varies from point to point due to the aerodynamic stretch induced due to gradients in the velocity field. Under contrasting conditions, however, the inner structure of the premixed flame may be entirely disrupted causing the flame to extinguish either locally (known as local extinction) or globally (known as global extinction or blow-off). Such opposing cases govern the operation of practical combustion devices such as SI engines as well as aero-engine afterburners. The prediction of the extent to which the inner structure of flame is affected in turbulent flow is a topic of extensive research. Premixed flame configuration The flow configuration of premixed gases affects the stabilization and burning characteristics of the Bunsen flame In a Bunsen flame, a steady flow rate is provided which matches the flame speed so as to stabilize the flame. If the flow rate is below the flame speed, the flame will move upstream until the fuel is consumed or until it encounters a flame holder. If the flow rate is equal to the flame speed, we would expect a stationary flat flame front normal to the flow direction. If the flow rate is above the flame speed, the flame front will become conical such that the component of the velocity vector normal to the flame front is equal to the flame speed. Stagnation flame Here, the pre-mixed gases flow in such a way so as to form a region of stagnation (zero velocity) where the flame may be stabilized. Spherical flame In this configuration, the flame is typically initiated by way of a spark within a homogeneous pre-mixture. The subsequent propagation of the developed premixed flame occurs as a spherical front until the mixture is transformed entirely or the walls of the combustion vessel are reached. Applications Since the equivalence ratio of the premixed gases may be controlled, premixed combustion offers a means to attain low temperatures and, thereby, reduce NOx emissions. Due to improved mixing in comparison with diffusion flames, soot formation is mitigated as well. Premixed combustion has therefore gained significance in recent times. The uses involve lean-premixed-prevaporized (LPP) gas turbines and SI engines. See also Flamelet generated manifold Luminous flame Oxy-fuel References Combustion Fire