An experimental investigation of spontaneous flame chemiluminescence of OH*, CH*, and C2* radicals was conducted for premixed propane-air flames in a micro flow reactor. Equivalence ratios from 0.7 to 1.4 were examined and correlated well to the ratio of OH*/CH* and C2*/CH* (R-2 > 0.999 for C2*/CH* power fit). The OH*/CH* ratio better correlated with equivalence ratio for lean flames, while the C2*/CH* ratio better correlated with rich flames. The equivalence ratio model was used to calculate the axial local equivalence ratio for a rich propane-air flame (4) of 1.5) exhibiting strong bifurcating FREI behavior, resulting in three visible flame fronts. The measured intensities of OH*, CH*, and C2* chemiluminescence, as well as the calculated local equivalence ratio along the reactor axis support the numerical model explanations of the observed bifurcating FREI flames available in the literature. This work highlights the novel application of this diagnostic technique in the context of micro flow reactors. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.