Optical sensors based on Ⅲ-nitride photodetectors for flame sensing and combustion monitoring

摘要

Combustion control requires visible photodetectors to sense the CH~* CL emission at 430 nm that combined with a visible-blind UV photodetector allows us to obtain the OH~*/CH~* ratio. UV-visible P-InGaN/GaN multiple quantum well-N photodiodes with 15-18 mm~2 areas were fabricated to conduct OH~* (308 nm) and CH~* CL detection without external filters. Bandpass detectors at 230-390 nm and 360-450 nm presented linear responses over five decades and rejection ratios > 10~3 at 430 and 308 nm, respectively. A full optical sensor system was built and detectors operated at 120℃ in a combustion chamber, showing linear responses within the dynamic range, maximum signal-to-noise ratios of 10~3 and response times of < 1 s. An exponential association dependence between the optical OH~*/CH~* CL signals and the gas/air ratios was found.