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Show blowout behavior associated with turbulent diffusion flames along with further detailed analyses is given by Pitts [21] . Flame lift -off heights and flame lengths were measured for a variety of turbulent diffusion flames by Kalghatgi [14]. The fuels studied included hydrogen, propane, methane and ethylene, all of which were combusted in still air. Kalghatgi [14] found that the lift-off height for the turbulent diffusion flames investigated varied linearly with exit velocity, and did not depend on the burner diameter. In addition, an expression [14] was developed in which all of his flame lift-off height data collapsed to a single line, and is given by, Eq.2 where h is the flame lift -off height from the burner base, SL is the maximum laminar flame speed, Vo is the kinematic viscosity of the jet fluid, Uo is the jet velocity at the injector exit and pis the ratio of the density of the jet fluid, Po, to that of the ambient fluid, Ps. The correlation given by Eq. 2 is valid for density ratios, p, between 0.5 and 2. The density ratios associated with the tests performed in this study were typically between 2.7 and 2.9. Pollutant Emissions The development process of any new industrial burner for commercial furnace applications must address the pollutant emissions of that burner, particularly carbon monoxide (CO) and nitrogen oxides (NOJ, due to stringent guidelines and regulations. Emissions data are often quantified in a number of ways [22], with NOx measurements typically expressed as a concentration on a dry basis (e.g., ppmd) corrected to a given oxygen level (e.g., 3 % O2 dry basis). In addition, the power emission index of species i, Pli, is often used, which is defmed as the ratio of the mass of species i emitted, IDj,c:mitted, to the amount of fuel energy supplied [22], Plj = mj,emitted mf,burnedMtc Eq. 3 where I11r,bumcd is the mass of fuel burned and ~ is the fuel heat of combustion. The power emission index is independent of any dilution of the product stream. EXPERIMENT AL The experimental program can be divided into two parts. In the first part, a series of bench-scale experiments were undertaken to enhance the understanding of the mixing and combustion characteristics of gaseous fuels and oxidants under previously unexplored . conditions. The second broad set of experiments concentrated on establishing the pollutant emissions of the dilute oxygen combustion (DOC) concept in a laboratory-scale furnace. Bench-Scale Apparatus The bench-scale combustion apparatus allowed for the entrainment and combustion stability characteristics of gas jets to be studied in a variety of surrounding gas environments. Typically, the combustion traits of a natural gas jet were investigated in a high-temperature 4 |
