Ignition Delay and Reaction Time Measurements of Hydrogen–Air Mixtures at High Temperatures

Abstract

Induction and reaction times of hydrogen–air mixtures (ϕ = 0.5–2) have been measured behind reflected shock waves at temperatures of 1000–1600 K, pressures of 0.1, 0.3, 0.6 MPa in the domain of the extended second explosion limit. The measurements were performed in the shock tube with a completely transparent test section of 0.5 m long, which provides pressure, ion current, OH and high-speed chemiluminescence observations. The experimental induction time plots demonstrate a clear increasing of the global activation energy from high- to low temperature post-shock conditions. This trend is strongly pronounced at higher post-shock pressures. For a high-temperature range of T > 1200 K, induction time measurements show an activation energy for the global reaction rate of hydrogen oxidation of 64–83 kJ/mole. Detected reaction times exhibit a big scatter and a weak temperature dependence. The minimum reaction time value was nearly 2 µs. Obtained induction time data were compared with calculations carried out in accordance with the known kinetic mechanisms. For current and former shock-tube experiments within a pressure range of 0.1–2 MPa, critical temperatures required for strong (1000–1100 K), transient and weak auto-ignition modes behind reflected shock waves were identified by means of the pressure and ion-probe measurements in stoichiometric hydrogen-air mixture. The transfer from the strong volumetric self-ignition near the reflecting wall to the hot spot ignition (transient) was established and visualized below <1200 K with a post-shock temperature decreasing.

Parametric Study of Flow and Combustion Characteristic in a Cavitied Scramjet with Multi-Position Injection

“…The diameter of each nozzle is mm, and they are perpendicular to the wall surface. A1 and A2 are located on the uppe Hydrogen-fueled scramjet engines, due to their high specific impulse characteristics, have broad application prospects in hypersonic vehicles; hence, researchers have conducted numerous simulations of hydrogen fuel combustion [23][24][25][26][27][28][29][30]. Wang et al [23] conducted research on the combustion performance of a hydrogen-fueled scramjet engine, revealing a positive feedback relationship between the lift shear layer in the recirculation zone and enhanced combustion, which demonstrates the strong robustness of the shear layer/recirculation stable combination mode.…”

“…Takeno et al [24] conducted research on the flame stabilization mechanisms of hydrogen jets and found that spherical flame structures are instrumental in sustaining the flame. Baranyshyn et al [25] studied the ignition timing of hydrogen-air mixtures at elevated temperatures and found that with the increase in temperature, the delay before spontaneous ignition sharply decreases from hundreds of mi-Fire 2024, 7, 176 3 of 20 croseconds to just a few microseconds. Koo et al [26] studied the effect of thermodynamic nonequilibrium on the flame structure of supersonic hydrogen combustion using direct numerical simulation (DNS).…”