Structure of turbulent nonpremixed syngas flames at high pressure

Abstract

The effects of both pressure and Reynolds number on the structure of turbulent nonpremixed flames are investigated experimentally. Syngas (CO/H2/N2) flames with constant composition are examined at pressures up to 12 bar and at Reynolds numbers up to 66,800. The baseline atmospheric pressure flame is identical to the “chnA” flame of the turbulent nonpremixed flames (TNF) workshop. Low-speed OH-PLIF is used to reveal the flame structure in a small region 7 diameters downstream of the nozzle. The thickness of the OH layer decreases monotonically with pressure. Increasing pressure inhibits local extinction when comparing conditions at constant Reynolds number; an effect of changing exit strain rate. Neither changes in Reynolds number nor changes in pressure affect the mean flame front location. Corrugation of the flame front is highly sensitive to changes in Reynolds number but relatively insensitive to changes in pressure. Blow-off velocity limits the highest Reynolds number achievable by the TNF jet flames. By increasing the pressure, this ceases to be the limiting parameter, meaning that we can study the effect of Reynolds number on the structure of the Sandia-ETH syngas jet flame over a wider range of turbulence, approaching what is encountered in practical combustors.