Laser-Induced Breakdown Spectroscopy

LIBS for Fuel-Air (F/A) Ratio Measurement

Laser-induced breakdown spectroscopy (LIBS) is a relatively straightforward and yet powerful technique that has been widely used for elemental-composition measurements in all forms of matter.  LIBS has been employed for gas-phase sensing, including measurements of alkali-containing-species concentration in furnace exhaust electron temperature and electron number density of air plasma, mixture fraction in turbulent flames, and F/A ratio in premixed combustion systems and practical engines .  The major advantages of LIBS-based F/A ratio measurement in practical combustion facilities are:

(1) ease of experimental setup with single-beam approach

(2) single-ended detection capability

(3) high spatial resolution.

Ns LIBS Mechanism

F/A Ratio Measurement at Elevated Pressure: Spectra and Image

[Hsu et al., Appl Opt 55 (28), 8042-8048 (2016)]


At elevated pressure generation of the high-density electrons by avalanche process causes huge signal instability in F/A ratio measurement.


Ultrashort-pulse laser-based plasma generation helps reduce or remove avalanche process.  The mechanism modifies to

Fs-LIBS is being explored for improving F/A ratio signal stability.