Thermal radiative ignition of liquid fuels by a CO? laser

Abstract

Abstract : This report summarizes progress in the study of the ignition mechanism of a liquid fuel by a continuous wave carbon dioxide laser; the period covered is from October 1, 1979 to September 30, 1982. It describes 1) new observations of liquid fuel behavior near and at the liquid/air interface during the laser irradiation with incident fluxes from 260 to 2500 W/sq. cm., 2) new time-resolved measurements of temperature and vapor concentration distributions in the gas phase using a newly-developed, high speed, two-wavelength holographic interferometer, and 3) the development of a technique to measure infrared absorption spectra of fuel vapors at elevated temperatures. High speed photographs reveal the complex behavior of n-decane and i-decane surfaces immediately after the onset of incident CO2 laser irradiation. In time sequence one sees the formation of a radial wave, a central surface depression, bubble nucleation/growth/bursting, followed by complex surface motion and further bubbling; typically several (or many) bubble cycles proceed the whole sequence of events leading to a dominance of bubbling phenomena and decreasing the ignition delay. An increase in oxygen concentration in the surrounding gas phase decreases the distance between the liquid surface and the location of the first appearance of visible emission. Prior to ignition there are two global chemical reaction stages in the gas phase. (AW)