Tomographic reconstruction of a jet engine exhaust plume using an infrared hyperspectral imager

Midwave infrared (MWIR) measurements of a well-characterized JetCat turbine engine were made using a Telops infrared Fourier transform spectrometer (IFTS) hyperspectral imager (HSI), which utilizes a 320 × 256 indium-antimonide (InSb) focal plane array, calibrated to give a spectral distribution of radiance for each pixel within the image. Measurements were also made using a Santa Barbara focal plane IR imager (InSb, 320 × 256 array) that reported integrated radiance values in the MWIR. These measurements were made at varying engine RPM and different nozzle orientations to determine temperature and concentrations of the flow. The different orientations allow for the determination of the degree of asymmetry in the flow in two dimensions. The spectral information from these measurements was used to determine temperature and species concentrations of carbon dioxide and water vapor produced by the combustion of the Jet-A fuel. This was done utilizing the hyperspectral tomography (HT) process, which combines multiple measurement paths and high-resolution spectral data to determine the temperatures and concentrations of CO2 and H2O throughout the volume. Corresponding local temperature and pressure readings were taken in order to corroborate the radiometric data. Solution sets on a grid of 0.15-in. spacing based on measurements made at 2 cm − 1 spectral resolution were generated for six exhaust planes throughout the exhaust flow of a 4 in . × 1 in . rectangular exhaust nozzle. The HT process generated core plume temperature values within ±35 K of measured thermocouple data for exhaust planes near the nozzle exit plane. These results show the successful application of the HT algorithms to IFTS HSI data for temperature and species concentration reconstruction.