Numerical simulation of premixed methane–air deflagration in large L/D closed pipes

A three-dimensional numerical model in which the heat loss through pipe walls was included was developed to simulate gaseous deflagration in pipes of large length to diameter ratio (L/D). The simulated pressure time histories are in good agreement with published data, and the error between experimental and computed maximum pressure is less than 15.3%. The attention is focused on the flame propagation and flow field during deflagrations, as well as the effects of ignition point (at the center or at one end of the pipe) and L/D (L/D = 6 − 10.35) of the pipe on them. The numerical results show that a tulip flame is formed during flame propagation, which is related to the reverse flow and vortices motion. The maximum fame speed is 30% higher with the ignition point at the end than that at the center, and it increases linearly with increasing L/D. The deflagration pressure decreases when the distance that flame travels increases due to the effect of the heat loss through pipe walls.

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► Methane–air deflagrations in closed pipes of large L/D were simulated.
► The heat loss through pipe walls was included in the model.
► The results reveal flame propagation in long closed pipes.
► The maximum flame speed increases linearly with increasing L/D.
► The maximum flame speed is 30% higher for end ignition than for center ignition.