Impact of injection conditions on flame characteristics from a parallel multi-jet burner

This numerical study systematically investigates the influence of initial injection conditions of reactants on flame characteristics from a parallel multi-jet burner in a laboratory-scale furnace. In particular, varying characteristics from visible flame to invisible Moderate or Intense Low-oxygen Dilution (MILD) combustion is explored. Different parameters examined include the initial separation of fuel and air streams (S), air nozzle diameter (Da), fuel nozzle diameter (Df), and air preheat temperature (Ta). The present simulations agree qualitatively well with previous measurements reported elsewhere for two reference cases investigated by experiment. A number of new and significant findings are then deduced from the simulations. For instance, all S, Da and Df are found to play significant roles in achieving a proper confluence location of air and fuel jets for establishing the MILD combustion. Particularly, varying Da is most effective for controlling the combustion characteristics. It is also found that the stability limits of the non-premixed MILD combustion varies with different combustor systems and inlet reactant properties. Moreover, for the first time, several analytical approximations are obtained that relate the flue-gas recirculation rate and the fuel-jet penetration to Da, Df, S and also reactant properties.