Tomographic imaging of carbon dioxide in the exhaust plume of large commercial aero-engines

Upadhyay, Abhishek and Lengden, Michael and Enemali, Godwin and Stewart, George and Johnstone, Walter and Wilson, David and Humphries, Gordon and Benoy, Thomas and Black, John and Chighine, Andrea and Fisher, Edward and Zhang, Rui and Liu, Chang and Polydorides, Nick and Tsekenis, Alex and Wright, Paul and Kliment, Joshua and Nilsson, Johan and Feng, Yutong and Archilla, Victor and Rodriguez-Carmona, Javier and Sanchez-Valdepenas, Jesus and Beltran, Marta and Polo, Valentin and Armstrong, Ian and Mauchline, Iain and Walsh, Douglas and Johnson, Mark and Bauldreay, Joanna and McCann, Hugh (2022) Tomographic imaging of carbon dioxide in the exhaust plume of large commercial aero-engines. Applied Optics, 61 (28). pp. 8540-8552. ISSN 1559-128X (https://doi.org/10.1364/AO.467828)

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Abstract

We report here the first implementation of chemically specific imaging in the exhaust plume of a gas turbine typical of those used for propulsion in commercial aircraft. The method used is chemical species tomography (CST) and the target species is CO2, absorbing in the near-infrared at 1999.4 nm. A total of 126 beams propagate transverse to the plume axis, along 7 m paths in a coplanar geometry, to probe a central region of diameter ≈1.5m. The CO2 absorption spectrum is measured using tunable diode laser spectroscopy with wavelength modulation, using the second harmonic to first harmonic (2f/1f) ratio method. The engine is operated over the full range of thrust, while data are recorded in a quasi-simultaneous mode at frame rates of 1.25 and 0.3125 Hz. Various data inversion methodologies are considered and presented for image reconstruction. At all thrust levels a persistent ring structure of high CO2 concentration is observed in the central region of the measurement plane, with a raised region in the middle of the plume assumed to be due to the engine’s boat tail. With its potential to target various exhaust species, the CST method outlined here offers a new approach to turbine combustion research, turbine engine development, and aviation fuel research and development.

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