Affiliations: Thermofluids Section, Department of Mechanical
Engineering, Imperial College of Science, Technology and Medicine, London SW7
2BX, UK.
Abstract: Photography and chemieluminescence from CH radicals have been used
to identify the reaction zones and quantify the areas and shapes of
kerosene-fuelled flames with swirl numbers of 0.7 and 0.8 and an overall
equivalence ratio of 0.25. The air flow was oscillated at a frequency of 350 Hz
and the results suggest that the oscillations caused a sequence of vortex rings
at the burner exit and that these distorted the reaction zone and increased its
area in the near burner region leading to an overall shorter flame. For the
swirl number of 0.7, the flame was lifted and the oscillations led to an
increase in the average lift off length whereas the higher swirl number caused
an attached flame with and without oscillations. The stretch rate, evaluated
from the variation of the flame area in time, was higher for the lifted flame
suggesting that lift off was caused by local extinction.