Experimental results of delayed ignition of impinging high-pressure hydrogen jet on pipe geometry in open atmosphere.

ABSTRACT In an accidental scenario often pipe systems are present around hydrogen systems. In case of unintended hydrogen releases from pressurized items (pipes, fittings, tank etc.) hydrogen jets can meet/impinge on obstacle. That can lead to accumulation of hydrogen and result in a delayed ignition. An under-expanded hydrogen jet can generate blast waves if ignited. It is important to have an understanding of the relation between the obstacle distance and the release point on the severity of possible explosions. The influence of the presence of an obstacle on the flame propagation is very well known. The concentration field plays a crucial role since hydrogen’s burning velocity changes with the concentration. Therefore, the location of ignition also affects the flame propagation. This article presents the results from an experimental campaign of an under-expanded hydrogen jet impinging onto a obstacle. 40 experiments were performed to investigate the flame propagation in an open atmosphere through a pipe geometry. The hydrogen was released through a 1.69 mm circular orifice at discharge pressure between 30 bar(g) – 80 bar(g). The releases were performed in a combination of different ignition locations and distances between obstacles and the release point. The flow regimes in the experiments were captured with a high-speed camera and analysed with a custom made image processing tool, resulting in flame speed measurements across the obstacles.