Effect of obstacle location on explosion dynamics of premixed H2/CO/air mixtures in a closed duct

An experimental study was presented to investigate the effect of obstacle location (OL) on explosion dynamics of premixed H2/CO/air mixtures. A fence-type obstacle providing the blockage ratio of 0.5 was mounted in the closed duct, and the distance from the ignition end increased from 100 mm to 600 mm. Therefore, the effect of the obstacle on flame exponential acceleration stage, flame deceleration stage, and tulip flame stage had been comprehensively discussed. When OL <= 400 mm, the turbulent finger-shaped flame front will invert into the tulip shape after the flame propagates through the obstacle channel. The competition between the flamelets' backward movements induced by the vortex motion and forward movement induced by the squish flow causes the turbulent finger-shaped flame front's inversion. The pressure dynamics are discussed in conjunction with flame tip dynamics. The prominent flame deformation and oscillation after the tulip flame is caused by the interaction of flame and pressure waves. However, the pressure waves make no difference on the finger-shaped flame front inversion. This indicates that the flame front inversion after the obstacle is a pure hydrodynamic phenomenon. What's more, for a given hydrogen volume fraction, the flame duration time first decreases and then decreases with obstacle location, the maximum flame tip speed and the maximum overpressure first increases and then decreases with obstacle location, and the maximum explosion severity occurs at OL = 400 mm.