Gaseous Detonations. IV. The Acetylene-Oxygen Mixtures

Abstract

Detonation velocities were accurately measured in acetylene-oxygen mixtures ranging in composition from 7 to 90 percent acetylene at 1 atmos total pressure. The velocities rise very sharply with concentration to 50 percent acetylene, then drop equally sharply to about 70 percent and from then on rise slightly to 90 percent. The thermodynamic calculations of velocities, in which no adjustable parameters were used, are in perfect agreement with experimental data in the range of 25 to 50 percent acetylene. The velocity at 7 percent, near the detonability limit, is distinctly higher than the calculated value. The calculated velocities from 50 to 90 percent acetylene lie on a smooth curve, showing no break near 70 percent acetylene as do the experimental data. They are higher than the experimental velocities, except at 85 to 90 percent acetylene, where the two curves join again. The disagreement in the intermediate composition range persists when the velocities are recalculated assuming a low heat of sublimation of carbon. A hypothesis is advanced that no solid carbon is formed in detonation waves of mixtures containing up to 70 percent acetylene, because of delays in the nucleation process. The velocities calculated with the assumptions of gaseous equilibria and of the formation of supersaturated carbon vapor, are in acceptable agreement with observations.