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

Accurate measurement of temperature in flames is a challenging problem that has been successfully addressed by hyperspectral imaging. This technique is able to provide maps of not only temperature T (K) but also of column density Q (ppm-m) of the main chemical species. Industrial applications, however, require cheaper instrumentation and faster and simpler data analysis. In this work, the feasibility and performance of multispectral imaging for the retrieval of T and QCO2 in flames are studied. Both the hyperspectral and multispectral measurement methods are described and applied to a standard flame, with known T and QCO2, and to an ordinary Bunsen flame. Hyperspectral results, based on emission spectra with 0.5 cm resolution, were found in previous works to be highly accurate, and are thus considered as the ground truth to compare with multispectral measurements of a mid-IR camera (3 to 5 mum) with a six interference filter wheel. Maps of T and Q obtained by both methods show that, for regions with T -1300 K, the average of relative errors in multispectral measurements is for T (and can be reduced to 2.5% with a correction based on a linear regression) and for Q. Results obtained with four filters are very similar; results with two filters are also similar for T but worse for Q.The authors acknowledge the financial support from EURAMET through 17IND04 EM PRESS 2 project. This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union Horizon 2020 research and innovation programme. This work has been supported also by the Madrid Government (Comunidad de Madrid-Spain) under the Multiannual Agreement with UC3M in the line of Excellence of University Professors (EPUC3M14), and in the context of the V PRICIT (Regional Programme of Research and Technological Innovation)

Direct hyperspectral dual-comb gas imaging in the mid-infrared

In this Letter, we present and experimentally validate the first direct hyperspectral dual-comb gas imaging system operating in the mid-infrared region. This method provides an unmatched combination of super-fine spectral characterization and high temporal resolution without the need for thermal contrast between the target molecules and the background. In a proof-of-concept experiment, the system has allowed us to perform precision hyperspectral imaging of butane in the 3.4 µm band with a time resolution of 1 s.Ministerio de Economía y Competitividad (TEC2017-86271-R); H2020 European Research Council (777222)

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

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. Non-perturbing 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.This project has received funding from the EMPIR programme co-financed by the Participating States and from the European Union’s Horizon 2020 research and innovation programme (Grant Number 14IND04