Temperature measurement with a conditional two-line OH-PLIF technique in an actively controlled coaxial jet flame

Abstract

A novel flame temperature measurement technique based on two-line OH planar laser-induced fluorescence (PLIF) is presented. In order to measure temperature of an unsteady flame using a single excitation laser and a single ICCD camera, a new conditional image processing method has been introduced. In this method, ensemble-averaged OH fluorescence intensities at the flame front, which are taken by two excitation lines, are used, and the mean temperature at each streamwise position is calculated. The present thermometry is applied to a methane/air coaxial jet flame, which is actively controlled by periodically driven magnetic flap actuators. The uncertainty interval at 95% coverage is estimated as +130K and -120K at the mean flame temperature of 2000K. The measured mean temperatures of controlled flames coincide with the theoretical adiabatic flame temperatures within the uncertainty intervals. When the stoichiometric mixture is supplied, the mean flame temperature is the highest (∼2200K), and thus CO emission is drastically reduced. On the other hand, when a lean flammable limit mixture is supplied, the mean temperature is decreased to 1 600 K, and this results in the increased CO emission.