Revealing the competitive relationship between soot formation and chemiluminescence

This paper reveals the competitive relationship between soot formation and chemiluminescence. Soot volume fraction (SVF) and chemiluminescence are measured in the experiment. A mechanism coupled with the soot model and OH*/CH*/C2*/CO2* reactions is constructed for kinetic analysis. By varying oxygen concentrations and CO2 additions, it is experimentally observed that chemiluminescence is inhibited in the soot-laden regions/flames rather than obscured by the soot radiation, implying that soot formation and chemiluminescence are in competition. Rate of production analysis shows that soot formation and chemiluminescence compete for fuel pyrolysis products (C2H3, C2H2, etc.) because their reaction paths are opposite. CH*, C2*, and OH* decrease with the increase of SVF because the pyrolysis products that can be used for chemiluminescence participate in soot formation. The rise in oxygen concentration also promotes the production of C4H4 from C2H. CO2 addition enhances the chemiluminescence by forming OH and CO to accelerate CH* and CO2* formation and consuming H to suppress the consumption of pyrolysis products in soot formation/inception.