The effects of pipe length on gas cloud explosion characteristics in the contraction pipe

To study the influence of pipe length on premixed gas explosion characteristics in a contraction pipe. A Large Eddy Simulation (LES) and Zimont combustion model was used to simulate the propane/air explosion process at different pipe lengths. The results show that the flame propagation velocity in the contraction pipe increases first and then decreases and reaches its peak at the change of pipe diameter. Compared with the diameter pipe, the flame propagation velocity in the first half of the contraction pipe is reduced by adding the contraction structure. Although the flame propagation velocity increases suddenly after the flame passes through the contraction pipe, the flame propagation process is effectively delayed. Compared with the diameter pipe, the total combustion time of the contraction pipe increases by 44.4%, 30%, and 30%, respectively. Under different pipe lengths, the trend of pressure change is to increase first and then decrease, and the longer the pipe, the greater the maximum explosion pressure in the pipe. The existence of the variable diameter structure leads to a significant increase of the peak pressure in the pipe, and the peak pressure in the contraction pipe is, respectively, 8, 4, and 7 times that in the diameter pipe of the same length. Therefore, in actual industrial production, it is necessary to take safety measures such as pressure relief at the change of pipe diameter to avoid accidents.