Characteristics of nitric oxide formation rates in turbulent nonpremixed jet flames

The formation of oxides of nitrogen, NOx, in turbulent nonpremixed flames is experimentally analyzed making use of velocity, temperature, and major species concentration measurements in jet propane flames. The analysis considered the contributions of Zeldovich (thermal) and Fenimore (prompt) mechanisms at different locations of attached vertical flames with Reynolds numbers of 20,400 and 37,600. The analysis of NO mass formation rates suggests that prompt mechanism dominates NO formation throughout the flames, with peak formation rates occurring in the rich flame region, at locations r/x approximately equal to 0.08, where r and x are the radial and axial coordinate, respectively. NO concentrations are shown to decrease with Reynolds number, as the gas residence times are reduced, although mass flow rates of NOx per unit mass flow rate of fuel are independent of Reynolds number. (C) 1999 by The Combustion Institute.