Ignition-delay times in laser initiated combustion

Abstract

A single pulse from a TEA CO₂ laser is used to heat 1:7:14 mixtures of SF₆:CH₄:O₂ to temperatures near 1000 K. A short- or long-duration pulse (one-half the energy deposited in 0.25 or 0.82 μsec, respectively) from a second TEA CO₂ laser is used to ignite the mixture. At comparable values of absorbed energy from the second laser, ignition-delay times for the long-duration secondary pulse are approximately twice those for the short-duration pulse. Ignition of the hot mixture requires about 10% less absorbed energy with the short-duration pulse than with the long-duration pulse. These results indicate the short-duration pulse is more effective in producing a high population density of reactive species that initiate the reactions necessary for ignition.