A new method for measuring local equivalence ratios in hydrocarbon mixture fields was established with an application of LIBS, Laser-Induced Breakdown Spectroscopy. Gas molecules of the mixture were separated to excited atoms by introducing the focused lights of Nd, YAG laser, to obtain atomic emissions from the excited atoms. The emission peaks of H, O, and N were observed at different wavelengths. The wavelengths for their representative peaks include 656 nm, 777 nm, and 871 nm respectively. The ratios of the emission intensity from H and O, FH/FN, or from H and N, FH/FN had a good correlation to the equivalence ratios, regardless of the laser power. The experimental results showed that local equivalence ratios above 0.01 thereabout were measured instantaneously and with high accuracy for propane-air mixtures.
