A study of the radiative ignition mechanism of a liquid fuel using high speed holographic interferometry

Abstract

The mechanism of radiative ignition of 1-decene is investigated experimentally using a high speed two-wavelength holographic interferometry technique. From the time of CO 2 laser irradiation up to ignition, motion pictures with a framing speed of 500 frames per second are used to measure the temperature and fuel vapor concentration distributions in the gas phase near the liquid surface. The effects of oxygen concentration on the growth of the fuel vapor plume are reported for three different environments of nitrogen, air and 40% O 2 /60% N 2 and for peak laser fluxes of 260, 520, and 780 W/cm 2 . Results indicate that the effects of oxygen concentration appear shortly after the appearance of fuel vapor in the gas phase instead of, as previously believed, only very near the final ignition events. An increase in oxygen concentration speeds the growth rate of the vapor plume and brings the location of ignition closer to the fuel surface at the same peak laser fluxes. Two stages of global chemical reactions, the first slow and the second fast, may be able to describe the behavior observed in oxygen containing environments. An increase in peak laser flux does not change the location of ignition but causes an unstable, complex fuel vapor cloud due to buddling and violent vaporization of the liquid.