Spherically propagating premixed laminar flames in a large volume bomb were studied at some initial mixture pressures in order to investigate the effects of pressure on the premixed flame, especially on the burning velocity and its variation by the flame stretch. They are quite important to the modeling of combustion in internal combustion engines because the burning velocity is one of the most essential parameters. The effects of the initial mixture pressure on the unstretched laminar burning velocity and the Markstein length were investigated using methane and propane-air mixtures in the wide range of the equivalence ratio from 0.8 to 1.4 varying the initial pressure from 0.10 to 0.50MPa. The Markstein length and its normalized number express the variation in the burning velocity by the flame stretch. In this study, the burning velocity was obtained not from the flame radius of the photographic image in the literature, but from the pressure history. It is related to the rate of mass burning rather than the rate of propagation of the flame. The unstretched laminar burning velocity decreased as the initial pressure increased. The Markstein number decreased with increasing the initial pressure at all the equivalence ratios irrespective of fuel. They were negative for the lean methane and the rich propane mixtures at elevated pressures. The burning velocity of the stretched laminar flame was affected by the pressure in the two ways, the variation in the unstretched laminar burning velocity and the variation in the sensitivity of the burning velocity to the flame stretch. The properties of the flame instability were investigated next. The flame became unstable with the increase in the mixture pressure. Flame was unstable under the condition of low Markstein number. Cellular flame structure due to the flame instability developed earlier in such cases. The cells became small as the Markstein number decreased. The flame instability might affect the burning velocity.
|Number of pages||8|
|Journal||The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines|
|Publication status||Published - 2004|