Spray dynamics simulations for pulsatile injection at different ambient pressure and temperature conditions

A numerical study on the transient characteristics of a pulsatile, iso-octane spray issuing from a pressure-swirl atomizer is presented. The effects of system pressure and temperature, as well as the initial fuel temperature on spray dispersion and evaporation, are highlighted. The computations were carried out using ANSYS FLUENT-15.0, assuming the spray dispersion to be axisymmetric. Gas phase turbulence is simulated using the renormalized group k-epsilon model, while the discrete phase model is used for tracking fuel droplets. The linear instability sheet atomization model is adopted for the primary breakup of the liquid sheet, and the Taylor Analogy Breakup and Wave Breakup models are adopted for the secondary breakup, depending upon the operating conditions. The drag force on the droplet is evaluated, after incorporating the effects of evaporation and neighbouring droplets, along with droplet shape distortion. The significance of droplet collision on the evolution of droplet size distribution is examined. The local mean drop sizes and spray penetration length are in agreement with the experimental results of the literature. The predicted results indicate that the spray is narrower and penetrates less at higher ambient pressure. In this respect, the additional force on droplets due to local static pressure gradient is examined in detail. The effect of ambient conditions on the spray evaporation process is studied based on the spatio-temporal evolution of the equivalence ratio of the mixture of fuel vapour and air.