The modelling of premixed laminar combustion in a closed vessel

Abstract

Premixed laminar combustion in closed vessels has been widely used for the determination of laminar burning velocities. A novel multiple burnt gas zone model has been developed to describe the different aspects of premixed laminar combustion in a closed spherical vessel. The mixture is divided into burnt and unburnt gases with the flame front as a discontinuity. Unburnt gases are assumed to be in a frozen chemical state. However, burnt gases are divided into a number of burnt gas zones. For the methane–air mixture the model is used to determine the temperature distribution within the burnt gas, the relationship between the pressure rise and mass fraction burnt, the variation of the combustion products with temperature and pressure, the spatial distribution of the gas density, the influence of elevated initial temperature, pressure and molecular structure. This computation allows for the variation in heat capacity of the constituents, and solves the equilibrium combustion equation for the ten major species (N₂, O₂, H₂, CO, CO₂, H₂O, O, H, NO, OH). This eliminates some of the simplifications made by Bradley and Mitcheson (1976 Combust. Flame 26 201–17) or Takeno and Iijima (1979 7th Int. Colloq. on Gas Dynamics of Explosions and Reactive Systems (Göttingen, Germany) pp 20–4), such as the constant specific heat for the burnt and unburnt gases, incorporation of the flame front thickness, use of the Rankine–Hugoniot relation for finding the burnt gas state.