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

In order to describe the influence of strain rate on the behaviour and on t he characteristics of premixed turbulent combustion, a methane-air flame st abilized 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 th e exit velocity at the nozzle. At low strain rates, the evolution of profil es of mean axial velocity along the centreline agrees with classical result s, and these results are used to characterise the flame. The variation of t hese characteristics with parameters such as plate temperature, equivalence ratio and strain rate is investigated. At the highest strain rates, the:he 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 conside red as well as the extinction strain rate K-EX,,. Measurements also demonst rate the existence of a virtual stagnation point that moves towards the pla te as the strain rate increases. The axial and transverse fluctuating compo nents of the velocity are analyzed along the centreline and very close to t he wall. These 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 tra nsverse velocity fluctuations.