A Liquid-Liquid Pintle Injector CFD simulation is a computer model of a very important part in rocket engines. These injectors control how fuel and oxidizer mix before they burn to create thrust. This Rocket Propulsion CFD analysis helps engineers design better and more reliable rocket engines. A Liquid-Liquid Pintle Injector Fluent model shows how two different liquids – fuel and oxidizer – come together and mix. In this study, we use N2O4 (nitrogen tetroxide) as the oxidizer and C12H23 (dodecane) as the fuel. The Fuel-Oxidizer Mixing Simulation is critical because good mixing means better combustion and more thrust. Using ANSYS Fluent, we can see exactly how the liquids spray, break apart, and mix together. This Spray Atomization Fluent analysis helps engineers optimize the injector design for maximum performance in space missions.

• Reference [1]: Cheng, Peng, et al. “On the prediction of spray angle of liquid-liquid pintle injectors.” Acta Astronautica138 (2017): 145-151.

Figure 1: Pintle injector concept showing the axial and radial injection configuration used in Rocket Propulsion CFD applications [1].

Simulation Process: Fluent Species Transport Setup, 3D Multiphase Modeling for Propellant Mixing

To perform this Liquid-Liquid Pintle Injector CFD study, we used a complete 3D model because pintle injectors have complex flow patterns that cannot be captured in 2D. The geometry includes the central pintle, the axial injection port, and the radial injection ports. This Combustion Injector CFD requires full 3D modeling to see how the fuel and oxidizer jets hit each other and mix.

We used ANSYS Fluent Meshing to create a high-quality computational mesh with 951,090 cells. In the ANSYS Fluent solver, we used the Species Transport model. This model is perfect for Propellant Injection Analysis because it can track three different materials at the same time: N2O4 (nitrogen tetroxide) as the oxidizer, C12H23 (dodecane) as the fuel, and air as the carrier gas. The model solves equations for each species to show exactly where each material goes and how they mix together. We set up two different inlet boundary conditions to match the real pintle injector design. The axial inlet carries the main oxidizer flow along the center, while the radial inlet injects the fuel sideways to create the impinging jet pattern.

Figure 2: The high-quality computational mesh with 951,090 cells, designed for accurate Liquid-Liquid Pintle Injector CFD simulation

Post-processing: CFD Analysis, Jet Impingement and Species Mixing in Propulsion Systems

The results of this Liquid-Liquid Pintle Injector Fluent simulation provide complete insight into the mixing process. From an engineering perspective, the velocity contours in Figure 3 show the fundamental mechanism that drives the entire injection process. The maximum velocity of 28.04 m/s occurs at the injection points (red regions), where both the oxidizer and fuel are accelerated through the narrow orifices. These high-speed jets are essential because they provide the energy needed to break the liquid into small droplets, a process called atomization. The velocity field clearly shows the axial oxidizer flow along the pintle centerline and the radial fuel jets that create the impingement zones. The areas where these jets meet (yellow-green regions) show intermediate velocities, which is direct evidence of turbulent mixing. The blue regions downstream show flow separation and recirculation, which is normal for this type of geometry and actually helps with mixing.

The species distribution results prove that the mixing is working effectively. The N2O4 mass fraction contours in Figure 4 show that the oxidizer starts as pure N2O4 (mass fraction = 0.99) in the central axial flow. As it moves downstream, it mixes with the fuel and air, creating the blue-green regions with lower concentrations. This gradual mixing is exactly what we want for good combustion. The C12H23 mass fraction contours in Figure 5 show the fuel jets (red regions) injected through the radial ports. The fuel maintains its identity initially but then rapidly mixes due to the turbulent flow. The intermediate colors show the formation of a combustible mixture that is neither pure fuel nor pure oxidizer.

Figure 3: Velocity contours from the Fluent simulation, showing flow acceleration and jet formation with maximum velocities of 28.04 m/s.

Figure 4: N2O4 mass fraction distribution from the Species Transport Modeling, revealing oxidizer flow patterns and mixing zones.

The velocity streamlines in Figure 6 reveal the most important achievement: the complex 3D flow patterns that make this injector work. The streamlines show helical motion, jet impingement, and downstream mixing. These patterns prove that our 3D simulation successfully captures the real physics of how fuel and oxidizer interact. The streamlines demonstrate that the impinging jets create strong turbulence, which is the key to good mixing and efficient combustion.

The most important achievement of this simulation is its successful prediction of the impinging jet mechanism that creates effective fuel-oxidizer mixing. By showing maximum velocities of 28.04 m/s at the injection points and demonstrating the gradual mixing of pure N2O4 and C12H23 into a combustible mixture, the model provides engineers with a validated tool for optimizing pintle injector designs for maximum thrust and combustion efficiency in rocket propulsion systems.

Figure 5: C12H23 mass fraction contours from the Fuel-Oxidizer Mixing Simulation, displaying fuel injection and radial spreading.

Figure 6: Velocity streamlines illustrating the complex 3D flow patterns and Impinging Jets CFD behavior in the pintle injector.