A Number Size Distribution Moments Based Solid Cone Diesel Spray Model: Assessment of Droplet Breakup Models Based on Different Distribution Functions

Creating small sized droplets is the primary reason for using sprays. In high-pressure diesel engine sprays, smaller sized droplets aid the combustion process, thus reducing emissions. Therefore, the adequate representation of the droplet breakup process in diesel engine spray models is essential. Two droplet breakup models have been applied in this study. These models have been developed based on whether the results of the droplet breakup processes have been derived from approximations, using an assumed size distribution function, or based on empirical data, using a gamma size distribution function. The effects of assumptions in the models, such as the number of sibling droplets produced during the breakup process, are also presented. The droplet breakup models have been integrated into a recently developed three moments solid cone diesel spray model in which the complete hydrodynamic characteristics of a spray can be represented by calculating three moments of the droplet-size distribution function from transport equations and one moment from a Gamma size distribution. This is in contrast to many diesel fuel spray models, which determine the spray characteristics by tracking droplet size classes. The results are characterized by the droplet sizes and fuel spray penetration results at different ambient pressure values, and compared with well-characterized experimental data from diesel injection spray cases. The computational expense of the droplet breakup models considered is also evaluated. The results indicate that the predicted results compare well with experimental data and the use of any particular breakup model could be based on the least possible assumptions, the required accuracy and computational expense required to attain these.