Observation of Vapor Generation Preceding the Ignition of Liquid n-Decane and 1-Decene by CO₂ Laser Radiation†

^†Contribution of the National Bureau of Standards, not subject to copyright in the United States.

Abstract

As an aid to understanding the ignition mechanism of liquid fuels under high intensity radiation, the time sequence of behavior of a liquid fuel and of the fuel vapor near the liquid surface was observed by high speed schlieren and direct photography. A CW CO₂ laser with fluxes up to 1000 W/cm² was used with beam incident angles of 30 and 90 degrees with respect to the liquid surface. Both n-decane and 1-decene were used as the liquid fuel. The pictures reveal, in time sequence, the formation of a radial wave, a central surface depression, bubble nucleation/growth/ bursting followed by complex surface motion and further bubbling. Effects of laser flux level, incident laser angle and absorption coefficient of the liquid (16 cm⁻¹ and 507thinsp;cm⁻¹) on the formation of bubbles, the size of the bubbles, the frequency of bubble formation and the vaporization process were studied. A simple order of magnitude analysis is applied to ascertain the dominant process that underlies these phenomena.

Notes

^†Contribution of the National Bureau of Standards, not subject to copyright in the United States.

On leave from Tokyo Tokyo Institute of Technology