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. With LIBS it is possible to quantify local concentrations accurately 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. The ratio has a strong linear relation with the ratio of the peak emission intensities regardless of phase of the fuel. As the full width at half maximum (FWHM) of the emission peak from the fuel-borne hydrogen increases linearly with the liquid fraction due to the Doppler shift with micro-explosions, the FWHM yields the fuel vapor fraction. Simultaneous, high-resolution measurements of equivalence ratios and vapor fractions in an intermittent fuel spray in a pressurized atmosphere were obtained with this method. The results showed that the tip of the intermittent spray has a richer mixture with a lower vapor fraction.