The current research reports gas composition measurements, based
on Laser Induced Breakdown Spectroscopy (LIBS) in non-reacting flows and flames of premixed streams in an opposed-jet burner
using both atomic and molecular emissions. The dependence of spectral intensity ratios of H/O and C2/CN on methane-air and propane-
air mixture composition was quantified over a wide range of conditions extending from pure air to pure fuel. The presence of a flame within the laser beam led to significant deterioration
of the signal-to-noise ratio of the instantaneous LIBS signal,
caused by the variability of the induced plasma, which led to
the increased uncertainty of the instantaneous gas composition measurements. The increase of the measurement uncertainty
in flames was quantified and corrected by increasing the laser pulse energy, which maintained the measurement uncertainty of
instantaneous gas composition below 20%. LIBS was successfully used to measure gas composition in mixtures of methane, propane and air and the results demonstrated its feasibility for instantaneous measurements of local air -fuel ratio.