Laser-induced spark for measurements of the fuel-to-air ratio of a combustible mixture

Abstract

This work investigates the use of the laser-induced gas breakdown for fuel-to-air ratio measurements. In essence, we examine the late time behavior of the line radiation at the wavelength of the H α-lines and the O I triplet emitted from the laser-induced spark in CH 4–air mixtures. Sparks were produced using a single-mode, Q-switched Nd-YAG laser. The laser produced a beam of 6 mm in diameter at the wavelength of 1064 nm and a pulse duration of 5.5 ns. For the equivalence ratio from 0.1 to 5.0, the radiation intensity ratio of the H α-lines to the O I triplet increased linearly with the equivalence ratio. For the laser energy from 10 to 50 mJ it was independent of the laser energy when the laser energy was higher than 20 mJ. The technique, therefore, has a potential for measuring the fuel-to-air ratio of a combustible flow environment.