Flame propagation of premixed hydrogen-air explosion in a closed duct with obstacles

To effectively examine the flame propagation of premixed hydrogen-air explosion in a closed duct with obstacles, this paper conducts a numerical study of the flame propagation during the hydrogen explosion in a closed duct with obstacles. Fractal dimensions are used to represent the flame structure. When the number of obstacles is 1, 2, and 3, the fractal dimensions corresponding to flame propagation are 1.632, 1.655 and 1.661 respectively. The research shows that the propagation of explosion flame under obstacle conditions accords with typical self-similarity. The more the number of obstacles, the stronger Kelvin-Helmholtz (K–H) instability and Rayleigh -Taylor (R-T) instability formed, the more obviously the flame is stretched, and the greater the turbulence of the flame propagation. When the number of obstacles is 1, 2 and 3, the corresponding maximum speeds are 108 m/s, 176 m/s and 196 m/s respectively, and thus the flame propagation speed is proportional to the number of obstacles. Flame acceleration is caused by the flow compression due to reduced flow area at the cross-section of obstacles. The flame propagation speed manifests different characteristics through the spherical flame propagation, transformation from the finger flame to twisted flame propagation, and the twisted flame propagation, corresponding to three stages of slow growth, continuous growth and turbulent growth in explosion overpressure.