The Pintle Ejector is a special kind of nozzle that is used in many spray and propulsion devices. It has a pintle, or needle, in the middle that can be moved to change the flow rate and pattern of the sprayed fluid. In spray applications, the Pintle Ejector often uses compressed air to break up the liquid even more, making a fine mist or spray that can help with coating, mixing, or burning, depending on the application. For the present simulation, two reference papers are considered, titled “ Design Procedure of a Movable Pintle Injector for Liquid Rocket Engines” & “ LAGRANGIAN APPROACH TO AXISYMMETRIC SPRAY SIMULATION OF PINTLE INJECTOR FOR LIQUID ROCKET ENGINES”.

Figure 1: Gas-liquid injection in pintle ejectors, adopted from reference paper

Simulation Process

The initial geometry model features from 2D axisymmetric method that half the computation cost. It is produced using Design Modeler, which considers proper blocking for structured grid generation. Unlike the reference paper, we adopted an Eulerian-Eulerian approach with the use of Volume of Fluid (VOF) multiphase model. In our model design, the gas gap is 0.8mm. Undoubtedly, the air gap plays a vital role in the break up of the nozzle spray.

Figure 2: Pintle ejector 2D axisymmetric domain design based on reference paper

Post-processing

The modeling of the Pintle Ejector Spray shows that the atomization process is both complicated and practical. The velocity profile shows a symmetrical spray pattern with fast streams (red) coming out of the nozzle. These streams slowly spread out and slow down as they interact with the gas around them, changing to green and blue. The spray has a wide distribution angle, which means it is atomizing well. The spray’s core stays moving faster (in green) for a longer distance, which suggests that there is a concentrated stream or bigger drops in this area. The slowing down of the flow further downstream shows how motion moves from the liquid to the air and how air resistance affects the flow. The modeling also indicates air entrainment near the edges of the spray, which can be seen as small speed boosts in the surrounding area. This adds to the mixing and atomization process.