Jingfang Ye

Investigations of secondary explosions induced by venting

A series of vented explosion tests were performed in a small‐scale cylindrical vessel using a short discharge duct. Overpressure–time profiles were recorded with five transducers both inside and outside of the vessel. Visualization of the flow field is provided by a high‐speed shadowgraph imaging system using sequential shadowgraphs. As is well known, two or more pressure peaks can occur during explosion venting, one from the vent rupture and the other from a secondary explosion induced by combustion of the vented combustible gases. Three typical distinct processes of vented explosions were found. Variations in intensity of the secondary explosion were measured as a function of vent burst pressure, ignition location, blockage ratio at the vent, and equivalence ratio of the fuel.

Investigation on External Explosions during Venting

The external explosions may occur in an explosion venting and give a potential risk. However, the basic dynamic process of external explosions during the venting to ambient air is yet not well understood. In this paper, a series of vented explosion tests in high failure pressure has been conducted in a cylindrical venting vessel. It has been demonstrated clearly from the pressure-time histories and the shadowgraphs of the external flow field that under some suitable venting conditions there exist two peak pressures in the external flow field, one is generated from the membrane rupture and the other is induced by the external explosion due to the violent combustion of the vented combustible gas. The effects on the flow patterns outside the venting vessel under different failure pressures, vent areas (blockage ratio) and chemical equivalent ratios are also discussed in the term of the experimental results. Moreover, the venting process was simulated numerically by using SIMPLE schemes in colocated grid, based on the k-e turbulent model and ‘eddy dissipation combustion model’. The calculated results are in good agreement with the measured results. The dominant mechanisms of the occurrence of the external explosion during the venting processes have been elucidated based on measured and calculated results.

Observations of flame behavior during flame-obstacle interaction

A series of experiments have been performed to investigate the premixed flame behavior during its propagation in a rectangle chamber with various obstacles mounted on its wall. A high speed shadowgraph system was used to visualize the flame front development. Three different obstacles were used, and their corresponding sequential images are presented and used to quantify the shape and location of the flame front during its propagation. Our experimental results for flame acceleration showed similar results as the literature: the flame accelerates as it passes over the obstacles and then decelerates due to the existence of a recirculation zone behind the obstacles. However, significant changes in flame structures and turbulent transitions were found for the three different obstacles. It is found that the passage, which is composed of the surface shape of the obstacle and the inner wall of chamber, is critical to the shape of the flame front and propagation of the flame. The obstacle with the largest volume results in the fastest flame acceleration.