Mole fraction measurement through a transparent quarl burner using filtered Rayleigh scattering

Abstract

A filtered Rayleigh scattering system is developed and applied to measure the mole fraction of methane in a methane-air swirl flow through a transparent conical quartz quarl. Light scattering from the location where the laser beam is incident on the surface of the quarl is orders of magnitudes larger than Rayleigh scattering from the gas mixture of interest. This diffusive scattering is suppressed using molecular absorption by an iodine cell and using spatial filtering by an optical aperture. Residual stray light accounted for up to 5% of the total signal and had to be removed for accurate measurements. The flow consisted of a non-premixed mixture of methane and air in the central jet surrounded by a strong swirling air flow. Measurements were conducted at a height of 4 mm from the fuel tube's exit for six different conditions of the swirl flow to demonstrate the ability of the instrument to study the effects of swirl strength and fuel flow rate on the mixing process. By using a 4-leg pulse stretcher to allow higher laser energies in the probe volume, large collection optics and a reference iodine cell to monitor laser wavelength variations, standard deviations of ~ 0.006 in air and ~ 0.012 in a laminar methane flow were achieved for mole fraction measurements.

Quantitative gas property measurements by filtered Rayleigh scattering: a review

“…Improvements in laser and detector technology have enabled the use of modern unintensified CCDs for FRS [61,92,93], which have much less noise than ICCDs. Another option demonstrated in FRS experiments is the electron-multiplied CCD (EMCCD) [67,94,95]. EMCCDs have the signal gain capabilities of an ICCD but make use of on-chip multiplication instead of traditional image intensification, resulting in higher quantum efficiencies and spatial resolution.…”

“…Krishna et al [95] used a 1D FRS instrument to measure the mole fractions of nonreacting methane and air in a transparent conical quarl burner. Here, the 1D instrument allowed for higher measurement precision with a 95% confidence interval of 0.02 in the mean methane mole fraction.…”

50-kHz-rate Rayleigh and filtered Rayleigh scattering thermometry using a pulse-burst laser

“…The Mie scattering from soot particles in flames as well as from droplets also has a similar effect. In most applications, these interferences are several orders of magnitude larger than the Rayleigh scattering signal from the atoms and molecules in the flame and compromise the accuracy of Rayleigh-based measurements [23,24]. The filtered Rayleigh scattering (FRS) technique overcomes this difficulty by absorbing the Mie/surface scattering components in the scattered light using a molecular filter [25,26].…”

Assessment of the stabilization mechanisms of turbulent lifted jet flames at elevated pressure using combined 2-D diagnostics

“…Due to interferences from stray light and Mie scattering, the Rayleigh scattering technique is very challenging to implement in a pressurized vessel such as the High-Pressure Combustion Duct (HPCD). Filtered Rayleigh scattering is an alternative but it comes with its own challenges [28][29][30][31] and it is not yet available for the HPCD. Therefore, in the present study, the CH4 concentration needed to infer the equivalence ratio is measured using 2-D CH4 Raman scattering.…”