Lagrangian CFD modeling of ammonia sprays: A correlation across flash boiling and evaporative conditions

Simulations of liquid ammonia spray are performed for different ambient pressures to investigate the transition between flash-boiling and non-flashing regimes, through Computational Fluid Dynamics (CFD). The Lagrangian particle method, within the Reynolds Averaged Navier Stokes (RANS) approach for turbulence is used. Numerical results are compared with experimental liquid and vapor tip penetrations, spray morphology and Sauter Mean Diameter (SMD) measurements, for a multi-hole injector. An adaptation of Kelvin-Helmholtz - Rayleigh-Taylor (KH-RT) breakup model constants and prescribed jet cone angle is necessary for each regime, as standard values used for traditional fuels, e.g., gasoline, appear not to work with ammonia. Capturing local spray details and SMD values across all regimes with a single model setup is very challenging, especially with a new fuel such as ammonia, whose properties differ by a large amount from more established values for hydrocarbons. In this study a correlation for ammonia is proposed for the KH-RT breakup model constants and jet cone angle as a function of operating conditions across flash-boiling and non-flashing regimes. In addition, local temperature predictions are extensively discussed, for both liquid and gaseous phases, highlighting and quantifying the strong cooling effect that ammonia produces during the phase change process.