TDLAS Tomography System for Online Imaging and Dynamic Process Playback of Temperature and Gas Mole Fraction

Abstract

Tunable diode laser absorption spectroscopy (TDLAS) tomography enables online diagnosis of dynamic flames by imaging its temperature variations and exhaust gases, owing to its rapid response. Each tomographic image requires huge laser absorption spectrum data along multiple laser paths. For a high temporal resolution, the data sampling rate needs to be as high as possible which challenges the hardware implementation of parallel data acquisition of multiple channels. An online TDLAS tomography system was designed on field programmable gate array (FPGA) and PC for temperature and gas mole fraction distributions measurement. An on-chip parameter extraction module based on digital lock-in amplifier (DLIA) extracts absorption spectrum parameters at 1000 frames per second (FPS), and the framerate of real-time reconstruction on host PC can reach up to 302 FPS. A high-speed buffer on FPGA termed as transient spectrum recorder continuously records the latest five seconds of raw data. Both the playback of absorption spectrum parameters and raw data provide a way for detailed and in-depth understanding of the dynamic combustion process. Experiments were carried out by using an alcohol burner to evaluate the online monitoring and offline playback abilities of the system.