Investigation and validation of 2000 nm region for the simultaneous measurement of water vapour and CO2 concentration and temperature

Previous work on ratio thermometry has focused on water vapour spectral features around the 1300-1400 nm range in the near-infrared, and regions around 4000-5000 nm in the mid-infrared. Both of these spectral regions pose a problem for multi-beam, multi-species imaging systems required for chemical species tomography, due to the lack of suitable optical amplification to provide the necessary power for the required number of beams. In the mid-infrared there is also the added complexity of attempting to distribute the light in the required optical beam array without the use of optical fibre networks.
We have previously used thulium doped fibre amplification and an optical fibre splitter network, designed for 2000 nm, to carry out 2f/1f TDLS-WMS across 126 beam paths and image CO2 concentration distribution of the exhaust of a large-scale, commercial aero-engine. A single DFB seed laser was modulated and used as the seed for the optical amplification stage. All of the TDLS-WMS
modulation characteristics were preserved during the amplification of the light from 2 mW up to 1 W, prior to distribution to the 128 launch optics. In this paper, we show a proposed scheme to further develop this system to allow the combined measurement of water vapour and CO2 concentrations, as
well as the measurement of temperature, using a 128-beam optical beam path arrangement in both engine exhaust and within mid-pressure combustion chambers. We will provide details of the spectral investigations, and the in-house validation of the chosen spectral features of water vapour and CO2
using our newly designed high temperature spectrometer. Furthermore, we will show a full schematic of the proposed system and initial results of single beam, and multi-beam trials, for measurements from the exhaust of an auxiliary power unit.