Numerical Study of Ammonia Spray with a GDI Engine Injector

With the aim of expanding the knowledge on liquid ammonia sprays, this paper investigates the injection process of ammonia through Computational Fluid Dynamics (CFD) using the Lagrangian particle method, within the Reynolds Averaged Navier Stokes (RANS) approach for turbulence modeling. Numerical results and experimental data are compared in terms of liquid and vapor tip penetration, local values of Sauter Mean Diameter (SMD) and global spray morphology. This model validation process allows to build a predictive simulation framework for ammonia injection. In order to explore also the flash boiling phenomenon, results of CFD simulations of ammonia spray and the comparison with experimental data are presented for different conditions, ranging from non-flashing regimes to flash boiling conditions. Breakup model constants need to be markedly tuned for each regime, and established values for traditional fuels, like gasoline, appear not to work well with ammonia. Ultimately, this study highlights that capturing spray local details (such as local SMD values) across all the regimes with a single model or setup is still challenging, especially with a new fuel such as ammonia, whose properties differ by a large amount from more established values for hydrocarbons.