Growth characteristics of polycyclic aromatic hydrocarbons in dimethyl ether diffusion flame

The growth characteristics of polycyclic aromatic hydrocarbons (PAHs) in laminar dimethyl ether (DME) diffusion flame were investigated experimentally, and we assumed that the growth of PAHs within the flame was predominantly due to methyl addition/cyclization (MAC) mechanism. Methane and propane laminar diffusion flames were also investigated for comparison, and their PAHs growth characteristics had been explained by reactions concerning acetylene and propargyl radical. Laser-induced fluorescence (LIF) and laser-induced incandescence (LII) techniques were used to measure the relative concentration of soot and PAHs, respectively. Two-dimensional images of the OH-LIF, PAHs-LIF, and LII from soot were measured in the test flames. Furthermore, to investigate the growth characteristics of the PAHs in the flames, the fluorescence spectra of the PAHs were measured at several heights in the flames, using a spectrograph. The molecular size of the PAHs was estimated based on an emission wavelength region of the PAHs-LIF that varied along with the PAH size. The results show that although the PAHs were widely distributed within the unburned region similar to that of the methane and propane flames, the intensity and detection region of LII were much smaller than that of the methane and propane flames. The PAHs-LIF spectra indicated that the growth of the PAHs within the DME flame was much slower than the methane and propane flames, and thus a large number of small PAHs were discharged into the OH region distributed around the outer edge of the flame.