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Show 9. Conclusion The present research shows that the CGRI burner, as intended, allows operation at high air preheats with very low N O x emissions. The burner may, in fact, represent the practical limit of low-NOx performance obtained with natural furnace aerodynamics (without, for example, mechanical, external recirculation of cooled fluegas). For given levels of air preheat and exhaust-gas temperature, it may not be possible to achieve lower N O x emissions. However, this performance is won at a cost in stability. Thus, the burner seems definitely unsuitable for use in cool furnaces The research, through a combination of experiment and theory, gives clear indications of the structure of C G R I burner flames. It provides guidance for optimum burner design, scaleup and operation. It has drawn attention to, and prompted a treatment of, some generally interesting problems, such as the strong-jet/weak-jet problem. However, it does not adequately answer all questions of practical and scientific interest. In particular, work on the following issues would be practically and/or scientifically worthwhile: 1. Exploration of the effects of the burner design variables in potentially significant areas not yet explored. The obvious candidates for such work are: (a) With the present air jet angle of 02 = 10°, the use of fuel jet angles 0\ smaller than 30°, or generally, limit angles P\2 between adjacent fuel and air jet axes smaller than 21°. The smaller fin is, the smaller is the flame, and the greater the combustion stability. However, at some point the N O x emissions are likely to rise to unacceptable levels. Thus, evidence for deciding an optimum is needed. (b) The use of air jet angles 02 other than 10°, both greater and smaller. Decreasing 02 diminishes the entrainment of recirculating combustion products by the air jets, but it is also expected to decrease the lateral dimensions of the combustion zone or flame. Evidence for deciding an optimum is needed. (c) The use of numbers, N, of fuel ports and of air ports other than seven. The Canadian gas Research Institute (CGRI) found indications in their early work that small values of N are disadvantageous for burner performance. However, definitive evidence for deciding an optimum is needed. 2. Comprehensive investigation of the fields of composition, temperature and velocity of CGRI burner flames for afew selected burner designs and operating conditions, to provide detailed information on the phenomena at a local level and support the development of a fundamental mechanistic assessment of burner performance. 3. Mechanistic mathematical modelling of CGRI burner flames in furnace environments, solving the governing partial differential equations numerically, with the help of suitable simplifying hypotheses (the approach popularly called computational fluid dynamics or CFD). W e currently have work underway on item 1(a), with our new X B M 3 burner which allows use of fuel nozzles providing 0\ < 30°, to as low as 0\ = 0 (our X B M 2 burner, the vehicle of the present investigation, didn't). If and when we build the X B M 4 burner, which has been designed, we will be able to deal with items 1(b) and 1(c). W e have a study underway on item 2, using gas 24 |