Current understanding for designing converging curves for shock tube applications has been limited to the two-dimensional (2D) theory, and design of effective three-dimensional (3D) converging curves was not available so far. The present study explores the feasibility and efficacy of designing a 3D converging curve to enhance shock intensity of chemical shock tubes, through a joint means of theoretical analysis, numerical simulation, and experimental validation. First, based on the known gas dynamics theories, the 2D converging curve was designed and optimized. Then, 3D studies based on computational fluid dynamics (CFD) simulations were performed to extrapolate and refine the 2D converging curve derived in the first step. The key to this process was constraining the characteristic parameters of the converging curve to ensure that the 3D converging curve, when used in the chemical shock tube, would achieve a stable shock wave waveform, a constant post-wave flow field, and sufficient test time. An optimal converging curve was thus achieved through the above 2D theoretical analysis and 3D numerical simulations. Finally, a chemical shock tube with the optimal 3D converging curve was constructed. Both chemically reactive and non-reactive experiments, including the pressure–time history and ethylene supercritical ignition properties, were performed to evaluate the pressure stability, the shock intensity enhancement, and the cost reduction of precious experimental chemicals of the constructed shock tube. Results indicated that the converging shock tube enhanced the Mach number (shock intensity) by a factor of 1.2, with very stable pressure–time profiles, which could last more than 4 ms. Compared to a conventional constant-diameter shock tube, the current converging shock tube was shown to reduce experimental costs by 47%–60%. The present study highlighted the superior performance of chemical shock tubes with the 3D converging curve in terms of pressure control, cost-effectiveness, and experimental reliability, demonstrating its potential for advancing fundamental combustion studies under high-pressure supercritical or extreme conditions.
Bai et al. (Fri,) studied this question.