Experimental study of spontaneous ignition and non-premixed turbulent combustion behavior following pressurized hydrogen release through a tube with local enlargement

Abstract

Pressure records, flame detection and high-speed photography are used to study the spontaneous ignition and non-premixed turbulent combustion behavior following high-pressure hydrogen release through a cylindrical tube with local enlargement into the semi-enclosed space. The study shows that the leading shock wave is partly reflected when it impacts on the vertical walls in the local enlargement section. The pressure behind the reflected shock wave has a significant increase compared with that behind the leading shock. Moreover, the leading shock wave speed decreases firstly and then increases as it passes through the enlargement. It is found that the presence of the local enlargement structure can significantly facilitate the occurrence of spontaneous ignition. The minimum storage pressure of spontaneous ignition is only 1.98 MPa in the tube with local enlargement, which is lower than that in a constant cross-section tube. The possible positions of initial ignition inside the tube and the delay times of ignition for different burst pressures are obtained. After the hydrogen flame comes out from the tube, a ball of flame is formed around the tube outlet and propagates outward. Then, the noticeable non-premixed turbulent combustion of hydrogen occurs in the semi-enclosed space, which leads to the increase of the pressure in the chamber. Twice peaks of overpressure are observed successively and the second pressure peak has a lower intensity compared with the first peak value. Moreover, the maximum overpressure of non-premixed turbulent combustion increases with the release pressure.