Mid-Infrared Polarization Spectroscopy Measurements of Species Concentrations and Temperature in a Low-Pressure Flame

Abstract

We demonstrate quantitative measurements of methane (CH 4 ) mole fractions in a low-pressure fuel-rich premixed dimethyl ether/oxygen/argon flat flame (Φ = 1.87, 37 mbar) using mid-infrared (IR) polarization spectroscopy (IRPS). Non-intrusive in situ detection of CH 4 , acetylene (C 2 H 2 ), and ethane (C 2 H 6 ) in the flame was realized by probing the fundamental asymmetric C–H stretching vibration bands in the respective molecules in the spectral range 2970–3340 cm −1 . The flame was stabilized on a McKenna-type porous plug burner hosted in a low-pressure chamber. The temperature at different heights above the burner (HAB) was measured from the line ratio of temperature-sensitive H 2 O spectral lines recorded using IRPS. Quantitative measurements of CH 4 mole fractions at different HAB in the flame were realized by a calibration measurement in a low-pressure gas flow of N 2 with a small admixture of known amount of CH 4 . A comprehensive study of the collision effects on the IRPS signal was performed in order to quantify the flame measurement. The concentration and temperature measurements were found to agree reasonably well with simulations using Chemkin. These measurements prove the potential of IRPS as a sensitive, non-intrusive, in situ technique in low pressure flames.

Mid-infrared laser polarization spectroscopy for quantitative measurement of species and temperature: a review

“…Comparing Eqs. (15) and (16), the PS signal is only dependent on the probe beam intensity under the saturating conditions. In many cases, the saturating conditions are usually selected to perform the experiments because of the low effect of intensity fluctuations and high signal intensity when using high pump energy.…”

“…Their experimental results showed a good agreement with the simulation spectra. More recently, by probing the C-H asymmetric stretching in the spectral range of 2970-3340 cm −1 , Sahlberg et al [16] demonstrated the non-intrusive detection of C 2 H 6 , C 2 H 2 , and CH 4 in the low-pressure flame. The collision effects on the IRPS signal were reported at sub-atmospheric pressure of 37 mbar.…”

“…On the other hand, IR polarization spectroscopy has the capability to be used as a tool to determine the temperatures of combustion species under low-pressure flames. In 2019, Sahlberg et al [16] investigated flame temperature via recording the line ratios of hot water around 3.1 µm. In their work, the H 2 O spectral line was selected, because its state energy difference is less sensitive to the changes in flame temperature.…”

“…In 2005, Li et al [14] performed the first IRPS measurement in laminar flames to detect CO 2 and H 2 O at atmospheric pressure, followed by measurements of OH and H 2 O at low-pressure laminar flame [15]. In addition, IRPS has also been used to measure the temperature of minor species in flames [16]. In contrast to other coherent techniques, IRPS can provide reasonable spatial resolution to detect species with instantaneous visualization of two-dimensional distribution [4].…”

Preparation and Performance of a Waterborne UV/Al Low Infrared Emissivity Coating

“…According to Figure 4 and Table 7, the wavenumber of 3343 cm −1 was an -OH stretching vibration [24]. A wavenumber of 1724 cm −1 was the characteristic absorption peak of C=O [25], while wavenumber 1530 cm −1 was the N-H bending vibration of the amide II band [26], indicating that there were a large number of carbamate bonds in the product.…”