Instantaneous Measurement of Local Concentration and Vapor Fraction in Liquid-Gas Mixtures by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) with atomic emission excited with a focused high-energy ND : YAG laser was applied to quantify the concentration and the vapor fraction of liquid-gas mixtures. LIBS can exactly quantify local concentration even in liquid-gas mixtures as the ratio of the number of fuel-borne hydrogen atoms to nitrogen or oxygen atoms in the ambient gas has a strong linear relation with the ratio of their peak emission intensities regardless of phase of the fuel. The full width half maximum (FWHM) of the emission peak from the fuel-borne hydrogen linearly increases with an increase in liquid fraction due to doppler shift with micro explosion, and the FWHM yields the fuel vapor fraction. Simultaneous, high-resolution measurements of equivalence ratio and vapor fraction in an intermittent fuel spray in a pressurized atmosphere were obtained with this method. The results showed that the tip of an intermittent spray has a richer mixture with lower vapor fraction.