Influence of strain rate on a premixed turbulent flame stabilized in a stagnating flow

Abstract

In order to describe the influence of strain rate on the behaviour and on the characteristics of premixed turbulent combustion, a methane-air flame stabilized by a stagnation plate is studied experimentally. The plate is set at a fixed distance from the nozzle and the strain is varied by changing the exit velocity at the nozzle. At low strain rates, the evolution of profiles of mean axial velocity along the centreline agrees with classical results, and these results are used to characterise the flame. The variation of these characteristics with parameters such as plate temperature, equivalence ratio and strain rate is investigated. At the highest strain rates, the shape of the axial velocity profiles along the stagnation line is modified. This change emphasises a critical strain rate K _C that has to be considered as well as the extinction strain rate K _EX. Measurements also demonstrate the existence of a virtual stagnation point that moves towards the plate as the strain rate increases. The axial and transverse fluctuating components of the velocity are analyzed along the centreline and very close to the wall. The results show the importance of the critical strain rate K _C , which is linked to a drastic change in the evolution of the axial and transverse velocity fluctuations.