Measurement of acetylene concentration in laminar flat flames by diode laser cavity ring-down spectroscopy

Continuous-wave cavity ring-down spectroscopy (cw-CRDS) has been applied to measure trace gas concentration in situ in flames using a near-infrared diode laser. Acetylene concentration was measured in laminar flat flames of premixed ethylene and air at atmospheric pressure for a range of fuel–air ratios. This was achieved by recording CRDS spectra of the P17e feature of acetylene near 1535 nm. The resulting concentration profiles show higher acetylene concentrations for increasing equivalence ratio. Downstream of the reaction zone, a trend of decreasing acetylene concentration with increasing height above the burner surface was observed in each of the flames studied. This would be consistent with the consumption of acetylene in the formation and growth of polycyclic aromatic hydrocarbons (PAHs) and soot. Extinction data are also reported and reveal significant broadband optical losses in the richer flames, including prior to the onset of soot formation, which may be attributable to near-infrared absorption by aromatic species.