Thermal radiation hazards of the external flow field for vented hydrogen-air explosion: Effect of nitrogen fraction

An experimental investigation is conducted to examine the impact of nitrogen fraction on vented explosions of hydrogen-air-nitrogen mixtures in a 1-m-long cylindrical duct at 1 bar and 281 K. The study employs high-speed shadowgraph imaging, a pressure testing system, and infrared thermal imaging to record the venting process. The results showed that as the nitrogen fraction increases, the rupture time of the vent cover gradually increases. However, the internal peak overpressure exhibits an opposite trend, with P-2 (caused by the ignition of unburned gas outside the tube by the escaping flame) near the vent consistently dominating. The frequency of Helmholtz oscillations initially decreases and then increases with increasing nitrogen fraction. Higher nitrogen fractions are associated with a greater likelihood of lower external peak overpressure but a decreasing trend in maximum external impulse. The maximum temperature shows an initial decrease followed by an increase with the addition of nitrogen fraction. This trend is also observed for flame length, flame width, high-temperature duration (>500(degrees)C), and heat energy. Furthermore, the study determined safety zones that are free from thermal radiation damage.