Thermometry for turbulent flames by coherent anti-Stokes Raman spectroscopy with simultaneous referencing to the modeless excitation profile

Abstract

An optimal system for temperature measurements by coherent anti-Stokes Raman spectroscopy (CARS) in turbulent flames and flows is presented. In addition to a single-mode pump laser and a modeless dye laser, an echelle spectrometer with a cross disperser is used. This system permits simultaneous measurement of the N 2 CARS spectrum and the broadband dye laser profile. A procedure is developed to use software to transform this profile into the excitation profile by which the spectrum is referenced. Simultaneous shot-to-shot referencing is compared to sequential averaged referencing for data obtained in flat flames and in room air. At flame temperatures, the resultant 1.5% imprecision is limited by flame fluctuations, indicating that the system may have a single-shot imprecision below 1%. At room temperature, the 3.8% single-shot imprecision is of the same order as the best values reported for dualbroadband pure-rotational CARS. Using the unique shot-to-shot excitation profiles, simultaneous referencing eliminates systematic errors. At 2000 and 300 K, the 95% confidence intervals are estimated to be Ϯ20 and Ϯ10 K, respectively.

Spray flame structure in conventional and hot-diluted combustion regime

“…A brief description of the CARS system and data post-processing procedure is reported here but for further details the reader is referred to van Veen and Roekaerts [38,39]. The rovibrational CARS system is based on an injection-seeded, frequency-doubled Nd:YAG laser (Spectron SL805 SLM).…”

Development of a dual-pump coherent anti-Stokes Raman spectroscopy system for measurements in supersonic combustion

“…In the presence of beam steering, the beam overlap changes on a shot-to-shot basis; therefore, the spectral profile of the Stokes beam changes at every shot. A shot-to-shot referencing scheme as used in [18] cannot take into account these changes in the excitation profile because it would be impossible to reproduce the same beam overlap geometry in two different volumes.…”

Experiments for Combustion-LES Validation

“…7 presents the temperature measurements along the vertically orientated symmetry axis. Along with the wall temperature measurement, gas phase temperatures were measured by ro-vibronic N 2 CARS taking advantage of the facility at Delft University [71]. These diagnostics at the surface and within the near wall region demonstrate that a simultaneous application allows the estimation of wall-normal temperature gradients.…”