Raman/Rayleigh and mie-scattering measurements in a reverse flow reactor close to extinction

A reverse flow reactor (RFR) has been designed and developed to create a partially premixed flame with intense turbulent mixing and mean mixture fraction close to stoichiometric with fluctuations such as to keep most of the mixture within the flammability limits. This is used to study chemical kinetics effects on turbulent flame structure at high mixing rate χ, as well as providing a bank of data for testing and developing theoretical models. Flame characteristics and extinction limits have been studied. Pulsed spontaneous Raman/Rayleigh measurements are presented and compared with Mie-scattering, and thermocouple measurements. The data presented in this paper are for flames close to extinction at low resisdence times (2 to 10 ms) and show significant effects of finite rate chemistry. Partially premixed flames show a lower stability limit compared with the fully premixed situation indicating faster chemistry due to the existence of rich pockets, which may be responsible for stabilizing the flame at low equivalence ratio. The mean concentrations by Mie scattering technique and temperature measured by a thermocouple are in good agreement with that of the Raman/Rayleigh technique, but the rms levels of the Mie concentration are much higher because of the noise associated with the Mie signal due to differential diffusion and other effects.