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Oxides of nitrogen emissions from turbulent jet flames: Part II—Fuel dilution and partial premixing effects

1993; Elsevier BV; Volume: 93; Issue: 3 Linguagem: Inglês

10.1016/0010-2180(93)90107-e

1556-2921

Stephen R. Turns, Franklin H. Myhr, Ramarao V. Bandaru, Ehren R. Maund,

Atmospheric chemistry and aerosols

Measurements of NOx emission indices, flame radiant fractions, and visible flame length were made for turbulent, nonpremixed, jet flames for which various amounts of inert diluent or air were mixed with the fuel. The objective of the study was to explore further the role of flame radiation in NOx production in jet flames. Vertical free jet flames were stabilized on a 4.12 mm diameter straight-tube burner. Four fuels, CH4, C2H4, C3H8, and a 95% CO5% H2 mixture (by mass); three inert diluents, N2, Ar, and CO2; and air premixing were employed in parametric tests. Complementary dilution experiments were run with laminar jet flames using the three hydrocarbon fuels and N2. For the turbulent flames, the results showed that the effects of dilution and premixing were strongly dependent on fuel type. Flame temperatures and NOx emissions increased when the more sooting fuels (C3H8 and C2H4) were diluted or partially premixed, resulting in increased NOx emissions. The opposite trend was observed for the nonluminous COH2 flames. Using the results reported here and from Part I [1] of this study, the effects of residence time, flame temperature, and departure from equilibrium on NOx emissions, regardless of what parameter affected the change, were well characterized by regressing characteristic NOx production rates as a function of nonadiabatic characteristic flame temperatures and global residence times. Separate regressions for the hydrocarbon and COH2 flames showed a weaker dependence of NOx on temperature for the hydrocarbons, suggesting that the prompt NO mechanism is quite active in these flames. The laminar flame experiments demonstrated the importance of the relative locations of NOx-producing regions and soot-containing (strongly radiating) regions of the flame.