Simulation of Liquid Jet Breakup Using a Combination of Particle and Grid Methods

Fine atomization of the liquid jet from a fuel injector in an automobile engine lowers engine emissions and improves fuel efficiency. The breakup length of liquid films and the lengths of ligaments near the injector outlet after the breakup of liquid films are important parameters for predicting the atomization. These parameters have been predicted mainly using the Eulerian-grid method. (We refer to this as the ‘grid method’.) However, the grid method causes a loss of the liquid film with numerical diffusion, and it requires a large amount of computation time in practical engineering aspect because fine meshes smaller than the ligaments must be used. On the other hand, the particle method, an alternative (particle-based) method for representing the continuum Navier-Stokes equation which can simulate a ligament using a group of particles, does not cause numerical diffusion. However, a large number of particles are needed to simulate the entire computational domain within the injectors. In this study, we have focused on the flow field only near the injector outlet, and have tried to simulate the breakup of liquid films by using groups of particles in the particle method. In the simulation, the particle method was applied only to the liquid film and the grid method was used in other regions to shorten the computation time. Furthermore, we tried to integrate Brackbill’s surface-tension model, which is widely used in the grid method, into the particle method. To evaluate this approach, we compared the breakup lengths obtained for a cylindrical liquid jet in a uniform air stream with measurements done by Arai and Hashimoto; the breakup lengths agreed well with their measurements. We then simulated the breakup of a liquid film near the outlet of a fuel injector used for automobile engine, and found that our hybrid method could simulate the breakup of the liquid film into ligaments.