Development of a Dual-Pump CARS System for Measurements in a Supersonic Combusting Free Jet

Abstract

This work describes the development of a dual-pump CARS system for simultaneous measurements of temperature and absolute mole fraction of N 2 , O 2 and H 2 in a laboratory scale supersonic combusting free jet. Changes to the experimental set-up and the data analysis to improve the quality of the measurements in this turbulent, high-temperature reacting flow are described. The accuracy and precision of the instrument have been determined using data collected in a Hencken burner flame. For temperature above 800 K, errors in absolute mole fraction are within 1.5, 0.5, and 1% of the total composition for N 2 , O 2 and H 2 , respectively. Estimated standard deviations based on 500 single shots are between 10 and 65 K for the temperature, between 0.5 and 1.7% of the total composition for O 2 , and between 1.5 and 3.4% for N 2 . The standard deviation of H 2 is ~10% of the average measured mole fraction. Results obtained in the jet with and without combustion are illustrated, and the capabilities and limitations of the dual-pump CARS instrument discussed.

Dual-Pump CARS Measurements in the University of Virginia's Dual-Mode Scramjet: Configuration "A"

“…Uncertainties in our measurement techniques have been discussed in detail by Magnotti. 12 The instrument precision stated therein (defined as ± one standard deviation) is <3.3% in temperature, <1.8% in O 2 and <3.4% in N 2 , both as a percentage of the total composition, and <10% in H 2 mole fractions, as a percent of the measured value. Mole fraction bias uncertainty for temperatures above 600 K is 0.5%, 1.5% and 1% of the total composition for O 2 , N 2 and H 2 , respectively.…”

“…12,18 The second pump frequency offset was 712-714 cm -1 for the non-reacting cases and was 618-621 cm -1 for the reacting cases. (The larger offset for the nonreacting cases was to raise the intensity of the signal from the H 2 lines by moving the frequency difference between the narrow-band and broad-band dye lasers towards the Raman shift of H 2 , at the expense of bringing the O 2 spectrum closer to the N 2 spectrum.)…”

Dual-Pump CARS Measurements in the University of Virginia's Dual-Mode Scramjet: Configuration "C"

“…The published standard deviation of the random errors of our CARS technique, based on measurements in an adiabatic flat flame ( ), is between 0.015 and 0.034 for N 2 (in absolute mole fraction), between 0.005 and 0.017 (in absolute mole fraction) for O 2 , and ~10% of the measured mole fraction for H 2 . 8 The standard deviation of the total oxygen error may be estimated for each measurement from the published errors (assumed independent) using Eqn. 6:…”

Miniaturized Combustor for Supersonic Methane–Air Flames

“…Despite that, incoherent Raman techniques have been used in isobaric environments using windows [13,14]. Optically accessible supersonic flames have been developed in the past that do not hinder techniques such as incoherent Raman [15,16]. These flames, however, operate in a mode that mixes and burns the fuel and oxidizer in a coflow shear layer external to the burner.…”