Abstract: In order to study the flame propagation characteristics of the unprotected side pipe when the flame arrestor fails, IIB3 (Explosion group) ethylene (C2H4) and air mixture were used to study the deflagration performance in pipelines with transparent quartz and arrestor. By image processing methods such as binarization, noise reduction filtering and edge detection, the accurate flame front profile was obtained, and then the relationship between the flame propagation velocity and the position in the pipe was obtained by the maximum similarity coefficient method. The results showed that during the first stage of flame propagation, the flame propagates like a "fingertip", the flame velocity increases linearly, and the pressure curve has two peaks. In the second phase of flame reverse propagation, the flame front is irregular, and the flame velocity and pressure show a downward trend In the third stage of flame propagation, the flame propagates in a "trailing" manner. The flame velocity oscillates with a large amplitude, and the pressure rises steadily with a small increase.

Key words: image processing, flame velocity, flame structure;maximum similarity coefficient method, flame arrester