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

Abstract

The FLITES project (Fiber-Laser Imaging of gas Turbine Exhaust Species) aims to provide a videorate 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.

Relative Entropy Regularized TDLAS Tomography for Robust Temperature Imaging

“…Image Error (IE): IE is defined as the relative error between the reconstructed and the true image, indicating the overall quality of the reconstructed image. T -T T (19) where Trec and Ttrue represent the reconstructed and the true temperature distributions, respectively.…”

“…The proposed RETRO algorithm promises to be highly beneficial for industrial applications of TDLAS tomography, e.g. gas turbine exhaust imaging [19] and power-plant boiler diagnosis [20], where significant noise contamination of TDLAS measurements is common due to the [21] or covariance estimation [22]. Although this paper does not address statistical inversion techniques, the proposed relative entropy regularization can also be used in the statistical inversion framework.…”

Cost-Effective Quasi-Parallel Sensing Instrumentation for Industrial Chemical Species Tomography

“…Facilitated by the rapid technology development of the telecommunications industry, the last decade has witnessed accelerating advancement in the application of CST to solve industrial process engineering problems, e.g. vapour fuel imaging in internal combustion engines [9,10], gas turbine exhaust imaging [11,12], and power-plant boiler pollutant diagnosis [13].…”

Error Correction Method of TIADC System Based on Parameter Estimation of Identification Model

“…Data acquisition systems have been widely used in instrument measurement, communication, aerospace and medical fields [1][2][3][4][5][6][7][8]. As the core component of a data acquisition system, an analog-to-digital converter (ADC) is the only way to achieve analog/digital conversion, the performance of the ADC has a direct impact on the performance of the data acquisition system [9].…”