A numerical study of the stabilisation of a lean laminar premixed V-shaped flame

The stabilisation of the base of a numerically computed lean methane/air V-shaped flame is investigated by calculating the different contributions to the stretch rate, the burning velocities in the burnt and unburnt mixtures and the flame temperature for various mixture velocities. The investigation shows that fluid dynamic phenomena are more important for the stabilisation of the flame base than flame stretch effects. On the one hand, flow straining in combination with thermal expansion leading to stream tube contraction is responsible for the increase of the mass flow rate above the flame holder. On the other hand, the stand-off distance in relation with the length of the recirculation zone above the flame holder is important for the mass flow rate towards the flame base. Furthermore, changes in flame stretch play a less dominant role: it is observed that the mass burning rate of the flame base is nearly independent of the inlet velocity and the effect of preferential diffusion on the flame temperature and the burning velocity is found to be small for the lean methane/air flame considered.