Most industrial applications consuming a much primary energy, such fuel and gas, used different technologies of burners. The thermal efficiency and polluting emissions depends on the burner nozzle, on the fuel type and oxidant type (air or pure oxygen). This article is interested by the dynamic study in a coaxial burner consisting by two coaxial circular jets: a central jet to inject natural gas and the annular jet for pure oxygen injection. The aim of this work is the experimental study of two free coaxial jets with flame disposed in ambient air and to have the effect of varying equivalence ratio on the flow structure. This study carried in three configurations; two configurations made in lean combustion mode (Φ = 0:65, Φ = 0:8) and the stoichiometric configuration (§ = 1). The variation in the amount of oxygen in the combustion reaction affects on the longitudinal velocity, on the transversal velocity and on the turbulent fluctuation. These parameters are very important and affect directly on the flame structure. The reduction of equivalence ratio leads to increased of longitudinal and transverse velocity and promotes the fluctuation in interaction zone between natural gas and oxygen. At the stoichiometric reaction, the turbulent intensity represents a maximum in the mixing zone. This maximum increases when the height above the burner increases. © 2014 Begell House, Inc.