One-dimensional full-range mixture fraction measurements with femtosecond laser-induced plasma spectroscopy

Femtosecond laser-induced plasma spectroscopy (FLIPS) was performed to achieve full-range mixture fraction measurements in non-reacting CH₄/air flow fields. A femtosecond laser at 800 nm was used to generate a plasma channel with a uniform intensity distribution. Through measuring spatially resolved spectra and calibration, we found that the spectral intensity ratios of CH (431 nm)/N₂ (337 nm), CH (431 nm)/N₂ (357 nm), C₂ (516.5 nm)/N₂ (337 nm), C₂ (516.5 nm)/N₂ (357 nm) and CH (431 nm)/O (777 nm) could be used to realize mixture fraction measurements, and the first four intensity ratios can achieve full-range mixture fraction measurements. Furthermore, through quantitative analysis of the distribution along the plasma channel, we analyzed the one-dimensional measurement capability of FLIPS. The main advantages of FLIPS for mixture fraction measurements are one-dimensional quantitative measurement, full-range measurement, high spatial resolution and no Bremsstrahlung interference.