Progress towards non-intrusive optical measurement of gas turbine exhaust species distributions

Paul Wright, David McCormick, Krikor Ozanyan, Mark Johnson, John Black, Edward Fisher, Andrea Chighine, Nick Polydorides, Hugh McCann, Yutong Feng, Khouler Khan, Paul Bastock, Fuqiang Jia, Dan Hewak, Johan Nilsson, Michael Lengden, David Wilson, Ian Armstrong, Thomas Benoy, Walter Johnstone

Research output: Chapter in Book/Report/Conference proceedingConference contribution


We report on the development of three systems intended to provide fast, non-intrusive measurement of cross-sectional distributions of pollutant species within gas turbine exhaust flows, during ground-based testing. This research is motivated by the need for measurement systems to support the introduction of technologies for reducing the environmental impact of civil aviation. Tomographic techniques will allow estimation of the distributions of CO2, unburnt hydrocarbons (UHC), and soot, without obstruction of the exhaust, bypass or entrained flows, from measurements made in a plane immediately aft of the engine. We describe a CO2 imaging system that performs wavelength modulation spectroscopy (WMS) simultaneously on 126 beam paths. Its novel architecture uses a Tm-doped fiber amplifier to generate sufficient optical power for the entire beam array (> 3 W) from a single 1997.2 nm diode-laser seed, reducing cost and enabling fully parallel detection and signal recovery. Various optical propagation issues are considered, including those arising from the varying degrees of interaction with the exhaust flow that exist within the beam array, as well as pointing errors arising from the limited rigidity of the measurement system's structure. We also report first steps towards a similar UHC measurement system, operating in the mid-infrared (MIR) region and targeting partially decomposed or oxidized fuel constituents, including formaldehyde and propene. Progress towards the chalcogenide glasses and fibers, needed for light delivery and/or amplification at these wavelengths is described. Finally, we report on the development status of a tomographic soot imaging system, based on laser induced incandescence (LII). We have demonstrated both long (192 ns) and short (17 ns) pulse variants of LII using fiber laser sources. Single path tests on a laboratory soot generator and, in the long pulse case, on a jet engine have confirmed that the energy and beam quality available from the fiber lasers is sufficient to enable an autoprojection approach, using just two intensified CCD cameras having 'near-orthogonal' views, with respect to the excitation laser.

Original languageEnglish
Title of host publication2015 IEEE Aerospace Conference, AERO 2015
PublisherInstitute of Electrical and Electronics Engineers (IEEE)
ISBN (Electronic)9781479953790
Publication statusPublished - 1 Jan 2015
Event2015 IEEE Aerospace Conference, AERO 2015 - Big Sky, United States
Duration: 7 Mar 201514 Mar 2015


Conference2015 IEEE Aerospace Conference, AERO 2015
Country/TerritoryUnited States
CityBig Sky


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