<title>Possibilities of NOx online control by using degenerate four wave mixing spectroscopy on intermediate species</title>

Abstract

ABSTRACT The DFWM (Degenerate Four Wave Mixing), used as a laser spectroscopy for gas phase trace detection, is receiving agreat deal of attention for on-line applications in industrial combustion diagnostics. Low release of NOx requires acomplete control of nascent NO formation, i.e. of the combustion chemistry involving the OH radical, and space resolvedtemperature measurements on each species. Both NO and OH have been detected on small hydrocarbon/air flames byDFWM in forward BOXCARS geometry. NO distribution has been investigated by exciting the y band, temperature andconcentration have been calculated after spectral simulation and calibration on doped flames. OH spectra of the A2 - x211, on the thndamental (0,0) and first vibrationally excited transition (1,0), have been used to monitor the radical spacedistribution and its temperature. Line broadening, shifting and intensity borrowing phenomena related to saturation havebeen investigated in order to correctly model the spectra. The technique has been used to detect OH (1,0) band in thecombustion chamber of a dry low NOx 130 KW prototype burner, obtaining relative OH concentration profiles. A singleshot broad band system, contemporary detecting a few OH lines in the (0,0) transition, has been built to operate inturbulent regime.Keywords: Combustion, OH, NOx, DFWM