Structure of ethylene based nonpremixed flames stabilised on a JHC burner

Abstract

The spatial distribution of OH, formaldehyde (H2CO) and temperature imaged by laser diagnostic techniques are presented using the Jet in Hot Coflow (JHC) burner. The measurements are of nonpremixed ethylene jet flames with various diluents in a hot and highly diluted coflow. These conditions emulate those of Moderate or Intense Low Oxygen Dilution (MILD) combustion. With a 3% O2 coflow a faint outline is seen to extend to the jet exit plane, whereas the higher 9% O2 flames visually appear lifted. In flames which appear lifted, a continuous OH surface has been identified which extends to the jet exit. Nevertheless, at the “lift-off” height a transition from weak to strong OH is observed. H2CO is also observed to exist upstream of the transition point, further evidence of a pre-ignition reaction taking place in the “lifted” flames.