Reaction Chemiluminescence and its Relationship to Emissions and Stability in a Model Industrial Burner

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REACTION CHEMILUMINESCENCE AND ITS RELATIONSHIP TO EMISSIONS AND STABILITY IN A MODEL INDUSTRIAL BURNER M. M. Miyasato and G. S. Samuelsen UCI Combustion Laboratory University of California Irvine, C A 92697-3550 [phone] [e-mail] Presented at the AFRC 1999 Fall International Symposium San Francisco. October 3-6. 1999 INTRODUCTION In order to meet the increasingly stringent emissions targets for stationary power production, combustion applications are moving toward a lean premixed strategy with the potential for high levels of flue gas recirculation. Although effective at reducing N O x emissions, this type of operation suffers from potential increases in C O emissions and decreases in stability. In order to operate safely and with the highest performance, a sensor capable of gauging stability is desired. Unlike the current industrial flame scanners which serve an "on-off' function, the desired stability sensor would quickly alert the operator of the onset of instability, thereby widening the operability envelope by encompassing regimes formerly believed "unstable." To be successful, this sensor must be robust, inexpensive, and semi-quantitative. This paper describes the investigation of flame radical chemiluminescence as a potential feedback sensor. The flame chemiluminescence measured were for O H , C H , and CO2. BACKGROUND The yellow-orange emission from radiating carbon particles is a well known charcteristic from rich or diffusion-dominated flames. Due to stringent N O x emissions regulations, these flames have long since been replaced by better mixed, lean reactions. These leaner, lower temperature reactions are typically blue-green in color due to chemiluminescence from C H and C2 flame radicals. The hydroxl radical, O H , and C 0 2 are also strong emitters in the ultraviolet. The reaction pathways for these reactions and the wavelengths at which they have the strongest emission are provided below: Table 1: Chemiluminescence Reactions and Dominant Waveleneth Emissions Reaction CH + 02 ->CO + OH* C2 + OH ^CO + CH* CH2 + C^>C2* + Hi co + o -> co2* Wavelength (nm) 306 431 517 310-600 Ref. 3 3 3 6 Numerous studies have been conducted on flame chemiluminescence as an indicator for different reaction characteristics dating back to the 1950's (Samaniego et al., 1995 provides good historical references). The interest in chemiluminescence is high since the measurement is straightforward, non-intrusive, continuous, and intuitively related to the general reaction structure. Since the specified wavelength of light emission is directly related to the number of radicals within the field-of-view, the intensity of the collected signal is proportional to the concentration of the radical species. As a result, studies have tried to empirically relate the chemiluminescence emission to reaction species concentrations, temperature, and heat release.