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Show Applications The simplicity of the chemiluminescence technique for visualizing NO production rates allows is to be applied to a wide variety of applications, ranging from the development of new low-NOx burners to diagnosing emission problems in existing combustion equipment installations. The main requirement for its use is the availability of optical access to observe the chemiluminescent emission. If necessary, the size of the optical access need only be large enough for the insertion of a fiber borescope to collect imagery of the emission. The easiest method for seeding the combustion reactants will usually be the addition of the boron seed compound to the fuel. Trimethyl borate ( T M B ) is an excellent seed compound for most applications because it can readily be added to liquid fuels, or vaporized and added to gaseous fuels. T M B poses no substantial safety or toxicity problems, although it is moisture-sensitive. For general characterization of the relative NO emission and fuel/air mixing characteristics of burners and combustors, measurements of the total chemiluminescence emission intensity and collection of video imagery for visual review are appropriate. A constant level of seed is added to the fuel for these measurements, although alternating between seed addition and no seed may allow better identification of regions of high chemiluminescent emission. For more detailed characterization of combustion equipment or diagnosing emission and mixing problems, the seed can be selectively added to individual fuel injectors. Alternatively, the seed can be added to all or selected portions of the combustion air flow to restrict the chemiluminescence to particular regions. (Experiments at Aerodyne Research have demonstrated that seeding of the air also effectively produces boron chemiluminescence from the flame region.) Because the chemiluminescence intensity is a strong function of the local equivalence ratio, this technique can also be very useful as an indicator for regions of incomplete or spatially and temporally varying mixing within burners and combustors. Conclusions A chemiluminescence technique has been identified for visualizing regions of high NO formation rates in combustion. Turbulent jet flame experiments with hydrogen showed very close correlation between the measured boron chemiluminescence intensity and the N O production rate for similar flames measured by Driscoll.34 Combustion modeling with detailed mechanisms for boron seed decomposition, boron chemiluminescence, and N O formation showed good correlation between N O production rates and boron chemiluminescence intensity for methane and hydrogen combustion at atmospheric and elevated pressures and over a range of equivalence ratios. A low boron seeding rate was found to be adequate for boron chemiluminescence visualization in nonluminous flames. Soot luminescence was found to interfere with observation of the boron chemiluminescence at low seeding rates. However, spectral measurements of the soot luminescence and boron chemiluminescence indicated that this interference can be reduced to low levels in luminous methane flames and to very low levels in nonluminous flames though the use of appropriate interference filters. 9 |