The imposition of an external electric field (EF) on the flame is considered as one of the most promising methods for solving problems of optimization of burning of fossil fuels that are relevant in the modern world. The paper presents the results of an investigation of the non-stationary effect of a weak EF on diffusion combustion of hydrocarbons by optical diagnostic methods that do not introduce perturbations into the structure of the object under study. In addition to direct photo and video recording, spectrozonal registration of the own flame radiation, PIV method was used to study the effect of EF on a diffusion flame in a co-flow air. Data are obtained (PIV), indicating the possibility of improving the mixing process, intensification of combustion in the case of the EF pre-set spatial-temporal configuration impact on a flame.