Experimental study of fuel-air mixture explosion characteristics in the short pipe containing weakly confined face at the end

In this paper, we studied the characteristics of the fuel-air mixture explosion using an experiment system built in a short pipe containing a weakly confined face at the end, with the following results achieved. (1) Multiple pressure peaks were observed due to the rupture, discharge, external explosion, accompanied with the Helmholtz oscillation. (2) The constraint surface produced a strengthening effect on the explosion overpressure, the maximum internal overpressure being 24.23 kPa and the maximum external overpressure being 5.45 kPa, respectively 4.9 and 2.7 times that of the pressure as compared in an unconstrained structure. (3) The morphological changes of the flame can be divided into four stages, those of the laminar combustion, the mutation and acceleration, the external explosion, and the extinction. Due to the influence of such factors as turbulence, interface instability and baroclinic effects, the flame shape was folded and crimped, forming a tulip during the mutation and acceleration stage and a sphere during the external explosion stage. (4) During the laminar combustion stage, the weakly confined face had a lessening effect on the flame speed, with 3.5 m/s as its maximum, which is reduced by 41.3%. In the states of mutation-acceleration and external explosion, the destruction of the confined surface had a strengthening effect on the flame speed, with 80.2 m/s as its maximum, which is enhanced by 106.2%. (5) The flame development made a significant difference at different concentrations. The flame can break through the weak confinement and form an external explosion at low and medium concentration, while at high concentration, the flame was unable to do so.