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A Custom, High-Channel-Count Data Acquisition System for Chemical Species Tomography of Aero-Jet Engine Exhaust Plumes

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Original languageEnglish
Pages (from-to)1-16
Number of pages16
JournalIEEE Transactions on Instrumentation and Measurement
StateAccepted/In press - 4 Jan 2019

Abstract

The FLITES project (Fiber-Laser Imaging of gas Turbine Exhaust Species) aims to provide a video-rate imaging (100 fps) diagnostic tool for application to the exhaust plumes of the largest civil aero-jet engines. This remit, enabled by chemical species tomography (CST) currently targeting Carbon Dioxide (CO2), requires system design that facilitates expansion of multiple parameters. Scalability is needed in order to increase imaging speeds and spatial resolutions and extend the system towards other pertinent gases such as the oxides of Nitrogen and Sulphur and unburnt hydrocarbons. This paper presents a fully-scalable, non-invasive instrument for installation in a commercial engine testing facility, technical challenges having been tackled iteratively through bespoke optical and mechanical design, and it specifically presents the high-speed data acquisition system (DAQ) required. Measurement of gas species concentration is implemented by tunable diode laser absorption with wavelength modulation spectroscopy (TDLAS-WMS) using a custom, high-speed 10-40 MS/s/channel 14-bit DAQ. For CO2 tomography, the system uses 6 angular projections of 21 beams each. However, the presented DAQ has capacity for 192 fully-parallel 10-Hz to 3-MHz differential inputs, achieving a best-case SNR of 56.5 dB prior to filtering. Twelve Ethernet-connected digitization nodes based on field-programmable gate array (FPGA) technology with software control, are distributed around a 7-m diameter mounting “ring”. Hence, the high data rates of 8.96-Gb/s per printed circuit board (PCB) and 107.52 Gb/s for the whole system, can be reduced using local digital lock-in amplifiers (DLIAs). We believe this DAQ system is unique in both the TDLAS and CST literature.

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