyzed. • The impact of rapture disk morphology on flow and self-ignition is fully obtained. [ABSTRACT FROM AUTHOR]

The phenomenon of spontaneous combustion during the release of high-pressure H 2 is critical to the safe storage and transportation. Besides physical methods to suppress self-ignition, the approach of mixing low-reactivity gases has gained increasing attention. Previous work has mainly focused on the flow, physical heating effects, and boundary conditions of self-ignition in mixed gases, while the intrinsic chemical reaction mechanisms of spontaneous combustion remain underexplored. To clear this issue, this work uses the ReaxFF MD simulation method to study the spontaneous combustion process of H 2 /CO and H 2 /CH 4 mixtures with various concentrations. The results indicate that: (1) in pure H 2 , H 2 /CO, and H 2 /CH 4 systems, the primary initial reaction mechanism is H 2 +O 2 HO 2 +H. Additionally, in some mixed systems, CO + O 2 CO 2 +O and CH 4 +O 2 CH 3 +HO 2 may also serve as initial reaction mechanisms. (2) Under fuel-lean combustion conditions, the RIDTs of the systems decrease, supporting the viewpoint that self-ignition typically occurs first in fuel-lean regions. The addition of CO and CH 4 increases the RIDTs, which helps inhibit the development of self-ignition. (3) In H 2 -rich environments, CO combusts to CO 2 through the formation of HOCO, while CH 4 undergoes dehydrogenation and oxidation processes through intermediates such as CH 3 , CH 3 O, and HCHO, leading to the formation of CO and CO 2. The combustion of H 2 is also influenced by these processes. (4) The addition of CO and CH 4 increases the activation energy of H 2 combustion, raising the reaction energy barrier that must be overcome for spontaneous combustion. This effectively helps to suppress the occurrence and development of self-ignition during the release of high-pressure gases. • Clear initial reaction mechanism of pure H 2 , H 2 /CO, and H 2 /CH 4 combustion systems. • RIDTs of H 2 , H 2 /CO, and H 2 /CH 4 systems are statistically analyzed and compared. • Reaction pathways of H 2 , CO, and CH 4 in mixed systems have been identified. • Combustion activation energies of H 2 in mixed systems are calculated. • Explained the inhibition of self-ignition from a molecular reaction perspective. [ABSTRACT FROM AUTHOR]

Exploring the development characteristics and influencing factors of the mixing layer (ML) inside the hydrogen recirculation ejector is of great importance for enhancing the recirculation properties of the ejector and promoting green and sustainable energy development. However, the evolution of ML in the ejector and the transport and diffusion characteristics of the fluid are problematic, in particular, the influence of the expansion ratio on the properties of the ejector is unclear. Therefore, in this study, a CFD numerical model of an ejector was established to simulate the flow of fluids in the ejector. The evolution of ML was elucidated, and the interaction mechanism between the mixing and the recirculation performance of the ejector was revealed. The findings showed that the velocity difference is a significant driving force for the development of ML, and the formation of an adverse pressure gradient contributes to the diffusion of hydrogen and the rapid development of ML. The development process of ML in the ejector can be divided into three stages under the interaction of the velocity difference and the convective Mach number: the rapid growth stage, the slow growth stage, and the exponential growth stage. By studying the evolution of ML at different expansion ratios, it was found that there exists a critical expansion ratio for the ejector, which results in the largest of the non-mixing length ratio and the effective mixing thickness, the strongest relative mass transfer capability of the entrained flow, the fullest development of ML, and the optimal hydrogen recirculation performance. • Mixing model of an ejector within the PEMFC system was established. • The radial transport properties of the fluid in the mixing layer were elucidated. • The development of the mixing layer at different expansion ratios were investigated. • The interaction mechanism between mixing and recycling performance was revealed. [ABSTRACT FROM AUTHOR]