Effect of an Axial Electric Field on Detonation Waves

The present thesis reports an investigation of the effects of an axial electric field (200V/cm – 8000V/cm) on the propagation of detonation waves in mixtures of 2CO+O2 and C2H2+O2+85%Ar. High speed streak camera together with photodiodes was used for detonation velocity and position measurements. Additionally, the voltage across the axial electrodes and the current in the field circuit were also monitored as the detonation traversed the electric field region. The experimental results show that the charged particles within the detonation reaction zone are attracted to the surface of the electrode creating a sheath at the boundary of the electrode that shields the bulk of the detonation plasma from further influence of the DC electric field of the electrode. The present results also show that the neither the detonation structure nor its velocity are influenced by the presence of the sheath and the resulting current to the electrode. It is also found that the conducting gas behind the detonation wave carries the voltage across the test section to the second (ground) electrode. In an axial electrode configuration the detonation wave essentially reduces the gap between the two electrodes progressively as it propagates in the test section. The increase of the electric field ahead of the detonation may result in a breakdown of the unburned mixture ahead of the detonation and the development of a discharge. For a sufficiently high electric field an arc discharge occurs ahead of the detonation igniting the unburnt mixture upstream of the detonation. The lack of fresh mixture ahead of the detonation results in failure of the detonation, but subsequent reinitiation of the detonation may occur. The present study also indicates that contrary to the previous observations by Bone et el, no significant effect of the applied electric field on the detonation is observed except for cases where breakdown of the unburned mixture ahead of the detonation occurs.