Effects of obstacles inside the tube on the shock wave propagation and spontaneous ignition of high-pressure hydrogen

Abstract

This paper is devoted to investigating the effects of obstacles inside the tube on the shock wave propagation and spontaneous ignition during high-pressure hydrogen release. The length of the obstacles area is 38 mm, which includes seven metal ring obstacles and six metal spacers. The hydrogen burst pressure varies from 2 to 8 MPa. The results show that the existence of obstacles in the tube has no significant influence on minimum burst pressure required for spontaneous ignition in our experiments, even though a reflected shock wave is formed from obstacle. When initial ignition has been induced in the tube before the obstacles, however, the appearance of the reflected shock wave can promote combustion and enhances the flame intensity. Combustion pressure wave originated from self-ignition is observed in the tube, which also increases flame intensity. Three possible spontaneous ignition mechanisms for the tube with obstacles are discussed. And it is found that although the strength of the leading shock wave decreases after passing through obstacles, the flame velocity relatives to the tube wall inside the tube increases significantly. This may be because large amount of hydrogen/air mixture, which produced by the turbulent mixing due to the presence of the obstacles, accelerates combustion in the tube. Nevertheless, the obstacles could not change the flame propagation characteristics outside the tube, such as flame morphologies and flame propagation velocity.