Ionization in Seeded Detonation Waves

This paper reports an investigation of equimolal oxy‐acetylene detonations at 1/10‐atm initial pressure, which were seeded with potassium acetylide (C2HK) to obtain good electrical conductivity. Finely ground (10‐μ mean diam) potassium acetylide was injected into the initial mixture and the density of the resulting aerosol was determined by a sedimentation technique. The electrical conductivity was determined by a magnetohydrodynamic interaction method developed by Lin. The measured conductivities were compared with the results of thermodynamic equilibrium calculations, which included the cooling effect due to the heat capacity of the additive. Predicted and measured conductivities have approximately the same dependence on the mole fraction of potassium which was varied from 0.1 to 10%. At the temperatures of interest (3500–4000°K), reported values of electron‐gas (CO, H, and H2) and electron‐potassium collision cross sections are about 10−15 cm2 and 40 × 10−15 cm2, respectively. With these values, the theoretical and measured electrical conductivities agreed within a factor of two, the agreement improving with increasing mole fraction of potassium. An electron‐gas cross section of 2.5 × 10−15 cm2 gave good agreement between theory and experiment. The maximum measured conductivity was 2.7 mho/cm and occurred at about 3% potassium in the product gases. Ionization was essentially complete within about 40 μ sec behind the wave front.