Flame Acceleration by a Postflame Local Explosion

Abstract

Delayed local explosion of segregated parts of an explosive gas mixture behind the flame front can lead to flame front acceleration and hence to increased overpressures. The effect of a local explosion on flame speed and overpressure during deflagration of a stoichiometric ethylene-air mixture was investigated in two different experimental configurations. In the first experimental setup, the interaction of a spherical shock front with a planar flame front was studied in a 1-m-diam tube. The effect of flame front acceleration was indicated by an increase of overpressure from 0.1 to 0.5 bar. In a second experimental setup, the interaction of a spherical shock front with a spherical flame front in an unconfined configuration was studied. The flame front, which moved with an initial velocity of about 10 m/s, became strongly folded and torn up during the interaction with the shock front. As a result, a large increase in the overall flame speed was observed. Different parts of the reaction zone attained velocities in the range between 75 and 125 m/s. The folding of the flame front due to the occurrence of the MarksteinTaylor instability is thought to be the main cause for this large increase of combustion rate and overall flame speed.