Validation of Emission Spectroscopy Gas Temperature Measurements Using a Standard Flame Traceable to the International Temperature Scale of 1990 (ITS-90)

Abstract

Accurate measurement of post-flame temperatures can significantly improve combustion efficiency and reduce harmful emissions, for example, during the development phase of new internal combustion engines and gas turbine combustors. Nonperturbing optical diagnostic techniques are capable of measuring temperatures in such environments but are often technically complex and validation is challenging, with correspondingly large uncertainties, often as large as 2 % to 5 % of temperature. This work aims to reduce these uncertainties by developing a portable flame temperature standard, calibrated via the Rayleigh scattering thermometry technique, traceable to ITS-90, with an uncertainty of 0.5 % of temperature (k = 1). By suitable burner selection and accurate gas flow control, a stable, square, flat flame with uniform post-flame species and temperature is realised. Following development, the standard flame is used to validate two IR emission spectroscopy systems, both measuring the line-integrated emission spectra in the post-flame region. The first utilises a Hyperspectral imaging FTIR spectrometer capable of measuring 2D species and temperature maps and the second, a high-precision single line-of-sight FTIR spectrometer. In the central post-flame region, the agreement between the Rayleigh and FTIR temperatures is within the combined measurement uncertainties and amounts to 1 % (k = 1) of temperature.

Multispectral Mid-Infrared Camera System for Accurate Stand-Off Temperature and Column Density Measurements on Flames

“…The flame was developed by the British National Physical Laboratory (NPL), and its temperature was measured by Rayleigh scattering thermometry (a technique traceable to the International Temperature Scale of 1990, ITS-90) at NPL, and by Fourier Transform Infrared (FTIR) emission spectroscopy by two research groups, one at the Technical University of Denmark (DTU) and the other at Carlos III University of Madrid (UC3M). It was found that the agreement between all measurements amounted to 1%, that is, ∆T ∼ 20 K for flame temperatures ∼2000 K [3]. This is a very good result that demonstrates the accuracy of flame temperature measurement based on emission spectroscopy.…”

Measurement of temperature in a standard flame using multispectral thermography

“…It must be stressed that simulated spectra have been calculated assuming a flat profile of (T,Q), and therefore the retrieved values must be understood as a line-of-sight effective average of the flame temperature. However, temperature profiles in the standard flame measured are very flat, and systematic errors due to spatial nonuniformity of temperature have been estimated to be smaller than 15 K [2]. Figure 2 shows the temperature maps obtained with the multispectral (left) compared to the hyperspectral (right) measurements.…”

“…Then, these calculated emission spectra can be used to fit iteratively a measured spectra, the best fit providing a retrieved (T,Q) value. This procedure has been applied, for the spectral region of CO2 emission, to spectra acquired by an FTIR hyperspectral imager with 0.5 cm -1 spectral resolution, and has demonstrated its ability to measure temperature in a standard flame (T≈2000 K) to an estimated uncertainty of ± 5 K (i.e., ≈0.25%) [2].…”

Measurement of Flame Temperature Using Simultaneous Dual- line Atomic Absorption of Two Elements

“…Therefore, flame temperature is a vital parameter for FAAS and is defined as the exterior characterization of an average kinetic energy of the flame. 5,6 Measurement of flame temperature is always an important research topic for physicists and spectrochemists. Although several methods have been developed for this purpose, they can mainly be divided into physical and optical methods.…”

“…These are mainly based on the thermometric atoms distribution and obey the Boltzmann distribution under local thermodynamic equilibrium (LTE) of a certain element at different energy levels of the atomization, such as a flame. 6 A premixed laminar air/acetylene flame is considered to follow the LTE conditions based on frequent collision of the particles in the flames, such as electrons, ions, atoms, molecules, and so on. 7,8 Therefore, the flame temperature can be deduced by dual-line atomic spectroscopy methods involving two different transitions with different excitation energies.…”