Mixing characteristics and emissions of strongly-forced non-premixed and partially-premixed jet flames in crossflow

The effects of forcing and partial premixing on the mixing characteristics and pollutant emissions of jet flames in crossflow (JFICF) are studied experimentally for 70% methane/30% hydrogen fuel blend and propane. For forced non-premixed JFICF, the jet fuel flow is modulated using an acoustic speaker system, which results in a drastic decrease in flame length and soot luminosity. Simultaneous planar laser Mie scattering and CH* chemiluminescence imaging is used to detail the flame structure and dynamics of the reacting forced non-premixed JFICF, whereas acetone planar laser-induced fluorescence is used to quantify the near-field mixing of the non-reacting case. Forced JFICF are characterized by periodic ejections of high-momentum, deeply penetrating vortical structures, which draw air into the jet nozzle and enhance mixing in the near-field region of the jet. The mixing enhancement effectively partially premixes the jet fluid below the flame base. Flame luminosity images and exhaust gas emissions measurements show that forced non-premixed JFICF exhibit similar characteristics to unforced partially-premixed JFICF. Both strong forcing and partial premixing result in net reductions in NOx, but increases in CO and unburned hydrocarbons. NOx   scaling analysis is presented for both forced non-premixed and unforced partially premixed flames. Using flame volume arguments, EINOxEINOx scales with amplitude ratio, but does not scale with partial premixing. The difference in scaling behavior is attributed to differences in flame structure.