Optical sensors based on III-nitride photodetectors for flame sensing and combustion monitoring
2006
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 mm2 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
>103 at 430 and
308 nm, respectively. A full optical sensor system was built
and detectors operated at
120 °C in a combustion chamber, showing linear
responses within the dynamic range, maximum signal-to-noise ratios of
103 and
response times of
<1 s. An exponential association dependence between the optical
OH*/CH* CL signals and the gas/air ratios was found.
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