This study investigates the impact of the near-wall temperature gradient on hydrogen auto-ignition characteristics using one-dimensional (1D) fully resolved simulations. Ten cases are simulated, one featuring normal combustion and the other nine simulating auto-ignitive combustion with different initial pressures, equivalence ratios and near-wall temperature gradients. The simulations show that the near-wall temperature gradient greatly affects the onset and intensity of the auto-ignition event. For cases with the initial conditions of 833.3 K and 15 bar, a small near-wall temperature gradient delays the timing of auto-ignition and places the auto-ignition kernel further away from the wall, facilitating deflagration-to-detonation transition of the auto-ignitive flame. This leads to a large increase in pressure oscillations within the domain and heat flux to the wall. When the initial conditions are changed to 900 K and 20 bar, the magnitude of the near-wall temperature gradient also affects the number of auto-ignition events, leading to a significant impact on the wall heat flux. The results suggest that an accurate modelling of the near-wall temperature gradient is necessary for the simulations of hydrogen end-gas auto-ignition. This requires special considerations in the near-wall region and a careful selection of the wall heat transfer model in Computational Fluid Dynamics (CFD) tools such as Reynolds-Averaged Navier-Stokes (RANS) and Large-Eddy Simulation (LES).

The turret seat ring assumes an important load transfer role in the gun firing process, and its stiffness has a great influence on the muzzle vibration response. Based on the basic theory of nonlinear finite element method, this paper establishes a high-precision refined finite element analysis model of the seat ring based on the contact and collision between the ring and the steel ball, the steel ball and the fixed ring, and the fitting gap between the steel ball and the ring and the fixed ring, and characterizes the equivalent stiffness of the seat ring by its axial equivalent stiffness, radial equivalent stiffness and overturning equivalent stiffness. The dynamic response is obtained by simulation. The results show that the axial equivalent stiffness, radial equivalent stiffness and overturning equivalent stiffness of the seat ring are non-linear in a certain load range, and the equivalent stiffness changes linearly and steadily with the increase of load, and fluctuates in a small range.

Mild auto-ignition initiated by a hot spot in the unburnt gas ahead of a lean hydrogen-air flame is studied using onedimensional (1D) direct numerical simulation (DNS). The impact of thermal boundary layer thickness and position of the hot spot on pressure oscillations in the domain as well as on the wall heat flux is investigated. The interaction of the sparkignited flame with the auto-ignitive front generated from the hot spot produces large pressure oscillations in the domain. A significant increase in the wall heat flux is observed when the autoignitive front quenches at the wall. The thermal boundary layer thickness has a negligible impact on these phenomena for the studied flames. Furthermore, the pressure oscillations appear only resulting in the fluctuations of the wall heat flux, and the significant increase in the wall heat flux appears primarily due to the quenching of the auto-ignitive front at the wall.