The present paper reports on an experimental study to determine the effects of air co-flow on the flickering behaviour of liquefied petroleum gas (LPG) laminar diffusion flames. This study is accomplished by using the fast Fourier transform (FFT) analysis on photomultiplier tube (PMT) time signals, image-processing technique and proper orthogonal decomposition (POD) analysis. In this experimental study, the flickering of a flame is described by its flame structure (mean flame height), oscillation amplitude, and percentage dominant mode energy. It is observed that the velocity of co-flow air strongly affects the flame dynamics and structure of the co-flow laminar diffusion flame. The PMT signals confirmed that increasing the velocity of co-flow air leads to an increase in the oscillation frequency and a decrease in oscillation amplitude. The effect of co-flow velocity disappears at critical values and the flame height becomes constant. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.